ENDO-A CYTOKERATIN EXPRESSION IN THE INNER CELL MASS OF PARTHENOGENETIC MOUSE EMBRYOS

During the preimplantation period of development, the first cellular p olarization and diversification of the mouse embryo occurs. This proce ss starts at the eight-cell stage and is directly driven by the cytosk eleton. Cell polarization finally leads to the first embryonic epithel ium. the trophectoderm, characterized by the presence of cytokeratins. It has not been described whether genomic imprinting, an epigenetic m odification of certain genes depending on the parent-of-origin. affect s preimplantation development. However, implantation is one of the ste ps in which an exceptionally high mortality rate is observed in mouse parthenogenetic embryos, a phenomenon that may be influenced by a defi ciency in trophectoderm differentiation. To assess this possibility we analyzed the expression of various cytoskeletal proteins in late prei mplanted embryos. Mo differences were observed in the expression of mi crotubules and microfilaments, but surprisingly, the undifferentiated cells of the parthenogenetic inner cell mass showed distinct cytokerat in staining. This anomalous cytoskeleton expression may be considered as one of the earliest manifestation described to date of the effect o f genomic imprinting in development.