WEBVTT - Listener Questions #37 0:00:07.800 --> 0:00:12.920 Bodies contain blood, bones, muscles, and everything in between. How 0:00:13.039 --> 0:00:16.400 is this all controlled at the level of the gene? 0:00:16.920 --> 0:00:20.360 How many unique cell types are inside of me? I 0:00:20.640 --> 0:00:23.880 count eighty three? Do you agree? 0:00:24.360 --> 0:00:28.560 Do clever tools require thumbs that neatly oppose? Or could 0:00:28.600 --> 0:00:32.400 alien minds build ships with tentacles? Or who knows? 0:00:32.920 --> 0:00:36.600 Whatever questions keep you up at night, Daniel and Kelly's 0:00:36.640 --> 0:00:39.760 answers will hopefully make it right. 0:00:40.920 --> 0:00:45.120 Welcome to Daniel and Kelly's Extraordinary Universe of Alien Biology. 0:00:45.560 --> 0:00:48.360 Listener Questions, episode number thirty seven. 0:01:01.520 --> 0:01:05.360 Hi Daniel, I studied particle physics and aliens. 0:01:05.920 --> 0:01:09.800 Hello, I'm Kelly Waidersmith. I studied parasites and space, and 0:01:09.880 --> 0:01:13.200 twenty five years ago I studied developmental biology. Do I 0:01:13.280 --> 0:01:15.680 remember any of it? Today? We find out. 0:01:17.280 --> 0:01:20.520 It's Kelly on the hot seat today, answering questions from 0:01:20.840 --> 0:01:25.360 listeners about how everything works inside these crazy meat sacks 0:01:25.520 --> 0:01:26.280 we call bodies. 0:01:27.400 --> 0:01:29.960 Right, And just to be clear, I'm not actually relying 0:01:30.000 --> 0:01:32.000 on what I learned twenty five years ago. I spent 0:01:32.040 --> 0:01:35.440 a lot of time reading about developmental biology again, but 0:01:35.520 --> 0:01:38.120 these are great questions and it was fun to revisit 0:01:38.160 --> 0:01:38.880 the field. 0:01:38.760 --> 0:01:41.000 And we thank you, thank you, thank you so much 0:01:41.040 --> 0:01:44.400 for sharing your curiosity with us, sending in the things 0:01:44.400 --> 0:01:47.000 that puzzle you, the things you would like to hear about. 0:01:47.360 --> 0:01:52.000 We thrive on your curiosity. It literally drives all of science, 0:01:52.440 --> 0:01:54.560 and so we're very glad to hear that you're curious 0:01:54.600 --> 0:01:56.480 about how the universe works, and we want to answer 0:01:56.760 --> 0:01:59.760 your questions about the universe. This podcast is not just 0:01:59.800 --> 0:02:02.640 a it's a conversation between you and us. 0:02:02.960 --> 0:02:06.200 Yes, and we are chatty people, so send us your 0:02:06.320 --> 0:02:10.480 questions at questions at Danielankelly dot org or join us 0:02:10.480 --> 0:02:14.200 on our discord channel. We have the world's best moderators, 0:02:14.280 --> 0:02:18.680 so our conversations are fascinating, funny and civil, which I 0:02:18.720 --> 0:02:19.840 love the civil parts. 0:02:20.200 --> 0:02:22.400 An actually friendly place on the internet. 0:02:22.480 --> 0:02:25.000 It's amazing. This is the only corner where you can 0:02:25.040 --> 0:02:28.160 find that friends join us, And if you go to 0:02:28.320 --> 0:02:30.400 Daniel and Kelly dot org you can find a link 0:02:30.440 --> 0:02:33.280 to our discord page and you can join us over there. 0:02:33.400 --> 0:02:36.200 And if you've written to us and haven't heard back, sorry, 0:02:36.240 --> 0:02:38.560 please try again. You may have been caught in our 0:02:38.680 --> 0:02:41.200 spam filter. We really try to get back to everybody 0:02:41.200 --> 0:02:44.320 within a couple of days, so please, please, please, reach 0:02:44.400 --> 0:02:46.840 out to us. We love to hear the things that 0:02:46.919 --> 0:02:50.480 make you wonder, and on today's episode, we're answering three 0:02:50.600 --> 0:02:54.600 fascinating questions from listeners, focusing on how the human body 0:02:54.639 --> 0:02:57.840 develops and how alien bodies might develop as well. 0:02:58.120 --> 0:03:00.840 That's right, and we're going to start with two questions 0:03:00.840 --> 0:03:03.840 I got that were related, and so usually each segment 0:03:04.000 --> 0:03:06.600 we air a question at the beginning of each segment. 