This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The use of embryonic stem cells to gain access to the germline of experimental animals has been important to our greater understanding of gene function. As valuable as this approach is, it has not worked for species other than mouse. While ES cells have been isolated from a variety of species including the rat, the cells have not so far proven to be sufficiently pluripotent to allow the creation of germline chimeras from them. Another approach to the germline, though, is nuclear transfer. Recent advances in the use of cultured cells as a source of genetic material to direct embryonic development of enucleated oocytes in rabbit, cow, and sheep offer an approach to homologous recombination in the rat. We have established procedures for the enucleation of rat oocytes, the injection of cumulus cells and of genetically marked embryonic fibroblasts from the rat resulting in advanced preimplantation development. If it proves feasible to recover live births from this approach, then knocking-out genes in the fibroblasts can be used to obtain mutant rats. Nuclear transfer results in a rat which is essentially the strain of origin of the cultured cells without subsequent breeding and therefore allows, in principle, the use of particular strains of rat for which given experiments make the most sense.
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