Nuclear transplantation of mouse fetal germ cells into enucleated two-cell embryos

Mouse fetal germ cells were fused with enucleated blastomeres of two-cell embryos. Donor germ cells were obtained from fetuses of albino CD-1 strain or pigmented F(1) (C57BL x CBA) female mice mated with the same strain males at 11.5 to 16.5 days post coitum. Recipient two-cell embryos, which were of a different strain from the donors, were obtained at 37 to 42 hours (Group 1), 42 to 47 hours (Group 2), and 47 to 52 hours (Group 3) after treatment with human chorionic gonadotropin (hCG). After removing the nucleus from one two-cell blastomere, a single germ cell was fused with the enucleated blastomere using the Sendai virus; the second blastomere was left intact. The reconstituted embryos were cultured for 3 days in vitro, to examine their developmental capacity. The fused blastomeres in Groups 1 and 2 did not divide, but a few transplanted blastomeres in Group 3 divided several times, and some of them developed into normal blastocysts. Most embryos developed into blastocysts from one blastomere, with an undivided blastomere remaining. Embryos developing into normal blastocysts or blastocysts with small blastomeres were transferred to the oviducts of Day-1 or the uteri of Day-3 pregnant albino CD-1 mice. None of the young showed any contribution of the germ cells, judging by the eye and coat colors and by the germ cells in the germ line following mating with albino mice. Possible reasons for failure of pluripotency of the germ cells are discussed here.