Increase in the Expression of c-erb A and c-erb B mRNAs in the Human Placenta in Early Gestation: Their Roles in Trophoblast Proliferation and Differentiation

Abstract

Previous studies have shown that human placental trophoblast is the site of the reception of thyroid hormone and epidermal growth factor (EGF) and that cellular levels of thyroid hormone receptor and EGF receptor are notably higher in early placenta than those in term placenta. On the other hand, it is now evident that a close similarity exists between thyroid hormone receptor and erb A protein and between EGF receptor and erb B protein. In the present study, we have therefore analyzed staged human placentas by Northern blot and In situ hybridization with c-erb A and c-erb B cDNA probes.In situ hybridization revealed that c-erb B mRNA is localized in the syncytiotrophoblast, consistent with our previous results, which showed the cytological localization of EGF receptor in developing human placenta. Northern blot analysis demonstrated that placental RNA contains c-erb A transcripts of 5.7-kb and c-erb B transcripts of 10.0-kb and 5.6-kb and that the amounts of the c-erb A and c-erb B transcripts vary remarkably during the course of gestation, being most abundant in early placenta, more abundant in midterm placenta, and least abundant in term placenta. It is therefore likely that the increased expression of c-erb A and c-erb B gene in early placental cells indicates an increase in cellular levels of thyroid hormone receptor and EGF receptor in early placental trophoblasts. These findings suggest an important role for the c-erb A and c-erb B oncogenes in the induction of trophoblast proliferation and differentiation in early gestation.