1 00:00:00,090 --> 00:00:02,490 The following content is provided under a Creative 2 00:00:02,490 --> 00:00:04,059 Commons license. 3 00:00:04,059 --> 00:00:06,330 Your support will help MIT OpenCourseWare 4 00:00:06,330 --> 00:00:10,720 continue to offer high quality educational resources for free. 5 00:00:10,720 --> 00:00:13,320 To make a donation or view additional materials 6 00:00:13,320 --> 00:00:17,280 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:17,280 --> 00:00:18,450 at ocw.mit.edu. 8 00:00:26,510 --> 00:00:31,930 HAZEL SIVE: I want to discuss with you today 9 00:00:31,930 --> 00:00:36,580 a very topical and interesting question, which 10 00:00:36,580 --> 00:00:38,110 is the notion of stem cells. 11 00:00:43,990 --> 00:00:49,420 In fact, I'm going to discuss two things, the first of which 12 00:00:49,420 --> 00:00:52,240 is another concept that you need, 13 00:00:52,240 --> 00:00:54,520 following on from the concepts we had right 14 00:00:54,520 --> 00:00:57,310 at the beginning of lecture. 15 00:00:57,310 --> 00:01:00,740 I feel like this microphone-- 16 00:01:00,740 --> 00:01:03,720 The first is a concept that you need in addition to the ones 17 00:01:03,720 --> 00:01:05,220 we started lecture with, and then 18 00:01:05,220 --> 00:01:06,550 we'll talk about stem cells. 19 00:01:06,550 --> 00:01:15,570 So today, we'll talk about potency, 20 00:01:15,570 --> 00:01:17,360 and then we'll talk about stem cells. 21 00:01:24,930 --> 00:01:29,070 Potency, along with fate, determination, 22 00:01:29,070 --> 00:01:32,160 and differentiation, is one of those terms 23 00:01:32,160 --> 00:01:35,070 that you need to know and you need to understand in order 24 00:01:35,070 --> 00:01:36,390 to understand stem cells. 25 00:01:41,820 --> 00:01:45,480 Potency refers to the number of possible fates 26 00:01:45,480 --> 00:02:04,370 that a cell can acquire, number of possible fates 27 00:02:04,370 --> 00:02:05,840 open to a cell. 28 00:02:08,800 --> 00:02:11,710 And this is a very important concept of development 29 00:02:11,710 --> 00:02:16,870 because, in general, potency decreases with age, 30 00:02:16,870 --> 00:02:20,680 and decreases as different parts of the organism 31 00:02:20,680 --> 00:02:23,740 become specialized. 32 00:02:23,740 --> 00:02:29,245 So in general, potency decreases with age. 33 00:02:34,880 --> 00:02:36,380 But I will put in here, and we'll 34 00:02:36,380 --> 00:02:51,100 explore this more in a moment, except for some stem cells. 35 00:02:51,100 --> 00:02:55,370 And we haven't defined a stem cell yet, but we will. 36 00:02:55,370 --> 00:02:57,890 What kinds of potencies are there? 37 00:02:57,890 --> 00:03:02,080 There's the big one, totipotent, where 38 00:03:02,080 --> 00:03:04,110 a cell can become all fates. 39 00:03:09,690 --> 00:03:11,500 And there's really only one cell that 40 00:03:11,500 --> 00:03:15,190 can do this in the normal animal, and is the zygote. 41 00:03:17,890 --> 00:03:20,800 And in most animals, even as the zygote 42 00:03:20,800 --> 00:03:24,880 becomes just two cells or a few cells, 43 00:03:24,880 --> 00:03:28,600 that full potency is lost. 44 00:03:28,600 --> 00:03:32,590 And cells instead, in the embryo, 45 00:03:32,590 --> 00:03:39,940 are multi or pluripotent, which means that they can acquire 46 00:03:39,940 --> 00:03:42,535 many fates, but not all fates. 47 00:03:46,300 --> 00:03:51,430 Embryonic cells, especially in the early embryo, 48 00:03:51,430 --> 00:03:54,790 and many stem cells can also become, 49 00:03:54,790 --> 00:03:58,030 are also multipotent or pluripotent. 50 00:03:58,030 --> 00:04:01,510 And then as time progresses-- is that a hand up? 51 00:04:01,510 --> 00:04:02,686 Yes, sir. 52 00:04:02,686 --> 00:04:08,518 AUDIENCE: How do you reconcile the fact that human cells, 53 00:04:08,518 --> 00:04:09,976 we can separate them. 54 00:04:09,976 --> 00:04:12,041 Even at the eight cell stage. 55 00:04:12,041 --> 00:04:13,540 HAZEL SIVE: That's a great question. 56 00:04:13,540 --> 00:04:15,204 The question is how do I reconcile 57 00:04:15,204 --> 00:04:16,620 what I'm telling you with the fact 58 00:04:16,620 --> 00:04:20,970 that you can get identical sextuplets, 59 00:04:20,970 --> 00:04:23,610 or octuplets actually? 60 00:04:23,610 --> 00:04:24,870 It's a good question. 61 00:04:24,870 --> 00:04:25,560 That's true. 62 00:04:25,560 --> 00:04:29,310 In different animals, the very early embryonic cells 63 00:04:29,310 --> 00:04:31,980 are sometimes totipotent up to a while. 64 00:04:31,980 --> 00:04:32,760 OK? 65 00:04:32,760 --> 00:04:35,220 And so for example, in armadillo, 66 00:04:35,220 --> 00:04:39,030 here's a piece of, you know, fact for your back pockets. 67 00:04:39,030 --> 00:04:43,230 In the armadillo, the eight-cell embryo almost always 68 00:04:43,230 --> 00:04:46,590 splits into eight single cells, each of which 69 00:04:46,590 --> 00:04:48,401 becomes a baby armadillo. 70 00:04:48,401 --> 00:04:48,900 OK? 71 00:04:48,900 --> 00:04:52,050 So those cells are totipotent. 72 00:04:52,050 --> 00:04:55,600 In mice, even at the two cell stage, 73 00:04:55,600 --> 00:04:59,880 the two mouse cells are probably not equivalently potent 74 00:04:59,880 --> 00:05:01,740 and they're not totipotent. 75 00:05:01,740 --> 00:05:03,600 So very, very seldom-- 76 00:05:03,600 --> 00:05:07,541 almost never-- get identical mouse twins. 77 00:05:07,541 --> 00:05:08,040 OK? 78 00:05:08,040 --> 00:05:10,530 So it's one of these generalities. 79 00:05:10,530 --> 00:05:15,650 And if you ask me, you get the specifics are a bit different. 80 00:05:15,650 --> 00:05:18,400 As cell fate restriction continues, 81 00:05:18,400 --> 00:05:23,600 cells can become bipotent, or unipotent, 82 00:05:23,600 --> 00:05:32,940 whereby one or just two fates are open to them. 83 00:05:32,940 --> 00:05:38,490 And so if we look, taking this concept, 84 00:05:38,490 --> 00:05:42,420 let's now start the lecture about stem cells. 85 00:05:42,420 --> 00:05:44,400 You're going to need this concept. 86 00:05:44,400 --> 00:05:48,440 Stem cells, I'll point out, whatever they are, 87 00:05:48,440 --> 00:05:51,880 got almost 3,000 hits yesterday on Google News. 88 00:05:51,880 --> 00:05:54,950 This is way below baseball, which got 45,000. 89 00:05:54,950 --> 00:05:55,530 I checked. 90 00:05:55,530 --> 00:05:58,350 But still, you know, as science topics go, 91 00:05:58,350 --> 00:06:00,630 stem cells are really up there. 92 00:06:00,630 --> 00:06:05,280 And they're on the covers of magazines, over and over again. 