In vitro and early in vivo development of sheep gynogenones and putative androgenones.

Genomic imprinting, where only one of the two parental genes is expressed, occurs in many phyla. In mammals, however, this phenomenon has been primarily studied in mice, and to a lesser extent, in humans. To understand how genomic imprinting may affect development in other species, particularly those with a different mode of placental development from mice and humans, 339 sheep zygotes were micromanipulated to contain either 2 large (presumptive male) or 2 small (presumptive female) pronuclei. One hundred and twenty-seven of these embryos and 86 manipulated and nonmanipulated control embryos were transferred to recipient ewes over 3 breeding seasons. Twenty-one control and 7 experimental conceptuses were recovered on day 21. Four of these conceptuses derived from zygotes with 2 small pronuclei were identified by karyotyping to be gynogenones (maternal-derived genome). While the gross morphology of the embryos appeared no different to those of normal controls, the extra-embryonic tissue from the conceptuses showed some hypertrophy and hypervascularization. Preliminary Northern blots of mRNA from allantoic and trophoblast tissue showed an overexpression of H19 and an underexpression of IGF2. Although the sheep gynogenetic phenotype contrasts with that seen in mice, these two genes appear to be similarly differentially expressed.