Prolonged development of normal and parthenogenetic postimplantation mouse embryos in vitro.

Parthenogenetic mammalian embryos show reduced placental development and do not develop beyond the 25-somite stage. But non-parthenogenetic embryos in culture, without a functional placenta, can develop to 40 somites or more. We have therefore examined the possibility that parthenogenetic embryos might also show prolonged development in culture. After parthenogenetic activation and diploidization, 23% of CBA and 56-58% of hybrid (CBAxC57BL/6) F1 mouse eggs developed in culture to blastocysts. When transferred to pseudopregnant recipients: 60% of the CBA blastocysts implanted and 26% of these developed to somite stage embryos; 71-72% of the hybrid blastocysts implanted and 11-17% of these developed to somite stage embryos. Improved development of postimplantation embryos explanted into culture at about the 15-20 somite stage was obtained by opening the visceral yolk sac (without exteriorizing the embryo). All the normal (non-parthenogenetic) embryos cultured in this way developed to more than 35 somites and many reached 45-55 somites. Under the same conditions, 11/17 diploid parthenogenetic CBA embryos developed in culture to more than 35 somites and 5 of these reached 45 somites; and 9/28 diploid parthenogenetic (CBAxC57BL/6) F1 embryos developed to 35 somites or more and 5 of these reached 45 somites. The size and protein content of the parthenogenetic embryos after culture was less than that of the normal embryos of equivalent stages. These results raise new possibilities for the analysis of parthenogenesis and genomic imprinting, including studies of the effects of adding to the culture medium specific growth factors and demethylating agents.