0:03:07.040 --> 0:03:10.520 This time around, I'm gonna air two questions together because 0:03:10.560 --> 0:03:14.280 Ali and Brian had very similar questions, and then I'm 0:03:14.320 --> 0:03:17.440 going to spend two segments doing my best to answer them, 0:03:17.840 --> 0:03:20.480 and then I will air their responses at the end 0:03:20.520 --> 0:03:23.560 of segment two. So let's go ahead and listen to 0:03:23.639 --> 0:03:25.560 these fantastic questions. 0:03:25.919 --> 0:03:30.600 Hello, O, Kelly, could you explain how DNA results into 0:03:30.720 --> 0:03:35.160 different cell behaviors, like when a fetus develop how does 0:03:35.360 --> 0:03:39.040 one cell end up as a muscle cell another as 0:03:39.040 --> 0:03:39.680 a bone sell? 0:03:40.320 --> 0:03:45.160 Thank you, hey, Kelly, it's Brian. As Daniel likes to say, 0:03:45.320 --> 0:03:49.400 this Rube Goldberg machine of a body is insanely complicated. 0:03:50.000 --> 0:03:53.600 I understand the basics of how cells differentiate and specialize 0:03:53.640 --> 0:03:57.680 based on which genes are turned on or off, but 0:03:57.760 --> 0:04:00.880 I've always wondered how many different types of cells there 0:04:00.880 --> 0:04:05.360 are in the human body. More specifically, I was hoping 0:04:05.400 --> 0:04:09.400 you could explain what actually makes them different. I remember 0:04:09.400 --> 0:04:12.400 building a cell diagram with Arts and Crafts in middle school, 0:04:12.560 --> 0:04:16.320 and it got me thinking, what about a cell's internal structure? 0:04:16.880 --> 0:04:19.680 Separates a cell in a tendon from a cell and 0:04:19.720 --> 0:04:23.640 a bone, muscle, artery, white blood cell, brain cell, and 0:04:23.680 --> 0:04:27.920 so on. As a related and follow up question, I'd 0:04:28.000 --> 0:04:31.560 also love to hear how new cells like know what 0:04:31.760 --> 0:04:34.719 to become in the first place, both as we grow 0:04:34.800 --> 0:04:37.760 in the womb and as we age out in the world. 0:04:38.320 --> 0:04:40.719 Thanks, oh boy. 0:04:40.760 --> 0:04:43.320 All right, So when you got these questions, Kelly, did 0:04:43.320 --> 0:04:46.159 you go yeah, I wonder that too, Or did you 0:04:46.200 --> 0:04:49.279 go ooh, here's a chance to learn developmental biology? Or 0:04:49.320 --> 0:04:51.120 did your stomach drop and you went uh oh, I 0:04:51.120 --> 0:04:54.320 should have paid attention in dev cell thirty years ago. 0:04:54.520 --> 0:04:57.320 I paid a lot of attention in dev bio. And 0:04:57.920 --> 0:05:01.039 if Professor Eileen Underwood were he, I think she'd tell 0:05:01.080 --> 0:05:03.400 you that I got an A in developmental biology. 0:05:03.640 --> 0:05:03.960 Nice. 0:05:04.240 --> 0:05:06.760 Yeah, but it was twenty five years ago, and. 0:05:07.040 --> 0:05:09.760 How much could have changed in twenty five years? 0:05:10.160 --> 0:05:14.080 Maybe everything you know I think even if nothing changed, 0:05:14.160 --> 0:05:17.640 the probability that I could answer this question without doing 0:05:17.680 --> 0:05:20.960 more research is pretty much zero. So I did a 0:05:20.960 --> 0:05:23.800 lot of different research. One thing that was particularly helpful 0:05:23.920 --> 0:05:26.400 in case anyone's interested in learning more was I found 0:05:26.440 --> 0:05:30.120 a book called Life Unfolding How the Human Body Creates 0:05:30.160 --> 0:05:34.680 Itself by James A. Davies. He's a professor of experimental anatomy. 0:05:34.880 --> 0:05:38.000 It's from twenty fifteen, so it's not, you know, from 0:05:38.040 --> 0:05:41.880 this year, but you know, it's got some general principles 0:05:41.880 --> 0:05:44.240 that have decades of research behind them. So that's what 0:05:44.240 --> 0:05:44.840 we're going with. 0:05:45.279 --> 0:05:47.560 And so we have a lot of related questions here. 0:05:47.560 --> 0:05:50.200 How are we going to tackle this whole big question 0:05:50.400 --> 0:05:51.600 and all the sub questions? 