Development to term of chimaeras between diploid parthenogenetic and fertilised embryos.

Abstract

PARTHENOGENETIC mouse embryos have the potential for extensive cellular proliferation as well as differentiation into various cell types1–3. But this potential has been realised only when parthenogenetic embryos have been transferred to extrauterine sites1, and in spontaneously occurring ovarian teratomas and teratocarcinomas of parthenogenetic origin2,3. The development of mammalian parthenogenetic embryos in utero is restricted, with no conclusive evidence that they can develop to term4,5. Several hypotheses have been proposed to account for their poor development. For example, deleterious recessive genes may affect the viability of their cells, possibly because of their extensive homozygosity2,5, or disorganised growth and limited life span may result from anomalies of cellular interactions5. But the extensive cellular proliferation and differentiation of parthenogenetically derived cells which occurs in extrauterine sites is not entirely consistent with these explanations, and indicates that parthenogenones probably have a relatively stable genetic constitution. Indeed, these studies stress the likely importance of cellular environment for cytodifferentiation, provided in this instance by the extrauterine host tissue. There is a precedent for supposing that if the environment is critical for cytodifferentiation, parthenogenetic cells should be able to form chimaeras with cells derived from fertilised embryos6. Teratocarcinoma cells7,8 and cells carrying known lethal alleles9,10 can develop into viable chimaeras when aggregated with cells from normal embryos. Previous attempts to achieve development to term of aggregation chimaeras between parthenogenetic and fertilised embryos were apparently unsuccessful11. We have introduced inner cell masses (ICMs) from diploid ,parthenogenetic embryos into intact fertilised mouse blastocysts, and we report here the development of a chimaera to term.