Web Conference with Dr. Derrick Rossi - 00:00 To the first point, career path, I don't know if you've all got maybe three or four hours to spend because I took some sort of very strange circuitous career path to ending up working on this subject. So I, just to let you know, I did my undergraduate, my graduate work in Toronto, Canada. I'm Canadian. And then I had the opportunity to go and do a Ph.D. in France. So as a young man when you're given the opportunity to go to France you should definitely go to France. I went to Paris for a couple of years and was in a Ph.D. program there. I was, first let you know, I was in a Ph.D. program in Toronto so that's Ph.D. program number one. Then Ph.D. program number two was in Paris. Then I had to leave Paris because I ran out of money. In Texas for some strange reason, and then I had an opportunity to go to Finland and yet another Ph.D. program at the University of Helsinki. So again as a young man you get the opportunity to go to Helsinki, you should go. And there I started to really get serious about science, not that I hadn't been before but I was kind of too young and maybe too immature to really focus. So I got down to business in Helsinki and did a lot of science. And then that I had a lot of success there. I published a lot of papers and that gave me great opportunity as a post-doctoral fellow. I could basically go wherever I wanted. So I had great offers to go to really fantastic labs. And I had not been in stem cell biology but I had been sort of paying attention to the literature and reading the literature and it was clear to me that stem cell biology was about to hit a golden age. So I thought I would go into that field so I started to do some research as to what would be the most optimal setting for that. Went to a lot of post-doctoral interviews, got a lot of great offers at a lot of great place, but when I got offered a position at Stanford University in the lab of this fellow named Weissman who basically is one of the founding fathers of hematopoietic stem cell biology, that was clearly a great opportunity so I went and I started to study hematopoietic stem cell biology. And I had, I was there for 4 1/2, five years studying how hematopoietic stem cells change during aging. We know that actually the hematopoietic system deteriorates quite dramatically with aging. You get hematopoietic malignancy. Your lymphoid, your adaptive immune potential goes down, become So I wanted to sort of find out how much of that decline of the hematopoietic system was due to the aging. Web Conference with Dr. Derrick Rossi The stem cell compartment it turns out number of studies that we did, quite a lot. So the stem cells really matter there. That was the focus of my post-doctoral work. When I started my lab I was working on truth related to hematopoietic stem cell biology mostly. But then Yamanakaalong and this was terribly exciting for everybody. Basically it was a see change moment in regenerative medicine. The reason for that is quite simple. Whereas human embryonic stem cells were great in that you can make presumably any type of cell or tissue that only you could imagine putting back into patients, they have a big problem that they're derived from embryos that aren't ones itself. So if you're going to transplant those cells or tissues back into patients you're always going to have to think about immune rejection and histic compatibility issues. So what was so exciting about Yamanaka was that now it was this ability to create personalized pluripotent stem cells from a patient who had been one you'd say derived cells or tissues from those cells you put back into the patient without a fear of immunorejection and this is really, really dramatic. Moreover you could basically make iPS cells from anybody in the room there with a skin fibroblast and within a few weeks you can have a pluripotent stem cell tailored to one's own cell so that amazingly the promise of that is enormous. So I think Michael also asked me give a sort of historical recap of pluripotency reprogramming, let's say. Actually it really all starts the 1950s in a frog called Xenopus with studies by guys named Briggs King and then later in the 1960s by Sir John Gurdon that showed that you could, well let me back up one sec. So what you need to know about reprogramming is how completely fantastic it actually is because normally developmental processes are completely unidirectional. You go from more primitive cell to less primitive cells to differentiated cells and that's a one-way street in biology. There's really no going back. And this is believed for many decade and centuries that really you couldn't turn back the developmental hand of time. So what these experiments in Xenopus by Gurdon and others showed is that that's actually not true. So they basically took oocytes from these Xenopus, large oocytes and they took out the nucleus of them and then they put in the nucleus of somatic cells of some differentiated cell type they introduced into the oocyte and amazingly it was something about the Web Conference with Dr. Derrick Rossi cellular milieu of the oocyte that was able to reprogram that introduced nucleus back to a pluripotent state. And the ultimate demonstration of that, in fact in the 1960s was the generation of cloned frogs and this is where cloning started. But really it's As I said it turns back our developmental pathway which up until that point had been unidirectional. So subsequent to experiments in the frogs somatic cell nuclear transfer, it's what it's called when you enucleate an oocyte by putting another nucleus in there and reprogram it. This was done with a number of different including most famously Dolly the sheep obviously you've heard about and cows. Basically anything could be reprogrammed in this setting but this doesn't get us superb stem cells. That kind of or it does but not in the way that Yamanaka does it. Yamanaka does it is particularly falling on the shoulders of work that was done in the late 1980s by Harold Weintraub and colleagues that showed actually that transcription factors are important for mediating cellular identity. So basically they did it with fibroblast cells and they isolated a transcription factor called MyoD and when you introduce this factor into these fibroblasts you birth them into myogenic lineage, muscle cells basically. And a single transcription factor could do that. So this started a whole field of research where people were looking at different transcription factors that they thought would be important for specifying the fate of different cell types and a lot of work in the 1990s showed for example that you could reprogram one type of blood lineage to another type of blood lineage. Work from Thomas Graf and colleagues using single factor, a transcription factor, ectopic expression one cell over another. And this culminated in this really spectacular discovery by Shinya Yamanaka that, you know, and I don't know if you've covered that original reprogramming paper. Have you done that in class? - I didn't assign it but I definitely talked about the work involved. - Yeah, you should assign that next year because it's so breath, I mean it's just spectacular science. It doesn't get any more spectacular than that if you want to be inspired. So as you know basically what Yamanaka did was he had this idea that if he took Web Conference with Dr. Derrick Rossi all the factors that they could imagine might be important for specifying a pluripotent state and introduced them into fibroblasts that somehow you could convert these cells back to a pluripotent state. And I can tell you that if he actually presented this idea for example to a granting board prior to actually doing it in '63 he probably would have been thrown out the window. I mean it's such a wild idea it's amazing that it actually worked. But it worked because they took a large-scale approach. They didn't just use one factor. One factor wouldn't have done it. They identified 24 factors, transcription factors that might be for specifying a pluripotent state, introduced these, and then as you know sort of found that this worked and then they whittled back 24 factors down to four factors. They're now the canonical Yamanaka factors, this Sox2, Klf4, c-Myc, and Oct4. Subsequent to that, might be a long answer. Sorry for that. Subsequent to that, others have now followed on the heels of that, show that various combinations of transcription factors could move the identity of one cell type to another. For example in the pancreatic lineage Doug Melton and colleagues show that ectopic expression of free transcription factors convert these exocrine cells to endocrine beta cells. Quite fantastic, it's been done in the neural lineage as well, possibly in the cardiac lineage as well. So it really is all the rage because many cell types though clinically useful cell types, they're actually really hard to get ahold of or to get in large numbers.