1 00:00:00,840 --> 00:00:03,180 [Instructor] Hello and welcome to module three, 2 00:00:03,180 --> 00:00:04,440 this is the first lecture 3 00:00:04,440 --> 00:00:06,000 and we're going to be talking about 4 00:00:06,000 --> 00:00:08,850 gene expression and regulation. 5 00:00:08,850 --> 00:00:11,070 This is definitely going to build on 6 00:00:11,070 --> 00:00:12,660 what we learned in module two. 7 00:00:12,660 --> 00:00:15,690 So if at any point you feel you might wanna go back 8 00:00:15,690 --> 00:00:18,990 and read through the materials from module two again, 9 00:00:18,990 --> 00:00:21,450 just revisit, especially if it's been a few days, 10 00:00:21,450 --> 00:00:23,940 you might just want to refresh yourself there. 11 00:00:23,940 --> 00:00:25,800 Maybe even just go back and look at the 12 00:00:25,800 --> 00:00:29,370 assignment, the definitions that you did for module two, 13 00:00:29,370 --> 00:00:31,860 or even have that sitting right next to you so that 14 00:00:31,860 --> 00:00:33,300 if there's a word that pops up 15 00:00:33,300 --> 00:00:35,100 that I start to use more regularly 16 00:00:35,100 --> 00:00:36,870 that you just learned about in module two, 17 00:00:36,870 --> 00:00:40,410 you can take a peek and know what it is I'm talking about. 18 00:00:40,410 --> 00:00:42,270 So let's start with just a quick review 19 00:00:42,270 --> 00:00:44,610 of what we learned in the last module. 20 00:00:44,610 --> 00:00:47,580 DNA is located in the nucleus and a segment of DNA 21 00:00:47,580 --> 00:00:48,960 that gives the instructions for making 22 00:00:48,960 --> 00:00:51,480 one particular protein is called a gene. 23 00:00:51,480 --> 00:00:53,490 Genes are transcribed in the nucleus 24 00:00:53,490 --> 00:00:55,890 into complementary mRNA sequence 25 00:00:55,890 --> 00:00:58,410 and that mRNA sequence moves out of the nucleus 26 00:00:58,410 --> 00:01:01,410 to the cytoplasm, where ribosomes read the sequence 27 00:01:01,410 --> 00:01:02,610 and assemble amino acids 28 00:01:02,610 --> 00:01:04,680 in the correct order to create the protein. 29 00:01:04,680 --> 00:01:07,680 And this is called, the process is called translation. 30 00:01:07,680 --> 00:01:11,430 And if you remember this whole process of going from 31 00:01:11,430 --> 00:01:15,120 DNA to being copied into RNA, 32 00:01:15,120 --> 00:01:19,710 which then gets read and translated into protein, 33 00:01:19,710 --> 00:01:23,220 that process was worked out as the central dogma, 34 00:01:23,220 --> 00:01:25,020 which we talked about in module two. 35 00:01:25,950 --> 00:01:27,480 Well, now we're going to be talking about 36 00:01:27,480 --> 00:01:31,680 how the cell actually regulates on many different levels, 37 00:01:31,680 --> 00:01:33,900 how it can regulate that process. 38 00:01:33,900 --> 00:01:37,050 In particular, the process of transcription. 39 00:01:37,050 --> 00:01:39,240 So let's first talk about a few important definitions 40 00:01:39,240 --> 00:01:41,130 that I'd like to make sure we all have clear 41 00:01:41,130 --> 00:01:42,660 before we move forward. 42 00:01:42,660 --> 00:01:43,980 When I say gene expression, 43 00:01:43,980 --> 00:01:45,330 this is the process by which 44 00:01:45,330 --> 00:01:47,130 that information encode in a gene 45 00:01:47,130 --> 00:01:50,010 is used to directly assemble a protein. 46 00:01:50,010 --> 00:01:53,310 So the expression of a gene is basically going from 47 00:01:53,310 --> 00:01:56,640 the gene sequence to having a protein 48 00:01:56,640 --> 00:01:58,920 at the end that is needed. 49 00:01:58,920 --> 00:02:03,240 And gene regulation is the actual process of modulating 50 00:02:03,240 --> 00:02:04,380 gene expression. 51 00:02:04,380 --> 00:02:06,840 So the extent to which a gene is expressed 52 00:02:06,840 --> 00:02:09,780 as in turning it on or off or up or down. 53 00:02:09,780 --> 00:02:13,320 And that usually occurs at the level of the mRNA. 54 00:02:13,320 --> 00:02:15,270 So either how much of it is swarmed 55 00:02:15,270 --> 00:02:18,330 or what version of it is actually used for translation, 56 00:02:18,330 --> 00:02:20,673 which we'll talk about in this lecture. 57 00:02:22,050 --> 00:02:23,430 Constitutive gene, 58 00:02:23,430 --> 00:02:26,070 so these are genes that are transcribed all the time. 59 00:02:26,070 --> 00:02:27,150 Facultative genes, 60 00:02:27,150 --> 00:02:29,880 these are genes that are transcribed only when needed. 61 00:02:29,880 --> 00:02:32,550 So let's pick up a metaphor here, right? 62 00:02:32,550 --> 00:02:34,230 You know, I love my metaphors. (chuckles) 63 00:02:34,230 --> 00:02:36,630 So what I'd like to use for this metaphor, 64 00:02:36,630 --> 00:02:41,310 let's think about the cell as your house, let's say, okay. 65 00:02:41,310 --> 00:02:42,330 And in your house, 66 00:02:42,330 --> 00:02:46,140 there are basic functions that always need to occur, 67 00:02:46,140 --> 00:02:47,580 always need to occur. 68 00:02:47,580 --> 00:02:50,190 These would be like the 69 00:02:50,190 --> 00:02:52,530 functions that constitutive genes that 70 00:02:52,530 --> 00:02:56,970 their proteins would address if this were a cell. 71 00:02:56,970 --> 00:03:00,600 Let's say in your house, you always need electricity, 72 00:03:00,600 --> 00:03:03,930 you always need plumbing, you need water supply, 73 00:03:03,930 --> 00:03:07,530 you need the basic roof over your head, 74 00:03:07,530 --> 00:03:09,543 walls, floor, that kind of thing. 75 00:03:10,380 --> 00:03:12,180 The proteins in a cell, 76 00:03:12,180 --> 00:03:14,100 which perform the functions that are needed 77 00:03:14,100 --> 00:03:15,990 for just every day run of the mill, 78 00:03:15,990 --> 00:03:17,670 keeping the cell up and running, 79 00:03:17,670 --> 00:03:19,110 those are constitutive, 80 00:03:19,110 --> 00:03:21,630 those are encoded by constitutive genes, 81 00:03:21,630 --> 00:03:23,850 which means they are always being expressed 82 00:03:23,850 --> 00:03:24,810 because they're always needed. 83 00:03:24,810 --> 00:03:26,580 No matter what's going on in the cell, 84 00:03:26,580 --> 00:03:30,390 it always needs to maintain its membrane, 85 00:03:30,390 --> 00:03:32,550 so basically keeping its roof over its head. 86 00:03:32,550 --> 00:03:35,850 It needs to maintain its basic metabolism, 87 00:03:35,850 --> 00:03:38,670 so kinda like the electricity going on. 88 00:03:38,670 --> 00:03:42,600 It needs to maintain the proper influx and efflux 89 00:03:42,600 --> 00:03:45,420 of materials like basically getting rid of waste, 90 00:03:45,420 --> 00:03:47,310 sort of like in plumbing, 91 00:03:47,310 --> 00:03:50,310 you always need the water coming in and water going out. 92 00:03:50,310 --> 00:03:51,750 Those are things you need all the time, 93 00:03:51,750 --> 00:03:53,450 no matter what's going on, really. 94 00:03:54,330 --> 00:03:57,690 Let's think about specific functions that might happen 95 00:03:57,690 --> 00:03:59,760 or might be needed in your house at certain times 96 00:03:59,760 --> 00:04:00,810 but not in others. 97 00:04:00,810 --> 00:04:02,283 Let's take today, for example, 98 00:04:02,283 --> 00:04:03,900 it's really cold outside, right? 99 00:04:03,900 --> 00:04:05,610 It's freezing cold outside, 100 00:04:05,610 --> 00:04:09,510 this is January and it's Vermont, so it's gonna be cold. 101 00:04:09,510 --> 00:04:12,090 But as a result, I have my heat turned all the way up 102 00:04:12,090 --> 00:04:14,490 in order to keep it warm enough in my house 103 00:04:14,490 --> 00:04:15,810 because it's really cold outside. 104 00:04:15,810 --> 00:04:18,030 So in response to the environmental condition 105 00:04:18,030 --> 00:04:22,020 of it being cold outside, I've cranked my heat way on up. 106 00:04:22,020 --> 00:04:24,870 Let's assume it's actually August now 107 00:04:24,870 --> 00:04:27,600 and it's 95 degrees and a hundred percent humidity, 108 00:04:27,600 --> 00:04:29,040 which is really hard for me to imagine 109 00:04:29,040 --> 00:04:31,410 what that feels like right now 'cause it's so cold. 110 00:04:31,410 --> 00:04:33,690 But let's say, let's just think of a time 111 00:04:33,690 --> 00:04:34,860 when that actually does happen 112 00:04:34,860 --> 00:04:37,560 and it will happen again in August, let's say. 113 00:04:37,560 --> 00:04:39,480 Instead of having my heat cranked all the way up, 114 00:04:39,480 --> 00:04:41,850 I want my heat off and I want my air condition 115 00:04:41,850 --> 00:04:43,260 cranked all the way up. 116 00:04:43,260 --> 00:04:45,960 So in my house, I don't always have my heat on, 117 00:04:45,960 --> 00:04:48,153 I don't always have my air conditioning on. 118 00:04:48,990 --> 00:04:50,910 In fact, it's very important sometimes, 119 00:04:50,910 --> 00:04:52,530 like if I need, like on a day like today, 120 00:04:52,530 --> 00:04:54,090 it's very important I have my heat on 121 00:04:54,090 --> 00:04:56,310 and my air conditioning off. 122 00:04:56,310 --> 00:04:57,330 And when it's really hot outside, 123 00:04:57,330 --> 00:05:00,060 it's important I have my A/C on and my heat off. 124 00:05:00,060 --> 00:05:02,400 This is very similar to facultative genes. 125 00:05:02,400 --> 00:05:04,500 So in the case of facultative genes, 126 00:05:04,500 --> 00:05:06,750 these would be genes that encode proteins 127 00:05:06,750 --> 00:05:10,740 that are only needed in response to certain things going on 128 00:05:10,740 --> 00:05:12,480 in and around the cell. 129 00:05:12,480 --> 00:05:15,270 In this case, in this particular metaphor, 130 00:05:15,270 --> 00:05:17,880 turning the heat on would be like turning on 131 00:05:17,880 --> 00:05:20,010 genes that would be responsive 132 00:05:20,010 --> 00:05:22,230 to those particular environmental conditions. 133 00:05:22,230 --> 00:05:23,520 And you want to be able to turn them on 134 00:05:23,520 --> 00:05:25,370 and turn them off when you need them. 135 00:05:27,420 --> 00:05:30,300 Coding sequence, these are segments of DNA or RNA 136 00:05:30,300 --> 00:05:32,010 which give instructions to ribosomes 137 00:05:32,010 --> 00:05:34,320 for proper formation of a protein. 138 00:05:34,320 --> 00:05:38,700 So these are the regions that contain those codons, 139 00:05:38,700 --> 00:05:42,060 remember what a codon is, a triplet of bases, 140 00:05:42,060 --> 00:05:43,590 so three bases in a row 141 00:05:43,590 --> 00:05:45,900 that encodes, that provides instructions 142 00:05:45,900 --> 00:05:47,760 for one specific amino acid. 143 00:05:47,760 --> 00:05:48,813 Coding sequence would be 144 00:05:48,813 --> 00:05:52,110 like a long stretch of these codons, 145 00:05:52,110 --> 00:05:56,040 all of which provide instructions for in total, 146 00:05:56,040 --> 00:05:59,523 all of which provide instructions for making one protein. 147 00:06:00,420 --> 00:06:01,500 Non-coding sequences, 148 00:06:01,500 --> 00:06:03,750 these are segments of DNA or RNA sequence 149 00:06:03,750 --> 00:06:06,600 which do not give instruction to ribosomes. 150 00:06:06,600 --> 00:06:08,610 Some of these sequences have other functions 151 00:06:08,610 --> 00:06:10,350 like regulating expression of genes. 152 00:06:10,350 --> 00:06:12,820 And I mentioned before that 153 00:06:13,740 --> 00:06:17,580 something only like 2% of our genome, 154 00:06:17,580 --> 00:06:20,040 of all of our DNA sequences is genes, 155 00:06:20,040 --> 00:06:21,870 so the remaining 98%, 156 00:06:21,870 --> 00:06:24,480 you might hear some people calling that junk DNA, 157 00:06:24,480 --> 00:06:26,760 it's not actually junk. (laughs) 158 00:06:26,760 --> 00:06:28,620 It's really, if you think about it, 159 00:06:28,620 --> 00:06:31,800 why would we as a species keep that much junk around 160 00:06:31,800 --> 00:06:34,410 and go to a lot of trouble to replicate that junk 161 00:06:34,410 --> 00:06:37,230 every time our cell divides and every time 162 00:06:37,230 --> 00:06:39,000 we produce a new offspring. 