Differences in early lineage segregation between mammals.

Two lineage segregation events in mammalian development form the trophectoderm, primitive endoderm, and pluripotent primitive ectoderm. In mouse embryos, Oct4, Cdx2, Nanog, and Gata6 govern these events, but it is unknown whether this is conserved between mammals. Here, the expression patterns of these genes and their products were determined in porcine oocytes and embryos and in bovine embryos. CDX2 and GATA6 expression in porcine and bovine blastocysts resembled that of mouse, indicating conserved functions. However, NANOG expression was undetectable in porcine oocytes and embryos. Some inner cell mass cells in bovine blastocysts expressed NANOG protein. OCT4 protein was undetectable in porcine morulae, but present in both the trophectoderm and the inner cell mass of blastocysts, suggesting that downregulation of OCT4 in the trophectoderm does not precede trophectoderm formation. Combined, the results indicate differences in lineage segregation between mammals.