Cloning livestock: a return to embryonic cells

Abstract

Restoring nuclear totipotency in differentiated somatic cells following nuclear transfer, to produce healthy cloned animals, remains remarkable but highly inefficient and prone to epigenetic errors. The high rates of mortality throughout development create serious animal welfare issues, which limit the acceptability of somatic cloning. We anticipate a renaissance of embryonic cloning to alleviate these problems. In animal breeding, improved genetic markers, correlated to specific livestock production traits, will provide confidence in cloning selected embryos and their derivatives, especially undifferentiated embryonic stem cells. This will enable rapid dissemination of the most recent elite genotypes to avoid the genetic lag associated with cloning adults. For the production of transgenic livestock, embryonic stem cells might also be beneficial, because they are more amenable to precise genetic modifications and result in higher cloning efficiencies than somatic cells in the mouse. We argue that for agricultural applications, embryonic cloning will ultimately prove more useful than somatic cloning.