163 00:06:39,000 --> 00:06:40,710 We wouldn't and we don't. 164 00:06:40,710 --> 00:06:43,350 That 98% is not just junk. 165 00:06:43,350 --> 00:06:46,350 While it doesn't code for a specific protein necessarily, 166 00:06:46,350 --> 00:06:48,870 what it does do is it regulates 167 00:06:48,870 --> 00:06:53,507 how, when, and in response to what the 2% 168 00:06:54,480 --> 00:06:57,180 and so the coding sequence, the 2% of the genome, 169 00:06:57,180 --> 00:07:00,063 those genes are expressed. 170 00:07:01,824 --> 00:07:03,990 So the 98%, I mean most of it, 171 00:07:03,990 --> 00:07:06,450 we don't actually know what all of that 98% does, 172 00:07:06,450 --> 00:07:08,910 but a good portion of it, we have come to find out, 173 00:07:08,910 --> 00:07:11,820 a good portion of it is involved in regulating 174 00:07:11,820 --> 00:07:14,280 the expression of that 2% of the genome, 175 00:07:14,280 --> 00:07:16,623 which actually encodes for proteins. 176 00:07:18,720 --> 00:07:21,240 So cells, as I talked about in that metaphor, 177 00:07:21,240 --> 00:07:23,340 cells must respond to changing environment, 178 00:07:23,340 --> 00:07:25,230 growth, signals from other cells and tissues, 179 00:07:25,230 --> 00:07:27,420 developmental timing, anything that's going on 180 00:07:27,420 --> 00:07:28,800 in and around it. 181 00:07:28,800 --> 00:07:30,840 And not all proteins are needed all the time 182 00:07:30,840 --> 00:07:33,990 or even good to have around all the time. 183 00:07:33,990 --> 00:07:36,420 So what in the end, can we boil this down to one problem? 184 00:07:36,420 --> 00:07:38,190 Yep, the problem is that cells 185 00:07:38,190 --> 00:07:41,370 must be flexible and responsive to their environment, 186 00:07:41,370 --> 00:07:44,580 yet receive no new genes after the time of conception. 187 00:07:44,580 --> 00:07:46,980 So at the time that the egg and the sperm fuse, 188 00:07:46,980 --> 00:07:48,390 you have your fertilized egg, 189 00:07:48,390 --> 00:07:51,780 you have all the DNA that you're ever going to have. 190 00:07:51,780 --> 00:07:53,460 And basically, I mean 191 00:07:53,460 --> 00:07:54,930 all the different DNA that you're going to have, 192 00:07:54,930 --> 00:07:56,670 the cells will replicate and divide 193 00:07:56,670 --> 00:07:59,820 and will duplicate that DNA 194 00:07:59,820 --> 00:08:01,770 but won't make exact copies of it. 195 00:08:01,770 --> 00:08:04,830 So it's not as though in say a kidney cell 196 00:08:04,830 --> 00:08:07,410 compared to a heart cell 197 00:08:07,410 --> 00:08:10,740 you have different genes or different DNA, no, 198 00:08:10,740 --> 00:08:12,780 all of it is still all there, 199 00:08:12,780 --> 00:08:14,820 it's just that some of those genes 200 00:08:14,820 --> 00:08:17,250 are expressed specifically in heart cells 201 00:08:17,250 --> 00:08:19,020 and some genes are expressed 202 00:08:19,020 --> 00:08:21,480 specifically in say kidney cells 203 00:08:21,480 --> 00:08:23,460 or liver cells or skin cells, 204 00:08:23,460 --> 00:08:27,450 which give them their specific qualities and functions. 205 00:08:27,450 --> 00:08:30,000 So what is the solution the cell has come up with 206 00:08:30,000 --> 00:08:31,560 to address this problem? 207 00:08:31,560 --> 00:08:33,270 Certain genes will be turned on 208 00:08:33,270 --> 00:08:35,430 and certain genes will be turned off. 209 00:08:35,430 --> 00:08:36,600 And the genes that are turned on 210 00:08:36,600 --> 00:08:38,040 are those that are needed at the time 211 00:08:38,040 --> 00:08:40,050 and those that are off or not expressed 212 00:08:40,050 --> 00:08:43,200 or not transcribed are those genes that are not necessary, 213 00:08:43,200 --> 00:08:45,900 they're proteins that they code for are not needed, 214 00:08:45,900 --> 00:08:47,670 those functions are not needed in the cell, 215 00:08:47,670 --> 00:08:50,730 are not desirable in the cell at that particular time. 216 00:08:50,730 --> 00:08:52,740 They can be turned on later if they're needed, 217 00:08:52,740 --> 00:08:55,230 but for now, for the particular situation, 218 00:08:55,230 --> 00:08:58,170 they can be turned off and the other genes that are needed, 219 00:08:58,170 --> 00:09:00,220 their proteins are needed, are turned on. 220 00:09:02,730 --> 00:09:05,790 So in which stages is this actually occurring? 221 00:09:05,790 --> 00:09:09,330 Well, if we look back at our DNA to mRNA to protein, 222 00:09:09,330 --> 00:09:10,170 we have transcription, 223 00:09:10,170 --> 00:09:12,570 which is the process of copying DNA to mRNA, 224 00:09:12,570 --> 00:09:15,480 translation being the process of reading mRNA 225 00:09:15,480 --> 00:09:18,873 and assembling the correct amino acids for protein. 226 00:09:20,130 --> 00:09:21,870 Most of what's actually occurring 227 00:09:21,870 --> 00:09:25,350 in gene regulation is actually, 228 00:09:25,350 --> 00:09:27,300 most gene regulation is actually occurring 229 00:09:27,300 --> 00:09:28,770 at the transcriptional level. 230 00:09:28,770 --> 00:09:30,840 So this is at the level of 231 00:09:30,840 --> 00:09:34,890 forming mRNA or what basically with the end result 232 00:09:34,890 --> 00:09:37,920 of that mRNA going into being translated. 233 00:09:37,920 --> 00:09:39,810 Let me make my disclaimer again. 234 00:09:39,810 --> 00:09:42,570 So this is a very complicated, 235 00:09:42,570 --> 00:09:46,230 complex subject of gene regulation, 236 00:09:46,230 --> 00:09:48,670 which can and does take 237 00:09:50,280 --> 00:09:53,070 entire lifetimes of careers contributing to this, 238 00:09:53,070 --> 00:09:54,224 including a lot of my own, 239 00:09:54,224 --> 00:09:57,840 so I'm just really gonna give you the highlights here. 240 00:09:57,840 --> 00:09:59,370 There are many other types of gene regulation 241 00:09:59,370 --> 00:10:00,780 that we're not going to cover, 242 00:10:00,780 --> 00:10:04,080 which may be specific to a certain subset of genes 243 00:10:04,080 --> 00:10:05,970 or this or that, but I'm really just gonna again, 244 00:10:05,970 --> 00:10:08,070 majority rule, just gonna give you 245 00:10:08,070 --> 00:10:11,700 the main ways in which this occurs 246 00:10:11,700 --> 00:10:13,890 and if there's something specifically 247 00:10:13,890 --> 00:10:14,760 that we don't talk about 248 00:10:14,760 --> 00:10:16,380 that comes up for you in your practice 249 00:10:16,380 --> 00:10:18,870 or something you came across and you want to discuss it, 250 00:10:18,870 --> 00:10:21,090 I'd be more than happy to talk with you about it. 251 00:10:21,090 --> 00:10:24,300 But with the goal of really just focusing 252 00:10:24,300 --> 00:10:26,400 on what I think will be most useful to you, 253 00:10:26,400 --> 00:10:29,460 I'm really just going to give you 254 00:10:29,460 --> 00:10:32,703 the sort of the primary ways in which genes are regulated. 255 00:10:33,840 --> 00:10:36,060 And that would include at the transcriptional level 256 00:10:36,060 --> 00:10:37,530 transcription factors, 257 00:10:37,530 --> 00:10:39,510 which we'll talk about momentarily, 258 00:10:39,510 --> 00:10:40,620 in the presence or absence 259 00:10:40,620 --> 00:10:43,350 of these transcriptional activators or repressors 260 00:10:43,350 --> 00:10:45,240 and epigenetic modifications, 261 00:10:45,240 --> 00:10:47,940 which include DNA methylation and histone modification, 262 00:10:47,940 --> 00:10:52,200 which affect early access to particular genes. 263 00:10:52,200 --> 00:10:53,700 And then it also occurs at the level 264 00:10:53,700 --> 00:10:55,920 of post-transcriptional regulation. 265 00:10:55,920 --> 00:10:58,320 And that means once you formed your mRNA, 266 00:10:58,320 --> 00:11:00,300 so transcriptional regulation is 267 00:11:00,300 --> 00:11:03,570 in the process of actually forming mRNA, 268 00:11:03,570 --> 00:11:05,070 post-transcriptional regulation 269 00:11:05,070 --> 00:11:08,070 would be what happens to mRNA after it's transcribed, 270 00:11:08,070 --> 00:11:09,660 but before it's translated. 271 00:11:09,660 --> 00:11:11,457 So this would be called post-transcriptional. 272 00:11:11,457 --> 00:11:14,550 And what we'll really focus on here are splicing variants, 273 00:11:14,550 --> 00:11:17,430 which I'll tell you what that means shortly, 274 00:11:17,430 --> 00:11:20,040 but there's also another way that it can be regulated 275 00:11:20,040 --> 00:11:21,660 through stability of mRNA, 276 00:11:21,660 --> 00:11:23,340 but we won't really focus on that here 277 00:11:23,340 --> 00:11:25,350 because I feel like that gets into 278 00:11:25,350 --> 00:11:28,680 a little too into the weeds for what we need to focus on. 279 00:11:28,680 --> 00:11:30,690 But if ever you want to talk about 280 00:11:30,690 --> 00:11:33,120 or you hear about something called microRNAs 281 00:11:33,120 --> 00:11:34,470 and you want to talk about that more, 282 00:11:34,470 --> 00:11:37,661 I'm more than happy to do it, but for the purpose of this, 283 00:11:37,661 --> 00:11:40,083 let's just kind of glaze over that for now. 284 00:11:41,520 --> 00:11:43,710 All right, a little more detail on transcription. 285 00:11:43,710 --> 00:11:46,050 A promoter is a region of sequence upstream 286 00:11:46,050 --> 00:11:47,070 from the start of a gene 287 00:11:47,070 --> 00:11:49,260 used to align the transcriptional machinery 288 00:11:49,260 --> 00:11:50,340 to start transcription. 289 00:11:50,340 --> 00:11:52,620 This is sort of like a staging area. 290 00:11:52,620 --> 00:11:56,460 So when I say a promoter is a region of sequence upstream, 291 00:11:56,460 --> 00:11:57,510 what do I mean by that? 292 00:11:57,510 --> 00:12:02,510 Well, if you recall the specific order in which bases align 293 00:12:02,670 --> 00:12:04,260 is actually very, very important 294 00:12:04,260 --> 00:12:09,210 and that gives the specific codons which codes for 295 00:12:09,210 --> 00:12:11,400 the amino acids which are used 296 00:12:11,400 --> 00:12:13,290 and this occurs linearly, right? 297 00:12:13,290 --> 00:12:17,610 So it's sort of like basically like letters forming a word 298 00:12:17,610 --> 00:12:20,190 that would be a linear arrangement of letters. 299 00:12:20,190 --> 00:12:21,540 So you have one letter, 300 00:12:21,540 --> 00:12:23,340 then the next, then the next, then the next. 301 00:12:23,340 --> 00:12:25,020 Similarly with bases you have one base, 302 00:12:25,020 --> 00:12:26,340 then the next, then the next, then the next, 303 00:12:26,340 --> 00:12:28,380 left to right, you can think of it that way. 304 00:12:28,380 --> 00:12:32,340 So upstream, when we say upstream, that means 305 00:12:32,340 --> 00:12:36,120 in that same strand of DNA, it's basically 306 00:12:36,120 --> 00:12:39,450 kind of before the start of that sequence. 307 00:12:39,450 --> 00:12:42,030 So along the line of that sequence, 308 00:12:42,030 --> 00:12:43,470 you can think of it as 309 00:12:43,470 --> 00:12:48,470 before you reach the first codon, right? 310 00:12:48,676 --> 00:12:51,093 What's the start codon, 311 00:12:51,990 --> 00:12:54,840 if you remember it is ATG, right that, 312 00:12:54,840 --> 00:12:58,860 that codon is ATG, which encodes for which amino acid? 313 00:12:58,860 --> 00:13:00,690 Methionine, that's right. 314 00:13:00,690 --> 00:13:02,700 So ATG, which is the start. 315 00:13:02,700 --> 00:13:06,960 So upstream of that, so before that sequence, 316 00:13:06,960 --> 00:13:11,100 along the same strand of DNA, you have other sequence 317 00:13:11,100 --> 00:13:14,670 which would be part of that non-coding, non-coding sequence. 318 00:13:14,670 --> 00:13:18,150 It's all attached and all part of the same strand of DNA, 319 00:13:18,150 --> 00:13:20,070 but before you reach that 320 00:13:20,070 --> 00:13:23,220 is a region of DNA called a promoter. 