Expression and distribution of cell adhesion molecule uvomorulin in mouse preimplantation embryos

We have examined the synthesis and distribution of the cell adhesion molecule uvomorulin in mouse preimplantation embryos. Uvomorulin can already be detected on the cell surface of unfertilized and fertilized eggs but is not synthesized in these cells. Uvomorulin synthesis starts in late two-cell embryos and seems not to be correlated with the onset of compaction. The first signs of compaction are accompanied by a redistribution of uvomorulin on the surface of blastomeres. During compaction uvomorulin is progressively removed from the apical membrane domains of peripheral blastomeres. In compact morulae uvomorulin is no longer present on the outer surface of the embryo but is localized predominantly in membrane domains involved in cell-cell contacts of adjacent outer blastomeres. On inner blastomeres of compact morulae uvomorulin remains evenly distributed. This uvomorulin distribution once established during compaction is maintained and also found in the blastocyst: on trophectodermal cells uvomorulin localization is very similar to that in adult intestinal epithelial cells while uvomorulin remains evenly distributed on the surface of inner cell mass cells. The possible role of the redistribution of uvomorulin for the generation of trophectoderm and inner cell mass in early mouse embryos is discussed.