A conversation with Rudolf Jaenisch

Ushma S. Neill

J Clin Invest. 2015;125(9):3305-3307. https://doi.org/10.1172/JCI82629.

Conversations with Giants in Medicine

Rudolf Jaenisch of the Whitehead Institute at MIT is a remarkable scientist at the center of the study of epigenetics. Jaenisch (Figure 1) created the very first transgenic mice and did the first experiment showing that therapeutic cloning could correct a genetic defect. He also conducted the first proof of principle experiments with induced pluripotent stem (iPS) cells to correct sickle cell anemia and Parkinson disease in rodents. Hear more of his stories about his first scientific experiments, how to effectively mentor trainees, and his views on the ethics of stem cell use on the JCI website at http://www.jci.org/videos/cgms JCI: What were you like as a kid? Jaenisch: I grew up in Germany, and my parents and my grandparents were medical doctors. I was also interested in medicine. My father was not so sure it was the right thing for me, but he consented and so I went to medical school. I liked part of it, but I didn’t like the more clinical part, as it was overcrowded and one couldn’t get into the lectures. The alternative I came up with was to do an experimental thesis at the Max Planck Institute in Munich on phage replication. It was an interesting time (the 1960s) because it was really the beginning of molecular biology. Bacteria and phages were really the workhorses […]

Find the latest version: https://jci.me/82629/pdf Conversations with giants in medicine

A conversation with Rudolf Jaenisch

Rudolf Jaenisch of the Whitehead Insti- his own laboratory at Princeton, working brain because these early cells would, tute at MIT is a remarkable scientist at the on animal viruses.” I wrote to him and of course, contribute to all parts of the center of the study of epigenetics. Jaenisch was amazed that Arnie wrote back saying, embryo. I thought this could solve my (Figure 1) created the very first transgenic “Yes, I accept you and here is a grant pro- question, so I was all excited. I called her mice and did the first experiment show- posal that you can submit, I have it lying up and asked if I could visit her. She was ing that therapeutic cloning could correct around. I don’t know how it would work, very friendly, very gracious, and I sug- a genetic defect. He also conducted the you can submit it to the NIH for support.” gested the experiment to her. She just had first proof of principle experiments with Immediately everything was effortlessly bought a microscope where one could do induced pluripotent stem (iPS) cells to cor- arranged, and I became his first postdoc. this experiment. Nobody had done injec- rect sickle cell anemia and Parkinson dis- He worked with a small tumor virus, tion of embryos with DNA before. But she ease in rodents. Hear more of his stories SV40. It has the same size DNA as a was very skeptical. I mean, who was I? about his first scientific experiments, how phage I’d worked with, so that was very A totally naive phage guy, right? She to effectively mentor trainees, and his views familiar, but it made tumors. Arnie had called me back a week later and said she’d on the ethics of stem cell use on the JCI chosen to work with this virus to probe thought about it and I could do the experi- website at http://www.jci.org/videos/cgms. into DNA replication and gene expression ment in her lab. And then Arnie came JCI: What were you like as a kid? in mammalian cells. I thought it was a back from sabbatical in Europe, and I told Jaenisch: I grew up in Germany, and valid approach and got hooked into it and him my plan. He told me I was nuts, but my parents and my grandparents were worked on replication. allowed me to do it. medical doctors. I was also interested in JCI: One of the things that puzzled you Mintz showed me really everything medicine. My father was not so sure it was was SV40’s viral tropism: infected mice I know about genetics, how you culture the right thing for me, but he consented got sarcoma, but not liver cancer or brain embryos and eventually how you make and so I went to medical school. I liked part cancer or other organ cancers. mice. I extracted SV40 DNA in Princ- of it, but I didn’t like the more clinical part, Jaenisch: It was a very naive question. eton, and I took it with me to Mintz’s lab as it was overcrowded and one couldn’t get If you inject SV40 into the skin, does it in Philadelphia and injected embryos into the lectures. only infect skin cells or alternatively could and, marvelously, I got mice. I was really The alternative I came up with was it infect all sorts of other cell types? Or was excited, but the mice were totally nor- to do an experimental thesis at the Max there something in the liver or the brain mal. Did the whole experiment work? Was Planck Institute in Munich on phage rep- that, even if infected by the virus, couldn’t there any SV40 information in these mice? lication. It was an interesting time (the express and induce a tumor? That was a Now, today, this is a trivial question, but 1960s) because it was really the beginning naive question, but I wondered how to then PCR or Southern blots had not been of molecular biology. Bacteria and phages study that. I had no idea until I read this invented. I ended up taking cells from were really the workhorses of understand- very influential paper from a prominent the ears of the mice and stained them for ing how RNA and DNA work, replicate, developmental geneticist, Beatrice Mintz. SV40 T antigen, which is a protein from and are transcribed. She used very early embryos from a the virus. I remember this very well. That JCI: Did you finish your clinical training? black and a white mouse strain, aggre- evening, they were all positive, so I got Jaenisch: I finished everything, but gated them in a culture dish, and then really excited. I couldn’t sleep. The next I had to promise I would never practice. I transplanted the aggregates into a foster morning, I did the assay with control cells. decided I wanted to go into science, and mother. The mice were now what’s called And they were all positive too; it was a bad almost every one of my friends went to the chimeric. Instead of two parents, they antibody. I was really stuck. United States because that’s where science had four parents. They were black and At that time, I got my first job at the occurred; I managed to get a postdoctoral white with stripes. She did this experiment Salk Institute, and this was really the great- fellowship in a laboratory at Princeton. because she wanted to study a develop- est thing that could have happened to me. I JCI: Why choose to do a postdoc with mental issue on coat color, which I did not got colleagues who really helped me along. Arnold Levine, who was just starting his lab? understand at all. But it just blew me away, Paul Berg had developed what’s called Jaenisch: I was totally naive, had no that you could manipulate cells in a culture nick translation, where you can radiola- idea where to go. I met someone who was dish and make a mouse. I thought this was bel a piece of DNA. Using nick translation working on phages and had just returned the coolest thing I’d seen. to analyze the DNA from the mice I had from Los Angeles. I asked him to suggest I thought, if you could introduce the generated in Mintz’s lab, I could see that someone and he said, “Yes, my bay mate SV40 DNA into these early embryos, the the SV40 DNA had integrated into their Arnold Levine in Los Angeles just set up virus would end up in the liver and the brains, livers, kidneys, and everywhere. These were the first transgenic mice, though the name “transgenic” was not Reference information: J Clin Invest. 2015;125(9):3305–3307. doi:10.1172/JCI82629. coined until 6 years later.