0:05:51.839 --> 0:05:54.280 Yeah? Okay, so I split it into four questions. I'm 0:05:54.279 --> 0:05:55.840 going to tell you what those four questions are, and 0:05:55.880 --> 0:05:57.960 then we'll tackle them one at a time. Great, So, 0:05:58.200 --> 0:06:01.120 question one is how do sells in a fetus know 0:06:01.160 --> 0:06:03.760 what they need to become? How do you sells in 0:06:03.880 --> 0:06:07.680 adults know what to become? How many cell types do 0:06:07.760 --> 0:06:11.120 we have? And what makes these cell types different? 0:06:11.680 --> 0:06:12.240 Okay? 0:06:12.279 --> 0:06:16.000 And right, there is just no way the answer can 0:06:16.040 --> 0:06:21.320 be comprehensive because there is a lot of variability depending 0:06:21.360 --> 0:06:24.000 on what cell type you're talking about. And so my 0:06:24.160 --> 0:06:27.680 strategy here is to kind of give like an overview 0:06:27.880 --> 0:06:31.280 of strategies that can be used by cells to figure out, 0:06:31.320 --> 0:06:33.640 you know, for example, what they need to become. Maybe 0:06:33.640 --> 0:06:36.960 dig into an example that I thought was particularly interesting. 0:06:37.560 --> 0:06:40.719 And if folks are just like, holy cow, we need 0:06:40.800 --> 0:06:45.120 like twenty more episodes on developmental biology, then I will 0:06:45.200 --> 0:06:47.800 find a developmental biologist to come on the show for 0:06:47.839 --> 0:06:50.160 twenty episodes, or I'll buy a textbook and this will 0:06:50.200 --> 0:06:52.840 be a series. But for this point, it's got to 0:06:52.839 --> 0:06:53.760 be a bit of an overview. 0:06:53.960 --> 0:06:56.160 Awesome. Well, our friend Matt Georgiani, who's been on the 0:06:56.160 --> 0:06:58.440 show a few times, he's a developmental biologist. 0:06:58.720 --> 0:07:04.720 Oh oh, why didn't you tell me that sooner? I 0:07:04.760 --> 0:07:06.960 guess I shouldn't let you know that I was spending 0:07:07.000 --> 0:07:09.760 the weekend with my nose in a developmental biology book. 0:07:10.040 --> 0:07:12.920 But my bad, which is good for you anyway. All right, Well, 0:07:12.920 --> 0:07:15.280 why don't we start in question one? And maybe a 0:07:15.320 --> 0:07:17.440 good way to start is for me to explain to 0:07:17.440 --> 0:07:20.520 you my understanding, which is probably wrong, so you can 0:07:20.520 --> 0:07:23.240 get a sense for where we're starting. Yeah, great, So 0:07:23.360 --> 0:07:25.200 question one is how does the cell and the feet 0:07:25.200 --> 0:07:27.440 is know what to become? To me, this is a 0:07:27.440 --> 0:07:31.440 fascinating question because the fetus begins with one cell. Right, 0:07:31.440 --> 0:07:33.600 you start with the egg and it's fertilized, but you 0:07:33.720 --> 0:07:36.840 have a single cell and everything that comes after that 0:07:36.880 --> 0:07:39.640 comes from that same cell. So literally, every cell in 0:07:39.680 --> 0:07:43.440 your body, even though they're different kinds, nerve, muscle, brain, whatever, 0:07:43.880 --> 0:07:46.880 have the same origin, right, the same grandpappy or grandma 0:07:47.040 --> 0:07:50.320 sell and so that means that they must have differentiated 0:07:50.480 --> 0:07:53.720 but they have the same origin. So like, that's confusing 0:07:53.760 --> 0:07:56.640 to me, Like this one became nerve, that one became muscle. 0:07:57.120 --> 0:07:59.520 If they have the same ancestry, how does that happen 0:07:59.560 --> 0:08:01.280 to me? That's the essence of the question. 0:08:01.520 --> 0:08:08.080 Yeah, it's fascinating. What's the answer? Keep going, that's a 0:08:08.080 --> 0:08:08.559 good start. 