Uterine epithelial cells are important in constantly maintaining a tissue protective barrier, and only under the specific hormonal conditioning of pregnancy which involves a remodelling of the cell ultrastructure termed the 'plasma membrane transformation'. This allows for the successful invasion of the blastocyst. Indirect immunofluorescence microscopy in rat uterine epithelial cells during pregnancy shows that ezrin and EBP50 are relocated to the apical membrane upon lumen closure at the time of implantation, and on average results in 90% colocalisation. Ezrin and EBP50 function as a linked protein complex at the time of implantation seen through immunoprecipitation results from day 6 of pregnancy. The ezrin-EBP50 complex is also associated with the membrane, shown using cell fractionation and western blotting analysis in which ezrin increased dramatically in the membrane concentrated fraction, and correspondingly decreased in the cytosolic fraction leading up to implantation. At the apical membrane these proteins are likely associating with intra-membranous signalling molecules which allow communication between contacting cells. The same protein complex is also relocated to the apical membrane when cells contact an inanimate filament inserted into the uterus of a non-pregnant rat. The only unique contacting circumstance in which these proteins are not seen at the apical membrane is within the implantation chamber itself, more specifically the cells in direct contact with the implanting blastocyst. These results highlight the unique situation that is implantation, which involves specific blastocyst signalling and influence upon the uterine epithelial cells lining the implantation chamber. It may be that the ezrin-EBP50 protein complex is critical at the earlier stage of apposition, and through blastocyst influence, are subsequently lost from the apical membrane to allow for successful invasion.
Lactosaminoglycan assembly, cell surface expression, and release by mouse uterine epithelial cells.