Expression pattern of Oct-4 in preimplantation embryos of different species

POU transcription factors are involved in transcriptional regulation during early embryonic development and cell differentiation. Oct-4, a member of t his family, has been shown to be under strict regulation during murine deve lopment. The expression of Oct-4 correlates with the undifferentiated cell phenotype of the mouse preimplantation embryo. In this study, expression of a gene construct consisting of selected parts of the region upstream from the murine Oct-4 gene as promoter/enhancer, enhanced green fluorescent prot ein (ECFP) as reporter and the five exons of the murine Oct-4 gene (GOF18-D elta PE EGFP) was evaluated in murine, porcine, and bovine preimplantation embryos. For comparison, expression of the endogenous Oct-4 gene was also a nalyzed in all three species by immunocytochemistry. The transgene construc t was microinjected into zygotes cultured in vitro to various developmental stages. The ECFP fluorescence was visualized in developing embryos by exci tation with blue light at different days following microinjection and showe d similar expression patterns in all three species. Most embryos displayed a mosaic pattern of transgene expression. The ECFP fluorescence was not res tricted to the inner cell mass (ICM) but was also seen in trophoblastic cel ls. An affinity-purified polyclonal antibody specific to Oct-4 was used for immunocytochemical analysis of in vivo- and in vitro-derived bovine and po rcine blastocysts and also of in vivo-derived murine blastocysts. In the in vivo-derived murine embryos, Oct-4 protein was detectable in the ICM but n ot the trophectoderm, whereas in porcine and bovine blastocysts, derived in vivo or in vitro, Oct-4 protein was detected in both the ICM and the troph ectoderm. Thus, in the two large animal species, Oct-4 expression from the endogenous gene was clearly not restricted to the pluripotent cells of the early embryo. These results show that Oct-4 regulation differs between thes e species and that the presence of Oct-4 protein may not be sufficient for selection of undifferentiated cell lines in domestic animals.