Modulation of connexin expression in sheep endometrium in response to pregnancy

The expression pattern of two typical gap junction channel proteins, connexin 43 and connexin 26 (Cx43 and Cx26), was identified in the endometrium of sheep, a species with epitheliochorial type of implantation, by indirect immunohistochemistry during the cyclic phases, early and late pregnancy, and immediately after birth. The extent of Cx43 immunoreaction bound to endometrial stromal cells of the early implantation stage (day 15 p.c.) was comparable to the situation observed in oestrus. The subsequent intensification of feto-maternal contact correlated with a striking increase of stromal Cx43 in the intercaruncular and caruncular regions of the uterus (days 18 and 21 p.c.) and the induction of Cx26 in the glandular epithelium of late implantation (day 21 p.c.). In contrast, both gap junction proteins, coexpressed in the stroma of placentomes and interplacentomal sections on days 131 and 145 p.c., decreased during late pregnancy, while an intense and augmenting staining for Cx26 was detected at the cell borders of the glandular and luminal epithelium. The spatial and temporal distribution of both connexins suggests that, under embryonal and hormonal influences, gap junctional communication is involved in the implantation process and the regulation of endometrial tissue functions during sheep pregnancy and indicates further, that this connexin expression path resembles more the invasive type of implantation.