Production of Cloned Mice and ES Cells from Adult Somatic Cells by Nuclear Transfer: How to Improve Cloning Efficiency?

摘要

Although it has now been 10 years since the first cloned mammals were generated fromsomatic cells using nuclear transfer (NT), most cloned embryos usually undergo developmental arrestprior to or soon after implantation, and the success rate for producing live offspring by cloningremains below 5%. The low success rate is believed to be associated with epigenetic errors, includingabnormal DNA hypermethylation, but the mechanism of "reprogramming" is unclear. We have beenable to develop a stable NT method in the mouse in which donor nuclei are directly injected into theoocyte using a piezo-actuated micromanipulator. Especially in the mouse, only a few laboratories canmake clones from adult somatic cells, and cloned mice are never successfully produced from mostmouse strains. However, this technique promises to be an important tool for future research in basicbiology. For example, NT can be used to generate embryonic stem (NT-ES) cell lines from a patient'sown somatic cells. We have shown that NT-ES cells are equivalent to ES cells derived from fertilizedembryos and that they can be generated relatively easily from a variety of mouse genotypes and celltypes of both sexes, even though it may be more difficult to generate clones directly. In general, NT-ES cell techniques are expected to be applied to regenerative medicine; however, this technique canalso be applied to the preservation of genetic resources of mouse strain instead of embryos, oocytesand spermatozoa. This review describes how to improve cloning efficiency and NT-ES cellestablishment and further applications.