How lessons from frogs help mend a broken heart - Professor Sir Jim Smith - 1 October 2025

Um, so welcome everybody to the 224th session of Can you hear me? Okay. Uh, okay. To the 224th session of the Royal Philosophical Society and it's a great pleasure to see you all here. Um, for those of you who don't know me, my name is Pat Monahan. I'm the president of the society and uh before I start introducing this evening's speaker, I'll just quickly remind you of the housekeeping rules, um you have to behave yourself. That's one thing. Um that there's no fire likely, but in the event that the fire alarm should go off. uh please leave either by the side doors or the door at the back and uh exit the building at the front. Um can you please make sure that your phone uh has been turned to silent now uh I'll introduce tonight's speaker. I'm really pleased uh I'm really pleased that he's here intact uh since he should have spoken to us last year but unfortunately he met with the slight accident which meant he was unable to come. So welcome Jim and we're glad to see you fully recovered. Now tonight's speaker is Professor Sir Jim Smith who is a developmental biologist. Jim studied at Cambridge and at Harvard and he's had really quite a stellar career. His he researches something which is very fundamental to our understanding of life. If I said he was a developmental biologist and what he studies is how when when animals are first formed, of course, they're formed from a single cell, but that cell then has to make all kinds of different cells using the same genetic material. Now, how does it do that? For example, in the human body, there are perhaps more than 200 different types of cell that turn into the trillions of cells that make up our body. So that's Jim's research area. How do we get the right cell to do the right thing in the right place? Jim's had many awards uh for his work. Uh I won't go through them uh because there's a lot of them, but he's been elected as a fellow of the Royal Society and a fellow of the Academy of Medical Sciences and he was kned for his work in 2017. He's also had very prestigious leadership roles uh in a number of research institutes, the Girden Institute, the Crick Institute, the National Institute for Medical Research and with the Welcome Trust. And currently he's president of the Zoological Society of London, which of course is a society as a zoologologist that is very close to my own heart. It's one of the world's foremost conservation organizations. It runs London Zoo and Whips Zoo and it also has a very strong research wing. So, uh, the title of Jim's talk, as you'll have seen in the program, is how lessons from a frog help us mend a broken heart. Thank you to Thank you, Pat. The first thing I've done is drop the microphone. So, I hope the microphone meister won't mind that too much and that you can still hear me. Can you hear me? >> Yeah. >> Great. So, I would like to apologize for my no show a year ago. I fell down the stairs into the basement and broke five ribs and messed up my lungs somewhat. I was all in favor of coming, but my kids told me that I was mad and I should go to hospital. I did go to hospital and they did tell me it was probably wise not to travel. So, thank you for your forbearance and thank you for inviting me back. The other thing I'd like to do, it's a little bit unconventional, is um my son is a master's student here and um he couldn't come this evening, but I want to show him that to my astonishment, I have a large audience. So, would you mind if I took a photograph of you and send it to him because um yeah, I'm just going to do that. A little unconventional perhaps, but camera. Oh, okay. I won't ask you all to wave, although you can if you like. Okay, thanks very much. So, yes, as Pat says, I'm a developmental biologist. I'm interested in how a single cell, the fertilized egg, divides and divides and divides to become eventually a human being. My first slide illustrates that in a very simple manner. See if I can make us go to the next slide, which I cannot. Maybe. Let me try. There's This is where I hope somebody's going to come up and help me. Here we go. Whoa. >> Careful. Oh, >> what did you do there? What have I done wrong? Oh, okay. So, here is here is my first slide. And the question I'm interested in is how that single cell there, which you can see in orange, artificially colored of course, with the blue sperm, in fact only one sperm gets in, eventually goes on to form a human being. To my mind, it's one of the most fundamental and interesting problems there is about being human. And it's a really difficult problem. And my this next slide illustrates the scale of the problem. So our bodies contain 37 trillion cells, 3.7* 10^ the 13 cells. As Pat says, there are about 200 different cell types. And how does the right kind of cell form in the right place? I've got two ways of illustrating the numbers here in a little more detail. First of all, if you imagine each of those cells was a child's marble, you little marbles one played with at school. Then those 37 trillion cells would fit into three million of those containers and they would fit into 140 of the largest containers ship that floats on the oceans. Now, so there's a lot of that's a lot of marbles, 200 different colors and you have to make a pattern from them. Challenging. And the other piece of information that is that can be quite useful and you can take home with you and amaze your friends and win some money. If I took all of the DNA out of you, madam, if I took all of your DNA, you know, which is as which is as you know, genetic material and stretched it out, how far do you think it would go? >> We have a we have a vote of a mile. Do I have any increase on a mile? a million miles. Second, it will go to the sun and back 70 times inside inside all of us. To the sun and back 70 times. And just thinking about that, one of the things about being a human, of course, is that you get cancer because there are mutations in your DNA. And there are molecules in your cells whose job it is to scan that DNA looking for mistakes. So just imagine when your neck's having difficulty falling asleep, thinking of that DNA going to the sun and back and there are molecules checking it for mistakes all the time. Astonishing. I think it's astonishing. So the question I want to try and answer today is or at least in the first half of my talk is how it is that the right kind of cell forms in the right place. And the first idea or one of the best ideas about this, how this might happen came from my my then PhD supervisor, a man called Lewis Walpert, who some of you may have heard of. He was a remarkable polymath. He did a lot of things, but he came up with a model he called the French flag model for deciding how cells might form the right cell in the right place. And his model was that imagine you have cells that can become blue, white or red. How can you instruct a field of cells, a group of cells to form such that they differentiate? They become blue in one area on the left near the flagpole, white in the middle and red further away, which is in microcosm what happens in us. And what he said was, and it's illustrated in that central section, but I can probably just explain it in words to you just as easily, that imagine that there's a special region in the embryo, in this case, near the flag pole, indeed maybe the flag pole itself. The flag pole releases a chemical signal. And you can imagine