Recapitulation of the ovum mutant (Om) phenotype and loss of Om locus polarity in cloned mouse embryos.

The ovum mutant (Om) locus in mice affects early interactions between sperm and egg that in turn affect viability of embryos beyond the morula stage. Crosses of DDK females to males of many other inbred strains are 95% lethal around the morula stage, whereas reciprocal crosses are fully viable. Available data indicate that the early lethality is the result of an interaction between a factor in the ooplasm and the paternal genome. In this study, we examined whether this lethal interaction would likewise occur in cloned embryos produced by somatic cell nuclear transfer. We find that the Om effect is recapitulated but that the parental origin effect at the Om locus is no longer evident in cloned embryos.