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could not make chimeras. He established the principle, but people didn’t believe it initially; it was too simple. I believed him, and a year later our group and two others published on the same day that iPS cells were identical to ES cells. They could make mice; they could contribute to the germ line. This led to an explosion of the field, which is sort of still ongoing because of its enormous potential for studying human disease. JCI: You’ve been very quick to pivot your lab, especially when it comes to new methods and technologies. Jaenisch: We have always developed methods to ask a question. I’m not inter- ested in developing methods for the sake of methods. The last one was a CRISPR tech- nology that we adapted for working with mice. It is certainly in my interest to use Figure 1. Rudolf Jaenisch on April 25, 2015. Image credit: Karen Guth. this technology to ask a relevant question. CRISPR technology is so efficient that we can introduce mutations into mice just But why were there no tumors? I didn’t I stayed there for seven years, and we by injecting the vectors into the zygote; know about epigenetics (the term was did some interesting things. We used the before, we had to use homologous recom- not invented as yet) or how to study it. viruses as probes to probe into develop- bination in ES cells, a long and complicat- Two other young faculty came to the Salk ment because these viruses, when they ed procedure, which takes a year, sophis- from David Baltimore’s laboratory. They integrate into the germ line, can mutate ticated technology, and knowledge. Now, brought with them an RNA tumor virus sys- genes. This “insertional mutagenesis” it’s very simple. CRISPR has really simpli- tem, the Moloney leukemia virus. I thought allowed us to mutate genes and to iso- fied things and has revolutionized the way using it would be helpful, since it would late the mutated genes because the virus we can manipulate genes. generate a phenotype (leukemia). Indeed, marked it. Only later, homologous recom- JCI: Should we use CRISPR in humans? when I generated infected mice, some got bination to target genes was invented. Jaenisch: We can ask the question leukemia, and they carried, like the SV40 David Baltimore had just founded the first, “Why should we?” The argument mice, the viral DNA in their tissues, and Whitehead Institute, and he offered me a you hear from those in favor is that you they transmitted it through the germ line. I job. That was very attractive for me, so I could eradicate a disease gene. I believe got hooked and wanted to understand epi- joined the Whitehead when it opened the this is a weak argument. There is no way genetics and development using these viral doors in 1984. I had terrific students, one to determine at the zygote stage which systems. If you think about development, who knocked out DNA methyltransfer- embryos are normal and which have a it’s all epigenetics. ase. This was a hugely informative muta- mutant disease gene. If you want to cor- I went from the Salk Institute to Ham- tion because it was the first time you could rect a mutation, you can’t genotype an burg, and there we found the answer to study epigenetics by genetic means. It got embryo at the one-cell stage. Therefore, your original question about viral silenc- me really thinking about epigenetics and if you want to correct a dominant muta- ing. It was caused by DNA methylation. then came Dolly, the first cloned mammal, tion such as in Huntington’s disease, 50% The virus gets immediately shut down by and a year later, the first cloned mouse. of the time, using CRISPR on zygotes will DNA methylation, which is a silencing I thought cloning was the greatest mutate a normal healthy embryo, and mechanism in embryonic stem cells, and thing, especially if you’re interested in this is totally unacceptable in my opinion. then embryos, but not in later stages. epigenetics. I switched my lab’s direc- Instead, we should use preimplantation JCI: You were surrounded by these tion, introduced cloning into the lab. diagnosis to test whether a given embryo brilliant minds at the Salk in an academic Many questions were raised — thera- carries the mutant gene. Some people Shangri-la, so why would you leave that to peutic potential, can you use cloning for argue, “Well, don’t do it at the zygote go back to Germany? patient-specific stem cells? We showed stage, but do it later through injectors.” Jaenisch: I got an offer to go to Hamburg, you could, in rodents. This also is not a good option, as one and I was very young. I almost felt obliged to And then Yamanaka described iPS would only correct a gene in some cells of go back. They offered me quite nice things, cells, with four factors being sufficient to the embryo. and Hamburg is an interesting city, but I was reprogram cells. The initial iPS cells were The only other use of human germ line very depressed when I arrived there. not really like normal ES cells, as they manipulation is for enhancement — if you