0:08:08.680 --> 0:08:11.280 The answer is, I have no idea why this part 0:08:11.400 --> 0:08:14.920 turns into head and that part turns into tail. It 0:08:14.960 --> 0:08:18.680 could be environmental, Like there's more hormones over here as 0:08:18.760 --> 0:08:21.840 this thing developing, and so maybe different genes are turned on. 0:08:21.920 --> 0:08:24.160 I mean, I know that every cell has a lot 0:08:24.200 --> 0:08:26.200 of genes, and not all of them are used. Some 0:08:26.280 --> 0:08:27.760 of them are turned on and some of them are not. 0:08:28.280 --> 0:08:31.239 But I have no idea what's controlling which get turned 0:08:31.280 --> 0:08:32.120 on and which aren't. 0:08:32.240 --> 0:08:33.880 Okay, all right, great, so that's where I come in. 0:08:34.000 --> 0:08:34.240 Great. 0:08:34.400 --> 0:08:37.160 So, first, I'd like to start by noting that most 0:08:37.200 --> 0:08:39.480 of what we know here comes from things like studies 0:08:39.480 --> 0:08:43.040 in fruit flies and mice, and for ethical reasons, we 0:08:43.080 --> 0:08:45.640 can't do the kind of manipulative experiments we'd like to 0:08:45.679 --> 0:08:49.439 do on human fetuses that you'd like to, sorry, that 0:08:52.480 --> 0:08:55.480 you would need to do to answer these questions definitively, 0:08:55.640 --> 0:08:59.400 but that for ethical reasons you will not do, don't 0:08:59.480 --> 0:09:01.360 want to do, but that you don't want to do 0:09:01.440 --> 0:09:04.000 because we are good people. Yes, I'm sorry, bad choice 0:09:04.040 --> 0:09:06.840 of words there, I was reading my notes well speaking, 0:09:07.440 --> 0:09:12.720 I do not want to experiment on fetuses. Okay, okay, 0:09:12.720 --> 0:09:15.160 So you've got this group of cells. How do you 0:09:15.360 --> 0:09:18.719 start telling quote unquote telling these cells what they need 0:09:18.760 --> 0:09:21.840 to become? Yeah, well, so very early on, one way 0:09:21.880 --> 0:09:24.840 the cells can start to figure out, like, you know, 0:09:24.880 --> 0:09:27.320 how do we know that we're different is that you 0:09:27.360 --> 0:09:30.120 can say, okay, well, some cells are on the inside 0:09:30.120 --> 0:09:32.160 of the ball and some cells are on the outside. 0:09:32.160 --> 0:09:34.960 So you start doing replication and when you've got enough 0:09:35.000 --> 0:09:38.000 cells that there are some cells that are touching other 0:09:38.080 --> 0:09:41.080 cells on all of their sides, but some cells are 0:09:41.160 --> 0:09:44.640 not touching other cells on the exterior because they're on 0:09:44.640 --> 0:09:46.960 the outside of the ball. Then they can say, Okay, 0:09:47.040 --> 0:09:49.480 we're going to do something different, and so they start 0:09:49.760 --> 0:09:52.360 turning on different genes when they realize that they've got 0:09:52.480 --> 0:09:54.600 part of their body that's not touching other cells. 0:09:54.880 --> 0:09:57.520 So already we have a way for the environment to 0:09:57.679 --> 0:10:02.080 influence what the cell turns into, not just the recipe. Now, 0:10:02.080 --> 0:10:04.240 it's input from the outside. 0:10:04.120 --> 0:10:07.640 Yes, right, And in things like insects, moms can get 0:10:07.640 --> 0:10:10.520 the ball rolling by doing things like putting stuff in 0:10:10.600 --> 0:10:14.760 the early embryo. And that stuff, in particular is what 0:10:14.800 --> 0:10:18.480 we call transcription factors. And I'm gonna not use a 0:10:18.480 --> 0:10:21.439 lot of jargon because I know Daniel's eyes are gonna 0:10:21.520 --> 0:10:23.240 roll back at his head and they might end up 0:10:23.320 --> 0:10:24.160 hurting his eyeball. 0:10:24.320 --> 0:10:26.360 I was just gonna ask, is there a Latin phrase 0:10:26.400 --> 0:10:27.520 for transcription factors? 