PROFILE PROFILE Profile of John Gurdon and Shinya Yamanaka, 2012 Nobel Laureates in Medicine or Physiology Alan Colman1 Executive Director, Singapore Stem Cell Consortium, A*STAR Institute of Medical Biology

We celebrate the 2012 Nobel Prize for genes and it was selective gene expression Medicine awarded to Sir John Gurdon and that accounted for cell fate choices. Al- Shinya Yamanaka for their groundbreaking though the initial “cloning” experiments contributions to the field of cell reprogram- generated swimming tadpoles, it wasn’t un- ming. In 1962, in a series of experiments til Gurdon showed that these tadpoles could inspired by Briggs and King (1), Gurdon mature into fertile adults (4) that it became demonstrated that the nucleus of a frog clear that the frog somatic cell nucleus con- somatic cell could be reprogrammed to be- tained all of the genes needed for full de- Sir John B. Gurdon (Left) and Shinya Yamanaka have like the nucleus of a fertilized frog egg velopment. The technical inefficiencies of (Right) during an interview with Nobelprize.org (2). By inserting the nuclei of intestinal ep- his experiments begged the question of ithelial cells into enucleated eggs, Gurdon whether the frogs created by Gurdon using on December 6, 2012. Image Copyright Nobel was able to create healthy swimming tad- SCNT in fact arose from unspecialized cell Media AB 2012/Niklas Elmehed. poles. These experiments were the first suc- donors present in the epithelial population. cessful instances of somatic cell nuclear Such doubts were dispelled when skin nu- The series of reprogramming successes transfer (SCNT) using genetically normal clei that were demonstrably specialized were that Gurdon’s work inspired involved radical cells. In 2006, Yamanaka made a further used successfully by Gurdon et al. in an ex- disruption to cell integrity; this was also true conceptual leap. With four defined tran- acting series of experiments performed in of the reprogramming seen when embryonic scription factors he induced intact mouse the early 1970s, when I was a doctoral stu- stem cells were fused to other differentiated somatic cells to revert to a pluripotent state dent in the laboratory (5). Thus, as well as cell types (8). Restoring the pluripotent state without an egg or embryo as intermediary yielding profound insight into mechanisms in an intact differentiated cell seemed an al- (3). These cells, dubbed induced pluripo- of development, these frog experiments also together more daunting proposition, but not tent stem (iPS) cells, have the capacity to proved that the genome of at least some spe- to Yamanaka. Armed with knowledge of ES turn into all of the cells of the adult mouse. cialized cell types could be reprogrammed cell biology, the history of frog and mamma- This result, now replicated with human to a totipotent state. Clearly, the frog egg lian SCNT, and the demonstration in 1987 cells, has enormous implications for basic cytoplasm contained factors capable of or- by Davis et al. (9) that the enforced expres- research, clinical medicine, and reproduc- chestrating the necessary changes in an in- sion of a single, added transcription factor tion. In the 44-year-long gap between coming nucleus. Interestingly, nuclei from (TF) gene could change fibroblasts into mus- ’ Gurdon and Yamanaka s respective discover- adult frog cells, unlike those taken from tad- cle-like cells, Yamanaka set out to reprogram ies, recombinant DNA technology emerged, poles, were never able to generate viable an intact differentiated somatic cell back to SCNT was successfully performed in mam- adult progeny. the pluripotent state. His “pluripotent” refer- mals, and embryonic stem (ES) cell research Nuclear transfer experiments by others in ence point was the ES cell. Transcriptional fl took ight. rabbits, mice, cows, and sheep followed analysis of mouse ES cells allowed him to ’ In the early 1960s there were divergent Gurdon s initial work with frogs. Many compile a hit-list of 24 TFs whose expression views about how a one-cell fertilized animal animals were generated but none through seemed to be associated with the mainte- egg could give rise to the more than 200 the use of somatic cell donors. Nevertheless, nance of the pluripotent state. All these TF different cell types that comprise the adult these experiments laid the groundwork for a genes were assembled into retrovirus vectors body. It was obvious that germ cells safe- breakthrough in 1996 when Campbell et al. and introduced into mouse fibroblasts in guarded the full complement of genes but in Edinburgh reported the generation of various combinations, ranging from indi- what about somatic cells? One prevailing two lambs by transfer of nuclei from an vidual factors to the complete set of 24. view was that redundant genes could be lost established, differentiated cell line derived The infected cells were cultured in condi- or permanently inactivated as somatic cells from nine-day-old sheep embryos (6). This tions known to support ES cell growth. This became specialized for certain activities. For same technology was used one year later in experimental approach struck many scien- example, a muscle cell might lose the genes a collaboration between my group and the tists working in the area as utterly naive. for neural activity or bone formation. A Edinburgh team using adult mammary cells. competing view, the one that Gurdon’s The birth of Dolly the Sheep proved that experiments in the frog ultimately confirmed, mammalian clones could be made from Author contributions: A.C. wrote the paper. was that somatic cells retained a full retinue of adult cell nuclei (7). 1E-mail: [email protected].