that that chemical signal leaves the flag pole, diffuses away from the flag pole such that the concentration of that signal is highest near the flag pole, intermediate further away and lower still further away from that. And that cells in some sense are clever enough and we can ask how they are clever later on. cells are clever enough to measure the concentration of that signal and differentiate as blue, white or red accordingly. So where the concentration is high they become blue where it's intermediate they become white and where it's lower they become red. So that was the model an attractive simple model. Is there any evidence for it? And in those early days, so this was this was 1969 1970 that these ideas were around and I began doing my PhD with Lewis Walpert in 1976. And at the time we were working on the development of the chicken limbbud. So if you can imagine a hen's egg there on the left and if you incubate that hen's egg in an incubator 38° for 3 days and then take off some of the shell and look inside. Then you can see can you little structure in the middle with the blood vessels all converging on it. That's the embryo. So that's what you see if you look in a look in an embryo at 3 days. In the middle of this image, you can see what the embryo itself looks like. And if I have a pointer, which I don't, but maybe this will here. Can you see? No, you can't. You see there it says wing bud. That's a little lump on the side of the embryo that will grow out and become the wing. down the bottom there's a leg bud which will grow out and become the chicken's legs. But we're going to focus on the the wing bud. And if that's three days, then by 10 days, 7 days later, that wing bud has grown out sufficiently that it forms a very creditable looking limb. The chicken's arm, the chicken's wing. And the thing about the chicken's wing is that where we have five fingers, it has three. But we can distinguish between each of those three fingers because they look very different from each other. There's a digit we call digit four, that slim one. There's a big one that we call digit three. And then there's a smaller one at the top that we call digit two. And in the experiments I'm going to show you on the next slide, what you have to imagine is that digit four is the red is is the blue stripe in the French flag. Digit three is the white flag, white stripe in the French flag. And digit two is the red stripe in the French flag. So what do I mean by this? So that's what I've just shown you. That's the limb bud growing out forming digits 2, three, and four. And you'll see that I've hatched an area in what we call the posterior part of the wing bud, the bit closest to the tail of the chicken embryo. And I've hatched it because that's the area that is effectively the flag pole that I mentioned in the French flag. That's the area that's producing the signal that I've been speaking about. So that if you dissect from another embryo that special region and transplant it to the anterior of the wing bud, now you have two regions, two flag poles making a signal. So I hope you can see that what will happen is that where the concentration is high you now get two digits four where it's lower you get two digits three and where it's lower still you get two digits two does that make sense good and now you can ask in fact I'll ask you the question and then I'll show you the result of the experiment what would happen do you think if you grafted that special region not to the far distant top but into the middle of the limb. What do you think would happen then? And I'm not going to ask Pat. In fact, I may not ask deformity. >> You deformity. >> You get a deformity. But the particular deformity is this. It's a it's a predictable deformity. So now you get near the near the host source you get a four. Then you get a three. Then you get another four. So you get a you get 434 because the space between those two regions isn't far enough that it gets low enough to form a digit two. See what I mean? And then as you go anterior again you get a digit four slightly small in this case then a digit three and then a digit two. So this again we argued is completely consistent with the idea that you form the digits you form in response to a concentration gradient produced by this special region in the chicken wing bud. But we think it was down to concentration and my PhD for what that was worth and it was worth a PhD as far as I was concerned was to show another kind of experiment where we were able to weaken the signal that came from that area. So if we took the norm this is now on the right hand side of this slide at the top if we if we graph the normal strength we get that 432 234. But if we graft a weaker version, the signal isn't high enough to make a digit four. So we get 3 2 3 4. If we weaken it further, we get 22 23 4. And if it's much much weaker, we don't get anything at all. So these experiments were consistent with the idea that digits in the chicken limb bud form where they form according to the concentration of a substance produced by this special hatched region. And I'm not going to talk about it because it's my work and I only like talking about my own work. But we do know what the nature of that signal is now. And it turns out that it's a protein that became known as Sonic Hedgehog for reasons that we don't need to go into. You can ask me afterwards why it's called Sonic Hedgehog, but we now know that this signal is called Sonic Hedgehog. So that was where I got to um at the end of my PhD. I was fascinated by this and I was really desperate to know a what those signals are and b whether the same principle applied at other stages of embryionic development both earlier and later. But I was particularly interested in the early stages. what happens in the early embryo to distinguish the first decisions that embryos make as to what different cells should form. And so I decided that I would move to a different species of embryo because chickens were slightly inconvenient. I'd move to a different species of embryo and go to an earlier stage of development. Now, you may or may not know that um developmental biologists work on a whole variety of different species. So we have the zebra fish at the top there, the fruitly that you will have heard of, this the the nematode worm, cenorabditis elegans, the mouse, and at the top right is the frog I work on called Zenapus leis. And that's the species that I've spent most of my scientific working life working on. Now you might say why would you work on this frog? And there are really good reasons for it. First of all, why this species Xenopus leas? There were lots of them about hospitals had them because they were the early pregnancy tests. So, did people know that early pregnancy tests were conducted by injecting urine from a woman who wanted to know whether she was pregnant into the dorsal lymph sack here of a female frog and if the woman was pregnant and her urine contained a particular hormone then the frog laid eggs and that was the test. These days, these days, as you know, we don't do that. But the tests that we use are based on an assay for precisely the same hormone. It's just that now we use what are effectively lateral flow tests. And in the old days, we use frogs. So, there were lots of these frogs around. Very easy to work on these embryos because they're laid outside the mother in water in frogs. So they're very readily accessible. As you'll see in a few minutes, the