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want to add a gene, let’s say, for growth. Jaenisch: We are close, but I would Can you get the money for an exciting and Adding a growth gene to a healthy embryo say it’s not around the corner. There were risky project? Trainees are now facing a could generate, for example, taller individ- quite a number of safety issues — we had very different situation than I did. I would uals. But then the question is, should we to make iPS cells that were not genetically think the goal should not be to have a paper do that? Is that something society wants to modified. We had to learn how to differen- in Nature. The goal should be, “I’m really do? And this is not a scientific question. It’s tiate these cells for the right cell type; that passionate about this. I want to solve this an ethical and moral question which needs works for some lineages, not for others. question,” and go after it, taking risks. to be debated. JCI: When your students are mature JCI: If you couldn’t be a scientist, what One opinion is to ban all manipula- enough to leave the lab, do you counsel them other vocation do you think could have tion of human embryos, period, while to take on high-risk, high-reward research, kept you enthralled? others argue to do the research under especially in the resource-poor environ- Jaenisch: Oh, that’s an interesting certain precautions and clearly defined ment, as we find ourselves in currently? question, which is hard to answer. I think conditions, but impose a moratorium on Jaenisch: I think this is a complex ques- I would want to address some of the issues any application at this point. I believe tion. How do you find your niche where that I feel very passionate about, like issues that banning everything is just not a you can shine and where you get promoted of protecting the environment. But I worry feasible thing to do. We should not ban because you’re successful? How do you I would not be very good at this. I would be research. It is fundamentally different secure funding? This has changed enor- passionate, but probably totally ineffec- from limiting the application to affect a mously. When I went to Salk, I had this idea tive. I like to build things out of wood, like human being who can’t be asked for its about transgenic mice, although the term a carpenter. It is a very satisfying thing: you permission because it is manipulated at hadn’t been coined yet, and I wrote a grant design something; you start and you finish the embryo stage. to the NIH. Mike Bishop was the study- it. In science you do something. It never JCI: Stepping back from genetic section chairman. They funded it immedi- works. We don’t finish it. That might be a manipulation to cell therapy and implanta- ately, but now, it would be triaged because nice alternative. tion of corrected cells — how close are we there were no data to support the prem- to actually being able to use cell therapy? ise. Study sections are now risk averse. Ushma S. Neill

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