CONDITIONAL KNOCKOUT OF CONNEXIN 43 IN MOUSE UTERUS UNCOVERS AN ESSENTIAL ROLE OF GAP JUNCTIONS DURING PREGNANCY

In most mammalian tissues, gap junction proteins connect cells by creating intercellular cytoplasmic channels clustered in the plasma membrane. These channels allow for communication between the cells by transferring ions and small molecules. Connexin 43 (Cx43) is one such gap junction protein that is present in multiple cell types. Our recent studies indicated that Cx43 is induced in the mouse uterus at the onset of implantation. The expression of Cx43 increased further during the decidualization phase of pregnancy and was localized in the proliferating as well as the decidualized stromal cells surrounding the implanted embryo. The Cx43 knockout mouse dies late in gestation or immediately following birth due to a developmental heart defect. Therefore, to address the functional role of Cx43 in the uterus during pregnancy, we created a conditional knockout mouse model by crossing transgenic mice harboring a “floxed”Cx43 gene (Cx43fl/fl) with progesterone receptor Cre knockin (PR-cre) mice. This mating generated female mice in which the Cx43 gene undergoes Cre-mediated excision in the reproductive cell types expressing the PR. The PR-Cre X Cx43fl/fl mice will be referred to as Cx43d/d mice. The impact of Cx43 deletion on mouse reproduction was examined by comparing the fertility of female Cx43d/d mice with that of female Cx43fl/fl mice. Fertility was assayed by housing Cx43fl/fl and Cx43d/d female mice with an equal number of wild type male mice. Our study revealed that Cx43d/d mice exhibited more than 60% reduction in birth rate when compared to the Cx43fl/fl (control) mice. To test whether or not this fertility defect is due to an impaired ovarian function, we subjected the mice to gonadotropin-induced superovulation. We observed that the number of released oocytes in Cx43d/d mice was comparable to that of Cx43fl/fl mice, suggesting that the reduced fertility in Cx43d/d mice is not due to a functional defect of the ovary. Further reproductive analyses indicated that the Cx43d/d mice were able to initiate embryo implantation and support pregnancy up to day 7 of gestation. However, starting on day 8 of pregnancy, the implanted embryos in Cx43d/d mice started to undergo resorption. Histological analysis of uterine sections of the Cx43d/d mice on day 8 of gestation revealed a striking decrease in the number of proliferating endothelial cells surrounding the embryo. Collectively, our studies indicated that Cx43 gap junctions in the stromal compartment play an essential role in the development of angiogenic network during early pregnancy. (Supported by NIH grants) (platform)