embryos once laid and fertilized develop beautifully synchronously. So you can do experiments on them predictably at different stages and you know you know what's happening because they all develop at the same rate. The frogs themselves are really easy to look after. So they live in water. You know they don't hop all over the place. They live in water. Very easy to care for. You can get lots of them. And as we'll see towards the end, the lessons we learn from the frog apply to other species as well. So the frog has been a very very powerful organism for understanding early development. And let me just show you to give you a sense of what these things look like. A movie I'm going to show you two movies. The first one is a group of frog embryos developing as I say synchronously. The film starts as soon as I switch onto the slide. So, just let me say to give you a sense of scale. Each of the embryos you'll see, each of the balls you'll see that begin to divide and divide is about 1.4 millimeters across. They're pretty small, but as you'll now see, they develop pretty synchronously. So, two cells, four 8 16. And they develop synchronously quite rapidly. Each division is about half an hour. Predictably in the sense that I can tell you what each of those cells at those early stages will become and we'll talk about that later. But they're very predictable. So I I can tell you that cell will make skin, that cell will make gut, that cell will make muscle. I can do that from a very early stage. So you can see that happening there. So these embryos develop rapidly, synchronously, and predictably. And that's a big help to us. So what I've shown you is the early stages up to a to a stage called gastrolation. And the next film I'm going to show you is just one of these embryos flipped over and viewed from below to show you the cell movements that occur to bring all the cells into the places that they need to be ultimately. This is a process of gastrolation which I shall now show you. So you can see there's a slit there and these there cells tunneling inside the embryo. those cells that will form the gut and the muscle moving inside the embryo. On the top there, you can see a thing a little bit shaped like a keyhole. Now, that's going to become the nervous system. The head is at 2:00. That's the nervous system folding up. It I'd have been happier if it had flipped the other side, actually, but there you go. And so, you got the nervous system at the bottom. There's an eye beginning to form in the top right. So, that's the species we work on. And yet I hope you can see that it's a convenient animal for me. Rapid external development, synchronous, predictable, quick. It's a great organism. So the question is, how do the cells in this embryo know what they want to form? And the cells I'm really, really interested in are the cells of what is called the misodome. So up the top there, we've got a swimming tadpole. That's about 3 days after fertilization. It's a it's a tadpole that you'd see swimming in a pond. And you can see it's got a head at the left side. It's got a nice big eye. There's a thing just below the eye and to the left called the cement gland that it uses to stick to leaves to eat. Along the back you can see heading towards the tail you might just be able to see some chevron shapes. Those are the muscle. The heart forms just uh below the eye and to the right. And that's the the stage at which as far as I'm concerned everything's finished. By then the really important cell types have formed and they're in the right place. Now if we if we take a section of that embryo, if we if you take a a sharp knife and cut it like that, then you can see what you see on the right hand side there. They are the different cell types that I'm I care about. On the outside, you've got the skin. Beneath the skin at the top there, you can see a structure I've called the neural tube, which is the beginning of the nervous system. There's then a structure called the noticord which is the primitive backbone blanking the noticord you can see muscle muscle forms really early in tadpoles because one of the things you have to do if you're a tadpole is get out of the way of various you know nasty predators so your muscle develops really fast then you've got kidney below that the limbs form where I've indicated blood at the bottom and in the middle do you see that gap That's the lumen of the gut. So, those are the cell types I'm interested in. But in particular, in particular, what I'm interested in are cells of the so-called misoderm. So, there's the ectoerm on the outside, endoderm in the middle, and miso, as the name implies, between the ectoerm on the outside and the endoderm on the inside. And the misoderm forms noticord, muscle, kidney and blood. And I want to know how the cells know they should form misoderm. And the interesting things happen if you take yourself back to the first movie I showed you at this stage here where there are about 2,000 4,000 cells. So that's that's when interesting things happen. So just remember that with me so far? I haven't said anything stupid. Okay. So, what goes on? Imagine taking those embryos bottom left and I'm going to take one of those. I'm going to draw you a schematic version of it and I'm going to turn it through 90°. So, just let me tell you that those cells you're looking at, you're looking down. And it so happens that we call those cells at the top the animal pole cells. And the cells on the other side are called the vegetital pole cells. And I'm trying not to introduce too many words, but I can't help myself. I have to say animal pole at the top and vegetital at the bottom. So in the next slide, this is a representation of that. Animal at the top, vegetital at the bottom. Okay? And you'll see that I've colored them red and blue. And I've colored them red and blue because those red cells, if you take them out of the embryo and grow them on their own, they'll make skin. And the blue cells, take them out of the embryo, grow them on their own, they'll make gut endodone. None of the cells if you take them out at this early stage will make misodome. We know because you can mark them that there are certain cells that will make misodone. We know that but the embryo doesn't. However, if you wait a bit, if you wait three cell cycles, an hour and a half to that later stage where you can see I've colored some cells yellow, then if you take those cells out, they will make misad. They will make muscle noticord. Okay? So something happens to those let's call them equatorial cells between the tropic of cancer and the tropic of capricorn if you will that tells those cells don't make ectoerm make misoderm instead. So what's going on and what's going on was discovered in 1969 by a Dutch embryologist called Peter no is anybody Dutch in the audience? good. I never know how to pronounce his name. And what he did was this. So, first of all, you can mark an embryo to make it green. You can inject into the embryo fluorescent markers. So, the entire embryo becomes fluorescently green. And you can take from that embryo prospective skin cells right from the top that you know if you take them out, they'll become skin. And those are from the green embryo. And then you can take prospective gut cells from the bottom and juxtapose them with those green cells. Okay? And if you do that and you grow them for 3 days, what do you think happens? They'll make they'll make misodome. So this is what we what