0:10:27.559 --> 0:10:30.160 We could use, right, probably, but I'm gonna try to 0:10:30.200 --> 0:10:34.280 avoid it anyway. But so, essentially, what a transcription factor 0:10:34.320 --> 0:10:37.800 does is it turns on certain genes, and so what 0:10:38.200 --> 0:10:41.439 they do is they dump a bunch of transcription factors 0:10:41.480 --> 0:10:44.800 into the early egg, and as the cells start dividing, 0:10:44.920 --> 0:10:47.480 the cells that are, for example, at the bottom of 0:10:47.520 --> 0:10:50.240 the egg are going to end up with more transcription 0:10:50.360 --> 0:10:52.280 factors in them than the cells at the top, because 0:10:52.280 --> 0:10:54.640 there's more transcription factors at the bottom than at the top. 0:10:55.000 --> 0:10:58.360 And that's how you start getting differences in the top 0:10:58.360 --> 0:10:59.880 of the egg from the bottom of the egg. Does 0:10:59.880 --> 0:11:00.439 that makes sense? 0:11:00.520 --> 0:11:00.679 Hey? 0:11:00.720 --> 0:11:03.040 That was my basically totally uninformed guests. 0:11:03.120 --> 0:11:04.880 Oh, fantastic, All right, I know. 0:11:05.840 --> 0:11:10.760 Okay, so transcription factor, because transcription is how DNA turns 0:11:10.800 --> 0:11:13.800 into proteins, right, You transcribe DNA into proteins, so that 0:11:13.880 --> 0:11:16.520 must be related, like, yeah, which ones get transcribed and 0:11:16.520 --> 0:11:17.240 which ones don't? 0:11:17.679 --> 0:11:21.920 Yes, I always forget translation and transcription. They're both teas, 0:11:21.960 --> 0:11:24.120 but I think, yes, that's if the first you translate, 0:11:24.160 --> 0:11:27.120 then you transcribe. Okay, Yeah, they're not just tea's their 0:11:27.160 --> 0:11:29.400 t are a. You see where I'm going. This is 0:11:29.520 --> 0:11:31.080 very complicated, but that's. 0:11:30.920 --> 0:11:33.440 The level we need to understand. It's just that helps 0:11:33.480 --> 0:11:35.680 determine what gets turned on and what doesn't. 0:11:35.920 --> 0:11:38.400 Yes, okay, all right, so those are early stage what 0:11:38.520 --> 0:11:43.120 gets turned on, what doesn't. Our embryos also have structures 0:11:43.280 --> 0:11:46.680 that like literally just show up in embryos so that 0:11:46.760 --> 0:11:51.120 they can be there to release cues to tell parts 0:11:51.160 --> 0:11:53.400 of our body to start becoming things. And then as 0:11:53.480 --> 0:11:57.560 our embryos get more advanced, these structures are told to 0:11:57.679 --> 0:12:00.240 die and then they disappear, so they're only there to 0:12:00.280 --> 0:12:03.280 be like you know, I'm just making up an example 0:12:03.360 --> 0:12:05.960 like this is where the head goes, this is where 0:12:05.960 --> 0:12:10.200 the anus goes, and then they disappear. They're just sort 0:12:10.200 --> 0:12:12.520 of like helping with layout stuff and then they go away. 0:12:13.240 --> 0:12:16.280 A lot of how things determine where they're going to go, though, 0:12:16.440 --> 0:12:21.760 are from cells releasing signals to impact what's happening with 0:12:21.920 --> 0:12:25.760 nearby cells. And so one cell will release a protein, 0:12:25.960 --> 0:12:30.079 and since a least question was about genes, I want 0:12:30.120 --> 0:12:32.400 to hammer home the point that when a cell is 0:12:32.480 --> 0:12:36.280 releasing a protein, proteins are coded for by genes. So 0:12:36.400 --> 0:12:38.800 there there is a cell that has a gene turned on, 0:12:39.360 --> 0:12:42.400 it's making a protein, it's releasing it out of the cell, 0:12:42.800 --> 0:12:46.040 and that protein is then going and like diffusing over 0:12:46.120 --> 0:12:49.880 to a nearby cell and it's essentially telling that nearby cell, 0:12:50.000 --> 0:12:52.559 Hey turn on some genes. We got to do something 0:12:52.640 --> 0:12:56.920 coordinated together, and that's turning on yeah, genes in the 0:12:56.920 --> 0:13:00.160 nearby cell. And so by communicating with each other nearby, 0:13:00.520 --> 0:13:02.440 they're able to tell each other like, all right, we 0:13:02.480 --> 0:13:05.640 need to coordinate to make a muscle cell together, or 0:13:05.679 --> 0:13:07.280 we are going to be the heart. 0:13:07.520 --> 0:13:07.720 Yeah. 0:13:07.800 --> 0:13:10.240 And so there's a bunch of signaling molecules that get 0:13:10.400 --> 0:13:13.240 used so that cells can communicate to one another. 