Cloned pigs produced by nuclear transfer from adult somatic cells

Since the first report of live mammals produced by nuclear transfer from a cultured differentiated cell population in 1995 (ref. 1), successful develo pment has been obtained in sheep(2,3), cattle(4), mice(5) and goats(6) usin g a variety of somatic cell types as nuclear donors. The methodology used f or embryo reconstruction in each of these species is essentially similar: d iploid donor nuclei have been transplanted into enucleated MII oocytes that are activated on, or after transfer. In sheep(2) and goat(6) preactivated oocytes have also proved successful as cytoplast recipients. The reconstruc ted embryos are then cultured and selected embryos transferred to surrogate recipients for development to term. In pigs, nuclear transfer has been sig nificantly less successful; a single piglet was reported after transfer of a blastomere nucleus from a four-cell embryo to an enucleated oocyte(7); ho wever, no live offspring were obtained in studies using somatic cells such as diploid or mitotic fetal fibroblasts as nuclear donors(8,9). The develop ment of embryos reconstructed by nuclear transfer is dependent upon a range of factors. Here we investigate some of these factors and report the succe ssful production of cloned piglets from a cultured adult somatic cell popul ation using a new nuclear transfer procedure.