93 00:06:05,280 --> 00:06:07,260 And we'll talk more about why that is. 94 00:06:07,260 --> 00:06:09,210 Here's a diagram-- it's not on your handouts-- 95 00:06:09,210 --> 00:06:10,043 that I drew for you. 96 00:06:10,043 --> 00:06:11,500 Let's not dwell on it. 97 00:06:11,500 --> 00:06:14,310 But let's now move on to Topic Number 98 00:06:14,310 --> 00:06:20,130 2, which will fold in this concept of potency 99 00:06:20,130 --> 00:06:23,220 and the concepts of fate, determination, 100 00:06:23,220 --> 00:06:26,805 and differentiation, and talk about stem cells. 101 00:06:33,940 --> 00:06:37,050 And let's do, as is our custom, let's 102 00:06:37,050 --> 00:06:39,900 define what a stem cell is. 103 00:06:39,900 --> 00:06:42,300 I think that a stem cell can be defined 104 00:06:42,300 --> 00:06:45,510 as a cell of variable potency that 105 00:06:45,510 --> 00:06:49,710 has the capacity to self-renew. 106 00:06:49,710 --> 00:07:06,560 Cells of variable potency that can self-renew. 107 00:07:06,560 --> 00:07:08,956 They can make more of themselves. 108 00:07:12,530 --> 00:07:16,250 Despite the hype, despite covers of Time Magazine 109 00:07:16,250 --> 00:07:20,540 and almost every front page of every newspaper 110 00:07:20,540 --> 00:07:26,150 across the world, stem cells are normally found in our bodies. 111 00:07:26,150 --> 00:07:32,360 And normally, as we'll explore, they're 112 00:07:32,360 --> 00:07:44,855 used for organ maintenance and repair, organ maintenance 113 00:07:44,855 --> 00:07:45,355 and repair. 114 00:07:48,220 --> 00:07:51,880 But the thing, you know, that has everyone fired up 115 00:07:51,880 --> 00:07:54,580 is that you can somehow harness these cells 116 00:07:54,580 --> 00:07:56,830 for therapeutic purposes. 117 00:07:56,830 --> 00:08:03,790 And that you can repair what the body cannot, by being clever, 118 00:08:03,790 --> 00:08:09,130 and using the power of these cells as they normally have it, 119 00:08:09,130 --> 00:08:11,420 or as you can give it to them. 120 00:08:11,420 --> 00:08:16,150 And so there's this question of therapy and therapeutic stem 121 00:08:16,150 --> 00:08:22,720 cells, where the idea, again, is that you would repair a damaged 122 00:08:22,720 --> 00:08:36,409 organ by introducing somehow, injecting 123 00:08:36,409 --> 00:08:45,150 or otherwise introducing, extra or somehow special stem cells-- 124 00:08:45,150 --> 00:08:51,190 which I am going to abbreviate heretofore as SC-- 125 00:08:51,190 --> 00:08:57,270 by introducing extra stem cells into a damaged body. 126 00:08:57,270 --> 00:08:58,480 Does this work? 127 00:08:58,480 --> 00:09:00,010 It does work. 128 00:09:00,010 --> 00:09:04,740 It works for the hematopoietic system, 129 00:09:04,740 --> 00:09:06,570 as in bone marrow transplants. 130 00:09:15,600 --> 00:09:18,310 And it also works for skin cell transplants. 131 00:09:25,040 --> 00:09:27,430 Well, let's just put skin cells. 132 00:09:27,430 --> 00:09:27,930 OK. 133 00:09:36,950 --> 00:09:42,470 Skin stem cells can be grown from your own skin. 134 00:09:42,470 --> 00:09:44,330 And in the case of burn victims, this 135 00:09:44,330 --> 00:09:46,130 has really saved countless lives. 136 00:09:46,130 --> 00:09:49,700 The original technology began to be developed here 137 00:09:49,700 --> 00:09:53,150 at MIT by Professor Howard Green, who is now at Harvard. 138 00:09:53,150 --> 00:09:56,420 But the idea is to take your skin 139 00:09:56,420 --> 00:09:59,480 and grow it on something like gauze 140 00:09:59,480 --> 00:10:02,330 or some kind of some solid support, 141 00:10:02,330 --> 00:10:10,640 and then to cover a burn patient with layers of support on which 142 00:10:10,640 --> 00:10:12,650 there are some stem cells. 143 00:10:12,650 --> 00:10:15,890 And these stem cells will help fill in the holes 144 00:10:15,890 --> 00:10:17,690 in the skin left by the burn. 145 00:10:17,690 --> 00:10:21,740 Normally when a wound heals, as I'm sure you've noticed, 146 00:10:21,740 --> 00:10:23,990 it heals from the sides. 147 00:10:23,990 --> 00:10:26,550 The only way a wound can heal is from the side. 148 00:10:26,550 --> 00:10:30,020 And if it's a big wound, it can take a very, very long time 149 00:10:30,020 --> 00:10:30,530 to heal. 150 00:10:30,530 --> 00:10:32,300 And you can get infections and so on 151 00:10:32,300 --> 00:10:34,580 while the healing process is going on. 152 00:10:34,580 --> 00:10:39,050 So seeding the inside of a wound with stem cells that 153 00:10:39,050 --> 00:10:41,840 can start the skin regeneration process 154 00:10:41,840 --> 00:10:43,850 and seal up the body against infection, 155 00:10:43,850 --> 00:10:45,540 that's been incredibly useful. 156 00:10:45,540 --> 00:10:49,805 And we'll talk more about bone marrow transplants in a moment. 157 00:10:49,805 --> 00:10:50,305 OK. 158 00:10:52,970 --> 00:10:59,090 We previously talked about this process by which cells decide, 159 00:10:59,090 --> 00:11:01,100 are undecided initially, they decide 160 00:11:01,100 --> 00:11:02,450 what they're going to become. 161 00:11:02,450 --> 00:11:05,300 And then they differentiate into their final function. 162 00:11:05,300 --> 00:11:08,510 Stem cells fit into this litany somewhere 163 00:11:08,510 --> 00:11:13,170 between the commitment stage and the differentiation stage. 164 00:11:13,170 --> 00:11:15,650 And in this diagram, these multiple arrows 165 00:11:15,650 --> 00:11:17,340 are there for a reason. 166 00:11:17,340 --> 00:11:21,890 There are multiple steps between commitment and differentiation. 167 00:11:21,890 --> 00:11:26,870 And somewhere along the way, a group of cells with capacities 168 00:11:26,870 --> 00:11:31,940 we'll talk about, leaves this lineage 169 00:11:31,940 --> 00:11:35,990 and sits around and waits, partially determined, 170 00:11:35,990 --> 00:11:39,836 so that it can go on and make more differentiated cells when 171 00:11:39,836 --> 00:11:40,460 they're needed. 172 00:11:48,310 --> 00:11:52,150 And I've added on there the potency timeline, decreasing 173 00:11:52,150 --> 00:11:55,770 with age, of the developing animal. 174 00:11:58,710 --> 00:12:04,000 But let's diagram the notion of stem cells on the board. 175 00:12:04,000 --> 00:12:07,195 Stem cells generally divide slowly. 176 00:12:13,700 --> 00:12:14,270 Here's one. 177 00:12:18,150 --> 00:12:20,090 It's a variable potency. 178 00:12:20,090 --> 00:12:21,820 It may be multipotent. 179 00:12:21,820 --> 00:12:24,870 It may be bipotential. 180 00:12:24,870 --> 00:12:34,660 And it is somewhat committed, which is 181 00:12:34,660 --> 00:12:36,340 a slightly difficult concept. 182 00:12:36,340 --> 00:12:38,080 Because last time we talked about 183 00:12:38,080 --> 00:12:40,186 committed versus uncommitted. 