321 00:13:23,220 --> 00:13:25,770 This is not code for a protein at all, 322 00:13:25,770 --> 00:13:28,710 nothing in there codes for protein, so it's non-coding, 323 00:13:28,710 --> 00:13:33,240 but it is necessary for the proper alignment of the 324 00:13:33,240 --> 00:13:34,073 transcriptional machinery, 325 00:13:34,073 --> 00:13:37,080 which is used to transcribe that RNA polymerase 326 00:13:37,080 --> 00:13:39,180 and other factors which are used to 327 00:13:39,180 --> 00:13:42,576 actually make the mRNA molecule off of 328 00:13:42,576 --> 00:13:44,253 one of the template strand. 329 00:13:45,990 --> 00:13:48,510 In facultative gene specific transcription factors, 330 00:13:48,510 --> 00:13:50,190 which are highly specialized proteins, 331 00:13:50,190 --> 00:13:52,410 are needed to bind to the promoter 332 00:13:52,410 --> 00:13:55,290 to enable proper alignment of transcriptional machinery 333 00:13:55,290 --> 00:13:56,760 and for transcription to start, 334 00:13:56,760 --> 00:13:58,620 we'll look at that in just a moment. 335 00:13:58,620 --> 00:14:00,780 If those transcription factors are not present, 336 00:14:00,780 --> 00:14:03,660 the gene is not expressed or not expressed as much, 337 00:14:03,660 --> 00:14:06,000 and genes use different transcription factors 338 00:14:06,000 --> 00:14:07,050 for the regulation. 339 00:14:07,050 --> 00:14:09,540 For example, if we were to take, say 340 00:14:09,540 --> 00:14:13,530 the gene which encodes for the protein insulin, 341 00:14:13,530 --> 00:14:15,630 the transcription factors which are used, 342 00:14:15,630 --> 00:14:18,780 which are needed for it to bind to its promoter 343 00:14:18,780 --> 00:14:21,750 and therefore initiate its transcription, 344 00:14:21,750 --> 00:14:24,630 are different than the transcription factors 345 00:14:24,630 --> 00:14:29,623 which bind to the promoter for say 346 00:14:30,960 --> 00:14:33,120 a gene which encodes a protein 347 00:14:33,120 --> 00:14:36,390 that is involved in say, cell proliferation. 348 00:14:36,390 --> 00:14:40,080 So something like the CD44 gene, 349 00:14:40,080 --> 00:14:43,020 which encodes for the CD44 protein, 350 00:14:43,020 --> 00:14:46,050 which is necessary for regulating cell proliferation. 351 00:14:46,050 --> 00:14:48,660 Its transcription factors are very different 352 00:14:48,660 --> 00:14:49,800 than the transcription fact, 353 00:14:49,800 --> 00:14:51,570 it use a different set of transcription factors 354 00:14:51,570 --> 00:14:53,370 than the transcription factors which are needed 355 00:14:53,370 --> 00:14:58,053 for the expression of say the insulin gene. 356 00:14:59,460 --> 00:15:02,310 And that's important because you need the insulin gene 357 00:15:02,310 --> 00:15:05,100 in response to very different external stimuli 358 00:15:05,100 --> 00:15:08,280 than something like the CD44 gene, 359 00:15:08,280 --> 00:15:10,350 which is only going to be needed 360 00:15:10,350 --> 00:15:12,513 when the cell needs to proliferate rapidly. 361 00:15:13,800 --> 00:15:14,640 All right, let's take a look 362 00:15:14,640 --> 00:15:16,050 at what it is I'm talking about. 363 00:15:16,050 --> 00:15:19,680 So here what we're actually looking at is a 364 00:15:19,680 --> 00:15:22,110 sort of a pictographic representation of a gene, 365 00:15:22,110 --> 00:15:23,910 which you might see quite often. 366 00:15:23,910 --> 00:15:27,000 It's really just for simplicity's sake that I am 367 00:15:27,000 --> 00:15:30,570 indicating all these different components in this way. 368 00:15:30,570 --> 00:15:31,470 You don't think of anything 369 00:15:31,470 --> 00:15:33,120 as actually being shaped this way 370 00:15:33,960 --> 00:15:36,720 with the exception of a DNA strand is 371 00:15:36,720 --> 00:15:38,280 kind of linear like this. 372 00:15:38,280 --> 00:15:40,320 But basically we're looking at a DNA strand. 373 00:15:40,320 --> 00:15:41,340 So it would be a sequence, 374 00:15:41,340 --> 00:15:42,900 you would have a sequence of bases, 375 00:15:42,900 --> 00:15:45,480 C-T-G-A-G-G-T-C-A, whatever. 376 00:15:45,480 --> 00:15:48,540 You know you have some combination of A's, T's, C's, and G's 377 00:15:48,540 --> 00:15:52,920 and a single line along here, so let's say then 378 00:15:52,920 --> 00:15:54,780 if this is your gene, if this is the start of your gene, 379 00:15:54,780 --> 00:15:58,290 it would read ATG as your first codon, 380 00:15:58,290 --> 00:16:00,630 then it would have whatever your next. 381 00:16:00,630 --> 00:16:02,460 whatever your next bases are in your gene, 382 00:16:02,460 --> 00:16:06,930 C-T-A-G-T-A-A-A-C-T, it goes along long, long, long. 383 00:16:06,930 --> 00:16:09,120 And this would be the coding portion, 384 00:16:09,120 --> 00:16:12,210 so this is a gene, so it encodes for protein. 385 00:16:12,210 --> 00:16:16,020 But it is, again, it's a part of a very long 386 00:16:16,020 --> 00:16:17,643 continuous DNA strand. 387 00:16:18,600 --> 00:16:21,360 So you have sequences which would be upstream. 388 00:16:21,360 --> 00:16:22,260 So when I say upstream, 389 00:16:22,260 --> 00:16:26,310 it's usually depicted to the left of the start of a gene, 390 00:16:26,310 --> 00:16:29,910 if this is where we're showing the gene starts here 391 00:16:29,910 --> 00:16:32,730 and the gene we're depicting in this rose color, 392 00:16:32,730 --> 00:16:35,010 then upstream of that, you still have sequence, 393 00:16:35,010 --> 00:16:37,683 I mean it's one long continuous DNA strand. 394 00:16:38,520 --> 00:16:41,400 It's just that this particular part of it starts, 395 00:16:41,400 --> 00:16:43,290 this is the start of a region 396 00:16:43,290 --> 00:16:46,500 and it would continue on through to the end 397 00:16:46,500 --> 00:16:49,083 or a stop codon would be in here somewhere. 398 00:16:51,000 --> 00:16:55,650 And the DNA sequence continues on past the end of that gene, 399 00:16:55,650 --> 00:16:56,970 right, it continues on past, 400 00:16:56,970 --> 00:16:59,940 it's just not a part of the gene, okay. 401 00:16:59,940 --> 00:17:00,930 So when we say upstream, 402 00:17:00,930 --> 00:17:03,450 this would be upstream of a gene group, 403 00:17:03,450 --> 00:17:05,460 this would be downstream of the gene. 404 00:17:05,460 --> 00:17:09,000 So kinda like left is upstream, right is downstream 405 00:17:09,000 --> 00:17:12,873 as is sort of how it's commonly drawn. 406 00:17:14,610 --> 00:17:16,320 All right, this yellow region here 407 00:17:16,320 --> 00:17:19,140 is what we would consider to be say the promoter sequence 408 00:17:19,140 --> 00:17:20,790 of this gene and it's just, again, 409 00:17:20,790 --> 00:17:22,290 it's just a part of the sequence. 410 00:17:22,290 --> 00:17:24,930 So if this is where we start with ATG, 411 00:17:24,930 --> 00:17:28,380 then you can think of this part of it, just again, 412 00:17:28,380 --> 00:17:32,430 it's just some, it's just some sequence. 413 00:17:32,430 --> 00:17:36,573 So C-T-G-A-G-G-C-T-A-G-G, whatever, you know? 414 00:17:37,590 --> 00:17:41,850 It's some combination of bases upstream 415 00:17:41,850 --> 00:17:43,413 of the start of the gene. 416 00:17:44,520 --> 00:17:46,080 And this is considered, 417 00:17:46,080 --> 00:17:48,183 would you call this coding or non-coding? 418 00:17:49,140 --> 00:17:50,430 It's non-coding, right? 419 00:17:50,430 --> 00:17:53,550 Because it's not actually a part of a gene, 420 00:17:53,550 --> 00:17:56,580 it doesn't give the instructions for a specific protein 421 00:17:56,580 --> 00:17:58,710 or amino acids for a protein. 422 00:17:58,710 --> 00:18:02,100 What its function is to align the machinery 423 00:18:02,100 --> 00:18:05,940 needed to transcribe this gene here. 424 00:18:05,940 --> 00:18:07,800 And what do I mean by that? 425 00:18:07,800 --> 00:18:09,390 Well, what's needed is, if you recall, 426 00:18:09,390 --> 00:18:11,130 I mentioned transcription factors, 427 00:18:11,130 --> 00:18:15,090 these are proteins which bind to specific sequences 428 00:18:15,090 --> 00:18:17,100 along the genome 429 00:18:17,100 --> 00:18:19,410 and these sequences are oftentimes found 430 00:18:19,410 --> 00:18:20,670 in promoter regions, 431 00:18:20,670 --> 00:18:23,340 so just upstream of the start of a gene. 432 00:18:23,340 --> 00:18:24,960 And why does that matter? 433 00:18:24,960 --> 00:18:27,450 So what happens is transcription factors will come in 434 00:18:27,450 --> 00:18:29,250 and just through sort of diffusion, 435 00:18:29,250 --> 00:18:31,770 they'll find their way into these sequences 436 00:18:31,770 --> 00:18:34,470 and they'll bind to it, so they'll stick through 437 00:18:34,470 --> 00:18:37,470 chemical bonding, they'll actually bond to, stick to 438 00:18:37,470 --> 00:18:41,830 the DNA but in very specific sequences, so let's say 439 00:18:42,868 --> 00:18:45,270 I'm depicting two different transcription factors here. 440 00:18:45,270 --> 00:18:47,340 Let's say that this transcription factor in white 441 00:18:47,340 --> 00:18:50,130 binds to C-C-A-G-G sequence, 442 00:18:50,130 --> 00:18:53,010 oh, it found a C-C-A-G-G here, it binds there. 443 00:18:53,010 --> 00:18:56,460 Let's say this transcription factor binds to T-T-A-G-T-C, 444 00:18:56,460 --> 00:19:00,033 it found a T-T-A-G-T-C sequence here, and it binds here. 445 00:19:01,020 --> 00:19:05,250 Once those two have bound in this particular arrangement, 446 00:19:05,250 --> 00:19:08,940 then that allows something called a scaffolding protein 447 00:19:08,940 --> 00:19:12,480 to come in, which is depicted with this pentagon here, 448 00:19:12,480 --> 00:19:15,450 not actually what it looks like, but you know, 449 00:19:15,450 --> 00:19:17,970 just for simplicity's sake drawing it that way. 450 00:19:17,970 --> 00:19:20,100 Scaffolding protein is another kind of protein 451 00:19:20,100 --> 00:19:22,920 that will bind to transcription factors 452 00:19:22,920 --> 00:19:26,610 that are bound to the DNA. 453 00:19:26,610 --> 00:19:28,200 So when the transcription factors are bound 454 00:19:28,200 --> 00:19:30,330 in their specific correct arrangement 455 00:19:30,330 --> 00:19:32,250 onto a promoter sequence, 456 00:19:32,250 --> 00:19:34,440 a scaffolding protein can come in and bind. 457 00:19:34,440 --> 00:19:35,670 And why is that needed? 458 00:19:35,670 --> 00:19:40,560 Well, it helps to align RNA polymerase in the right location 459 00:19:40,560 --> 00:19:44,100 at the very beginning or start of the gene. 460 00:19:44,100 --> 00:19:46,530 So that way the RNA polymerase can go along 461 00:19:46,530 --> 00:19:51,000 and can actually transcribe the gene into mRNA, right? 462 00:19:51,000 --> 00:19:54,060 So this is another common depiction 463 00:19:54,060 --> 00:19:57,990 of transcription is and it's not particularly creative, 464 00:19:57,990 --> 00:20:00,960 but it is efficient in looking at it. 465 00:20:00,960 --> 00:20:04,500 Transcription is usually depicted from the start of the gene 466 00:20:04,500 --> 00:20:06,150 as a line going up 467 00:20:06,150 --> 00:20:08,550 and then a line going to the right to demonstrate 468 00:20:08,550 --> 00:20:11,160 the direction in which transcription occurs. 469 00:20:11,160 --> 00:20:13,530 Transcription always occurs from the start of the gene 470 00:20:13,530 --> 00:20:14,943 to the end of the gene. 471 00:20:15,780 --> 00:20:18,270 And if transcription is occurring in this gene, 472 00:20:18,270 --> 00:20:21,660 it will be demonstrated by an arrow going left to right, 473 00:20:21,660 --> 00:20:23,010 coming up from the start of the gene 474 00:20:23,010 --> 00:20:25,410 and continuing to the end of it. 475 00:20:25,410 --> 00:20:26,640 All right, so that's what happens 476 00:20:26,640 --> 00:20:28,140 if the transcription factors are present 477 00:20:28,140 --> 00:20:29,820 then everything else, which we'll talk about 478 00:20:29,820 --> 00:20:31,710 what everything else means momentarily, 479 00:20:31,710 --> 00:20:35,220 everything else is conducive to the gene being transcribed, 480 00:20:35,220 --> 00:20:37,860 you will get the mRNA being formed 481 00:20:37,860 --> 00:20:41,943 and that mRNA can then go on to be translated into protein. 