we see here. So those green cells will now make noticord. You can recognize noticord cells very easily and muscle and you can use all sorts of ways of demonstrating unequivocally that those cells are noticord and muscle. So this was something that yuku showed in 1969 and my claim to fame such as it is was that I became I mean actually obsessed with this interaction and I really wanted to know what those what the signal what's the molecule that passes from the white endoderm cells into the green cells what is it and this is one of those things where um where you know you're giving a lecture and five years, six years of really hard work goes past and you describe it in a quarter of a slide. I mean, it breaks my heart actually to do it, but nevertheless, that's what happened. So, what I found and then others followed up was that we could identify what these so-called misoderm inducing factors were. And it turns out that they all fall that, you know, I found some then other people But there was a sort of gold rush you might say. So I found molecule called actin molecule called veg one. Then later on I was involved in discovering zenopus nodal related one two. There was a nodal related 456 a protein called derriè because it was discovered by a Frenchman in the rear end of a frog. So this thing called derriè BM. So we discovered that there were all these misoderm inducing factors that would have this effect and I'm going to show you in a minute that those misoderm inducing factors behave as we'd hope as I hope you'd hope in a concentration dependent fashion. That's what you'd hope. But before showing you that slide and to give you context for what is going to come in the second half of the talk, I just want to emphasize that there are now I'm going to say innumerable. Let's just say many protein factors that we know about from zenopus, from mouse, from drosophila, from um from zebra fish and so on that do influence early development. So top left there is is my paper about actin. Um immediately under that where it says ectopic expression of the protoontagene encoagene int1. So there are molecules called the wints and the ins that have an effect. Retinoic acid has an effect. And by the way women are warned not to ingest retinoic acid when they're pregnant. That's because retinoic acid has an effect on the nervous system and so you don't want to ingest too much retinoic acid when you're pregnant. There's another molecule you'll hear about later called fibroblast growth factor for example. So there's a whole range of molecules but what we're going to do here is focus on the ones that I mentioned in the slide before in particular the activein family. And the question I'm now going to ask is whether we can show as we would predict and as I hope you're on my side here as we might hope that actin functions in a concentration dependent fashion to cause cells to become misodome. So what do we do? And I'm aware that we're getting a little bit technical. If if I'm going too technical, shout. So this is the concentration dependence thing. And on the left, I hope you'll still be with me. So you'll recognize that's another section through these embryos. At the top is the animal, the cells that will become skin. At the bottom are the vegetital cells, the cells that will become gut. And you'll see that there's some cells that are red and those cells are in that equatorial region. And these cells are cells that have turned on a particular gene. A particular gene that is turned on only in the misodome. And this gene is called brachiuri. I'm sorry, it just is. I can't do anything about it. Those of you with a classical education will know that brachiuri is the Greek for short tail. Thank you sir. Um because it was originally discovered in a mouse which had a short tail and when the when the protein was identified short tail but I care about it because it's expressed in those cells that will become misodome. So what was the experiment we did and it was tricky but here it here it is and it's it's it's such a beautiful experiment. So what we did was this. That's that's a zenopus embryo frog embryo looking this time from above looking at the cells that will become skin. Okay. And I'm just showing you the micro dissection we do using a very sharp tungsten needle. So just to remind you, it's a 1.4 millimeters across. So we're cutting out quite small pieces of tissue. And we cut out those those regions. We call them animal caps. And we disper we cut out several hundred of them. And we disperse them into a single cell suspension. If we didn't do it on single cells, then cells in the middle of a group would see a lower concentration of stuff than those cells on the outside. So we disperse them to make a single cell suspension. That's what we do there. Then we treat them with different concentrations of actin and then look for expression of our gene brachiuri. And the next slide all you need to know is if you see a horizontal band that means the gene has been switched on and these cells are miso that's all you need to know and the experiment the result of the experiment is this. So where the concentration of actin is low that is zero 0.06 06 or 0.13 nanogs per milliliter. That's not very much. Nothing happens. But suddenly you go from.13 to 0.25. Bang. The gene comes on. It remains on until you get to 2 nanogs per mill and then it goes off. So the clear model to my mind at the time is that we have an actin or actin like molecule in those vegetital cells. The concentration there it's so high you don't get brachiuri expressed. It's like the blue stripe of the French flag diffuses away a bit. Then there's a zone in which brachiuri is expressed like the white flag in the middle there. And then as you go further away still it's not expressed. So this I I loved this experiment and it was published in 1992 and I still love it like a baby. So this was a great result and it it to me what it did was it showed that my PhD supervisor whom I love dearly got it right that cells can measure the concentration of different substances and they can do it in an incredibly accurate way. They can you can go from.13 nanogs per mill to 0.25 25 and that makes effectively a qualitative difference in the way the cells behave between on between I'll pick it up off and on. Amazing. Now, one thing we don't know about is how that happens. We don't really know how it is that cells are clever enough to do that. And we messed around for some time and I'm going to show you um some experiments we did early on that tried to give us an understanding of how it worked but didn't quite get there. And if if if nothing else it's an illustration of how difficult science can sometimes be that you know it would be lovely to be able to tell you a finished story but even after all these years we haven't got there. So the next slide is about how you make a white stripe. And the first image you see the first graph shows you expression of this gene xenopus brachiuri on the the y- axis and concentration of actin on the x- axis. And you can see when the concentration is low we don't have much brachiuri. As the concentration goes up brachiuri is turned on. and then later on it declines and that this is a representation of what you saw in that previous experiment. Now that's after 5 hours 5 hours after treatment. We wondered what happens if we if we leave it for a shorter period of time. What happens if we only leave it for two hours? Then we get this. It never goes