184 00:12:40,186 --> 00:12:41,560 But now I'm telling you something 185 00:12:41,560 --> 00:12:43,450 can be somewhat committed. 186 00:12:43,450 --> 00:12:45,700 And that gets to this multiple arrows 187 00:12:45,700 --> 00:12:49,810 there were as cells progress in their fate decisions, 188 00:12:49,810 --> 00:12:52,330 they change their molecular signature 189 00:12:52,330 --> 00:12:55,240 and they really do become closer and closer 190 00:12:55,240 --> 00:12:57,310 to a cell that's made a decision. 191 00:12:57,310 --> 00:13:00,250 But it's kind of like, you know, if you're weighing up 192 00:13:00,250 --> 00:13:03,610 going to med school or going to graduate school 193 00:13:03,610 --> 00:13:05,860 in bioengineering, you know, you have 194 00:13:05,860 --> 00:13:07,960 decided that it will be one or the other, 195 00:13:07,960 --> 00:13:09,580 but you haven't decided which. 196 00:13:09,580 --> 00:13:10,972 You're somewhat committed. 197 00:13:10,972 --> 00:13:12,430 And then when you make the decision 198 00:13:12,430 --> 00:13:15,510 to go to graduate school, you have now become committed. 199 00:13:15,510 --> 00:13:16,010 OK? 200 00:13:16,010 --> 00:13:20,210 So the cell is doing the same kind of notion there. 201 00:13:20,210 --> 00:13:23,110 There's your stem cell, variable potency. 202 00:13:23,110 --> 00:13:26,230 Under the correct stimulus, that stem cell 203 00:13:26,230 --> 00:13:31,330 will divide to give rise to two different cells. 204 00:13:31,330 --> 00:13:33,265 One is another stem cell. 205 00:13:36,170 --> 00:13:38,870 And the other is something we'll call a progenitor. 206 00:13:43,980 --> 00:13:47,760 The progenitor is more committed than the stem cell. 207 00:13:54,900 --> 00:13:58,100 The progenitor cell is going to go on 208 00:13:58,100 --> 00:13:59,625 and divide, usually a lot. 209 00:14:09,150 --> 00:14:11,295 Progenitors divide rapidly. 210 00:14:15,880 --> 00:14:17,620 And their progeny will eventually 211 00:14:17,620 --> 00:14:22,390 go on and differentiate into one or more different kinds 212 00:14:22,390 --> 00:14:34,910 of cells, maybe a stripey cell, and a spotted cell type, 213 00:14:34,910 --> 00:14:37,230 and a cell type with squiggles. 214 00:14:37,230 --> 00:14:39,505 And so here are the differentiated cell types. 215 00:14:48,870 --> 00:14:52,380 And the number of different differentiated cells 216 00:14:52,380 --> 00:14:55,050 that comes out of this process is 217 00:14:55,050 --> 00:14:58,480 a reflection of the potency of the stem cell. 218 00:14:58,480 --> 00:14:59,370 OK? 219 00:14:59,370 --> 00:15:01,830 So here you've got these progenitors. 220 00:15:01,830 --> 00:15:05,080 The idea is that these progenitors 221 00:15:05,080 --> 00:15:06,460 will have similar potency. 222 00:15:06,460 --> 00:15:10,380 But as I'll show you, there's a whole variation on this. 223 00:15:10,380 --> 00:15:16,640 But here the number of differentiated cell types, 224 00:15:16,640 --> 00:15:22,730 the number of cell types reflects 225 00:15:22,730 --> 00:15:29,070 potency of the stem cell. 226 00:15:29,070 --> 00:15:29,570 OK? 227 00:15:32,970 --> 00:15:36,420 This kind of diagram is called a lineage diagram. 228 00:15:36,420 --> 00:15:38,100 It tells you what-- 229 00:15:38,100 --> 00:15:40,650 not only what the final fate of the cell is, 230 00:15:40,650 --> 00:15:42,810 it tells you something about the progress 231 00:15:42,810 --> 00:15:44,880 towards that final fate. 232 00:15:44,880 --> 00:15:51,960 So a lineage we can define as the set 233 00:15:51,960 --> 00:16:03,460 of cell types arising from a stem cell or a progenitor. 234 00:16:23,510 --> 00:16:26,180 Let's talk about the discovery of stem cells, because this 235 00:16:26,180 --> 00:16:29,930 is something that really was pivotal in helping 236 00:16:29,930 --> 00:16:33,290 understand whether or not there was some way that the body 237 00:16:33,290 --> 00:16:35,180 normally repaired itself. 238 00:16:35,180 --> 00:16:37,520 It was clear that during early development, 239 00:16:37,520 --> 00:16:40,580 there was lots of cell division and lots of changes. 240 00:16:40,580 --> 00:16:43,520 Cell types were formed and organs were formed. 241 00:16:43,520 --> 00:16:46,040 But it really wasn't clear in the adult 242 00:16:46,040 --> 00:16:50,030 how much repair there was, how much turnover of tissues 243 00:16:50,030 --> 00:16:53,480 there were, and really what the whole dynamic process 244 00:16:53,480 --> 00:16:55,250 of maintaining the adult was. 245 00:17:01,960 --> 00:17:04,630 And the discovery of stem cells came about 246 00:17:04,630 --> 00:17:10,329 because people looked to see how long cells lived. 247 00:17:10,329 --> 00:17:14,550 And what they found was found using 248 00:17:14,550 --> 00:17:21,360 a turnover assay that measures the half life of cells. 249 00:17:28,890 --> 00:17:32,070 And they found that in almost all organs, 250 00:17:32,070 --> 00:17:36,790 in fact, probably in all organs, cells did not live forever. 251 00:17:36,790 --> 00:17:37,560 They turned over. 252 00:17:37,560 --> 00:17:38,280 They died. 253 00:17:38,280 --> 00:17:39,870 And they were replaced by new cells. 254 00:17:43,280 --> 00:17:46,760 And this turnover assay implied that there 255 00:17:46,760 --> 00:17:49,490 was some kind of replacement. 256 00:17:49,490 --> 00:17:52,250 And the cells doing the replacement 257 00:17:52,250 --> 00:17:53,510 were called stem cells. 258 00:17:58,440 --> 00:18:09,965 You find this by a pulse/chase assay, which we'll go over 259 00:18:09,965 --> 00:18:13,150 on your handout in a moment. 260 00:18:13,150 --> 00:18:17,670 And what was found was really variable for different organs. 261 00:18:17,670 --> 00:18:26,990 Firstly, all organs, about, show cell turn over. 262 00:18:33,690 --> 00:18:37,095 Red blood cells have a half life of about 120 days. 263 00:18:40,920 --> 00:18:43,080 There are a lot of red blood cells in your body. 264 00:18:49,190 --> 00:18:51,600 And in fact, that implies that there are about 10 265 00:18:51,600 --> 00:18:55,560 to the seventh new red blood cells made a day. 266 00:18:59,730 --> 00:19:02,280 In your intestine, the half life of cells 267 00:19:02,280 --> 00:19:05,660 is three to five days, in the small intestine. 268 00:19:15,240 --> 00:19:20,195 And the hair on your head has a half life of about four years. 269 00:19:24,510 --> 00:19:28,220 So it's variable for different kinds of cells. 270 00:19:28,220 --> 00:19:30,590 If you look at your first handout, 271 00:19:30,590 --> 00:19:34,050 it diagrams a pulse/chase assay where 272 00:19:34,050 --> 00:19:41,470 a cell population is labeled with a nucleotide analog. 