482 00:20:43,920 --> 00:20:46,170 Well, let's say the transcription factors are not present, 483 00:20:46,170 --> 00:20:47,310 what happens then? 484 00:20:47,310 --> 00:20:49,290 So if the transcription factors are not present, 485 00:20:49,290 --> 00:20:50,553 if they're not binding, 486 00:20:51,510 --> 00:20:52,740 then the scaffolding protein 487 00:20:52,740 --> 00:20:54,900 has no idea where it's supposed to go, it can't bind. 488 00:20:54,900 --> 00:20:57,270 So while it's diffusing around in the nucleus, 489 00:20:57,270 --> 00:21:00,540 it doesn't bind there because it doesn't have those 490 00:21:00,540 --> 00:21:02,643 transcription factors to stick onto. 491 00:21:04,200 --> 00:21:06,030 So as a result, RNA polymerase comes in 492 00:21:06,030 --> 00:21:07,790 and woo, I don't know where I'm supposed to go. 493 00:21:07,790 --> 00:21:11,190 So it doesn't actually transcribe the gene. 494 00:21:11,190 --> 00:21:15,000 This means the gene is what we would call off, it is off. 495 00:21:15,000 --> 00:21:17,970 mRNA is not being formed, it is not transcribed, 496 00:21:17,970 --> 00:21:19,743 it's protein is not being made. 497 00:21:21,000 --> 00:21:22,710 All right, so let's think about 498 00:21:22,710 --> 00:21:26,220 the second form of transcriptional regulation, 499 00:21:26,220 --> 00:21:28,830 which I mentioned are epigenetic modifications. 500 00:21:28,830 --> 00:21:31,170 So this is a real up and coming field 501 00:21:31,170 --> 00:21:32,680 epigenetic modifications 502 00:21:33,810 --> 00:21:37,230 and I wanted to at least scratch the surface of this 503 00:21:37,230 --> 00:21:39,840 so you have an idea of what people are talking about 504 00:21:39,840 --> 00:21:41,520 when they talk about this because this, 505 00:21:41,520 --> 00:21:43,710 I'd say over the next five to 10 years is going to 506 00:21:43,710 --> 00:21:48,690 really start to dramatically change the way that 507 00:21:48,690 --> 00:21:52,440 drug development occurs, diagnostics occur, 508 00:21:52,440 --> 00:21:56,190 it's going to be really the next Human Genome Project. 509 00:21:56,190 --> 00:21:59,280 So we know now where really all the genes are, 510 00:21:59,280 --> 00:22:01,473 we understand the sequence of the DNA. 511 00:22:02,730 --> 00:22:04,950 Epigenetic modifications is really like 512 00:22:04,950 --> 00:22:07,317 a sequence on top of our DNA sequence. 513 00:22:07,317 --> 00:22:09,210 And I can talk about that in more detail with you 514 00:22:09,210 --> 00:22:12,210 if you are interested in more on epigenetics, 515 00:22:12,210 --> 00:22:13,890 but really just to give you the basics of it 516 00:22:13,890 --> 00:22:15,540 so you know what we're talking about. 517 00:22:15,540 --> 00:22:17,640 When we say epigenetic modifications, 518 00:22:17,640 --> 00:22:20,790 these are heritable and changeable modifications 519 00:22:20,790 --> 00:22:22,200 and affect gene expression, 520 00:22:22,200 --> 00:22:24,120 but not the actual sequence of DNA. 521 00:22:24,120 --> 00:22:26,130 When I say the sequence of DNA, that's the order of 522 00:22:26,130 --> 00:22:29,010 A's, T's, C's, and G's that are found. 523 00:22:29,010 --> 00:22:30,240 So it doesn't actually change that, 524 00:22:30,240 --> 00:22:33,210 but it does change how genes are expressed 525 00:22:33,210 --> 00:22:36,393 and certainly can have a huge impact on that. 526 00:22:37,290 --> 00:22:39,810 There's two main classes of epigenetic modifications 527 00:22:39,810 --> 00:22:42,060 that we'll talk about in humans at least. 528 00:22:42,060 --> 00:22:45,750 Those include DNA methylation and histone modifications. 529 00:22:45,750 --> 00:22:48,480 So if we start with DNA methylation, what is that? 530 00:22:48,480 --> 00:22:51,600 It's basically adding a methyl group onto cytosine. 531 00:22:51,600 --> 00:22:52,980 So just cytosine, 532 00:22:52,980 --> 00:22:56,190 not the A, not the T, not the G, just the C. 533 00:22:56,190 --> 00:23:01,050 So only the C can be methylated, again, in humans. 534 00:23:01,050 --> 00:23:05,220 So, which is really, that's kind of what we care about here. 535 00:23:05,220 --> 00:23:10,220 So in DNA methylation, what occurs, 536 00:23:10,350 --> 00:23:11,850 again, just showing you the chemical structure 537 00:23:11,850 --> 00:23:14,820 of the cytosine base, remember as a nucleotide 538 00:23:14,820 --> 00:23:17,520 it's attached to the sugar phosphate backbone, 539 00:23:17,520 --> 00:23:20,070 but here we're just looking at the base of cytosine. 540 00:23:20,070 --> 00:23:23,520 A methyl group is attached into the carbon ring, 541 00:23:23,520 --> 00:23:26,767 just sort of on the outside of the carbon ring here 542 00:23:26,767 --> 00:23:28,040 to form 5-methylcytosine. 543 00:23:28,040 --> 00:23:31,920 So it still base pairs with guanines, 544 00:23:31,920 --> 00:23:35,490 so C still binds with G across the two strands of DNA 545 00:23:35,490 --> 00:23:37,800 even if the cytosine is methylated, 546 00:23:37,800 --> 00:23:40,260 it can still bind to its other strand. 547 00:23:40,260 --> 00:23:42,060 What can't happen, 548 00:23:42,060 --> 00:23:44,310 what's different about it when it's methylated 549 00:23:44,310 --> 00:23:47,200 is that transcription factors that would bind 550 00:23:48,120 --> 00:23:50,850 to a specific sequence that contains a cytosine. 551 00:23:50,850 --> 00:23:53,040 If that cytosine is methylated 552 00:23:53,040 --> 00:23:56,160 most of the time, pretty much all of the time, 553 00:23:56,160 --> 00:23:58,890 that transcription factor can no longer bind. 554 00:23:58,890 --> 00:24:00,000 And you can start to imagine 555 00:24:00,000 --> 00:24:02,010 what the implications of that would be. 556 00:24:02,010 --> 00:24:05,220 Basically means that if a promoter region, 557 00:24:05,220 --> 00:24:08,250 if the cytosines in a promoter region for a gene 558 00:24:08,250 --> 00:24:11,490 are methylated, that shuts off 559 00:24:11,490 --> 00:24:13,170 the transcription of that gene 560 00:24:13,170 --> 00:24:16,020 because you can no longer bind transcription factors 561 00:24:16,020 --> 00:24:17,853 to that promoter region. 562 00:24:20,224 --> 00:24:23,400 The protein or enzyme that's responsible 563 00:24:23,400 --> 00:24:25,680 for this process of DNA methylation 564 00:24:25,680 --> 00:24:28,140 is called DNA methyltransferase. 565 00:24:28,140 --> 00:24:30,660 It's actually has a very nice and descriptive name, 566 00:24:30,660 --> 00:24:32,433 many of proteins do. 567 00:24:33,810 --> 00:24:36,300 So if we look at this, if we break down this word, 568 00:24:36,300 --> 00:24:41,160 transfers methyl onto DNA. 569 00:24:41,160 --> 00:24:46,160 So it's a DNA methyltransferase or DNMT for short. 570 00:24:46,230 --> 00:24:48,060 And I bring this up because 571 00:24:48,060 --> 00:24:51,900 we will probably touch on this when we are talking about 572 00:24:51,900 --> 00:24:54,450 certain genetic diseases which involve 573 00:24:54,450 --> 00:24:58,950 changes in DNA methylation, specifically cancer is a big one 574 00:24:58,950 --> 00:25:03,950 that involves DNA methylation changes many times. 575 00:25:05,820 --> 00:25:08,790 The other modification is histone modifications 576 00:25:08,790 --> 00:25:10,890 and here I'm going to just show you 577 00:25:10,890 --> 00:25:13,590 a picture of sort of the end result of that. 578 00:25:13,590 --> 00:25:14,610 We're not going to talk about 579 00:25:14,610 --> 00:25:18,960 the specific histone modifications that can occur. 580 00:25:18,960 --> 00:25:21,360 It's a long list and it gets kind of confusing 581 00:25:21,360 --> 00:25:23,850 and you just really don't need to know that at this point, 582 00:25:23,850 --> 00:25:25,830 again, unless you are interested 583 00:25:25,830 --> 00:25:27,360 in something specifically there, 584 00:25:27,360 --> 00:25:29,700 then please feel free to ask, but otherwise 585 00:25:29,700 --> 00:25:31,620 we'll just kind of glaze over it 586 00:25:31,620 --> 00:25:34,320 and say that there are different histone modifications 587 00:25:34,320 --> 00:25:38,460 and the end result of those histone modifications is 588 00:25:38,460 --> 00:25:42,240 either tightening DNA around histones, if you remember, 589 00:25:42,240 --> 00:25:43,323 what are histones? 590 00:25:44,550 --> 00:25:48,270 Histones are those proteins around which DNA is wrapped 591 00:25:48,270 --> 00:25:50,460 like the spool and DNA is like 592 00:25:50,460 --> 00:25:52,710 the thread that winds around it. 593 00:25:52,710 --> 00:25:54,810 So what actually happens is 594 00:25:54,810 --> 00:25:57,930 depending upon how those histones are modified, 595 00:25:57,930 --> 00:26:00,240 they can actually contract into one another 596 00:26:00,240 --> 00:26:03,540 and bring all the spools really close together 597 00:26:03,540 --> 00:26:06,900 and really, really tight, tight, tight kind of ball of 598 00:26:06,900 --> 00:26:10,980 thread or DNA and the end result of that, 599 00:26:10,980 --> 00:26:12,330 what that structure is actually called 600 00:26:12,330 --> 00:26:14,040 when it's all tightened and packed up together 601 00:26:14,040 --> 00:26:15,453 is called heterochromatin. 602 00:26:16,770 --> 00:26:19,560 And you can have regions along a single strand of DNA 603 00:26:19,560 --> 00:26:22,050 that are tightly packed like heterochromatin 604 00:26:22,050 --> 00:26:24,810 and those that are loosely organized, 605 00:26:24,810 --> 00:26:26,550 which we'll talk about momentarily. 606 00:26:26,550 --> 00:26:28,590 But within a region of heterochromatin, 607 00:26:28,590 --> 00:26:29,640 what happens is that, 608 00:26:29,640 --> 00:26:31,830 let's say that this particular part of the DNA 609 00:26:31,830 --> 00:26:35,190 actually is the gene that you're interested in 610 00:26:35,190 --> 00:26:37,170 and this gene needs to be transcribed, 611 00:26:37,170 --> 00:26:39,820 so its promoter would be, let's say right about here, 612 00:26:40,740 --> 00:26:41,580 what's the problem? 613 00:26:41,580 --> 00:26:43,920 Like what could you anticipate being a problem here? 614 00:26:43,920 --> 00:26:47,310 Well the problem is it's all tightly mushed up together, 615 00:26:47,310 --> 00:26:49,740 wound up together with all these other proteins 616 00:26:49,740 --> 00:26:52,890 and all this other DNA, there's no access, 617 00:26:52,890 --> 00:26:54,390 you can't get into it. 618 00:26:54,390 --> 00:26:56,070 So transcription factors can't actually 619 00:26:56,070 --> 00:26:58,110 get into where the promoter is 620 00:26:58,110 --> 00:27:00,870 to bind into initiate transcription. 621 00:27:00,870 --> 00:27:03,720 So it's basically there's no access, it's shut down, 622 00:27:03,720 --> 00:27:06,480 that means the gene is off. 623 00:27:06,480 --> 00:27:08,700 Even if the transcription factors are present 624 00:27:08,700 --> 00:27:12,210 and are around in the area, it can't turn on 625 00:27:12,210 --> 00:27:15,000 because it is currently in this tight 626 00:27:15,000 --> 00:27:16,750 heterochromatin formation 627 00:27:18,210 --> 00:27:20,640 because these histones are modified in such a way 628 00:27:20,640 --> 00:27:23,760 to bring it all to kind of like shrink it all together 629 00:27:23,760 --> 00:27:25,683 and really make it a tight structure. 630 00:27:26,940 --> 00:27:28,950 On the other hand, there are different modifications 631 00:27:28,950 --> 00:27:32,850 to histones which can occur that result in 632 00:27:32,850 --> 00:27:34,890 a structure called euchromatin 633 00:27:34,890 --> 00:27:39,420 or stretch or region of the DNA, which is loose. 