off. So what this suggested to us is that there are some sorts of interactions going on between inside cells that cause an initial activation to decline. Does that make sense? Something happens during that period of 3 hours between two and five. And we worked out that that something requires protein synthesis. So this is the same experiment again. Obviously slightly different because you know that's life but it looks pretty similar. But if we take those cells and this time leave them for 5 hours but stop protein synthesis then what happens then is exactly the same as before. The brachauri stays on. So there's something that goes on inside these cells. Some sort of intracellular jigory pokery that causes the high concentrations of actin not to turn on brachiure. And I'm not going to spend ages on this because it is complicated and I don't really get it myself. But we developed we a mathematical model where we said that the actin here represented as M turns on both turns on brachiuri and something else and they inhibit each other and we can make mathematical models in which if you're if you're above if you're just above one threshold then it flips that way and if you're just below another threshold then it flips that way and you can make models that that that that that looked reasonable and we thought might well work. In other words, you've got two things being turned on. And in a nutshell, at the high concentrations of actin, you turn on something that turn brechuri off. See what I mean? And if you failed to turn that something on, then the brachiuri would remain on. Just one more slide on this before I I leave this rather complicated area. What we wondered was does do the high concentrations of actin turn on the expression of something that turns brachiuri off. So what we did was we did find a gene called goosecoid and we can talk about why it's called goosecoid later on. that is present at 2 hours. So we get brachiuri and goosecoid and at five hours the goosecoid would switch off the brachiuri but the goosecoid would remain on. So that's a simple model and we began to design experiments to find out whether goosecoid was the gene that keeps brachiuri off at the high concentrations. So we did an experiment in the whole embryo where we misexpressed goosecoid and sure enough brachiuri switched off. So this is a view from the bottom of the embryo. We expressed goosecoid in that trapezoid and brachiuri was off. So we thought great brachiuri can be switched off by goosecoid. We then did some fancy stuff where we took the brachiuri gene and the elements of the brachiuri gene that are responsible for turning the gene on and off. So upstream sequence that regulates brachiuri expression and had a link that to a gene that we could measure called luciferase. And what we found was that when we measured luciferase activity, we found exactly the same thing. So look at the top right. Activin low concentrations turned it on a lot, medium and high turned it off. So we thought we've recapitulated the whole response. You'll also see that we can turn luciferase activity, brachiuri expression on with another gene called fibroblast growth factor FGM. And what we found then was that if we add goosecoid into this system binding to the upstream sequence of this protein then when we treated with fibroblast growth factor the level of expression of this reporter in the presence of goosecoid was way down. So we were quite excited by all this. We thought we've worked out what brachiuri how brachiuri is switched off at these high levels of activin. And the key experiment in the end then was to do the experiment that I've shown you already where we have active in concentrations just as I've shown you before and in this experiment we'd inhibit goosecoid and the idea there would be that brachiri would remain on at high concentrations of actin but because this is science and because the embryo doesn't always behave as we'd want it to we saw absolutely absolutely no effect. So we really don't know how this whole system works. It will be lovely if it worked in the way we want it to work. But as the great Johnny Nash sang, there are more questions than answers. And it's perhaps one of the delights of doing science that, you know, we never really know what's going on. And um this is for somebody else to discover. But Breakuri is still interesting. And I just want to and I've just looked at the time so I should go a little bit faster that brachiuri is still interesting because brachiuri in and of itself once turned on by actin is enough to make cells become misoderm. will make them become muscle. So if you take cells that will become skin, force brachiorury to be expressed in them, then those cells become muscle. And if you block the expression of brachiuri in an embryo, then levels of muscle being formed are dramatically reduced and you get no tail. No tail at all in this case. So, Rea Yuri clearly of interest. Now, I'm going to miss the next slide because um I do want to get on to the heart stuff that I was speaking about and I've just noticed that it's um 8:15. So, we'll we'll skip this. You can ask me about it later if you want to. But what I want to do is finish with a discussion of the ways in which the work I've been talking about might actually have real world applications. You know, you might well say who cares about frogs, you know, except for me. But I think the lessons we learn from these frogs are important and interesting. And I'm now going to tell you in a few minutes why that is. So cardiovascular disease is one of the major causes of death in the western world. 45% of deaths in the western world are down to cardiovascular disease and in particular heart attacks, mioardial inffection and in particular the cells that are particularly damaged in heart attacks in mioardial inffection are the the muscle cells the cardiomyia of the left ventricle of the Not. So, a block in the artery causes those cells to die. And the question we were asking, which we've only been doing for the last six or seven years, is to ask, can we use the lessons we've learned from the frog in driving cells to become different cell types? Can we use those lessons to recreate cardiammyioytes specific to the left ventricle of the heart? maybe for you know regenerative medicine for example rather than use animal pole cells from frog embryos we clearly need to use human cells to do this work and we can do one of two things we can either use so-called embryionic stem cells from humans discovered by Martin Evans and Martin was able to take cells from an early human embryo In fact, he did last embryo, but you can do it for human embryos. Cultivate these cells in a dish and make embryionic stem cells that that for my purposes are the equivalent of the animal pole cells. These are cells that can produce anything. And so these are the cells we hope we can treat with our factors to make them become what we want them to become. So we can do our experiments on embryionic stem cells or we can do what Shinya Yamanaka did which was to take cells from adult human beings isolate them expose them to particular proteins which causes them to become what we call induced pleuropotent stem cells take them backwards in developmental time as it were so that those cells are now susceptible to being treated with the molecules that we've discovered. Okay? So what I'm telling you, what I'm suggesting to you is that those molecules that we discovered in frogs, can