www.pnas.org/cgi/doi/10.1073/pnas.1221823110 PNAS Early Edition | 1of2 Downloaded by guest on October 1, 2021 Extraordinarily, it worked and four TF genes of their respective contributions to the field it is unclear how much overlap, if any, there were identified that, in combination, reprog- of reprogramming is clear and will endure. is between the reprogramming triggered by rammed the fibroblasts into iPS cells. These However, our knowledge of the reprogram- SCNT and that seen using defined factors. first iPS cells had similar although not iden- ming process remains patchy; for example, Back to the bench! tical properties to murine ES cells. Subse- quently, using improved assays, Yamanaka and colleagues (10), as well as other groups, fi 1 Briggs R, King TJ (1952) Transplantation of living nuclei from 6 Campbell KH, McWhir J, Ritchie WA, Wilmut I (1996) Sheep were able to con rm that the canonical set of blastula cells into enucleated frogs eggs. Proc Natl Acad Sci USA cloned by nuclear transfer from a cultured cell line. Nature four TFs could not only reprogram fibro- 38(5):455–463. 380(6569):64–66. blasts to an ES-like pluripotent state, but also 2 Gurdon JB (1962) The developmental capacity of nuclei taken from 7 Wilmut I, Schnieke AE, McWhir J, Kind AJ, Campbell KH (1997) intestinal epithelium cells of feeding tadpoles. J Embryol Exp Morphol Viable offspring derived from fetal and adult mammalian cells. Nature that the same procedure would work on 10:622–640. 385(6619):810–813. many different adult cell types from mice 3 Takahashi K, Yamanaka S (2006) Induction of pluripotent stem 8 Tada M, Takahama Y, Abe K, Nakatsuji N, Tada T (2001) Nuclear cells from mouse embryonic and adult fibroblast cultures by defined reprogramming of somatic cells by in vitro hybridization with ES cells. and humans. factors. Cell 126(4):663–676. Curr Biol 11(19):1553–1558. It is salutary to note that in an era of in- 4 Gurdon JB, Uehlinger V (1966) “Fertile” intestine nuclei. Nature 9 Davis RL, Weintraub H, Lassar AB (1987) Expression of a single tense competition between scientists, Gurdon 210(5042):1240–1241. transfected cDNA converts fibroblasts to myoblasts. Cell 51(6): ’ 5 Gurdon JB, Laskey RA, Reeves OR (1975) The developmental 987–1000. and Yamanaka s place in Nobel history is capacity of nuclei transplanted from keratinized skin cells of adult 10 Takahashi K, et al. (2007) Induction of pluripotent stem cells from neither begrudged nor disputed. The impact frogs. J Embryol Exp Morphol 34(1):93–112. adult human fibroblasts by defined factors. Cell 131(5):861–872.

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