DIFFERENTIAL-EXPRESSIONS OF COLLAGEN TYPE-IV, TYPE-III, AND TYPE-I DURING THE DEVELOPMENT OF INVASIVE TROPHOBLASTS IN RATS

We examined the differential expressions of collagen types IV, III, an d I in the developing feto-maternal placental tissue of pregnant rats by a combination of in situ hybridization and immunohistochemistry. At day 9.5 of gestation, polygonal invasive cytotrophoblasts from the ec toplacental cone, which was modifying the maternal central artery, rev ealed intensely expressed alpha 1(IV) and alpha 1(III) collagen mRNAs. The localization patterns of these translated products, collagen type IV and procollagen type III, were slightly different in the invasive cytotrophoblasts. Collagen type IV densely deposited intracellularly a nd intercellularly in the maternal central artery and in the thickened basement membranes of the cytotrophoblasts. However, expression of al pha 1(I) collagen mRNA and procollagen type I was hardly detectable in the cytotrophoblasts. At day 13 of gestation, a high level of alpha 1 (IV) collagen mRNA was expressed in the cytotrophoblastic cell layer ( totrophospongium) and in the invasive large cytotrophoblasts. A modera te level of alpha 1(III) collagen mRNA was also expressed mainly in th e cytotrophoblasts, while alpha 1(I) collagen mRNA was expressed at ve ry low levels. Interestingly, procollagen type III failed to show line ar immunoreactivity in the subepithelial extracellular matrix beneath the maternal artery with the invasive cytotrophoblasts. Additional qua ntitative analyses of these type IV, III, and I collagen mRNA levels i n in situ hybridization experiments between several cell types also re vealed significant differences individually. Electron-microscopic stud y detected no cross-striated collagen fibers in the thickened basement membrane-like structures adjacent to the invasive cytotrophoblasts. F ibrillar and basement membrane collagen gene expressions, their protei n syntheses, and the processing of these procollagens seem to be devel opmentally regulated in the invasive cytotrophoblasts during the organ ization of feto-maternal placental tissue. The remodeling of the mater nal central artery by the invasive cytotrophoblasts is important for e nsuring ing the adequate blood supply to the developing placenta and f etus. (C) 1996 Wiley-Liss, Inc.