Lessons learned from nuclear transfer (cloning)

Somatic cell nuclear transfer (SCNT) has been accomplished in an ever-growing list of species. In each case, an enucleated oocyte has successfully reset the nucleus of a somatic cell such that the embryonic program could progress to the production of a live offspring. The overall efficiency of the process remains low due to a combination of biological and technical challenges, some of which are known and others remain to be elucidated. Comparative studies between livestock and laboratory species may help improve not only nuclear transfer efficiencies but also uncover basic underlying developmental principles.