273 00:19:41,470 --> 00:19:45,880 It's a normal nucleotide, but it's got a bromine added to it. 274 00:19:45,880 --> 00:19:51,340 And it acts like deoxythymidine, gets incorporated into DNA, 275 00:19:51,340 --> 00:19:56,170 and you give just a short pulse of this nucleotide analog. 276 00:19:56,170 --> 00:19:58,810 So only some of the cells get labeled. 277 00:19:58,810 --> 00:20:01,480 And you only give it for a short time. 278 00:20:01,480 --> 00:20:04,210 So you get a labeled cell population. 279 00:20:04,210 --> 00:20:06,370 And then you stop the labeling by adding 280 00:20:06,370 --> 00:20:10,840 lots of unlabeled thymidine, and that's called a chase. 281 00:20:10,840 --> 00:20:14,680 And you follow the cells over this long chase period. 282 00:20:14,680 --> 00:20:17,860 And then you can watch and see what happens to those cells 283 00:20:17,860 --> 00:20:21,680 that you initially labeled over a very short time. 284 00:20:21,680 --> 00:20:25,720 And so in this example, I've got four cells initially labeled. 285 00:20:25,720 --> 00:20:28,520 Over time, they're only two cells left. 286 00:20:28,520 --> 00:20:32,380 And if you measure the time from going from four cells 287 00:20:32,380 --> 00:20:35,830 to two cells, you can get to the half life of that cell 288 00:20:35,830 --> 00:20:37,180 population. 289 00:20:37,180 --> 00:20:37,680 OK? 290 00:20:40,350 --> 00:20:42,720 You can also-- if you don't have a handout for this, 291 00:20:42,720 --> 00:20:44,230 just look on the screen-- 292 00:20:44,230 --> 00:20:46,800 you can also follow the labeled cell population 293 00:20:46,800 --> 00:20:48,810 and see what those cells become. 294 00:20:48,810 --> 00:20:51,000 And you can see that they go on to differentiate 295 00:20:51,000 --> 00:20:52,900 as particular cell types. 296 00:20:52,900 --> 00:20:54,720 So this is a kind of way of labeling 297 00:20:54,720 --> 00:20:56,640 the lineage of these cells. 298 00:20:56,640 --> 00:20:57,900 And that is useful, too. 299 00:21:01,410 --> 00:21:05,820 This was the theory behind stem cell definition. 300 00:21:05,820 --> 00:21:07,830 But what is a stem cell look like, 301 00:21:07,830 --> 00:21:09,390 and how do you isolate one? 302 00:21:15,270 --> 00:21:18,190 It turns out that that's really difficult. 303 00:21:18,190 --> 00:21:26,930 So isolation and assay in the adult 304 00:21:26,930 --> 00:21:29,070 stem cells are very, very rare. 305 00:21:33,130 --> 00:21:36,970 And that is one of the issues with using 306 00:21:36,970 --> 00:21:39,460 stem cells for therapy. 307 00:21:39,460 --> 00:21:42,970 There are very few of them and they're hard to isolate. 308 00:21:42,970 --> 00:21:49,570 Hematopoietic stem cells comprise 309 00:21:49,570 --> 00:21:55,820 about 0.01% of the bone marrow, which 310 00:21:55,820 --> 00:21:59,150 is where the stem cells reside, and where 311 00:21:59,150 --> 00:22:03,050 the precursors of your whole blood and immune system reside. 312 00:22:05,890 --> 00:22:09,610 The way that this was dealt with was 313 00:22:09,610 --> 00:22:12,430 through a really clever technique 314 00:22:12,430 --> 00:22:15,160 that has the acronym of FACS. 315 00:22:15,160 --> 00:22:16,610 I'll give you a slide in a moment. 316 00:22:16,610 --> 00:22:20,230 It stands for Fluorescence Activated Cell Sorting. 317 00:22:20,230 --> 00:22:21,850 We'll go to a slide in a moment so we 318 00:22:21,850 --> 00:22:23,960 don't have to spell it out. 319 00:22:23,960 --> 00:22:29,950 And the idea behind FACS is that you label stem cells. 320 00:22:29,950 --> 00:22:32,110 And you might be guessing what to label them with. 321 00:22:32,110 --> 00:22:42,050 But you label them usually via their cell surface proteins 322 00:22:42,050 --> 00:22:47,290 with some kind of tag, often an antibody tag. 323 00:22:50,930 --> 00:22:55,010 And then you can use that tag to make them different colors. 324 00:22:55,010 --> 00:22:57,950 And you can then sort them, cell by cell, 325 00:22:57,950 --> 00:23:01,690 through the Special Fluorescence Activated Cell Sorter. 326 00:23:01,690 --> 00:23:09,560 Sort individual cells, and then you 327 00:23:09,560 --> 00:23:14,870 can assay individual cells or small groups of them 328 00:23:14,870 --> 00:23:17,210 for stem cell properties. 329 00:23:21,160 --> 00:23:23,970 Let's look at a slide of how the FACS, the Fluorescence 330 00:23:23,970 --> 00:23:25,500 Activated Cell Sorter works. 331 00:23:25,500 --> 00:23:26,460 No, let's not. 332 00:23:26,460 --> 00:23:28,200 I've really gotten ahead of myself here. 333 00:23:28,200 --> 00:23:34,040 And I'm going to go back because I want to show you this. 334 00:23:34,040 --> 00:23:35,900 Hold on to that thought and let's 335 00:23:35,900 --> 00:23:40,880 go back to this notion of a pulse/chase assay. 336 00:23:40,880 --> 00:23:42,130 I forgot that I had this here. 337 00:23:42,130 --> 00:23:43,830 This is really important. 338 00:23:43,830 --> 00:23:47,870 This is a pulse/chase assay of intestinal cells. 339 00:23:47,870 --> 00:23:54,770 And so your small intestine lies inside your belly. 340 00:23:54,770 --> 00:23:57,080 And if you look at its anatomy, it 341 00:23:57,080 --> 00:24:01,450 contains many tubes whose surface 342 00:24:01,450 --> 00:24:03,980 is thrown into folds to increase the surface 343 00:24:03,980 --> 00:24:06,170 area for food absorption. 344 00:24:06,170 --> 00:24:11,810 And if you look at these folds, they are very closely packed. 345 00:24:11,810 --> 00:24:14,720 So you get a huge surface area increase. 346 00:24:14,720 --> 00:24:16,430 And the cells of these folds that 347 00:24:16,430 --> 00:24:19,340 are doing the food absorption turn over 348 00:24:19,340 --> 00:24:20,600 every three to five days. 349 00:24:20,600 --> 00:24:22,710 Those are the ones I was talking about. 350 00:24:22,710 --> 00:24:25,100 So if you blow up one of these folds, which 351 00:24:25,100 --> 00:24:27,140 is called a villus, there's the part 352 00:24:27,140 --> 00:24:29,330 that's sticking up into the cavity, 353 00:24:29,330 --> 00:24:31,850 into the lumen of the small intestine. 354 00:24:31,850 --> 00:24:33,830 And then there's this part that kind of dips 355 00:24:33,830 --> 00:24:36,380 down into the lining of the intestine, which 356 00:24:36,380 --> 00:24:38,120 is called a crypt. 357 00:24:38,120 --> 00:24:41,270 The stem cells lie somewhere at the base of the crypt. 358 00:24:41,270 --> 00:24:44,750 It's not exactly clear where. 359 00:24:44,750 --> 00:24:47,660 But the idea is that somewhere at the bottom of this crypt 360 00:24:47,660 --> 00:24:51,410 there are these stem cells that under specific conditions 361 00:24:51,410 --> 00:24:53,450 will start to proliferate. 