Nuclear transplantation: A monoclonal mouse?

One potential use of nuclear-transplantation — cloning — technology is to generate genetically matched tissues for treating adult patients. But there's a debate about whether mature adult cells are a good source of nuclei. Behind all the fuss about the cloning of animals and prospects for cloning humans, some interesting scientific issues remain. For instance, can the nucleus of even the most specialized adult cell be completely 'reprogrammed', so that it can direct the development of a whole new embryo? Or are there subsets of cells in adult organisms — perhaps representing the unspecialized cells known as stem cells — that can be reset more easily? Hochedlinger and Jaenisch1 tackle the question on page 1035 of this issue, and claim success in producing cloned mice by using nuclei from mature T or B cells. The results provide strong evidence that the nucleus of a differentiated cell can indeed be reprogrammed. Given all the current hype, it might seem odd that the most commonly used approach to cloning — 'somatic-cell nuclear transfer ' — was in fact developed some 40 years ago in amphibians purely to address such fundamental questions. The technique involves replacing the nucleus of an egg with that of a more specialized cell from an embryo or adult. The idea is that the egg's cytoplasm somehow reprogrammes the nucleus so that it is as developmentally versatile as that of a fertilized egg, and able to direct the formation of all the tissues that mak