The Culture of Preimplantation Rat Embryos and the Production of Allophenic Rats

Summary. Rat embryos at all cleavage stages of development were cultured in vitro. The various cleavage stages were successfully cultured through at least one mitotic cycle with the exception of the four-cell stage. No instance of development through the four-cell stage was observed. The eight-cell stage was cultured to the blastocyst stage with about 80% success. There was no difference in viability of eight-cell embryos if they were cultured without the zona pellucida. Despite some difficulties with adhesion of embryos and cellular death, denuded embryo pairs aggregated into a single blastocyst during a 24-hr culture period. Of all such aggregation attempts, 45% proved successful. Twenty-five aggregate blastocysts were transferred to eight recipient females. Subsequently, seven transferred embryos were born to four of the host females. Five of these transferred embryos were externally female while the remaining two were normal males. Two of these females were sibling aggregates (identical phenotypes) and no evidence of mosaicism should have been observed. Of the remaining five animals, three were of one parental phenotype or the other, while the remaining two (one male and one female) expressed some degree of parental phenotype mosaicism.