362 00:24:53,450 --> 00:24:56,690 And they will move up into the villus 363 00:24:56,690 --> 00:24:59,570 and replace the villus cells that are dying. 364 00:24:59,570 --> 00:25:03,540 You can monitor this by doing a pulse/chase experiment. 365 00:25:03,540 --> 00:25:05,210 So here's the crypt. 366 00:25:05,210 --> 00:25:07,340 And they've given, in this experiment, 367 00:25:07,340 --> 00:25:10,160 a pulse of thymidine has been given. 368 00:25:10,160 --> 00:25:12,110 And you're looking kind of at time 0, 369 00:25:12,110 --> 00:25:15,890 right after the pulse of thymidine has been given. 370 00:25:15,890 --> 00:25:18,380 Here the cells, the black cells are in the crypt. 371 00:25:18,380 --> 00:25:19,460 They're labeled. 372 00:25:19,460 --> 00:25:22,280 And then if you look over time, you 373 00:25:22,280 --> 00:25:26,540 can see that these black cells move away from the crypt. 374 00:25:26,540 --> 00:25:28,790 They're moving up into the villus. 375 00:25:28,790 --> 00:25:31,580 And here they are actually right on top of the villus, 376 00:25:31,580 --> 00:25:34,110 replacing the cells that were turning over. 377 00:25:34,110 --> 00:25:35,960 So that's a really beautiful demonstration 378 00:25:35,960 --> 00:25:38,130 of a pulse/chase assay. 379 00:25:38,130 --> 00:25:38,630 OK. 380 00:25:38,630 --> 00:25:41,210 Now we can go to our Fluorescence Activated Cell 381 00:25:41,210 --> 00:25:41,710 Sorter. 382 00:25:45,220 --> 00:25:47,321 The idea is that you take a mix of cells-- 383 00:25:47,321 --> 00:25:48,820 you don't have this on your handout, 384 00:25:48,820 --> 00:25:50,860 just look on the screen-- the cells are labeled 385 00:25:50,860 --> 00:25:52,900 with fluorescent antibodies. 386 00:25:52,900 --> 00:25:55,570 And you put them into a reservoir and droplet 387 00:25:55,570 --> 00:25:56,920 generator. 388 00:25:56,920 --> 00:26:01,460 And the cells drop out of this reservoir, one at a time. 389 00:26:01,460 --> 00:26:05,320 And as they drop out, they go past a laser. 390 00:26:05,320 --> 00:26:08,410 And you can tune the laser to whatever wavelengths you want. 391 00:26:08,410 --> 00:26:10,150 It excites the cells. 392 00:26:10,150 --> 00:26:13,060 And if the cells emit in the particular wavelength 393 00:26:13,060 --> 00:26:16,720 you're interested in, the detector will detect that. 394 00:26:16,720 --> 00:26:18,880 And then it actually gives a charge to the cell 395 00:26:18,880 --> 00:26:21,340 that it is the correct fluorescence. 396 00:26:21,340 --> 00:26:23,800 And as the cells are dropping down, 397 00:26:23,800 --> 00:26:26,350 the cells of the correct color are deflected 398 00:26:26,350 --> 00:26:28,060 by an electric charge. 399 00:26:28,060 --> 00:26:30,430 And different color cells can be collected 400 00:26:30,430 --> 00:26:32,500 into different flasks. 401 00:26:32,500 --> 00:26:33,100 OK? 402 00:26:33,100 --> 00:26:34,280 This really works. 403 00:26:34,280 --> 00:26:36,040 It's a fantastic machine. 404 00:26:36,040 --> 00:26:38,620 You can collect cells about, you know, 405 00:26:38,620 --> 00:26:40,720 you can collect millions of cells an hour. 406 00:26:40,720 --> 00:26:41,920 It's pretty quick. 407 00:26:41,920 --> 00:26:44,140 But you do it one cell at a time. 408 00:26:44,140 --> 00:26:46,750 And in that way, you can isolate cells, which 409 00:26:46,750 --> 00:26:49,010 have got stem cell properties. 410 00:26:49,010 --> 00:26:49,510 OK. 411 00:26:52,300 --> 00:26:54,247 So you've used your FACS machine. 412 00:26:54,247 --> 00:26:56,080 You've got cells that look as though they've 413 00:26:56,080 --> 00:26:58,610 got stem cell properties. 414 00:26:58,610 --> 00:27:10,760 And now, let's look at the assays that may be used. 415 00:27:10,760 --> 00:27:13,730 And there are three assays that you should know. 416 00:27:13,730 --> 00:27:18,640 One is a repopulation assay to test stem cellness. 417 00:27:23,330 --> 00:27:29,980 And this is a transplant assay where you're transplanting test 418 00:27:29,980 --> 00:27:39,960 cells, test stem cells, into the adult. 419 00:27:39,960 --> 00:27:46,320 And you have removed from the adult, endogenous cells that 420 00:27:46,320 --> 00:27:48,675 might be competing with those stem cells. 421 00:27:56,310 --> 00:27:58,290 That would include the stem cells. 422 00:27:58,290 --> 00:27:59,880 We'll go through a slide in a moment. 423 00:27:59,880 --> 00:28:01,380 I'm going to list them here. 424 00:28:01,380 --> 00:28:09,160 Another one is an in-vitro induction assay, 425 00:28:09,160 --> 00:28:13,860 where you are going to take isolated cells 426 00:28:13,860 --> 00:28:16,620 and you're going to treat them with various inducers, 427 00:28:16,620 --> 00:28:19,680 various signaling molecules, and you're 428 00:28:19,680 --> 00:28:23,760 going to test and see what fates those cells can acquire. 429 00:28:23,760 --> 00:28:31,070 And a third assay is called an embryo incorporation assay, 430 00:28:31,070 --> 00:28:35,100 where you are going to take cells that may be stem cells, 431 00:28:35,100 --> 00:28:40,200 and you're going to test them in a chimeric embryo. 432 00:28:43,740 --> 00:28:46,560 Let's go through your next slides 433 00:28:46,560 --> 00:28:50,760 to discuss each of these points. 434 00:28:50,760 --> 00:28:54,690 Bone marrow transplants resulted in a Nobel Prize in 1990 435 00:28:54,690 --> 00:28:56,760 for E. Donnall Thomas and Joseph Murray. 436 00:28:56,760 --> 00:28:59,790 It's a technique that saved millions of lives, 437 00:28:59,790 --> 00:29:02,250 and here how it works in a mouse. 438 00:29:02,250 --> 00:29:05,160 You take the mouse and you irradiate the mouse 439 00:29:05,160 --> 00:29:08,490 to destroy the bone marrow and the stem cells associated 440 00:29:08,490 --> 00:29:09,480 with the bone marrow. 441 00:29:09,480 --> 00:29:14,350 If it's a person, to destroy the diseased burned bone marrow. 442 00:29:14,350 --> 00:29:18,600 And then you replace that bone marrow with normal bone marrow 443 00:29:18,600 --> 00:29:21,660 to either try to make the person better, or in this case, 444 00:29:21,660 --> 00:29:24,210 to test something about stem cells. 445 00:29:24,210 --> 00:29:27,480 The irradiated mouse or person would die, 446 00:29:27,480 --> 00:29:31,660 but the normal bone marrow will cause the mouse to live. 447 00:29:31,660 --> 00:29:34,440 And if you've put stem cells into that mouse, 448 00:29:34,440 --> 00:29:38,000 you can start getting them out of that mouse whose life you 449 00:29:38,000 --> 00:29:42,890 have saved, and isolate more stem cells. 