we use them to treat human embryionic cells, either induced pluropotent stem cells or embryionic stem cells to make them become left ventricle cardiammyes highlighted here, which we can use to treat myioardial inffection, heart failure, can use them to understand development or we can use them to create models for disease. So how will how will we do this? One way is as I've is as I've discussed to use the molecules we've isolated. Another way would be to take those intracellular molecules like brachiuri. We we're not doing that. Those are two ways of doing it. But what we're doing is taking the signaling pathways that I described earlier. Can we treat cells with those factors to drive differentiation along the pathway we're looking for? Okay. And to do that, we have to spend a bit of time understanding early heart development. And these are images of mouse embryos. On the left, we can see a a mouse embryo developing following the trajectories of the cells as they move through the embryos. And we can predict through a knowledge of the early mouse embryo and thereby inferring what happens in the human embryo what those cells become exposed to. So just by following cells, by knowing what genes are expressed where in the embryo, we can infer what molecules we should use to treat those cells to cause them to become left ventricle cardomytes. So I'm going to skip because I am going a little bit more slowly than I meant to. But what we can do is we can we can study gene expression in those cells as well. We can show that the left ventricle cardomytes that we're interested in in particular express two genes. They turn on the expression of two genes. One is called meosin light chain 2 V and the other is called hand one. And if we can see cells that express those two genes, we know we've made left ventricle cardiumtites. Okay. So this is another example I'm going to show you of the process of years of work by several people summarized in three minutes maybe even two minutes. So to make left ventricle cardomytes we begin with human pluropotent stem cells at day zero and we cause which are expressing two genes called nanogan sock 2 and the first thing we do in the pathway to becoming muscle cells is make them make misoderm which we do with actin fibroblast growth factor which you've heard of BMPPS we switch on the wint pathway and they become misoderm and they express brachiuri. We then take those cells and we switch off those signals and we inhibit retinoic acid signaling, vitamin A signaling and that gets them to the step of being cardiac muscle misin. We then add insulin at 8 days. they express new genes and eventually they become left ventricle like cardiammyasite. So they express the right genes and the next slide which I'm I'm terribly conscious of time will show you that they're pretty much homogeneous. We get a population of near homogeneous left ventricle heart muscle cells. And let me just show you what they look like at 6 days and 10 days. So if you look carefully at 6 days, you'll just see them. Can you see them beginning to beat? They're just beginning to do something. At 10 days, they're beating pretty reasonably, I'd have said. So we've got heart muscle cells beating in a dish. We leave them until 20 days. That beating becomes slower, which is which is what we want because in the normal heart, you need to stimulate the heart muscles to beat. So here the beats are slow and coordinated and you can just see as the refractive index of this culture changes. That's the muscles beginning to beat. How does that coordination happen? It happens because these cells are electrically coupled. And you can show if I can here we go. And you can show if you seed those cells on little electrodes and stimulate them, you can show a wave of calcium signaling, a wave of ionic signaling spreading across the cells, which is just what you'd expect to happen in the mature heart. Other markers that we've really got mature cells is that these cells are elongated as they should be. And on the left hand side you can see elongated cells. And if we look in the electron microscope you can see heart muscle so-called sarcimeir that are of the correct length. So by all criteria these cells are bonafide human heart muscle cells in a homogeneous population. And the last thing we did to make these cells, to convince ourselves that we had a decent population of cells that could exert force, is we took two posts in a little dish, and I'm going to use these as an example, which I'm sure our friend at the back will be very upset about. We stick two posts and straddle between them some of the cells that we've isolated. So, we make a sort of string of cells between the two. And we can then allow those cells to sit there for a bit and every now and again spontaneously they'll contract. So those two posts go like that and like that. And you'll see that where do these go in this final slide. So this is what we call human engineered heart tissue. So the two posts are at the top and bottom. And if I press and run this little movie, you'll see that these cells in a minute will beat and they'll do it again. So we think that using those lessons we got from the frog, applying them to human embriionic stem cells, we've been able to make cells that resemble very closely left ventricle heart muscle cells. So to summarize these lessons from Xenopus have allowed us to make near homogeneous populations of left ventricle like cardiammyasytes. They show slow spontaneous beating as we'd hope. Electrical coupling as I showed you elongated shape. They express a particular receptor. The the striations look perfect for heart muscle cells. They have mitochondria that resemble neonatal cells. They have a specific action potential I haven't shown you. And they can form, as I've just shown you, engineered heart tissue. We hope that those cells could be used in regenerative medicine and to create models for disease and cardiotoxicity. And my final slide scientist story is to show you the people involved in the work. Andrea Bernardo did a huge amount of this work. Camille helped Nicola Marie Victto and I think you've heard from Sean Harding previously in this group. Sean was fantastic. Elizabeth, Lena, Lewis, Stefan, and Victor. Um, and for any young women in the audience, I'm really pleased that so many people involved in this work with young women. They did fantastic stuff. So, I hope that has given you um a summary in essence what amounts to my scientific career. Beginning with this work on the chicken limbbud, convinced that there must be molecules that act in a concentration dependent fashion, showing in the frog that they do, and then transferring that knowledge much more recently into embryionic stem cells and forming a cell type that we hope will be able to help people in the future. So, thank you very much. So, we have time for some questions from the audience. >> Sir, >> uh please please wait till you have a microphone so that people listening at home can hear. But the question was about AI, I think. But ask it ask it in full. >> So the question because I'm not sure the microphone was working was you better make sure yours is. Um, so I don't know much about I'm too old to know much about my daughter works in AI. She's just started a job in AI and um the short answer is I would like to think so. The thing we don't understand, and I was alluding to it at probably too greater a length and too ponderously, is this question of what happens