Changing distribution of cadherins during gestation in the uterine epithelium of lizards

The uterine epithelium provides the interface between an embryo and its mother during pregnancy. Calcium-dependent cadherins are adherens junction proteins that undergo major shifts in the uterine epithelium to facilitate the communication between maternal cells and the embryonic milieu during implantation in mammals. They are, therefore, important in trophoblast invasion and the maintenance of pregnancy. We investigated spatiotemporal changes of cadherins throughout pregnancy in the uterine epithelium of two viviparous skinks and one oviparous population, which all exhibit a noninvasive (epitheliochorial) placenta. Cadherins were identified for the first time in squamate reptiles. In all species, cadherins are reduced in the uterine epithelium as gestation progresses, which would lessen the attachment between uterine epithelial cells and allow them to stretch to accommodate embryonic growth. Interestingly, cadherins were reduced sooner after ovulation in the oviparous species than in the viviparous species. In viviparous species, the different expression of cadherins between barren and pregnant uteri from the same mother indicates that expression of cadherins may not be driven solely by maternal hormones, but also by the presence of an embryo. The redistribution of cadherins in squamates is comparable to that of mammals, reflecting establishment of feto-maternal communication during the peri-implantation period. As there is no breaching of maternal tissue in lizards, the change in adherens junctional properties are thus not exclusive to mammals with invasive placentae, which suggests that similar molecular mechanisms regulate changes to uterine epithelia during pregnancy across placental types.