450 00:29:42,890 --> 00:29:46,010 Those kinds of assays led to the definition 451 00:29:46,010 --> 00:29:48,470 of the hematopoietic stem cell. 452 00:29:48,470 --> 00:29:49,250 Here it is. 453 00:29:49,250 --> 00:29:52,400 It's a pluripotent stem cell that gives rise 454 00:29:52,400 --> 00:29:56,390 to all of these different kinds of cells, the immune cells, 455 00:29:56,390 --> 00:29:57,740 and all of the blood cells. 456 00:29:57,740 --> 00:30:00,560 It's a very, very powerful stem cell. 457 00:30:00,560 --> 00:30:04,340 And the ability to actually make this diagram and say that there 458 00:30:04,340 --> 00:30:08,510 was a single cell that gave rise to all these different lineages 459 00:30:08,510 --> 00:30:12,350 was because of a titration assay where you could take these 460 00:30:12,350 --> 00:30:16,370 putative hematopoietic stem cells that were difficult 461 00:30:16,370 --> 00:30:20,120 to isolate-- and still haven't been isolated in their purity-- 462 00:30:20,120 --> 00:30:22,500 but you can titrate them down. 463 00:30:22,500 --> 00:30:25,790 And you can introduce what you think is one stem cell, 10 stem 464 00:30:25,790 --> 00:30:30,350 cells, 100 stem cells, and so on, into an irradiated mouse, 465 00:30:30,350 --> 00:30:32,270 and ask how many stem cells does it 466 00:30:32,270 --> 00:30:36,686 take to repopulate the entire blood system and immune system. 467 00:30:36,686 --> 00:30:38,060 And it turns out, you have to mix 468 00:30:38,060 --> 00:30:41,450 these cells with carrier cells, otherwise it doesn't work. 469 00:30:41,450 --> 00:30:44,750 But it turns out that one cell can repopulate 470 00:30:44,750 --> 00:30:48,380 the entire hematopoietic system, which is really extraordinary, 471 00:30:48,380 --> 00:30:53,730 and led to the diagram that I showed you in the slide before. 472 00:30:53,730 --> 00:30:54,750 OK. 473 00:30:54,750 --> 00:30:55,920 Here's another assay. 474 00:30:55,920 --> 00:30:58,500 This is an in-vitro induction assay. 475 00:30:58,500 --> 00:31:00,810 And the idea here is that you start off 476 00:31:00,810 --> 00:31:04,230 with something, which you think might be stem cells, 477 00:31:04,230 --> 00:31:06,330 by various criteria. 478 00:31:06,330 --> 00:31:08,970 And then to test what these cells can do, 479 00:31:08,970 --> 00:31:12,990 you put them into plastic tissue culture dishes, 480 00:31:12,990 --> 00:31:15,000 and you add some nutrients and so on 481 00:31:15,000 --> 00:31:17,190 to allow the cells to divide. 482 00:31:17,190 --> 00:31:19,350 And then you add some inducers. 483 00:31:19,350 --> 00:31:21,300 And you remember a couple of lectures back, 484 00:31:21,300 --> 00:31:25,170 inducers are just ligands for various signaling systems. 485 00:31:25,170 --> 00:31:27,840 You might add fibroblast growth factor to this one, 486 00:31:27,840 --> 00:31:30,390 and retinoic acid to that one, and then you 487 00:31:30,390 --> 00:31:32,700 ask what happens to the cells. 488 00:31:32,700 --> 00:31:35,160 They will go on, in general, to differentiate 489 00:31:35,160 --> 00:31:36,780 into different cell types. 490 00:31:36,780 --> 00:31:39,630 And depending on what they differentiate into, 491 00:31:39,630 --> 00:31:43,570 you can say something about the potency of these putative stem 492 00:31:43,570 --> 00:31:44,070 cells. 493 00:31:44,070 --> 00:31:46,260 You can't test if they're really stem cells, 494 00:31:46,260 --> 00:31:50,338 but you can say something about their potency. 495 00:31:50,338 --> 00:31:55,560 You can do a similar experiment, but in a whole mouse. 496 00:31:55,560 --> 00:31:58,380 The mouse is made from, the embryo 497 00:31:58,380 --> 00:32:02,670 is made from a part of the very early embryo called 498 00:32:02,670 --> 00:32:04,350 the inner cell mass. 499 00:32:04,350 --> 00:32:08,040 And you can inject labeled, putative stem cells 500 00:32:08,040 --> 00:32:11,700 into an early mouse embryo, into this inner cell mass 501 00:32:11,700 --> 00:32:18,840 part of the embryo, put it into a mother, a recipient mother, 502 00:32:18,840 --> 00:32:21,420 and then ask what comes out, what kind of embryo 503 00:32:21,420 --> 00:32:23,800 comes out of that process. 504 00:32:23,800 --> 00:32:26,310 And if you see that the baby that comes out 505 00:32:26,310 --> 00:32:32,070 of this chimeric embryo has got a green liver and green ears 506 00:32:32,070 --> 00:32:35,430 and green whiskers, you'll know that these cells that you 507 00:32:35,430 --> 00:32:37,650 put into the chimeric embryo, that you made 508 00:32:37,650 --> 00:32:40,170 the chimeric embryo with, had the capacity 509 00:32:40,170 --> 00:32:43,570 to give liver, ears, and whiskers. 510 00:32:43,570 --> 00:32:44,070 OK? 511 00:32:44,070 --> 00:32:46,770 So this is a powerful assay to, again, 512 00:32:46,770 --> 00:32:49,740 look at the potency of cells, not, in this case, 513 00:32:49,740 --> 00:32:51,600 the stem cellness of cells. 514 00:32:56,740 --> 00:33:01,050 One of the things about stem cells 515 00:33:01,050 --> 00:33:03,150 is that you only want them to work 516 00:33:03,150 --> 00:33:04,860 when you want them to work. 517 00:33:04,860 --> 00:33:07,920 If you cut yourself, in the normal process 518 00:33:07,920 --> 00:33:10,230 of keeping your liver the right size, 519 00:33:10,230 --> 00:33:13,590 in the normal process of keeping your heart muscle correct, 520 00:33:13,590 --> 00:33:16,740 you want your stem cells to be working and keeping 521 00:33:16,740 --> 00:33:19,820 everything homeostatic. 522 00:33:19,820 --> 00:33:22,130 You don't want them to be dividing out of control, 523 00:33:22,130 --> 00:33:24,140 because then you'll get cancer. 524 00:33:24,140 --> 00:33:27,960 And so something has to control what stem cells do 525 00:33:27,960 --> 00:33:29,300 and when they do it. 526 00:33:29,300 --> 00:33:35,340 And this is a question of regulation 527 00:33:35,340 --> 00:33:42,090 and the notion of a stem cell niche. 528 00:33:42,090 --> 00:33:51,570 Stem cells are kept quiescent, usually in G0 529 00:33:51,570 --> 00:33:55,170 that we talked about in the cell cycle lecture. 530 00:33:55,170 --> 00:33:58,530 And they're kept quiescent by signals from the surrounding 531 00:33:58,530 --> 00:33:59,070 cells. 532 00:33:59,070 --> 00:34:07,150 So their cell-cell interaction, and by signals 533 00:34:07,150 --> 00:34:10,719 from the surrounding cells. 534 00:34:10,719 --> 00:34:15,130 And those are given a special name by stem cell biologists. 535 00:34:15,130 --> 00:34:19,449 They're not that special, but they're given a special name. 536 00:34:19,449 --> 00:34:22,640 They're called niche cells, or the niche. 537 00:34:22,640 --> 00:34:23,139 OK? 538 00:34:23,139 --> 00:34:25,555 They're just surrounding cells that are secreting signals. 