634 00:27:39,420 --> 00:27:43,710 And so there's very few histones say in the area 635 00:27:43,710 --> 00:27:46,470 and that gives the DNA space to breathe a little bit. 636 00:27:46,470 --> 00:27:49,560 You know, let's say that this is where your gene is 637 00:27:49,560 --> 00:27:52,020 and let's say this is where your promoter is, 638 00:27:52,020 --> 00:27:53,400 well now you have lots of space, 639 00:27:53,400 --> 00:27:55,500 the transcription factors can come in and bind 640 00:27:55,500 --> 00:27:57,270 and they can initiate transcription 641 00:27:57,270 --> 00:28:00,450 and so all can be good and happy 642 00:28:00,450 --> 00:28:02,613 with transcribing your gene there. 643 00:28:05,460 --> 00:28:08,130 Again, let's just reinforce what what I just covered. 644 00:28:08,130 --> 00:28:09,750 So DNA methylation can block 645 00:28:09,750 --> 00:28:11,640 transcription factor binding to promoters, 646 00:28:11,640 --> 00:28:12,990 thus shutting off transcription 647 00:28:12,990 --> 00:28:15,930 even when transcription factors are present. 648 00:28:15,930 --> 00:28:18,060 So they're present, they just can't bind the DNA 649 00:28:18,060 --> 00:28:19,710 because they don't recognize it anymore 650 00:28:19,710 --> 00:28:20,730 'cause they don't recognize 651 00:28:20,730 --> 00:28:23,430 when there's a methyl group on the cytosine. 652 00:28:23,430 --> 00:28:25,890 Histone modifications that constrict DNA structure 653 00:28:25,890 --> 00:28:28,500 block access of transcriptional machinery. 654 00:28:28,500 --> 00:28:30,720 And DNA methylation, I also want to mention, 655 00:28:30,720 --> 00:28:33,840 so these are not just completely separate processes, 656 00:28:33,840 --> 00:28:36,030 they can actually compliment one another. 657 00:28:36,030 --> 00:28:38,130 DNA methylation being commonly associated 658 00:28:38,130 --> 00:28:39,330 with histone modifications 659 00:28:39,330 --> 00:28:41,490 that constrict DNA structure further 660 00:28:41,490 --> 00:28:44,670 reinforcing the repression of transcription 661 00:28:44,670 --> 00:28:46,440 for that particular gene. 662 00:28:46,440 --> 00:28:47,340 So you can imagine 663 00:28:47,340 --> 00:28:49,650 you can have any combination of transcription factors 664 00:28:49,650 --> 00:28:51,000 being present or not. 665 00:28:51,000 --> 00:28:54,630 You can have, whether the promoter is methylated or not, 666 00:28:54,630 --> 00:28:56,580 and you can have whether the gene 667 00:28:56,580 --> 00:28:59,190 is in a region of heterochromatin or euchromatin, 668 00:28:59,190 --> 00:29:01,980 all of those together can kind of, 669 00:29:01,980 --> 00:29:03,990 you can have really any versions of those 670 00:29:03,990 --> 00:29:07,140 coming together to determine the overall 671 00:29:07,140 --> 00:29:08,670 level of transcription for a gene. 672 00:29:08,670 --> 00:29:09,990 So this regulation is happening 673 00:29:09,990 --> 00:29:11,553 on a lot of different levels. 674 00:29:13,110 --> 00:29:15,810 Let's take a quick peek at pulling this all together. 675 00:29:15,810 --> 00:29:17,670 So again, if you have a chromosome 676 00:29:17,670 --> 00:29:18,750 and you stretch it out. 677 00:29:18,750 --> 00:29:21,000 Chromatin, you can just kind of think of it 678 00:29:21,000 --> 00:29:23,580 as another word for chromosome, so chromosome, 679 00:29:23,580 --> 00:29:25,320 this is basically like a chromosome stretched out 680 00:29:25,320 --> 00:29:27,240 looking at chromatin. 681 00:29:27,240 --> 00:29:31,410 And again that's a double stranded DNA molecule 682 00:29:31,410 --> 00:29:33,690 wrapped around histones. 683 00:29:33,690 --> 00:29:35,730 These are the histones again. 684 00:29:35,730 --> 00:29:37,302 And if we zoom in on 685 00:29:37,302 --> 00:29:38,310 some of the epigenetic modifications 686 00:29:38,310 --> 00:29:40,380 that can be occurring here, 687 00:29:40,380 --> 00:29:41,760 what we can see is that 688 00:29:41,760 --> 00:29:44,910 histones themselves can be modified with different groups, 689 00:29:44,910 --> 00:29:48,210 so like a phospho group, a methyl group, acetyl group, 690 00:29:48,210 --> 00:29:50,940 you don't need to know these specific modifications 691 00:29:50,940 --> 00:29:54,783 just telling you for your own information. 692 00:29:56,250 --> 00:29:59,370 And the combination of different modifications here 693 00:29:59,370 --> 00:30:01,920 can determine whether or not those histones 694 00:30:01,920 --> 00:30:03,240 really tighten up with one another 695 00:30:03,240 --> 00:30:04,980 or they say really loosey goosey 696 00:30:04,980 --> 00:30:08,140 and allow those genes to be 697 00:30:08,993 --> 00:30:11,400 in a euchromatin state 698 00:30:11,400 --> 00:30:14,310 where they can actually be transcribed. 699 00:30:14,310 --> 00:30:17,850 You can also have methylation on cytosines 700 00:30:17,850 --> 00:30:19,830 and this really matters a lot 701 00:30:19,830 --> 00:30:22,140 if this methylation on cytosine is occurring 702 00:30:22,140 --> 00:30:24,240 in promoter region of a gene 703 00:30:24,240 --> 00:30:28,200 because that can block the binding of what? 704 00:30:28,200 --> 00:30:30,390 Of transcription factors, that's right. 705 00:30:30,390 --> 00:30:33,390 So those transcription factors are necessary 706 00:30:33,390 --> 00:30:36,003 for initiating transcription of the gene. 707 00:30:37,440 --> 00:30:39,450 Okay, let's put this all together. 708 00:30:39,450 --> 00:30:42,450 And in this depiction they're showing white circles, 709 00:30:42,450 --> 00:30:43,470 well they're showing the circles, 710 00:30:43,470 --> 00:30:47,370 let's say these small circles as cytosine bases 711 00:30:47,370 --> 00:30:50,910 along the stretch of DNA, these are your histones, 712 00:30:50,910 --> 00:30:53,310 and let's say in this particular state 713 00:30:53,310 --> 00:30:54,990 in order for transcription to occur, 714 00:30:54,990 --> 00:30:59,460 so there's a lot of hurdles that need to be crossed, 715 00:30:59,460 --> 00:31:00,660 barriers that need to be crossed 716 00:31:00,660 --> 00:31:04,170 before a gene is transcribed. 717 00:31:04,170 --> 00:31:06,900 So first of all, you need to have, what? 718 00:31:06,900 --> 00:31:08,790 You need to have your transcription factors present 719 00:31:08,790 --> 00:31:10,737 that are needed for that particular gene, okay? 720 00:31:10,737 --> 00:31:12,540 You need to have those there. 721 00:31:12,540 --> 00:31:14,400 Then you also need to make sure, 722 00:31:14,400 --> 00:31:15,840 if you want to transcribe this gene, 723 00:31:15,840 --> 00:31:18,600 you need to make sure that the cytosine residues 724 00:31:18,600 --> 00:31:20,520 or that the cytosine bases 725 00:31:20,520 --> 00:31:24,040 in the promoter region for this gene are 726 00:31:25,380 --> 00:31:27,210 unmethylated, right? 727 00:31:27,210 --> 00:31:28,680 Okay, so if they're unmethylated 728 00:31:28,680 --> 00:31:31,830 that allows the transcription factors to be able to bind 729 00:31:31,830 --> 00:31:33,270 into their promoter. 730 00:31:33,270 --> 00:31:35,460 Then what's the third thing that needs to be there? 731 00:31:35,460 --> 00:31:39,120 Well, you need to have your gene in a euchromatin region 732 00:31:39,120 --> 00:31:43,290 or a region where the histones are more relaxed 733 00:31:43,290 --> 00:31:45,240 and are more loosely spaced. 734 00:31:45,240 --> 00:31:48,210 And this is what is showing here on transcription. 735 00:31:48,210 --> 00:31:49,800 Possible, possible. 736 00:31:49,800 --> 00:31:51,690 Remember that it's possible 737 00:31:51,690 --> 00:31:53,670 for a gene to be transcribed 738 00:31:53,670 --> 00:31:55,710 if it's in a region where there's no 739 00:31:55,710 --> 00:31:57,536 methylation on the cytosines 740 00:31:57,536 --> 00:32:00,690 and the histones are modified in such a way 741 00:32:00,690 --> 00:32:04,293 that the DNA is more loosely stretched out. 742 00:32:05,310 --> 00:32:06,450 What else do you need to have 743 00:32:06,450 --> 00:32:08,400 before transcription would happen here? 744 00:32:09,420 --> 00:32:11,550 That's right, you need to have the correct transcription 745 00:32:11,550 --> 00:32:13,050 factors being present. 746 00:32:13,050 --> 00:32:15,030 So this is saying transcription is possible. 747 00:32:15,030 --> 00:32:16,890 If the transcription factors are present, 748 00:32:16,890 --> 00:32:19,500 then transcription would actually occur here. 749 00:32:19,500 --> 00:32:22,260 On the other side, there are a lot of ways 750 00:32:22,260 --> 00:32:24,390 in which transcription can be shut down. 751 00:32:24,390 --> 00:32:25,470 Any one of which 752 00:32:25,470 --> 00:32:28,170 can either completely shut down transcription 753 00:32:28,170 --> 00:32:29,850 or really, really slow it down. 754 00:32:29,850 --> 00:32:32,980 And that would be either/or 755 00:32:33,930 --> 00:32:35,610 methylating the cytosines 756 00:32:35,610 --> 00:32:38,670 specifically in the region of the promoter, 757 00:32:38,670 --> 00:32:41,280 which would prevent transcription factors binding 758 00:32:41,280 --> 00:32:46,280 or condensing the DNA down into heterochromatin 759 00:32:46,650 --> 00:32:49,400 because of histone modifications that cause tightening. 760 00:32:50,850 --> 00:32:53,160 And the other way that you can impede transcription, 761 00:32:53,160 --> 00:32:57,300 not shown here, is just that the transcription factors 762 00:32:57,300 --> 00:32:59,700 needed for that particular gene are not present. 763 00:33:00,600 --> 00:33:02,520 There are lots of ways that can shut it down, 764 00:33:02,520 --> 00:33:05,370 any one of which can shut down transcription, 765 00:33:05,370 --> 00:33:08,670 but you need all of them to be in the on state 766 00:33:08,670 --> 00:33:10,570 before you actually get transcription. 767 00:33:11,760 --> 00:33:13,350 Let's take a quick peek at, 768 00:33:13,350 --> 00:33:18,090 let's go back to our depiction of the gene and its promoter 769 00:33:18,090 --> 00:33:19,740 and sort of its surrounding sequence 770 00:33:19,740 --> 00:33:22,230 and look at what happens with methylation. 771 00:33:22,230 --> 00:33:25,470 The first epigenetic modification that we're talking about. 772 00:33:25,470 --> 00:33:27,600 So let's say you have, I'm depicting, 773 00:33:27,600 --> 00:33:29,500 let's say these are where your cytosines, 774 00:33:29,500 --> 00:33:30,870 there are a couple of cytosines located, 775 00:33:30,870 --> 00:33:31,923 and let's say that they're methylated, 776 00:33:31,923 --> 00:33:34,923 it's depicted by these red M's in the promoter. 777 00:33:36,270 --> 00:33:38,640 So you do have your transcription factors around, 778 00:33:38,640 --> 00:33:39,510 but guess what? 779 00:33:39,510 --> 00:33:41,850 They can't bind, they don't know what's going on 780 00:33:41,850 --> 00:33:45,180 because they no longer recognize their normal sites here 781 00:33:45,180 --> 00:33:46,786 because they're methylated, 782 00:33:46,786 --> 00:33:48,780 those cytosines are methylated, so they can't bind. 783 00:33:48,780 --> 00:33:51,240 So they just go on about their business, they leave, 784 00:33:51,240 --> 00:33:53,430 they don't bind to the promoter. 785 00:33:53,430 --> 00:33:54,960 And what does that mean? 786 00:33:54,960 --> 00:33:58,137 Well that means the scaffolding protein has nowhere to land 787 00:33:58,137 --> 00:33:59,610 and so it doesn't bind. 788 00:33:59,610 --> 00:34:01,200 And then subsequently that also means 789 00:34:01,200 --> 00:34:02,700 RNA polymerase cannot bind. 790 00:34:02,700 --> 00:34:05,160 If you don't have RNA polymerase binding, 791 00:34:05,160 --> 00:34:07,080 you cannot have transcription of the gene. 792 00:34:07,080 --> 00:34:09,330 So even though transcription factors were present, 793 00:34:09,330 --> 00:34:11,460 if the promoter was methylated, 794 00:34:11,460 --> 00:34:13,110 you're not getting transcription. 795 00:34:14,430 --> 00:34:19,430 Okay, the big red X across the line depicting transcription. 796 00:34:19,650 --> 00:34:21,960 So this would be considered the gene being off 797 00:34:21,960 --> 00:34:24,303 or the mRNA is not transcribed. 