Effect of enucleation procedures and maturation conditions on the development of nuclear-transferred rabbit oocytes receiving male fibroblast cells.

Enucleated oocytes matured in vitro, from which chromosomes were removed by treatment with ionomycin and demecolcine, were used as recipient oocytes for nuclear transfer of fibroblast cells from a mature male rabbit. The enucleated oocytes with donor nuclei were electrically activated 2 h after fusion. The potential of nuclear-transferred oocytes matured in vitro and ovulated oocytes to develop into blastocysts was high (33-55%), except for oocytes cultured for 8.0 (19%) and 8.5 h (25%) in vitro. After transfer of nuclear-transferred oocytes to recipients, ten of 62 (16%) and one of eight (13%) recipients that received in vitro-matured and ovulated oocytes, respectively, had 19 (1%) and one (0.6%) implantation sites at the time of laparotomy on days 8-17 after transfer. Four fetuses, including two with beating hearts, were obtained on day 15 of gestation after transfer of nuclear-transferred oocytes matured in vitro. The reason for the low efficiency of fetus production was not clear. One possibility is chromosomal abnormalities of nuclear-transferred oocytes, as most (21 of 22) of the oocytes had chromosomes dispersed along the spindle fibre at the first cell cycle. This is the first report of successful production of fetuses after nuclear transfer of rabbit somatic cells.