Dynamics of βig-h3 mRNA expression during pregnancy in the uterus and the placenta of the mouse:: A possible regulatory factor for trophoblastic invasion

Changes in the betaig-h3 gene expression levels in the uterus during different reproductive stages and those in the placenta on different days of gestation in the mouse were examined by Northern blot analysis. The levels of betaig-h3 expression rose steeply from the baseline level at proestrus to the maximum at estrus and then declined rapidly from 1st day of diestrus onward. During pregnancy, high levels of betaig-H3 mRNA were detected in the uterus on Day 4 of gestation, when the trophoblastic invasion of the implanted blastocysts was very active. In the pseudopregnant uterus, the betaig-h3 expression levels exhibited the same patterns as those in the pregnant uterus, although the levels were much lower at all stages than those in the pregnant uterus. In the placenta, the betaig-h3 expression levels gradually increased from Day 7 onward and peaked on Day 18 of gestation. In situ hybridization analysis of the pregnant uterine tissues revealed that the luminal as well as the glandular epithelium expressed betaig-h3 mRNA at high levels. In the placenta, high levels of betaig-h3 transcripts were detected in the decidual cells and the giant trophoblast cells. These findings suggest that betaig-h3 might play a role in regulating the invasiveness of trophoblast cells during implantation and placentation of hemochorial type when extensive trophoblastic invasion of the endometrium takes place.