Desmosomes are reduced in the mouse uterine luminal epithelium during the preimplantation period of pregnancy: A mechanism for facilitation of implantation

Dynamic regulation of intercellular junctions is an essential aspect of man y developmental, reproductive, and physiological processes. We have shown t hat expression of the desmosomal protein desmoplakin decreases in the lumin al uterine epithelium during the preimplantation period of pregnancy in mic e. By the time of implantation (between Days 4.5 and 5 of pregnancy), desmo plakin protein can barely be detected by SDS-PACE and Western blotting, and by immunocytochemistry, it is restricted to well-spaced, punctate dots at the apicolateral junction. Using confocal XZ series and electron microscope quantitation, both the density and distribution of desmosomes along the la teral cell surfaces of luminal epithelial cells were observed to change dur ing early pregnancy. On Day 1 of pregnancy, desmosomes were found at high d ensity in the apicolateral junctional complex, being present here in 79% of ultrathin sections examined, whereas on Day 5, the density was much reduce d (present in only 18% of ultrathin sections examined). Desmosomes were fou nd along the lateral surfaces, at or below the level of the nucleus, in 15% of ultrathin sections examined on Day 1 of pregnancy but in only 1% on Day 5. Desmoplakin mRNA declined during the first 4-5 days of pregnancy, along with the protein, suggesting that these changes are controlled at the leve l of mRNA. This study shows that desmosomes are regulated during early preg nancy, and we propose that a reduction in desmosome adhesion facilitates pe netration of the luminal epithelium by trophoblast cells at implantation.