Differential ability of male and female rabbit fetal germ cell nuclei to be reprogrammed by nuclear transfer

The pluri- or totipotency of gonial cells, isolated from rabbit fetuses at 18-20 days of pregnancy, has been investigated by transferring their nuclei into enucleated oocytes and following the development of the resulting reconstituted embryos both in vitro (in a total of 726 embryos) and in vivo (in 135 embryos). The gonial cells exhibited pseudopodial activity like that of primordial germ cells and ultrastructural studies confirmed that neither male nor female cells had entered meiosis. When the gonial cells were used immediately after isolation, about 37% of the reconstituted embryos of both sexes cleaved, with no significant difference according to sex. However, after a further 4-day culture of the cleaved embryos, the blastocyst formation rate was four times higher in those made with male (16%) than with female (4%) gonial cells. No implantation sites were detected following transfer of reconstituted embryos into recipient females. These results show that the nuclei of male and female rabbit diploid germ cells differ in their capability to be "reprogrammed" and bring about development to the blastocyst stage following nuclear transfer. The origin of this difference, which is evidenced long before the onset of meiosis is discussed.