inside cells that allows the cells to interpret the extracellular concentration that will then influence the genes that are turned on and off and the concentrations and what they bind to. And it's I think it's too complicated to understand mathematically. And I think AI is probably going to be the only way that we can a understand it and b make predictions that will allow us to drive differentiation in the way we want to. You know, I was at some pains to emphasize what a pain it was to do all that work. I didn't say in detail. We tried all sorts of different factors. We tried them at all sorts of different concentrations for all sorts of durations. It was a it was tough going and it's one of those things that can be you know if you're a scientist science you know it's wonderful to be able to talk about results but actually the slog is unbelievable and if we can work out using AI a way of shortcutting the slog and making predictions as to what the likely outcomes are going to be fantastic and I think we will be able to but I'm afraid I'm a bit too long in the tooth to be able to do it herself. Mr. Gent. Yeah. Thank you very much for a very very interesting talk. Uh some of which I think I've understood. Um, can I ask a philosophical question? >> Oh. >> At what point do you declare these cells as being life? >> At what point do I declare them? >> No. As being life. When does life happen? >> Life. Because if you're putting it in your heart as life. >> So these cells, I mean, they are alive. They are living cells. There's no question about that's the first thing. The question of whether what one answer to your question is when would one feel comfortable introducing these cells into a human being. And you know um there there are difficulties to do with um imunological rejection obviously um which can be overcome. there are worries to do with whether these cells might become malignant but actually those worries I think have been overstated. So I think that um I would with suitable safety precaution regular I think they could be after I'm being very careful in using my words with suitable tests I think there's a chance that they could be used in human beings who have heart failure that's one of the purposes of our doing the work. Are they life? Well, you know, you tell me what you mean by life, but I think um I think they might well be able to serve a purpose. And if the option for me would be to have heart failure or have these cells introduced into me, then I would go for the cells being introduced into me. >> Hello. Thank you. Um you you said that you identified you were the first to identify I think the molecule or the >> I can't see who's oh there you are. Yeah the >> protein which uh the cells measure the concentration of to become red blue or white. >> Yeah I did say that. Yeah. >> So this you identified this I think in the 60s be uh anyway or the 70s before the before AI you had to do the slog. How it could have been any number of molecules. How did you decide to go to look for that one? Did you theorize that it would be that and then look for it? >> Yeah. So the question I think is how did we decide on activ? Yeah. Well, I'm glad you asked me that question because this is another example of slogging away. So if I may indulge for a second in all these things of course are history and you know it's a it's a commonly misunderstood fact that scientists are human beings and we we arrive at experiments through random processes and my particular random process if I may indulge myself for a minute was to have done the experiments I did on the chicken recognized that there are molecules we need to find. I worked for a while in a laboratory at Harvard Medical School, as Pat mentioned, where I was studying the regulation of what makes cells divide. And it struck me that here's an example. There are there are molecules that we know make cells divide. And it struck me that similar molecules to those could be the molecules that determine what cells become. What I should have done was taken cocktails of these so-called growth factors and just shoved them onto the frog cells. I didn't do that. What I did was I took xenopus cells growing in petri dishes and I discovered that one of those one type of zenapus cell in a petetro dish secreted an unknown factor that caused ectoerm cells to become muscle. And I spent three years growing these bloody cells, purifying and purifying and purifying, slogging away until I eventually managed to get the amino acid sequence of the active principle and found to my pleasure and horror that it was a molecule that was already known about. So, you know, that was active in and if id had my brothers, I believe is the Scottish expression, I would have done it the other if I'd had any brains, I would have done it the other way around. But, you know, hindsight is so easy in science, but that's how it happened. >> Okay. Thank you very much for that talk. um you stimulated my interest in one particular aspect when you talked about a concentration gradient allowing cells at one end to differentiate one way differentiate the other way at the other. I wonder what your thoughts are on the zebra. Good question. So the question was what about the zebra or zebra as I call it. Um, so it turns out we don't know the the exact answer to this, but you will have heard of Alan Turing, I'm sure. So Alan Turing wrote a a classic paper in the mid50s along these lines. Turing's model wasn't the same as Walput's model. Turing's model effectively involved um an activator and a repressor. And if I can remember correctly, there was a repressor that diffused a long way and an activator that diffused a short way. And by following mathematically the way the activator and the repressor interacted with each other, that would allow you to make spots. And you can imagine, I think without too much imagination, how an elaboration of that scheme would allow you to make stripes. So the Allen Turing reaction diffusion kind of idea would help you make stripes. But they all it's all down to concentration. Is that a decent answer? It'll do. >> I I never thought we >> I never thought we would hear a lecture that proved that we can actually turn a frog into a prince. But my question though is um does this mean that in the future we can look forward to organs being routinely repaired rather than replaced? So the question is can we repair organs rather than replace them? Um you know the thing I mean yes you can imagine it but you you you need a certain amount of imagination. I'm about to make one of my favorite jokes now which I hope you'll forgive me. When scientists talk about this sort of thing, they always say it'll be five or 10 years before it happens and that you know it's you almost always longer. And I always think why do we say five, you know, five or 10 years and it's because of course we have five fingers on each hands and if you were Homer Simpson who has only four fingers, you'd probably say four or eight years. So um anyway, I can imagine it. I can imagine it. It would take artificial intelligence. It would take a lot more understanding of what the molecules are. It would take a knowledge of how to apply these molecules at the right concentration for the right period. You'd have to be sure you had the right stem cells. So, complicated business. Um, the surgery you'd need to do would be complicated. But the mere fact that we can articulate the question I think says that it might well happen. My