539 00:34:28,000 --> 00:34:30,530 On some kind of activation-- 540 00:34:30,530 --> 00:34:37,170 you cut yourself, your organ normally needs repair-- 541 00:34:37,170 --> 00:34:38,560 things change. 542 00:34:38,560 --> 00:34:46,409 So on activation, by some kind of environmental input-- 543 00:34:46,409 --> 00:34:50,850 local or less local-- 544 00:34:50,850 --> 00:34:55,755 niche cells induce the stem cells to divide. 545 00:35:04,200 --> 00:35:05,580 And they do this-- 546 00:35:05,580 --> 00:35:08,100 and they induce the stem cells to divide 547 00:35:08,100 --> 00:35:14,160 into a stem cell plus a progenitor, which then goes on 548 00:35:14,160 --> 00:35:17,370 to do all the things that I diagrammed that progenitors do, 549 00:35:17,370 --> 00:35:19,630 on the first board. 550 00:35:19,630 --> 00:35:22,150 And the niche cells do this because they 551 00:35:22,150 --> 00:35:23,700 have changed their signaling. 552 00:35:34,270 --> 00:35:37,810 This is yet another use, or a very related use, 553 00:35:37,810 --> 00:35:41,830 of the notion of cell-cell signaling in controlling life. 554 00:35:41,830 --> 00:35:43,500 Here's a diagram. 555 00:35:43,500 --> 00:35:44,447 Here are niche cells. 556 00:35:44,447 --> 00:35:45,280 You don't have this. 557 00:35:45,280 --> 00:35:46,810 Just look on the screen. 558 00:35:46,810 --> 00:35:51,430 Surrounding cells, maintaining stem cells quiet. 559 00:35:51,430 --> 00:35:56,080 When there's an environmental input, the niche cells change. 560 00:35:56,080 --> 00:35:59,530 They activate the stem cells to divide and form more stem 561 00:35:59,530 --> 00:36:01,650 cells and progenitor cells. 562 00:36:04,470 --> 00:36:07,440 One really fantastic example of the niche, 563 00:36:07,440 --> 00:36:10,080 and the interaction between stem cells and the niche, 564 00:36:10,080 --> 00:36:11,730 is in the hair. 565 00:36:11,730 --> 00:36:14,770 This is from my colleague Elaine Fuchs at Rockefeller, 566 00:36:14,770 --> 00:36:18,720 who over many years has figured out that in the hair follicle-- 567 00:36:18,720 --> 00:36:22,290 this is the hair sticking out of the skin-- 568 00:36:22,290 --> 00:36:24,450 in the hair, there's a small group 569 00:36:24,450 --> 00:36:28,500 of cells on one side of the hair shaft called the bulge cells, 570 00:36:28,500 --> 00:36:32,820 and these bulge cells are the stem cells. 571 00:36:32,820 --> 00:36:36,130 Her investigators isolated these bulge cells 572 00:36:36,130 --> 00:36:38,110 and did the following experiment to show 573 00:36:38,110 --> 00:36:40,720 that they were hair stem cells. 574 00:36:40,720 --> 00:36:43,810 There's a kind of a mouse called a nude mouse that 575 00:36:43,810 --> 00:36:45,690 has a very bad immune system. 576 00:36:45,690 --> 00:36:48,190 So it's useful for immune system experiments. 577 00:36:48,190 --> 00:36:50,470 But it also has no hair. 578 00:36:50,470 --> 00:36:53,330 And you can do a transplant into this mouse 579 00:36:53,330 --> 00:36:55,570 of these bulge cells. 580 00:36:55,570 --> 00:36:58,060 And you get little tufts of hair growing where 581 00:36:58,060 --> 00:36:59,890 the rest of the mouse is nude. 582 00:36:59,890 --> 00:37:01,840 And you've done a careful experiment 583 00:37:01,840 --> 00:37:05,080 where you've labeled the cells you have transplanted in so 584 00:37:05,080 --> 00:37:07,240 that you can show that they actually 585 00:37:07,240 --> 00:37:09,940 came from the transplanted tissue and not 586 00:37:09,940 --> 00:37:12,100 from the mouse, the nude mouse tissue. 587 00:37:12,100 --> 00:37:14,470 And you can do that because you labeled them with GFP 588 00:37:14,470 --> 00:37:15,400 and they're green. 589 00:37:15,400 --> 00:37:17,050 So this the green hair. 590 00:37:17,050 --> 00:37:21,520 And it shows you that these bulge cells are stem cells. 591 00:37:21,520 --> 00:37:24,070 During the life of a hair-- 592 00:37:24,070 --> 00:37:27,160 your hair has a life, we discussed four years 593 00:37:27,160 --> 00:37:28,450 on your head-- 594 00:37:28,450 --> 00:37:34,230 during the life of a hair, the bulge cells and the niche cells 595 00:37:34,230 --> 00:37:36,010 are in different places. 596 00:37:36,010 --> 00:37:39,250 And depending on whether they're touching or far apart from one 597 00:37:39,250 --> 00:37:43,600 another, there's induction of hair growth or not. 598 00:37:43,600 --> 00:37:46,170 So at a particular stage of the hair cycle-- 599 00:37:46,170 --> 00:37:48,460 this is called the hair cycle, look on the bottom 600 00:37:48,460 --> 00:37:49,810 of the screen here-- 601 00:37:49,810 --> 00:37:52,300 the bulge cells and a group of cells 602 00:37:52,300 --> 00:37:55,030 called the dermal papilla that lies right 603 00:37:55,030 --> 00:37:58,900 at the bottom of the hair shaft are touching one another. 604 00:37:58,900 --> 00:38:01,570 And at that point, a particular signaling pathway 605 00:38:01,570 --> 00:38:04,390 called the Wnt pathway is activated. 606 00:38:04,390 --> 00:38:08,170 And these dermal papilla cells tell the bulge cells 607 00:38:08,170 --> 00:38:12,430 to start dividing and start making a new hair shaft. 608 00:38:12,430 --> 00:38:15,400 After that's happened, the bulge cells 609 00:38:15,400 --> 00:38:18,310 move away from the dermal papilla cells. 610 00:38:18,310 --> 00:38:21,190 Here they are during growth, the growth period. 611 00:38:21,190 --> 00:38:23,710 You see the bulge and the dermal papilla cells 612 00:38:23,710 --> 00:38:25,360 are no longer touching. 613 00:38:25,360 --> 00:38:28,660 At this point, the stem cells become quiescent. 614 00:38:28,660 --> 00:38:31,870 And there are enough progenitor cells in the hair shaft 615 00:38:31,870 --> 00:38:34,120 to give you formation of the hair. 616 00:38:34,120 --> 00:38:37,780 And then the stem cells remain quiescent until the next hair 617 00:38:37,780 --> 00:38:41,200 cycle starts and they get in contact with the dermal papilla 618 00:38:41,200 --> 00:38:43,630 again and start making new hair. 619 00:38:43,630 --> 00:38:45,880 This is a really beautiful story that's 620 00:38:45,880 --> 00:38:48,760 shown us quite clearly how the niche cells can 621 00:38:48,760 --> 00:38:51,720 control these stem cells. 622 00:38:51,720 --> 00:38:52,860 All right. 623 00:38:52,860 --> 00:38:56,370 So let's spend the last minutes talking about therapeutics. 624 00:39:10,640 --> 00:39:12,960 Here's the dream. 625 00:39:12,960 --> 00:39:15,930 You know, the dream is that you have a stem cell 626 00:39:15,930 --> 00:39:19,820 population for every organ in the body, 627 00:39:19,820 --> 00:39:23,290 including things like limbs, such 628 00:39:23,290 --> 00:39:26,350 that if your limb gets severed or your heart 629 00:39:26,350 --> 00:39:30,550 becomes really diseased or your spinal cord is injured 630 00:39:30,550 --> 00:39:33,760 and you can't walk anymore, that you can just inject 631 00:39:33,760 --> 00:39:37,510 into a patient the correct stem cells and everything 632 00:39:37,510 --> 00:39:38,920 gets repaired. 