798 00:34:25,530 --> 00:34:28,110 Let's take a look at what this means in heterochromatin 799 00:34:28,110 --> 00:34:30,960 or when you have those histone modifications that 800 00:34:30,960 --> 00:34:34,200 result in a tightening around the histones 801 00:34:34,200 --> 00:34:39,200 and basically constriction of access to the DNA sequences. 802 00:34:40,260 --> 00:34:42,060 So this is the promoter 803 00:34:42,060 --> 00:34:43,200 and this is basically the DNA 804 00:34:43,200 --> 00:34:44,610 that's kinda wrapping itself around, 805 00:34:44,610 --> 00:34:46,350 it's no longer like nicely stretched out, 806 00:34:46,350 --> 00:34:49,380 it's all smushed together. 807 00:34:49,380 --> 00:34:51,030 So here's your promoter, 808 00:34:51,030 --> 00:34:53,970 but it's all bound up to these histones. 809 00:34:53,970 --> 00:34:56,700 It doesn't have space to breathe, which means 810 00:34:56,700 --> 00:34:59,010 that even though the transcription factors are there, 811 00:34:59,010 --> 00:35:00,150 they don't know where to land 812 00:35:00,150 --> 00:35:02,430 so they can't bind to the promoter, 813 00:35:02,430 --> 00:35:05,580 which means scaffolding protein can't bind, 814 00:35:05,580 --> 00:35:08,850 which means RNA polymerase cannot bind. 815 00:35:08,850 --> 00:35:12,090 And the result of that is no transcription. 816 00:35:12,090 --> 00:35:13,653 So the gene is off. 817 00:35:14,911 --> 00:35:16,860 And even if there's no DNA methylation, 818 00:35:16,860 --> 00:35:20,430 even if the transcription factors are present, 819 00:35:20,430 --> 00:35:23,100 if this is in a heterochromatin formation, 820 00:35:23,100 --> 00:35:24,750 you're not getting transcription. 821 00:35:25,650 --> 00:35:27,060 Cell types have variable patterns 822 00:35:27,060 --> 00:35:28,500 of epigenetic modifications 823 00:35:28,500 --> 00:35:29,910 which contribute significantly 824 00:35:29,910 --> 00:35:32,190 to the differences in which genes are expressed. 825 00:35:32,190 --> 00:35:35,190 So while, let's take for example a kidney cell 826 00:35:35,190 --> 00:35:37,200 and a heart cell. 827 00:35:37,200 --> 00:35:38,940 So they have very different functions, 828 00:35:38,940 --> 00:35:40,800 they look quite different from one another, 829 00:35:40,800 --> 00:35:44,610 they have exactly identical genetic material, 830 00:35:44,610 --> 00:35:46,860 so their genomes are 100% the same, 831 00:35:46,860 --> 00:35:48,810 they all came from the same original cell 832 00:35:48,810 --> 00:35:50,730 that had the same DNA, right? 833 00:35:50,730 --> 00:35:52,920 They all have the same looking DNA, 834 00:35:52,920 --> 00:35:55,710 but they have different proteins being expressed 835 00:35:55,710 --> 00:35:57,240 and that's because they have different 836 00:35:57,240 --> 00:35:59,400 epigenetic modifications. 837 00:35:59,400 --> 00:36:01,500 And those epigenetic modifications 838 00:36:01,500 --> 00:36:04,680 can be inherited from one cell division to the next. 839 00:36:04,680 --> 00:36:07,140 So as a cell progresses down a particular lineage, 840 00:36:07,140 --> 00:36:09,150 say the kidney cell lineage, 841 00:36:09,150 --> 00:36:11,820 it's accumulating epigenetic modifications 842 00:36:11,820 --> 00:36:14,760 that result in the proper genes being expressed 843 00:36:14,760 --> 00:36:16,740 for kidney cell function. 844 00:36:16,740 --> 00:36:18,960 On the other hand, heart cells are accumulating 845 00:36:18,960 --> 00:36:21,990 epigenetic modifications that allow only 846 00:36:21,990 --> 00:36:24,180 the genes that are needed to be expressed 847 00:36:24,180 --> 00:36:26,190 in heart cells to be expressed. 848 00:36:26,190 --> 00:36:28,050 Epigenetic modifications accumulate 849 00:36:28,050 --> 00:36:29,940 and change in response to the environment, 850 00:36:29,940 --> 00:36:32,040 so that would be in response to stress, diet, 851 00:36:32,040 --> 00:36:34,950 toxin exposure, and most of these are set 852 00:36:34,950 --> 00:36:36,030 during early development. 853 00:36:36,030 --> 00:36:38,640 So maternal nutrition, stress, toxin exposure 854 00:36:38,640 --> 00:36:41,610 can impact gene expression for the lifetime 855 00:36:41,610 --> 00:36:43,473 of her child or of her offspring. 856 00:36:44,490 --> 00:36:47,700 And I want to give you an example of that in mice here. 857 00:36:47,700 --> 00:36:50,490 This is a pretty striking example. 858 00:36:50,490 --> 00:36:54,330 These two mice are genetically identical. 859 00:36:54,330 --> 00:36:55,500 Genetically identical. 860 00:36:55,500 --> 00:36:58,140 So think of them as like identical twins 861 00:36:58,140 --> 00:36:59,648 or clones of one another. 862 00:36:59,648 --> 00:37:02,700 Their DNA is exactly the same, 863 00:37:02,700 --> 00:37:04,650 but why do they look so different? 864 00:37:04,650 --> 00:37:06,210 This one's orange, this one's brown, 865 00:37:06,210 --> 00:37:09,240 this one is obese, and this one is a normal weight. 866 00:37:09,240 --> 00:37:12,150 This one also was very susceptible over its entire lifetime 867 00:37:12,150 --> 00:37:13,740 to cancer development. 868 00:37:13,740 --> 00:37:16,440 While this mouse on the right is not, 869 00:37:16,440 --> 00:37:20,943 it has a normal chance of developing cancer. 870 00:37:22,200 --> 00:37:24,000 So what's the difference? 871 00:37:24,000 --> 00:37:26,370 The mother of this mouse on the left, 872 00:37:26,370 --> 00:37:28,170 while this mouse was in utero, 873 00:37:28,170 --> 00:37:31,260 the mother ate a diet that was a very poor diet, 874 00:37:31,260 --> 00:37:33,600 that contained very few 875 00:37:33,600 --> 00:37:36,600 methyl groups in the food that she ate. 876 00:37:36,600 --> 00:37:39,030 And methyl groups are found 877 00:37:39,030 --> 00:37:41,070 and it's sort of basic nutrition. 878 00:37:41,070 --> 00:37:43,770 It's anything that you think is kind of healthy food, 879 00:37:43,770 --> 00:37:48,660 fresh, more plant-based foods have more methyl groups 880 00:37:48,660 --> 00:37:52,770 and it's just like it's basic food 881 00:37:52,770 --> 00:37:56,040 that's generally healthy for you are usually 882 00:37:56,040 --> 00:37:58,560 are relatively high in methyl groups. 883 00:37:58,560 --> 00:38:01,710 So this mouse's mother, while this mouse was in utero, 884 00:38:01,710 --> 00:38:04,770 it had a very poor, methyl poor diet. 885 00:38:04,770 --> 00:38:06,270 While this mouse on the right, 886 00:38:07,350 --> 00:38:09,120 its mother while it was in utero, 887 00:38:09,120 --> 00:38:11,430 ate a normal sort of healthy diet 888 00:38:11,430 --> 00:38:13,560 that contained plenty of methyl groups. 889 00:38:13,560 --> 00:38:14,790 Why do you need methyl groups 890 00:38:14,790 --> 00:38:17,220 and why is this associated with epigenetic modifications? 891 00:38:17,220 --> 00:38:19,890 Well if you think about all the DNA methylation that occurs 892 00:38:19,890 --> 00:38:23,250 and the histone modifications that include methylation 893 00:38:23,250 --> 00:38:26,370 of histones, well those need methyl groups 894 00:38:26,370 --> 00:38:27,933 in order to form properly. 895 00:38:28,890 --> 00:38:30,450 So this mouse on the left, 896 00:38:30,450 --> 00:38:33,270 while it has the same exact kind of DNA 897 00:38:33,270 --> 00:38:35,010 as this mouse on the right, 898 00:38:35,010 --> 00:38:38,130 it has a very different pattern of epigenetic modifications, 899 00:38:38,130 --> 00:38:40,080 the result because of the diet 900 00:38:40,080 --> 00:38:42,480 its mother consumed while this mouse was in utero 901 00:38:42,480 --> 00:38:44,040 compared to this mouse. 902 00:38:44,040 --> 00:38:46,110 So as I'm sure you're aware 903 00:38:46,110 --> 00:38:49,560 and I'm sure you express to your patients as well, 904 00:38:49,560 --> 00:38:54,540 the diet and stress, the toxin exposure that a mother 905 00:38:54,540 --> 00:38:58,590 exposes her child in utero to 906 00:38:58,590 --> 00:39:02,310 can affect not only the way that child develops initially, 907 00:39:02,310 --> 00:39:04,410 but also how its genes are expressed 908 00:39:04,410 --> 00:39:08,100 for its entire lifetime, for its entire lifetime. 909 00:39:08,100 --> 00:39:12,683 So huge implications on the overall health of that child. 910 00:39:15,090 --> 00:39:18,090 All right, let's go back to what we were talking about, 911 00:39:18,090 --> 00:39:20,880 where does gene regulation occur? 912 00:39:20,880 --> 00:39:22,830 So we talked about transcriptional regulation 913 00:39:22,830 --> 00:39:24,930 and transcription factors being present or not 914 00:39:24,930 --> 00:39:26,670 and epigenetic modifications, 915 00:39:26,670 --> 00:39:29,100 let's talk about some post-transcriptional regulation, 916 00:39:29,100 --> 00:39:30,930 specifically splicing variants. 917 00:39:30,930 --> 00:39:32,610 And where are we talking about that? 918 00:39:32,610 --> 00:39:37,610 That is after mRNA has been copied off of the DNA 919 00:39:38,400 --> 00:39:41,070 for a particular gene, you have your mRNA, 920 00:39:41,070 --> 00:39:43,770 but it's not quite ready for showtime. 921 00:39:43,770 --> 00:39:45,390 So you know, it's not quite there, 922 00:39:45,390 --> 00:39:48,000 not quite ready to be translated by the protein. 923 00:39:48,000 --> 00:39:50,460 There's another stage that we have yet to talk about 924 00:39:50,460 --> 00:39:52,293 and that would be splicing. 925 00:39:53,400 --> 00:39:55,380 What do I mean by splicing? 926 00:39:55,380 --> 00:39:57,960 Well I apologize that this 927 00:39:57,960 --> 00:40:00,450 particular image is a relatively low resolution, 928 00:40:00,450 --> 00:40:03,030 but it actually is a nice way to show 929 00:40:03,030 --> 00:40:05,730 what I wanted to sort of piece together for you. 930 00:40:05,730 --> 00:40:07,320 So if we're thinking about a gene, 931 00:40:07,320 --> 00:40:08,910 so let's say this is a gene, 932 00:40:08,910 --> 00:40:11,601 so it's your DNA along your DNA strand, 933 00:40:11,601 --> 00:40:12,870 it's in your nucleus, right? 934 00:40:12,870 --> 00:40:13,860 Here's your promoter, 935 00:40:13,860 --> 00:40:17,490 which is upstream of the start of your gene. 936 00:40:17,490 --> 00:40:19,740 Well, so far we've been talking about a gene 937 00:40:19,740 --> 00:40:23,340 as coding for a protein and it does, 938 00:40:23,340 --> 00:40:26,670 but there are some parts of it that don't actually code, 939 00:40:26,670 --> 00:40:27,930 that are non-coding, 940 00:40:27,930 --> 00:40:32,880 even within the stretch of sequence that is called a gene 941 00:40:32,880 --> 00:40:36,660 there are regions called introns 942 00:40:36,660 --> 00:40:39,150 or intervening sequences. 943 00:40:39,150 --> 00:40:44,150 Introns do not code for amino acids, 944 00:40:44,400 --> 00:40:46,140 do not code for protein, 945 00:40:46,140 --> 00:40:50,070 and they have to be cut out of the RNA 946 00:40:50,070 --> 00:40:53,190 that has been transcribed before that RNA is ready 947 00:40:53,190 --> 00:40:55,380 to be translated into protein. 948 00:40:55,380 --> 00:40:58,050 This process is called splicing. 949 00:40:58,050 --> 00:41:02,340 Splicing, so that just means cutting out the introns 950 00:41:02,340 --> 00:41:04,893 and sticking together the exons in the order, 951 00:41:06,240 --> 00:41:07,740 remaining in their linear order. 952 00:41:07,740 --> 00:41:10,830 So if this is your primary transcript 953 00:41:10,830 --> 00:41:13,410 that was copied directly off of your DNA, 954 00:41:13,410 --> 00:41:15,450 basically what's going to happen is that 955 00:41:15,450 --> 00:41:16,860 you can take like a little pair of scissors 956 00:41:16,860 --> 00:41:18,360 and cut right here, 957 00:41:18,360 --> 00:41:20,370 cut right here on either side of this intron, 958 00:41:20,370 --> 00:41:23,190 and glue stick these two exons together 959 00:41:23,190 --> 00:41:24,360 and you do the same thing here, 960 00:41:24,360 --> 00:41:26,340 you cut that out and you cut that out 961 00:41:26,340 --> 00:41:29,130 and you glue stick these two exons together 962 00:41:29,130 --> 00:41:30,060 and you do that again 963 00:41:30,060 --> 00:41:33,600 for every one of your introns that's found in a transcript. 