Gene expression in preimplantation embryos of the mouse, pig and cow

Early mammalian embryo development prior to blastocyst elongation can be achieved in vitro, which allows a unique opportunity to study phenomena which normally occur in vivo. In vitro culture also permits the manipulation of early embryos and the development of new technologies, such as the generation of transgenic animals and selection for offspring sex. These studies describe efforts to improve our understanding of early embryos by analysis of expression from endogenous and exogenous genes.; Interferon-tau is a conceptus secretory protein necessary for maternal recognition of pregnancy in ruminant species. In red deer, production of interferon-tau differs between male and female blastocysts in vivo. Experiments were conducted to determine whether blastocyst production of interferon-tau differs between the sexes in cattle, as assessed after culture in vitro. The media from individually cultured bovine blastocysts were analyzed for interferon content by antiviral assay, and blastocysts were sexed retrospectively by PCR. Female blastocysts produced significantly more interferon-tau than male blastocysts in eight out of ten replicates examined, regardless of such variables as blastocyst quality, hatching and length of time in culture. However, significantly more male embryos reached the blastocyst stage of development, which implies that in vitro culture preferentially supports male embryo development over that of female embryos. Nevertheless, female bovine blastocysts may be better able to signal their presence to the dam than male blastocysts.; The production of transgenic mice by pronuclear microinjection is a ubiquitous technique, while production of transgenic domestic species remains an inefficient process. In vitro reporter constructs were injected into embryos of the mouse, pig and cow to allow visualization of exogenous gene expression from these three species. The proportion of embryos expressing the reporter constructs declined from the mouse to the pig to the cow. Concurrently, the proportion of embryos mosaic in expression increased from the mouse to the pig to the cow. These results of in vitro expression mirror the efficiencies with which transgenic animals are produced from these three species. As activation of the embryonic genome occurs at successively later stages in these species, it is likely that integration of foreign gene constructs occurs coincident with the initiation of transcription in early mammalian embryos.