633 00:39:38,920 --> 00:39:39,940 That's the dream. 634 00:39:39,940 --> 00:39:43,750 And that's really the holy grail of what 635 00:39:43,750 --> 00:39:47,500 thousands and thousands of investigators are going after. 636 00:39:47,500 --> 00:39:50,950 And it's given precedence by bone marrow transplants, which 637 00:39:50,950 --> 00:39:53,050 really are very successful. 638 00:39:53,050 --> 00:39:55,870 Turns out that it's kind of tough. 639 00:39:55,870 --> 00:39:59,850 It's tough because these adult stem cells are really rare. 640 00:39:59,850 --> 00:40:02,680 The hematopoietic stem cells are special because they're 641 00:40:02,680 --> 00:40:03,580 kind of liquid. 642 00:40:03,580 --> 00:40:04,560 They're single cells. 643 00:40:04,560 --> 00:40:06,280 They're not attached to anything. 644 00:40:06,280 --> 00:40:09,260 And they are relatively easy to identify. 645 00:40:09,260 --> 00:40:11,840 But other stem cells are very difficult. 646 00:40:11,840 --> 00:40:20,110 So the idea is that you inject stem cells to repair a damaged 647 00:40:20,110 --> 00:40:20,610 organ. 648 00:40:30,180 --> 00:40:34,750 You need stem cells of the correct potency, 649 00:40:34,750 --> 00:40:38,560 otherwise you're not going to repair the specific organ. 650 00:40:45,240 --> 00:40:47,950 But adult stem cells are very rare. 651 00:40:51,680 --> 00:40:55,240 And so the quest has been to find some kind of substitute 652 00:40:55,240 --> 00:40:56,485 for adult stem cells. 653 00:41:01,050 --> 00:41:07,620 And those substitutes come in two flavors. 654 00:41:07,620 --> 00:41:17,650 One are embryonic stem cells, abbreviated, ESCs. 655 00:41:17,650 --> 00:41:20,380 Embryonic stem cells are cells that 656 00:41:20,380 --> 00:41:25,900 grow from the inner cell mass of an early mammalian embryo. 657 00:41:25,900 --> 00:41:28,450 And you can grow from them groups 658 00:41:28,450 --> 00:41:31,030 of cells that will keep growing in the laboratory 659 00:41:31,030 --> 00:41:34,610 for a long time and have variable potency. 660 00:41:34,610 --> 00:41:39,340 So the embryonic stem cells are derived 661 00:41:39,340 --> 00:41:44,700 from the inner cell mass of an early mammalian embryo-- 662 00:41:52,650 --> 00:41:54,750 human in the case of human. 663 00:41:57,850 --> 00:42:08,030 And you grow out so-called ESC lines, 664 00:42:08,030 --> 00:42:14,825 which means that these cells grow continuously in culture. 665 00:42:21,110 --> 00:42:31,620 And each embryonic stem cell line has a unique potency 666 00:42:31,620 --> 00:42:35,520 and can be used to do different things, in terms 667 00:42:35,520 --> 00:42:37,530 of theoretical repair. 668 00:42:37,530 --> 00:42:39,210 If you look on your next handout, 669 00:42:39,210 --> 00:42:43,320 the idea is that you take this inner cell mass, 670 00:42:43,320 --> 00:42:46,960 you plate the cells as single cells, 671 00:42:46,960 --> 00:42:50,690 they grow and grow and grow. 672 00:42:50,690 --> 00:42:53,920 And if you treat them with various inducers, 673 00:42:53,920 --> 00:42:58,210 you can get them to become heart or neuron progenitors, 674 00:42:58,210 --> 00:43:01,850 inject those into animals and make them better. 675 00:43:01,850 --> 00:43:05,860 There are some issues with embryonic stem cells. 676 00:43:05,860 --> 00:43:08,890 And the problems are twofold. 677 00:43:15,170 --> 00:43:22,470 One is ethical in that you have to harvest human embryos. 678 00:43:22,470 --> 00:43:25,740 You have to obtain and harvest human embryos 679 00:43:25,740 --> 00:43:27,660 to get these human stem cell lines. 680 00:43:38,930 --> 00:43:40,960 And currently, you're really not allowed 681 00:43:40,960 --> 00:43:46,390 to do much human embryo work to obtain human stem cells. 682 00:43:46,390 --> 00:43:49,240 But the second, even if you were, 683 00:43:49,240 --> 00:43:53,860 is that these cells are non-autologous. 684 00:43:53,860 --> 00:44:01,960 They do not match the person into which you're putting them. 685 00:44:01,960 --> 00:44:05,290 They do not match the immune system of the recipient. 686 00:44:05,290 --> 00:44:07,180 And so they'll be rejected. 687 00:44:07,180 --> 00:44:09,100 And it's the same as an organ transplant. 688 00:44:09,100 --> 00:44:12,230 You have lots of problems of rejection. 689 00:44:12,230 --> 00:44:17,860 So the latest thing that is very exciting and wonderful 690 00:44:17,860 --> 00:44:25,510 and potentially might be very useful, is the use of things 691 00:44:25,510 --> 00:44:38,630 called IPS cells, in which you convert adult cells 692 00:44:38,630 --> 00:44:41,390 into stem cells. 693 00:44:41,390 --> 00:44:45,440 And you do so, as I'll tell you, by adding some transcription 694 00:44:45,440 --> 00:44:47,030 factors to them. 695 00:44:47,030 --> 00:44:51,650 The advantage of these is that they are self cells. 696 00:44:51,650 --> 00:44:53,600 You could do them from yourself. 697 00:44:53,600 --> 00:44:57,770 The disadvantage is that they're really not proven. 698 00:44:57,770 --> 00:45:02,810 And there is still, I will just say, lots of problems. 699 00:45:06,730 --> 00:45:09,080 But there are a lot of people, including 700 00:45:09,080 --> 00:45:11,780 some of the top investigators in the world, 701 00:45:11,780 --> 00:45:13,540 working on these IPS cells. 702 00:45:13,540 --> 00:45:16,340 So look at your last handout. 703 00:45:16,340 --> 00:45:22,660 We will remove our interesting calendar reminders there. 704 00:45:22,660 --> 00:45:26,620 Adult differentiated cells, which are unipotent, 705 00:45:26,620 --> 00:45:31,390 can be treated with three or four transcription factors. 706 00:45:31,390 --> 00:45:34,780 And finding these transcription factors is the key. 707 00:45:34,780 --> 00:45:37,690 And once you express these transcription factors 708 00:45:37,690 --> 00:45:42,730 in these adult cells, like magic, they become stem cells. 709 00:45:42,730 --> 00:45:45,920 It really was like magic. 710 00:45:45,920 --> 00:45:48,830 You can test the potency of these stem cells 711 00:45:48,830 --> 00:45:50,810 in the same way we discussed. 712 00:45:50,810 --> 00:45:53,850 And Professor Yamanaka in Japan and Professor Jaenisch 713 00:45:53,850 --> 00:45:57,560 here have shown that these are really very powerful cells. 714 00:45:57,560 --> 00:45:59,650 And those are the promise of the future. 715 00:45:59,650 --> 00:46:02,920 And we'll stop there and meet on Friday.