0:13:13.320 --> 0:13:16.880 Does that make sense, Yeah, And so cells turn on 0:13:17.040 --> 0:13:20.080 these genes to make proteins to signal to other cells 0:13:20.400 --> 0:13:22.880 that they need to work together. Yes, But something must 0:13:22.920 --> 0:13:25.520 have told that cell to start that signal, right, So 0:13:25.559 --> 0:13:28.720 there's something upstream from that that's some environmental factor like 0:13:28.920 --> 0:13:30.680 we're in this part of the body, or we're close 0:13:30.720 --> 0:13:34.160 to the anus, or there's this guy thing on our outsides. 0:13:34.480 --> 0:13:37.880 Yeah, or it could be that the structure that showed 0:13:37.920 --> 0:13:40.640 up just to tell us where we're supposed to become 0:13:40.720 --> 0:13:43.640 has started to release that signal. And you know, so, 0:13:43.760 --> 0:13:47.240 like very early on in development, there are cells with cilia, 0:13:47.280 --> 0:13:49.160 which are like hairs that are on the outside of 0:13:49.160 --> 0:13:51.320 the cell, and they are told to beat in a 0:13:51.360 --> 0:13:54.480 certain direction. And when they beat in that particular direction. 0:13:55.080 --> 0:13:59.600 They start sending a bunch of compounds in a certain direction, 0:13:59.720 --> 0:14:02.200 so that cells that are in that direction get a 0:14:02.240 --> 0:14:05.080 lot more of this stuff than cells on the other 0:14:05.160 --> 0:14:07.240 side of the body or sells on the other side 0:14:07.240 --> 0:14:10.520 of the fetus. And this starts setting up the fact 0:14:10.559 --> 0:14:13.440 that not everything in our body is symmetrical. And so 0:14:13.520 --> 0:14:15.560 this sets up that, like, your heart goes on this 0:14:15.640 --> 0:14:17.960 side of the body, and the stuff that's getting sent 0:14:18.080 --> 0:14:21.480 to one side of the body are things like transcription factor, 0:14:21.560 --> 0:14:25.000 so it's like your body has more of chemicals on 0:14:25.000 --> 0:14:27.280 one side that will tell your body like this is 0:14:27.280 --> 0:14:29.400 the side that the heart goes on, and stuff like that. 0:14:29.520 --> 0:14:32.720 So there's different like so there's environmental cues that we 0:14:32.760 --> 0:14:36.080 talked about earlier, Like I'm on the outside. There's cues 0:14:36.360 --> 0:14:39.240 like we are beating in a certain direction, so that 0:14:39.400 --> 0:14:43.000 fluids in the embryo are getting sent in a particular direction, 0:14:43.120 --> 0:14:46.960 so this side has a higher concentration than the other side. 0:14:47.280 --> 0:14:49.840 And then there's cells talking to one another. These are 0:14:49.840 --> 0:14:53.400 all sort of various ways that your body can communicate 0:14:53.480 --> 0:14:56.560 where things need to go and what needs to be happening. 0:14:56.960 --> 0:15:00.440 So there really is a very rich environmental content for 0:15:00.480 --> 0:15:03.720 all of these cells. The idea that how your body 0:15:03.800 --> 0:15:07.200 is built comes just from your DNA is missing a 0:15:07.200 --> 0:15:09.520 big part of the picture, right, Like these structures and 0:15:09.560 --> 0:15:13.120 the relative context and all these cues are a huge 0:15:13.160 --> 0:15:15.520 part of the recipe for building your body. Right, It's 0:15:15.600 --> 0:15:17.480 not just encoded in your DNA. 0:15:17.600 --> 0:15:21.240 Well, I mean, so DNA, most of this stuff is 0:15:21.360 --> 0:15:25.880 like proteins moving around and telling cells what to do, 0:15:26.320 --> 0:15:30.560 and those proteins are made by the genes, and so 0:15:31.240 --> 0:15:33.600 you know, none of this happens without the genes for 0:15:33.640 --> 0:15:34.280 the most part. 0:15:34.600 --> 0:15:37.240 I see. So for example, those structures you talked about 0:15:37.240 --> 0:15:40.800 that say, like put the mouth here, that's from proteins 0:15:40.800 --> 0:15:42.080 that are encoded by the genes. 