DIFFERENTIAL ABILITY OF MALE AND FEMALE RABBIT FETAL GERM-CELL NUCLEITO BE REPROGRAMMED BY NUCLEAR TRANSFER

The pluri- or totipotency of genial cells, isolated from rabbit fetuse s at 18-20 days of pregnancy, has been investigated by transferring th eir nuclei into enucleated oocytes and following the development of th e resulting reconstituted embryos both in vitro (in a total of 726 emb ryos) and in vivo (in 135 embryos). The gonial cells exhibited pseudop odial activity like that of primordial germ cells and ultrastructural studies confirmed that neither male nor female cells had entered meios is. When the genial cells were used immediately after isolation, about 37% of the reconstituted embryos of both sexes cleaved, with no signi ficant difference according to sex. However, after a further 4-day cul ture of the cleaved embryos, the blastocyst formation rate was four ti mes higher in those made with male (16%) than with female (4%) gonial cells. No implantation sites were detected following transfer of recon stituted embryos into recipient females. These results show that the n uclei of male and female rabbit diploid germ cells differ in their cap ability to be ''reprogrammed'' and bring about development to the blas tocyst stage following nuclear transfer. The origin of this difference , which is evidenced long before the onset of meiosis, is discussed.