964 00:41:33,600 --> 00:41:37,700 All introns are always removed and that leaves, what? 965 00:41:37,700 --> 00:41:40,590 It basically leaves an mRNA transcript, 966 00:41:40,590 --> 00:41:44,040 which is shorter than what was originally transcribed, 967 00:41:44,040 --> 00:41:46,080 copied from that particular gene, 968 00:41:46,080 --> 00:41:48,660 but only contains sequences which are coding, 969 00:41:48,660 --> 00:41:51,300 only contains sequences which are going to 970 00:41:51,300 --> 00:41:54,270 provide ribosomes, the information for 971 00:41:54,270 --> 00:41:56,850 knowing which amino acids to assemble together 972 00:41:56,850 --> 00:41:58,293 to properly make a protein. 973 00:41:59,550 --> 00:42:02,460 Okay, I know that can be a little confusing, 974 00:42:02,460 --> 00:42:04,650 I know that can be a little confusing, so 975 00:42:04,650 --> 00:42:06,240 think about that for a minute 976 00:42:06,240 --> 00:42:08,310 and let me know if you have questions on that 977 00:42:08,310 --> 00:42:10,080 and we're gonna build off of that 978 00:42:10,080 --> 00:42:14,630 as another mechanism for gene regulation here 979 00:42:14,630 --> 00:42:15,900 in the next slide. 980 00:42:15,900 --> 00:42:18,120 Okay, so let's build off of that. 981 00:42:18,120 --> 00:42:20,400 Let's say you have your exons, right? 982 00:42:20,400 --> 00:42:22,680 Depicted here in these different colors. 983 00:42:22,680 --> 00:42:24,150 This is all one gene. 984 00:42:24,150 --> 00:42:28,110 One gene has many different exons, okay? 985 00:42:28,110 --> 00:42:33,110 So each exon codes for a part of a protein, 986 00:42:33,750 --> 00:42:37,530 so each exon codes for a part of a protein. 987 00:42:37,530 --> 00:42:41,400 And when they're all stuck together in the proper way 988 00:42:41,400 --> 00:42:45,090 the single transcript, the single mRNA 989 00:42:45,090 --> 00:42:47,100 can be read and will be read 990 00:42:47,100 --> 00:42:49,260 and translated into a single protein. 991 00:42:49,260 --> 00:42:52,620 Okay, but where can we get some variability? 992 00:42:52,620 --> 00:42:55,470 So we talked about there being 25,000 genes. 993 00:42:55,470 --> 00:42:58,950 Well there are over a hundred thousand different proteins. 994 00:42:58,950 --> 00:43:02,070 How is that possible if we only have 25,000 different genes? 995 00:43:02,070 --> 00:43:03,960 Well, the cells pretty smart 996 00:43:03,960 --> 00:43:06,780 and it's come up with a kind of a cool way to do it 997 00:43:06,780 --> 00:43:09,720 and it does it in sort of a modular fashion. 998 00:43:09,720 --> 00:43:11,550 And what do I mean by that? 999 00:43:11,550 --> 00:43:15,000 Well it kind of takes each of these exons as a model 1000 00:43:15,000 --> 00:43:19,170 and can stick them together remaining in its linear fashion, 1001 00:43:19,170 --> 00:43:21,330 but can choose, for example, 1002 00:43:21,330 --> 00:43:23,850 in one version of the transcript, 1003 00:43:23,850 --> 00:43:27,090 it can choose to only include, say exons one, two, 1004 00:43:27,090 --> 00:43:29,070 oh we'll skip exon three, 1005 00:43:29,070 --> 00:43:31,050 we'll include exon four, five, and six. 1006 00:43:31,050 --> 00:43:32,610 So that's one type of mRNA 1007 00:43:32,610 --> 00:43:35,220 that can form from this single transcript. 1008 00:43:35,220 --> 00:43:38,613 You could also then say, oh, and instead I'll do exon one. 1009 00:43:39,642 --> 00:43:42,300 In this case the cell doesn't actually need the protein 1010 00:43:42,300 --> 00:43:44,070 to have this particular region. 1011 00:43:44,070 --> 00:43:45,180 So it's going to cut that out 1012 00:43:45,180 --> 00:43:48,180 and instead do one, three, doesn't need four, 1013 00:43:48,180 --> 00:43:49,560 let's say it needs five and six, 1014 00:43:49,560 --> 00:43:51,990 so it'll form this particular version. 1015 00:43:51,990 --> 00:43:54,540 Or it can form any other version of this, 1016 00:43:54,540 --> 00:43:57,160 just remember it always stays linear, so 1017 00:43:58,140 --> 00:44:00,363 exon one always has to come before, 1018 00:44:02,130 --> 00:44:04,380 so you can't say for example, 1019 00:44:04,380 --> 00:44:09,380 do exon one, then four, then two, then six, then three. 1020 00:44:09,450 --> 00:44:10,980 It has to be linear so 1021 00:44:10,980 --> 00:44:13,050 you can basically remove certain exons 1022 00:44:13,050 --> 00:44:16,980 or not include them in the final mRNA that gets translated, 1023 00:44:16,980 --> 00:44:20,070 but you can't rearrange the order of exons. 1024 00:44:20,070 --> 00:44:22,080 Okay, I know that's confusing, 1025 00:44:22,080 --> 00:44:23,220 but just think about it for a second 1026 00:44:23,220 --> 00:44:24,390 and really look at this picture 1027 00:44:24,390 --> 00:44:27,453 'cause I think this particular picture demonstrates it well. 1028 00:44:28,770 --> 00:44:30,390 The end result of which would be 1029 00:44:30,390 --> 00:44:32,490 three different versions of a protein 1030 00:44:32,490 --> 00:44:34,770 or three different proteins I guess you could say 1031 00:44:34,770 --> 00:44:36,090 that are similar to one another, 1032 00:44:36,090 --> 00:44:39,030 but are not identical because they contain different, 1033 00:44:39,030 --> 00:44:40,217 this would be a single protein. 1034 00:44:40,217 --> 00:44:43,260 I know it's shown as like different blobs, 1035 00:44:43,260 --> 00:44:44,940 but those are all strung together 1036 00:44:44,940 --> 00:44:48,090 as one long chain of amino acids that then forms 1037 00:44:48,090 --> 00:44:49,620 these different structures. 1038 00:44:49,620 --> 00:44:53,940 And I want to mention that this is not a rare event 1039 00:44:53,940 --> 00:44:56,370 where you have alternative splicing occurring. 1040 00:44:56,370 --> 00:44:58,560 This occurs in 90% of genes. 1041 00:44:58,560 --> 00:45:01,560 So most genes you can have different 1042 00:45:01,560 --> 00:45:04,080 what are called splice variants. 1043 00:45:04,080 --> 00:45:06,003 Splice variants, which is just, 1044 00:45:06,930 --> 00:45:08,850 say this is one splice variant, 1045 00:45:08,850 --> 00:45:11,610 this is another splice variant, this is another 1046 00:45:11,610 --> 00:45:14,550 which are each translated into different versions of 1047 00:45:14,550 --> 00:45:17,070 protein, which can have very different function. 1048 00:45:17,070 --> 00:45:22,070 Just want to mention here, introns are cut out of the RNA. 1049 00:45:22,230 --> 00:45:26,730 We never ever, ever, ever change our DNA. 1050 00:45:26,730 --> 00:45:29,490 Think of DNA, our actual genes, 1051 00:45:29,490 --> 00:45:32,193 think of those as like read only files. 1052 00:45:33,090 --> 00:45:36,030 So you can open it, you can look at it, you can copy it, 1053 00:45:36,030 --> 00:45:37,410 but you cannot change it. 1054 00:45:37,410 --> 00:45:41,670 You cannot make any changes to the DNA, so as a result, 1055 00:45:41,670 --> 00:45:45,210 all of the changes are occurring really at the RNA level. 1056 00:45:45,210 --> 00:45:48,600 Let's look at an example of gene regulation 1057 00:45:48,600 --> 00:45:51,670 and this would be more transcriptional control where 1058 00:45:52,800 --> 00:45:56,310 this might be very applicable in some of your practices, 1059 00:45:56,310 --> 00:45:58,380 specifically response to estrogen 1060 00:45:58,380 --> 00:46:00,600 to prepare for possible pregnancy. 1061 00:46:00,600 --> 00:46:04,200 So estrogen, as you probably know, is a hormone. 1062 00:46:04,200 --> 00:46:07,560 It is what we call a small molecule, so it's not a protein. 1063 00:46:07,560 --> 00:46:11,070 Estrogen is not a protein, it is a small molecule. 1064 00:46:11,070 --> 00:46:14,880 It's produced in females, it's produced by the ovaries, 1065 00:46:14,880 --> 00:46:18,840 but I'm sure you're all aware of estrogen therapy, which 1066 00:46:18,840 --> 00:46:21,600 basically is you can take a pill. 1067 00:46:21,600 --> 00:46:24,960 Birth control pills contain estradiol or estrogen 1068 00:46:24,960 --> 00:46:27,060 as well as hormone replacement therapy 1069 00:46:27,060 --> 00:46:28,923 can also contain estrogen. 1070 00:46:30,450 --> 00:46:31,960 So these are small molecules 1071 00:46:32,861 --> 00:46:35,190 and they're small molecules that have a big impact. 1072 00:46:35,190 --> 00:46:38,673 And here's why, they actually affect gene expression. 1073 00:46:39,510 --> 00:46:41,400 So cells respond to estrogen in part 1074 00:46:41,400 --> 00:46:43,500 through changes in gene expression. 1075 00:46:43,500 --> 00:46:47,130 Estrogen receptor acts, so an estrogen receptor is a protein 1076 00:46:47,130 --> 00:46:50,430 that we produce in certain cells. 1077 00:46:50,430 --> 00:46:51,990 Actually in a lot of our different cells 1078 00:46:51,990 --> 00:46:55,140 contain estrogen receptor, it's quite interesting. 1079 00:46:55,140 --> 00:46:58,350 I mean primarily we focus on cells in breast tissue 1080 00:46:58,350 --> 00:47:01,620 and say in the uterus, 1081 00:47:01,620 --> 00:47:03,360 but certainly there are other cells 1082 00:47:03,360 --> 00:47:05,040 that also express estrogen receptor, 1083 00:47:05,040 --> 00:47:08,520 including some cells in the heart, cells in the brain, 1084 00:47:08,520 --> 00:47:10,110 and in other locations. 1085 00:47:10,110 --> 00:47:13,050 And you can start to imagine the impact of that 1086 00:47:13,050 --> 00:47:16,890 as we talk through the dramatic impact 1087 00:47:16,890 --> 00:47:19,740 that estrogen can have on gene expression. 1088 00:47:19,740 --> 00:47:23,730 So estrogen receptors, again, proteins that bind to estrogen 1089 00:47:23,730 --> 00:47:25,140 act as transcription factor 1090 00:47:25,140 --> 00:47:27,510 when estrogen is present in the cell. 1091 00:47:27,510 --> 00:47:28,680 So they enter the nucleus 1092 00:47:28,680 --> 00:47:31,080 and bind to specific sequences in the DNA 1093 00:47:31,080 --> 00:47:33,600 called estrogen responsive elements or EREs 1094 00:47:33,600 --> 00:47:36,330 and this is just really like a specific sequence, so 1095 00:47:36,330 --> 00:47:38,490 I don't actually recall off the top of my head 1096 00:47:38,490 --> 00:47:41,250 what the sequence is, but it's like a specific 1097 00:47:41,250 --> 00:47:43,470 set of six bases in a row 1098 00:47:43,470 --> 00:47:45,060 say that the estrogen receptor 1099 00:47:45,060 --> 00:47:48,360 when it's bound to estrogen will bind to 1100 00:47:48,360 --> 00:47:49,983 wherever it finds it in DNA. 1101 00:47:51,450 --> 00:47:53,880 And they can activate transcription of genes 1102 00:47:53,880 --> 00:47:57,450 with these estrogen response elements in their promoters. 1103 00:47:57,450 --> 00:47:58,770 When estrogen is absent, 1104 00:47:58,770 --> 00:48:01,410 estrogen receptors cannot bind to DNA. 1105 00:48:01,410 --> 00:48:04,200 So some genes that code for cell proliferation proteins 1106 00:48:04,200 --> 00:48:06,480 have these estrogen response elements 1107 00:48:06,480 --> 00:48:07,560 and thus their transcription 1108 00:48:07,560 --> 00:48:10,140 is activated in the presence of estrogen. 1109 00:48:10,140 --> 00:48:12,240 Not all cells express estrogen receptor, 1110 00:48:12,240 --> 00:48:14,400 thus not all cells are responsive to estrogen, 1111 00:48:14,400 --> 00:48:17,730 but as I mentioned, there actually are quite a few that do. 1112 00:48:17,730 --> 00:48:19,860 Cells in breast tissue and uterine lining 1113 00:48:19,860 --> 00:48:22,230 along with certain other tissues proliferate 1114 00:48:22,230 --> 00:48:26,160 in preparation for possible pregnancy. 1115 00:48:26,160 --> 00:48:29,010 So let's take a look at what that actually means. 1116 00:48:29,010 --> 00:48:32,230 If we have estrogen, let's say being shown with this 1117 00:48:33,090 --> 00:48:35,710 purple molecule here, it enters the cell 1118 00:48:35,710 --> 00:48:37,890 so it actually can just diffuse into the cell. 1119 00:48:37,890 --> 00:48:40,380 So this is again, a small molecule, not a protein, 1120 00:48:40,380 --> 00:48:42,480 but a small molecule diffuses into the cell 1121 00:48:42,480 --> 00:48:45,060 can bind to the protein that we 1122 00:48:45,060 --> 00:48:47,280 have present in certain cells, right? 