0:15:42.360 --> 0:15:44.840 Yeah, So that structure needs to be made by genes, 0:15:44.880 --> 0:15:48.200 and then they're releasing chemicals that say, see the structure 0:15:48.240 --> 0:15:51.480 goes here, and those chemicals, yeah, are encoded by genes. 0:15:51.640 --> 0:15:54.400 But there's a reason that structure is created over here 0:15:54.400 --> 0:15:56.960 in the mouth the area, right, and not over there 0:15:57.000 --> 0:16:00.680 in the finger area. And that comes down to environmental 0:16:00.720 --> 0:16:02.360 cues that happen upstream. Right. 0:16:02.640 --> 0:16:05.760 So when I talked about the environmental cues early on, 0:16:06.520 --> 0:16:10.160 as I understand it, those environmental cues like I am 0:16:10.200 --> 0:16:13.400 on the outside of the ball are helpful for like 0:16:14.040 --> 0:16:17.560 maybe the first week or something very very early on. 0:16:17.920 --> 0:16:20.400 But once you start getting to things like you know, 0:16:20.440 --> 0:16:24.320 the head is here, the high knees here, stuff like that, 0:16:24.520 --> 0:16:27.840 A lot of that has to do with chemical cues. 0:16:28.160 --> 0:16:32.280 And those chemical cues are emanating from things like what's 0:16:32.320 --> 0:16:34.680 called the notochord, which is one of those structures I 0:16:34.720 --> 0:16:38.640 was talking about that gets made and then mostly disappears 0:16:38.680 --> 0:16:40.840 in humans. I think it still shows up as like 0:16:41.200 --> 0:16:44.320 the discs in between our vertebra, but it is hugely 0:16:44.360 --> 0:16:47.160 important in developmental biology for giving us cues for what 0:16:47.200 --> 0:16:49.840 goes where, but then becomes, you know, something that we 0:16:49.880 --> 0:16:52.160 mostly forget about unless our back hurts when we're older. 0:16:52.360 --> 0:16:56.360 So yeah, I think environmental cues become less important after 0:16:56.400 --> 0:16:59.200 the very very early phases, and then it's a lot 0:16:59.240 --> 0:17:02.280 more about what cues are being found where, and that 0:17:02.640 --> 0:17:04.800 is coded for by genes I see. 0:17:04.920 --> 0:17:08.359 But those later signals which come from genes are just 0:17:08.400 --> 0:17:12.520 like cascades from the original environmental cues, right Otherwise, every 0:17:12.520 --> 0:17:15.360 cell is the same originally, so even though they're coming 0:17:15.440 --> 0:17:18.680 from proteins which are encoded in the DNA you can 0:17:18.720 --> 0:17:22.000 like trace them upstream to environmental cues earlier. 0:17:22.080 --> 0:17:24.880 Right, Yeah, I think you could probably make that argument. 0:17:25.119 --> 0:17:27.240 The picture I have in my mind is like every 0:17:27.280 --> 0:17:30.200 cell is like go into the hardware store, Like, yes, 0:17:30.280 --> 0:17:32.159 you can make a cabinet, or you could make a 0:17:32.160 --> 0:17:34.520 sculpture or whatever. All the things you need are there, 0:17:34.800 --> 0:17:37.280 but somebody has to decide, like what we're building today. 0:17:37.960 --> 0:17:40.560 Yeah, yeah, OK. I was looking for an example that 0:17:40.600 --> 0:17:42.879 I could give that would be like really satisfying, Like 0:17:42.920 --> 0:17:45.439 here's how a liver is made. But the problem with 0:17:45.560 --> 0:17:47.959 trying to explain this sort of stuff is that a 0:17:48.000 --> 0:17:53.800 fetus has layers that are not easily analogous to you know, 0:17:53.880 --> 0:17:55.720 like our human body, right, And so in order to 0:17:55.800 --> 0:17:59.239 explain it, it's hard to do without pictures, and it's 0:17:59.280 --> 0:18:02.000 hard to do in a podcast and without like introducing 0:18:02.000 --> 0:18:04.240 a bunch of jargon. And so to try to give 0:18:04.359 --> 0:18:08.439 a better sense for how this kind of thing works, 0:18:08.520 --> 0:18:10.560 I'm going to go ahead and use an example from 0:18:11.000 --> 0:18:13.560 an adult and so this isn't a fetus, but this 0:18:13.680 --> 0:18:16.520 is going to give you a sense for how genes 0:18:16.560 --> 0:18:19.200 help cells decide how to behave and how to make 0:18:19.240 --> 0:18:23.199 decisions about what to become every cell in your body 0:18:23.880 --> 0:18:27.560 needs to be able to get oxygen and like relieve waste. 