Oct 9, 2008 - embryos remains important, because ESCs are the gold standard ... Jamie Thomson and others, or is it something else? I think we have to ...
INTERVIEW SERIES Celebrating 10 Years of hESC Lines: An Interview with Rudolf Jaenisch About Dr. Jaenisch Dr. Jaenisch received his M.D. from the University of Munich in 1967. He then undertook 2 years of postdoctoral research on the replication and transcription of the Escherichia coli phages M13 and Phi174 at the Max Planck Institute for Biochemistry, followed by a further 2 years studying the replication, transcription, and transformation of the SV-40 virus in Dr. Arnold Levine’s laboratory in the Department of Biochemistry at Princeton University. He spent an important 8 months as a visiting fellow in the laboratory of Dr. Beatrice Mintz at the Fox Chase Institute for Cancer Research in Philadelphia, learning micromanipulation techniques and investigating the in vitro cultivation and reimplantation of isolated mouse embryos. He continued to collaborate with Dr. Mintz during his assistant research professorship at The Salk Institute in La Jolla, California, during which time they published their results on the generation of the first transgenic mice. He then spent 7 years as the Head of the Department of Tumor Virology at the Heinrich Pette Institute for Experimental Virology and Immunology at the University of Hamburg, continuing his work on genetic disease, cancer, mammalian development, and the interaction of viruses with early mammalian embryos. In 1984 he became a founding member of the Whitehead Institute for Biomedical Research, where today he holds the position of Professor of Biology, Massachusetts Institute of Technology, and is world renowned for his work on nuclear transfer (NT), as well as cancer, epigenetic regulation, and mammalian development. His many awards and honors include the 2006 Max Delbru¨ck Medal for Molecular Medicine and the 2007 Vilcek Foundation Prize for Achievements of Prominent Immigrants. He is also a member of the National Academy of Sciences and serves on the advisory board of the Genetics Policy Institute. STEM CELLS recently spoke with Dr. Jaenisch about his past achievements and about the future of stem cell research.
The First Transgenic Mice “When I was working with the SV-40 tumor virus as a postdoctoral fellow in the 1970s, I questioned whether one could put a gene into an early embryo and then have that gene show up in all cells of the animal” recounts Dr. Jaenisch. “Beatrice Mintz’s lab had produced chimeric mice, and when I read her 1967 paper, I was just blown away. She was taking embryos, manipulating them and then aggregating them, and I thought, this technology somehow should enable us to put the SV-40 DNA into those embryos. I suggested this experiment to her, and although she was initially skeptical, she eventually allowed me to do this experiment in her lab. I produced the SV-40 DNA in Princeton, and she taught me how to manipulate embryos and then we made the first transgenic animal.” This incredible step forward allowed Dr. Jaenisch and others to begin using this method to study genes and development in a whole new way,
leading to profound new discoveries is these fields. “Later, I used retroviruses to generate mice with insertional mutations. This, of course, did not involve direct gene targeting but rather was caused by random viral insertions into the genome” explains Dr. Jaenisch. “So when ESCs were introduced in the 1980s and when homologous recombination was described, it was very clear that this was superior and would be a very important technology for embryology, for mouse development, and for medicine. So immediately I adopted the ESC work and technology to my laboratory.” Since then, Dr. Jaenisch’s laboratory has worked extensively on hESCs and murine ESCs, and it has been a leader in the newer technique of somatic cell nuclear transfer (SCNT), or therapeutic cloning.
“The Generation of Dolly . . . Really Influenced My Thinking and My Career” “When Dolly was first cloned, I had already been interested in epigenetics for many years, and I thought that cloning was nothing more than an epigenetic problem. Obviously there is no genetic difference between the donor fibroblast and the clone; the difference is only in the cell’s epigenetic state. I immediately adopted the cloning technology in my laboratory to study epigenetics in a most unbiased way. The most important parameter of what differentiates one cell type from another is the epigenetic conformation of the genome, and cloning has shown that these differences are fully reversible.” Epigenetic mechanisms also explained the results of the transgenic experiments years before. “The SV-40 virus induces sarcomas when injected into animals, but the first SV-40 transgenic animals that we made did not develop any tumors. And we didn’t know why. It was only years later that we understood the reason: the viral genes were silenced through epigenetic mechanisms such as de novo methylation. But it took 20 years to find that out. It needed a lot of technology development by many people to come into play, and now we have quite a good idea about what happens to the virus in the transgenic embryo. It is shut off. It’s methylated.” “I think the generation of Dolly was very important, because Dolly gave the proof of principle that you can reprogram a somatic cell to an embryonic state, which is then totipotent, and can make a new animal. And the mouse system was important as it allowed us to define some of the molecular parameters of reprogramming, as well as why cloning works well sometimes or doesn’t work well at other times. I think this information paved the way for the possibility of direct reprogramming that wouldn’t use eggs anymore. So this very important finding significantly influenced my thinking and my career, because it was really the opening experiment and I was amazed that it worked.”