experience in science has always been nature and technology always surprises us. So I I would say possibly but you know not in my lifetime I would say. So >> are these techniques being used for testing uh toxicity currently? >> Yes. Yes, they are. So one of the things about um heart muscle cells is they are one of they are one of the cell types in the human being that is most vulnerable to the side effects of drugs. So my colleague Andrea Bernardo who's been driving this work on the left ventricle cardiammyittes has is working with a company to um commercialize our procedure in the hope that that drug developers can use our results to do an early screen for potential side effects and intoxic effects of drugs. A good question and that's one of the reasons we are doing what we're doing and our cells are really good very good mimics of those cells. So we think it's a good good example. >> This working I'm amazed at the speed at which the differentiation occurs in the frog embryo because you were saying the cells divide every half hour. >> Yeah. >> Is it possible to say to what extent the structure is laid down in the single egg cell originally? perhaps even before it's fertilized. Yeah. Does everything develop as it goes along? >> Yeah, that's a really good question. Um, by which I mean I can answer it. Um, so the early frog embryo, the early frog egg is it's not unusual in terms of eggs in the animal kingdom, but it's very different from mamalian eggs because early frog eggs during the process of oagenesis um lay down particular RNA molecules and protein molecules in different parts of that egg. And I I don't know how familiar you are with cell biology, but there are structures called microtubules that act as a sort of railway line if you like. I hesitate to to carry molecules to different parts of the egg. And in particular, in the vegetital part of the egg at the bottom, there's a an RNA that encodes a protein called veg one that I had on one of my slides. And veg one is a member of the family of molecules of which actin is a member and veg one is probably the misoderm inducing fac or one of the misodum misoderm inducing factors in the embryo. So veg one is in the vegetital half and there are molecules you won't be surprised to hear called an one and two and n3 in the animal pole that direct the differentiation of ectomal tissue. But the point is that you can only get so far with that sort of level of detail. You can't make it as fine grained as making a whole frog. You have to set up the the the initial polarity and then allow interactions between those regions to set up the additional information. So great question and I should have said it actually earlier on. Excellent presentation. I understood some of it, but I have a question and don't feel you need to answer it, but I'm looking at that slide that you've put up and I only see three names that are stereotypically British. Now, we as a nation have voted for at least two consecutive governments that are making it harder and harder for people to come in to the UK and many of those people are working in research. So, how much is your research threatened by things like that? Let me just put that slide back up again. So to make There we go. So I'm called Jim Smith. You can't get much more. Um I think the point is that science is genuinely an international activity. And you know we we honestly don't think particularly about where our research has come from. Um my lab has quite a lot of people coming particularly from Europe and when when we left the EU there was a great deal of anxiety about you know are we losing some of the best people but the point about internationality of science is that the place I work the Francis Crick Institute its objective is to bring people in from all the very best scientists from around the world bring them then train them up and with a bit of luck have them remain in the country as they do and contribute to the scientific enterprise in this country. At the same time we have people from this country going abroad as well learning about science abroad and very frequently coming back. You know I told you I went to Harvard Medical School. I learned a lot at Harvard Medical School and I came back. So I I think the international nature of science is key to its success. And we we welcome people from wherever they come from. We train them. We work with them. And those people there there at the bottom uh for for example Lo and Luis are from Portugal. They don't work with us. We work with them in Portugal because they happen to work on things we're interested in. Andrea's from Portugal herself, but she now lives in Britain. She has a British passport. Camille was from France. She's now gone back to France. Now my lab is closed. Nicola is, as you've guessed from her name, is British and is doing a PhD at Imperial College. Marie is from France and she is still here. So we're bringing the best people in. And I'm proud of the fact that we've trained the best scientists from around the world. And as you will see from this that we've actually trained some of the best women in the world as well. So I have no difficulty with that at all. >> Maybe I could just ask you a question Jim about cancer cells um and and the you know their rapid proliferation and sometimes differentiation. How much do we know about what's happening there? Well, people have been worried that when we take human embriionic stem cells um induce puropotent stem cells. There's there's been a worry that we introduce them into human beings and that and and they will form cancer. So far that that has not been the problem that people worried it might be. It just hasn't happened. I don't know why but it hasn't. I mean, who knows in the future, but so far so good. >> Okay. Uh, if there are no more questions, I just remind you that there's going to be a glass of wine uh available afterwards and Jim will be around for a little bit before we take him off to dinner. Um, I just like to say that, you know, we've seen a lot of very interesting things about being a scientist. We've seen the enthusiasm and the excitement of science. We've heard about barking up the wrong tree sometimes. We've heard about disappointment. Uh we've heard that we don't know necessarily everything and there's still uh a lot to find out. We've learned that, you know, development is a wonderfully complex process orchestrated so magnificently well that you wonder how did that complexity evolve even in what we think of as relatively simple organisms. There's a great orchestration that's going on. Um the kind of work that Jim's been telling us about of course is very challenging and and as the point that was raised about uh science being under threat is a very important one and one that is possibly going to get worse. But also as somebody else raised there are ethical issues around quite a lot of this work and you have to consider those. But also sometimes you're plunging into the unknown and you you have to take risks. So it's a very complex arena uh within which Jim is working. Uh the last thing I just like to say though it was mentioned that uh you can turn a frog into a prince. You do it through a kiss. Okay? So remember that one kiss and you're there. So >> got those upright. >> So thank you. Uh join me. Oh, first no no not yet. I have to give uh first give Jim uh the society paper weight. Thank you. Right. See two weeks time we have an economist. >> Thank you everyone. I had a great time.