0:18:28.040 --> 0:18:31.720 But you like grow over time, right, and so or 0:18:32.320 --> 0:18:35.720 I grow over time. And when you grow and you 0:18:35.800 --> 0:18:38.080 end up with like more cells in an area, your 0:18:38.119 --> 0:18:40.919 body needs a way to say, Okay, you know what, 0:18:41.040 --> 0:18:43.600 Actually I need more blood vessels over here because there's 0:18:43.680 --> 0:18:46.280 like more cells and no, they're no longer getting as 0:18:46.320 --> 0:18:49.000 much oxygen as they need. So how does your body 0:18:49.119 --> 0:18:52.760 know when an area needs more blood vessels? So what 0:18:52.880 --> 0:18:56.560 happens is that your cells make a protein all of 0:18:56.600 --> 0:19:00.640 the time. And this protein whose name I'm not going 0:19:00.640 --> 0:19:04.560 to burden you with for Daniel's sake, this protein is 0:19:04.640 --> 0:19:08.760 actually constantly made, and when your cell is getting enough oxygen, 0:19:09.040 --> 0:19:12.119 your body just regularly destroys it. It's like I got 0:19:12.200 --> 0:19:14.160 enough oxygen, I'm getting rid of this protein. I don't 0:19:14.160 --> 0:19:17.719 need it. But when you don't get enough oxygen, this 0:19:17.880 --> 0:19:22.320 protein stops getting broken down and it goes into the 0:19:22.400 --> 0:19:25.240 nucleus of the cell and it starts activating more genes. 0:19:26.119 --> 0:19:27.720 And one of the things that it does is it 0:19:27.760 --> 0:19:31.840 tells your cell, hey, we are in a low oxygen situation. 0:19:32.359 --> 0:19:35.679 You should stop multiplying you should stop doing anything that 0:19:35.720 --> 0:19:38.919 isn't critical because we only have so much oxygen. And 0:19:38.960 --> 0:19:42.080 then the other thing that it does is it gets 0:19:42.119 --> 0:19:47.080 the cell to start producing something else. And this is 0:19:47.119 --> 0:19:50.000 a signal that gets released from the cell, and this 0:19:50.080 --> 0:19:53.679 signal calls the blood vessels over to it, and it's like, 0:19:53.760 --> 0:19:55.679 you need to start heading over to me because I 0:19:55.720 --> 0:19:58.480 am not getting enough oxygen. And so now it starts 0:19:58.480 --> 0:20:01.760 growing towards the cell that needs or oxygen. And once 0:20:01.800 --> 0:20:04.960 that cell starts getting all of the oxygen that it needs, 0:20:05.560 --> 0:20:08.919 it goes back to destroying the protein that it was making, 0:20:09.320 --> 0:20:11.199 just like it usually does. So as I mentioned earlier, 0:20:11.200 --> 0:20:14.520 when it has enough oxygen, it just regularly destroys this protein. 0:20:15.040 --> 0:20:17.439 And so now that it's got as much of the 0:20:17.440 --> 0:20:20.080 protein as it needs, it just destroys it. It's got 0:20:20.160 --> 0:20:22.520 the blood vessel giving it as much oxygen as it needs, 0:20:22.800 --> 0:20:25.040 and so now it's fine. So does that kind of 0:20:25.040 --> 0:20:25.560 make sense? 0:20:26.320 --> 0:20:29.440 The body is building cell types of different kinds based 0:20:29.480 --> 0:20:31.560 on signals that come from the body. 0:20:31.240 --> 0:20:35.200 Itself, right, that are coated for by genes, and proteins 0:20:35.240 --> 0:20:38.960 are acting on genes to try to like tell the 0:20:38.960 --> 0:20:41.040 blood vessels that hey, you need to make more cells 0:20:41.080 --> 0:20:43.360 to come over here to feed us, and then that 0:20:43.480 --> 0:20:45.760 is acting on the genes again to tell the cell Okay, 0:20:45.800 --> 0:20:48.080 I've got enough oxygen. I can go back to destroying 0:20:48.080 --> 0:20:50.600