Correspondence: Miodrag Stojkovic´, Ph.D., Centro de Investigacion Principe Felipe-Cellular Reprogramming Laboratory C/E.P. Avda. Autopista del Saler 16-3 (junto Oceanografico) Valencia 46013 Spain. Received October 9, 2008; accepted for publication October 9, 2008; available online without subscription through the open access option. ©AlphaMed Press 1066-5099/2008/$30.00/0 doi: 10.1634/stemcells.2008-1019
STEM CELLS 2008;26:3005–3007 www.StemCells.com
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“[Implantation of the Embryo] Is a Black and White Situation; It’s Not a Slippery-Slope Type of Situation. I Think It’s a Reasonable Compromise Between Different Opinions in Society” “I have no ethical problems with SCNT if you do it the way that the British Parliament has approved for NT and hESC work. I think the question here really is not when does life begin, but when is the embryo a person, or have the traits of a person that need to be fully protected. There is no scientific answer to this question, and society needs to come up with a reasonable compromise. The British and many other countries have adopted the premise that after implantation, no manipulations with human embryos are allowed. But before implantation, under very defined conditions, they can be used for research or eventually for therapy. I think that this was a reasonable compromise. What followed from this debate was legislation that allowed so-called therapeutic cloning under strict guidelines, but prohibited reproductive cloning. This is banned in every country that has a law on the books—implanting the modified or cloned embryo is outlawed, whereas it is allowable to use this embryo in a Petri dish to generate an NT-derived ESCs. And I don’t have any problem with that. You either implant or you don’t implant. It is a black and white situation; it’s not a slippery-slope type of situation. I think it’s a reasonable compromise between different opinions in society. And in my opinion this makes it a workable solution.”
“Generating hESCs from Embryos Remains Important” “However, NT in humans is difficult, and many barriers have to be overcome, such as getting human eggs. I can see that some people think SCNT in humans will still be useful, because NT is the only way, with our current knowledge, to generate a non-genetically modified, patient-specific ESC. The current in vitro methods produce heavily genetically modified stem cells, because they carry all these viruses. I think the induced pluripotent stem (iPS) cells will eventually take over, but we are not there yet. On the other hand, I think that generating hESCs from embryos remains important, because ESCs are the gold standard for pluripotency as far as we know. And we don’t really know how to define a good ESC. Because these cells were isolated using certain protocols, we don’t know whether the present protocols are the most suitable ones to obtain the best ESCs. When you think of in vitro reprogramming, you want to be able to compare that to a gold standard, but what is that gold standard? Is it the original cell lines derived in the 1990s by Jamie Thomson and others, or is it something else? I think we have to figure this out. So I think there is a place for continuing to isolate ESCs, probably transiently. I think it would be a mistake to say we can do everything in vitro.”
“iPS Cells [Will Be] a Very Powerful Way to Study Disease” “I think iPS cells will have enormous influence and importance in studying human diseases because for research we don’t have to eliminate the viruses. If you make an iPS cell from a patient, it will carry all of the genetic alterations which led to the disease, and this is the enormous potential of the approach. Using the iPS approach, we can generate patient-specific ESCs or iPS cells, and then determine if these cells develop a phenotype in the Petri dish, which corresponds to a disease, when differentiated into the appropriate cell type. For instance, one could derive iPS cells from a Parkinson’s patient, differentiate them into dopaminergic neurons, and investigate whether a relevant phenotype would develop in vitro. If this is the case, it
Figure 1. Rudolf Jaenisch, M.D. The Whitehead Institute for Biomedical Research, Cambridge, MA.
will be very interesting, because it opens the opportunity to study the disease in the test tube, and to screen for compounds that slow or prevent the phenotype. This type of experiment can, of course, not be done in patients. It would, therefore, be a very powerful way to study a complex disease. There is already evidence that for some diseases this approach might work— amyotrophic lateral sclerosis (ALS) for example. As Kevin Eggan has shown, cultured ESCs that are derived from a mutant superoxide dismutase (SOD)-ALS mouse develop a phenotype when differentiated into motor neurons: the ALS neurons die earlier than motor neurons derived from control ESCs.”
“Cell Therapy Is Not Around the Corner, but I Think at Some Point It Will Become Reality” “Will iPS cells be useful for therapy? Well, I think that is further away, and there may not be all that many diseases that are open for treatment. Diseases of the bone marrow might be one of the first places where people will be able to use the iPS approach, because delivery is simple. Can it be used for complex diseases such as Parkinson’s disease, as many people think? The bar is much higher for such diseases as delivery of the therapeutic cells may be more difficult. A key problem remains, however, and this is how to produce the cells one wants to transplant in the Petri dish. I think the reprogramming part, going from the somatic cell of a patient to an iPS cell, is solved in principle. There are just technical issues that need to be solved such as how to replace the viruses and to produce iPS cells that are not genetically modified. But the differentiation issue is not resolved yet; which are the best cells to transplant? So cell therapy is not around the corner, but I think at some point it will become reality.”
Interview Series
“You Can’t Be in a More Exciting Field than This One. . . . You Need to be Curious and Daring” “I would say that this is one of the most exciting times in science that I have experienced. Things have really opened up. This whole cloning and iPS cell work has shown us that one can convert any cell type into another cell type. This is relevant not only for embryology but also for diseases such as cancer. There are many deep biological questions you can approach experimentally. There is enormous promise for what we can do now, and, combined with genomic technology, it is transforming biology. One can hardly imagine being in a more exciting field than this one, I think. But one needs to be curious and daring and willing to take risks and not be intimidated by daunting obsta-
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cles. But it can be difficult to take risks with the current granting system. When I wrote my first grant in the 1970s, I was proposing to make transgenics, although the name wasn’t even invented then. And it sort of seemed like fantasy, but the NIH funded it and gave me a chance. It might be difficult to get that type of study funded now. But I’m not sure what we can do to overcome this problem. The NIH system is one of the best systems there is, but the money just gets shorter and shorter, and people don’t dare to do something risky; they do more ‘bandwagon’ stuff. That’s not so good. I think it’s a tough situation.” Miodrag Stojkovic´ Susan Daher
To Read More from Our Interview with Dr. Jaenisch, to Read About Dr. Jaenisch’s Laboratory, and to Join Our Discussion Forums, Visit the STEM CELLS Portal at http://www.stemcellsportal.com.
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