1123 00:48:47,280 --> 00:48:49,650 So this estrogen receptor is present. 1124 00:48:49,650 --> 00:48:52,740 The estrogen molecule binds to this protein. 1125 00:48:52,740 --> 00:48:56,940 The estrogen receptor can now act as a transcription factor. 1126 00:48:56,940 --> 00:48:58,980 So remember what is a transcription factor? 1127 00:48:58,980 --> 00:49:01,110 It's a protein that binds specifically 1128 00:49:01,110 --> 00:49:05,430 to certain sequences on DNA 1129 00:49:05,430 --> 00:49:07,680 and specifically in a promoter region. 1130 00:49:07,680 --> 00:49:09,670 So this particular gene here 1131 00:49:10,680 --> 00:49:13,980 has within its promoter region an estrogen response element, 1132 00:49:13,980 --> 00:49:18,540 which just simply means the sequence of DNA that 1133 00:49:18,540 --> 00:49:21,630 the transcription factor binds to specifically. 1134 00:49:21,630 --> 00:49:23,910 So the estrogen receptor 1135 00:49:23,910 --> 00:49:27,510 with its bound estrogen will bind to the promoter 1136 00:49:27,510 --> 00:49:29,070 for say this particular gene. 1137 00:49:29,070 --> 00:49:31,110 And let's say this gene is involved in 1138 00:49:31,110 --> 00:49:33,123 inducing cell proliferation. 1139 00:49:34,020 --> 00:49:36,240 So the estrogen receptor 1140 00:49:36,240 --> 00:49:38,550 with its estrogen binds to the promoter. 1141 00:49:38,550 --> 00:49:39,660 In this particular diagram, 1142 00:49:39,660 --> 00:49:41,040 they're calling these coactivators, 1143 00:49:41,040 --> 00:49:43,890 what I was calling like the scaffolding proteins, 1144 00:49:43,890 --> 00:49:47,610 and you know, transcriptional machinery all can now bind 1145 00:49:47,610 --> 00:49:52,530 and you have transcription of this particular gene. 1146 00:49:52,530 --> 00:49:55,920 Transcription means that the mRNA is produced, remember, 1147 00:49:55,920 --> 00:49:58,290 and now what happens to mRNA once it's produced? 1148 00:49:58,290 --> 00:50:02,730 It has to be spliced in order to remove those introns 1149 00:50:02,730 --> 00:50:04,500 and just allow the exons to be present. 1150 00:50:04,500 --> 00:50:08,430 So let's say now you have your fully formed mature 1151 00:50:08,430 --> 00:50:11,130 messenger RNA which exits the nucleus, 1152 00:50:11,130 --> 00:50:13,560 and in this diagram, they're not showing translation. 1153 00:50:13,560 --> 00:50:16,080 But remember ribosomes will bind to this mRNA 1154 00:50:16,080 --> 00:50:18,510 and will produce the specific proteins 1155 00:50:18,510 --> 00:50:20,430 that this gene encodes. 1156 00:50:20,430 --> 00:50:21,450 These specific proteins, 1157 00:50:21,450 --> 00:50:23,880 let's say in this case for this gene, 1158 00:50:23,880 --> 00:50:28,290 let's say these proteins play a role in cell proliferation, 1159 00:50:28,290 --> 00:50:32,253 so increasing the amount the cell will grow and divide. 1160 00:50:33,690 --> 00:50:36,210 And so that's what occurs as a result. 1161 00:50:36,210 --> 00:50:38,490 So the cell will, let's see, 1162 00:50:38,490 --> 00:50:40,950 let's just do a diagram of what would happen here. 1163 00:50:40,950 --> 00:50:42,930 You have high levels of estrogen, 1164 00:50:42,930 --> 00:50:46,140 it gets into the cell, estrogen receptor can go in 1165 00:50:46,140 --> 00:50:49,120 and bind to the promoter for these 1166 00:50:50,040 --> 00:50:52,560 cell proliferation genes, activates them, 1167 00:50:52,560 --> 00:50:54,300 turns on transcription, 1168 00:50:54,300 --> 00:50:57,390 the mRNA for those genes gets translated, 1169 00:50:57,390 --> 00:50:59,580 so you have these functional proteins 1170 00:50:59,580 --> 00:51:01,140 that are involved in proliferation, 1171 00:51:01,140 --> 00:51:03,990 and boom, you have these cells dividing like crazy, 1172 00:51:03,990 --> 00:51:05,850 specifically breast or uterine cells. 1173 00:51:05,850 --> 00:51:08,100 And the breast tissue is proliferating 1174 00:51:08,100 --> 00:51:10,530 in preparation for lactation 1175 00:51:10,530 --> 00:51:13,680 and the uterine cells are proliferating 1176 00:51:13,680 --> 00:51:15,580 in preparation for possible pregnancy. 1177 00:51:18,292 --> 00:51:20,910 As we all know, in the normal menstrual cycle, 1178 00:51:20,910 --> 00:51:24,000 there are various levels of estrogen that occur 1179 00:51:24,000 --> 00:51:27,060 and in the high peak levels of estrogen, 1180 00:51:27,060 --> 00:51:30,210 this is when, say in the example of breast cells, 1181 00:51:30,210 --> 00:51:32,040 you have the most proliferation. 1182 00:51:32,040 --> 00:51:34,320 And this is when you know breast tissue will actually 1183 00:51:34,320 --> 00:51:37,950 increase during the cycle as a result of estrogen 1184 00:51:37,950 --> 00:51:40,140 because estrogen is, what? 1185 00:51:40,140 --> 00:51:43,080 It's activating estrogen receptor, which is a 1186 00:51:43,080 --> 00:51:46,350 transcription factor which will bind to 1187 00:51:46,350 --> 00:51:50,280 say cell proliferation genes in their promoter 1188 00:51:50,280 --> 00:51:52,530 and induce their transcription, 1189 00:51:52,530 --> 00:51:55,023 which then results in cell proliferation. 1190 00:51:57,750 --> 00:51:59,070 And as this goes through, 1191 00:51:59,070 --> 00:52:01,590 so you have a breast cell proliferation 1192 00:52:01,590 --> 00:52:04,590 and increase in the tissue density at that time. 1193 00:52:04,590 --> 00:52:08,250 And then when pregnancy does not occur, 1194 00:52:08,250 --> 00:52:10,200 the estrogen levels will decline 1195 00:52:10,200 --> 00:52:12,720 and as a result you lose that proliferation 1196 00:52:12,720 --> 00:52:15,030 and the cell starts to die off and 1197 00:52:15,030 --> 00:52:19,800 the tissue returns to its normal density and normal state. 1198 00:52:19,800 --> 00:52:22,890 The reason why I wanted to bring up this particular 1199 00:52:22,890 --> 00:52:25,830 example is because we will discuss in more detail 1200 00:52:25,830 --> 00:52:28,440 breast cancer and its genetic implications. 1201 00:52:28,440 --> 00:52:30,090 But I wanted to start you out here 1202 00:52:30,090 --> 00:52:31,680 with just a basic understanding 1203 00:52:31,680 --> 00:52:33,840 of how estrogen receptor works 1204 00:52:33,840 --> 00:52:35,733 because it is a transcription factor. 1205 00:52:37,200 --> 00:52:39,690 All right, let's summarize what we have learned. 1206 00:52:39,690 --> 00:52:41,220 Cells need to regulate the extent 1207 00:52:41,220 --> 00:52:43,440 to which certain genes are expressed to control 1208 00:52:43,440 --> 00:52:45,690 how much of a specific protein is around 1209 00:52:45,690 --> 00:52:47,310 to perform functions as needed. 1210 00:52:47,310 --> 00:52:51,390 Remember, not all proteins should be present all the time, 1211 00:52:51,390 --> 00:52:54,390 only really in response to certain environmental cues 1212 00:52:54,390 --> 00:52:58,740 or for the specific function of a particular cell. 1213 00:52:58,740 --> 00:53:00,365 The genes are regulated both 1214 00:53:00,365 --> 00:53:02,340 transcriptionally and post-transcriptionally 1215 00:53:02,340 --> 00:53:03,810 and by that I mean 1216 00:53:03,810 --> 00:53:08,810 the both in how much mRNA is actually transcribed 1217 00:53:09,060 --> 00:53:10,770 or when mRNA is actually transcribed. 1218 00:53:10,770 --> 00:53:13,140 And then for post-transcriptionally, 1219 00:53:13,140 --> 00:53:16,947 once the mRNA has been formed in the splicing of that mRNA 1220 00:53:16,947 --> 00:53:19,200 and which exons will make it on 1221 00:53:19,200 --> 00:53:21,840 to the final mature mRNA product 1222 00:53:21,840 --> 00:53:25,290 and therefore will affect which protein 1223 00:53:25,290 --> 00:53:27,123 is actually translated. 1224 00:53:28,980 --> 00:53:30,210 Transcriptional regulation involves both 1225 00:53:30,210 --> 00:53:32,370 the presence and absence of transcription factors 1226 00:53:32,370 --> 00:53:35,490 and also access of transcription factors to promoter 1227 00:53:35,490 --> 00:53:38,160 controlled by epigenetic modifications. 1228 00:53:38,160 --> 00:53:40,740 So you have two levels here, you have both 1229 00:53:40,740 --> 00:53:43,380 whether or not transcription factor is present, 1230 00:53:43,380 --> 00:53:45,690 but also can the transcription factor even reach 1231 00:53:45,690 --> 00:53:48,150 its promoter or bind to its promoter 1232 00:53:48,150 --> 00:53:51,033 and that's the epigenetic modification side of things. 1233 00:53:51,870 --> 00:53:53,850 Post-transcriptional regulation affects 1234 00:53:53,850 --> 00:53:56,790 the final mRNA sequence through alternative splicing 1235 00:53:56,790 --> 00:54:00,720 as we discussed and if you have questions on that, 1236 00:54:00,720 --> 00:54:02,430 I'm more than, or that or anything, 1237 00:54:02,430 --> 00:54:05,010 I'm more than happy to discuss with you. 1238 00:54:05,010 --> 00:54:06,540 It seems like it's working out really well 1239 00:54:06,540 --> 00:54:09,720 to just go ahead and post those onto the discussion board 1240 00:54:09,720 --> 00:54:11,070 because if you have a question about it, 1241 00:54:11,070 --> 00:54:13,170 probably someone else does and 1242 00:54:13,170 --> 00:54:15,960 I'm sure everyone would be happy to 1243 00:54:15,960 --> 00:54:20,190 see both your question and the response to that 1244 00:54:20,190 --> 00:54:21,870 or clarification to that. 1245 00:54:21,870 --> 00:54:24,570 So please feel free to post away 1246 00:54:24,570 --> 00:54:26,373 any questions that you might have. 1247 00:54:27,900 --> 00:54:29,640 So what's next in this module? 1248 00:54:29,640 --> 00:54:31,260 We're going to switch gears a little bit 1249 00:54:31,260 --> 00:54:33,420 and start talking about two aspects 1250 00:54:33,420 --> 00:54:35,640 that really fit hand in hand with one one another 1251 00:54:35,640 --> 00:54:37,620 and those would be DNA replication 1252 00:54:37,620 --> 00:54:40,980 and then meiosis and mitosis, which would be cell division. 1253 00:54:40,980 --> 00:54:44,100 DNA replication being the process of actually 1254 00:54:44,100 --> 00:54:47,640 creating exact duplicates of all of your DNA 1255 00:54:47,640 --> 00:54:50,370 in preparation for one cell becoming two cells. 1256 00:54:50,370 --> 00:54:53,730 So and that process of one cell becoming two cells 1257 00:54:53,730 --> 00:54:57,540 is mitosis and the process of forming 1258 00:54:57,540 --> 00:54:59,580 egg or sperm cells is called meiosis. 1259 00:54:59,580 --> 00:55:02,670 And we'll get into all of the details of that next, woo. 1260 00:55:02,670 --> 00:55:06,270 So, thank you for hanging with me through this lecture 1261 00:55:06,270 --> 00:55:08,040 and, again, please let me know 1262 00:55:08,040 --> 00:55:10,020 if you have any questions or comments. 1263 00:55:10,020 --> 00:55:11,490 So remember, you will get this, 1264 00:55:11,490 --> 00:55:12,720 you are absolutely getting there, 1265 00:55:12,720 --> 00:55:14,520 think of how much farther along you are now 1266 00:55:14,520 --> 00:55:16,980 than you were at the beginning of module two. 1267 00:55:16,980 --> 00:55:18,270 I mean, even if you already knew 1268 00:55:18,270 --> 00:55:20,598 a lot of what we covered in module two, 1269 00:55:20,598 --> 00:55:23,250 it was a lot of refreshing, I hope, 1270 00:55:23,250 --> 00:55:26,190 and you know, you're making a lot of progress 1271 00:55:26,190 --> 00:55:29,250 and getting there and you are going to get there. 1272 00:55:29,250 --> 00:55:30,810 We are absolutely going to get there, 1273 00:55:30,810 --> 00:55:32,310 we're gonna get there together. 1274 00:55:32,310 --> 00:55:34,860 So if you have questions, let me know, 1275 00:55:34,860 --> 00:55:38,643 and otherwise I will talk with you in the next lecture.