An Interview with John Gurdon Aidan Maartens*,‡
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© 2017. Published by The Company of Biologists Ltd | Development (2017) 144, 1581-1583 doi:10.1242/dev.152058 SPOTLIGHT An interview with John Gurdon Aidan Maartens*,‡ John Gurdon is a Distinguished Group Leader in the Wellcome Trust/ Cancer Research UK Gurdon Institute and Professor Emeritus in the Department of Zoology at the University of Cambridge. In 2012, he was awarded the Nobel Prize in Physiology or Medicine jointly with Shinya Yamanaka for work on the reprogramming of mature cells to pluripotency, and his lab continues to investigate the molecular mechanisms of nuclear reprogramming by oocytes and eggs. We met John in his Cambridge office to discuss his career and hear his thoughts on the past, present and future of reprogramming. Your first paper was published in 1954 and concerned not embryology but entomology. How did that come about? Well, that early paper was published in the Entomologist’s Monthly Magazine. Throughout my early life, I really was interested in insects, and used to collect butterflies and moths. When I was an undergraduate I liked to take time off and go out to Wytham Woods near Oxford to see what I could find. So I went out one cold spring day and there were no butterflies about, nor any moths, but, out of nowhere, there was a fly – I caught it, put it in my bottle, and had a look at it. The first thing that was obvious was that it wasn’t a fly, it was a hymenopteran, but when I tried to identify it I simply could cells in the body have the same genes. One way to determine this not work out what it was. I don’t like to be defeated, so I went to the was to take a nucleus from one kind of cell, put it into the egg, and Hope Department in Oxford and they didn’t know what it was see if it can develop. This experiment was conceived as far back as either, and then to the Natural History Museum, where a curator told the late 19th century: there’s a paper by a man named Rauber who me that, amazingly enough, this was a species never recorded in describes an experiment of putting a toad nucleus into a frog egg, England before! This was intensely irritating to the Entomology and simply says he didn’t get a result, so it’s not clear whether he did Department in Oxford because the professor at the time had a major the experiment or not! ecological study of all the insects in those woods, and here was a Anyway, in the 1950s Briggs and King, two Americans, student who had just caught the first thing he could find, and picked developed the technique of transplanting the nucleus, and up a new species. So I wrote a couple of paragraphs announcing the Fischberg decided we should try this in Xenopus. There were discovery, and that’s how I came to have that paper. several very troublesome technical difficulties which we eventually overcame – as much by luck as skill – and the end result was that you And did you keep up your interest in insects? can get essentially normal development by taking the nucleus of a Not really in a proper scientific way, though I keep thinking I’d like specialised cell, in this case an intestinal cell, and transplanting it to to go back to that, mainly because the colour patterns of an enucleated egg. That clearly said that the same genes are present lepidopterans are so remarkable. We really know almost nothing in all different kinds of cells. about how colour patterns are formed – in any species. You won’t And then there was this gap of 50 years before Yamanaka have a gene that puts a spot on one wing, it’s a more complicated developed the induced pluripotent stem cell technique, which really process, including diffusion of molecules. I keep thinking that when opened the field to useful clinical potential. The frog experiments I actually retire I’ll take that up, but I’ve yet to get to that point! (and much subsequent work, including the generation of Dolly the sheep in the 1990s) said you can reverse or rejuvenate a specialised Half a century ago you started your nuclear transfer nucleus right back to the beginning again, but clinical translation experiments, and today your lab is still publishing on it. Why became a realistic possibility in humans only when Yamanaka do you think such a conceptually simple experiment has had showed you did not need to obtain human eggs or embryos to make such a remarkably long shelf life? stem cells. This idea that you could derive new cells of one kind When I was doing those early nuclear transfer experiments – and I starting with adult cells of a completely different kind obviously am permanently grateful to my supervisor, Michael Fischberg, for chimed with our work from half a century beforehand but, putting me onto that work – the question at the time was whether all interestingly enough, this was absolutely not evident when these early experiments were done. ‘Reprogramming’ wasn’t even the aim of the experiments. I imagine I would not get support for *Online Editor, Development carrying on these nuclear transfer experiments today were it not for ‡ Author for correspondence ([email protected]) their relevance to reprogramming in humans. DEVELOPMENT 1581 SPOTLIGHT Development (2017) 144, 1581-1583 doi:10.1242/dev.152058 So then the question is how does this process work? What Jean Brachet, and told him that what I’d really like to do is to underlies the egg’s ability to rejuvenate a nucleus? We were always transplant not nuclei but mRNA into eggs. He gave me an interested in that question, but it became increasingly interesting with introduction to Chantrenne, who was making rabbit globin RNA Yamanaka’s experiments. And I would point out that people still and gave us some, thanks to Brachet. The stuff was known to be don’t really know why the Yamanaka procedure works – even after extremely RNase sensitive, so you almost had to take a bath in ten years, they don’t really understand the mechanism. So we take the chromic acid before you touched anything! Now had I proposed that view, and it is true, that the egg does a rather better job of reversing experiment as a grant it would have been rejected because the egg differentiation compared with overexpressing transcription factors, was known to be full of ribonucleases: to put sensitive mRNA into a and therefore think that if you knew what all the egg components are, ribonucleic environment would make no sense. Nevertheless, it and knew how to make them exchange with the somatic ones, you worked, and astonishingly well – the globin message went into wouldn’t need the Yamanaka factors. That is why we are actively eggs, and by the time the eggs had turned into tadpoles there was pursuing the mechanism of reprogramming by the egg, using the still rabbit globin being made. Almost certainly the reason for the same procedure as was done 60 years ago, but with a whole lot of new success is that microinjection doesn’t open up the lysosomes, where ways of investigating it. To me, this exemplifies the interesting the ribonucleases are partitioned. So there’s another interesting principle that work which was done at one time can have a principle: when someone tells you something won’t work, it’s much subsequent, much greater relevance in the light of later advances. better to try it than to take their word for it. And mRNA injection has turned out to be a very useful approach for all sorts of questions. These RNA experiments were really a derivative of the We are actively pursuing the mechanism technological results of nuclear transfer – if it works for nuclei, of reprogramming by the egg, using the what else can you transfer? Eddy de Robertis and I even had a paper Xenopus same procedure as was done 60 years calling the egg a living test tube. ago, but with a whole lot of new ways of You were also interested in the process of induction, and investigating it identified a ‘community effect’ in the induction of the Xenopus mesoderm. What is the basis of this effect? For many decades people had been transplanting tissue – take a And what is your current understanding of the molecular piece of tissue and graft it onto another host. But the tissue is mechanisms of reprogramming by the egg? obviously composed of many cells, which may not all be the same, It’s almost certainly due to a high concentration in the egg of and for me it was always desirable to do a single-cell transplant. And chromatin components, particularly histones. There are numerous so I did a lot of those, moving single progenitor cells from one part variants of histones, in terms of how they are modified, and quite a of the embryo to another, but I could never get it to work – the cells lot of our recent work has been describing the histone changes that always died. There must have been some reason why you can are imposed by the egg on an incoming nucleus. This chromatin successfully transplant multiple cells but not single cells. That led change is perhaps the first key stage – there’s a particular histone me to perform injections of smaller and smaller numbers of cells. It variant present in eggs which is very important, and it’s likely that turned out that transplanted cells release secreted molecules – the replacement of adult chromatin components by ones present in signalling proteins for instance – that are necessary for them to do the egg is ultimately what helps to cause the change.