Here we investigate whether normal development to term is possible when donor cells derived from fetal or adult tissue are induced to exit the growth cycle and enter the G0 phase of the cell cycle before nuclear transfer. Nuclear transfer was carried out according to one of our established protocols 1 and reconstructed embryos transferred into recipient ewes. Increased prenatal loss has been reported after embryo manipulation or culture of unreconstructed embryos 5 . Two fetuses had abnormal liver development, but no other abnormalities were detected and there was no evidence of infection. The ewes are arranged from left to right in the same order as the lambs.
Lambs have the same genotype as the donor cells and differ from their recipient mothers.
As assessed 1 h after fusion by examination on a dissecting microscope. As a proportion of morulae or blastocysts transferred. Not all recipients were perfectly synchronized. This lamb died within a few minutes of birth. All three cell populations were represented.