gp46 is a collagen-binding heat-shock glycoprotein with a possible rol
e in the biosynthesis of collagen as well as in cell differentiation a
nd fusion. In this study, the relative levels of gp46 protein and its
mRNA transcript were examined, as well as the mRNA levels of collagen
types I and IV in first trimester and term human placental tissues. We
stern blot analysis revealed substantially higher levels of gp46 in fi
rst trimester placentae than in term placentae. Similarly elevated lev
els of type TV collagen transcript were detected in first trimester re
lative to term tissues. Interestingly, the levels of gp46 and type I c
ollagen mRNA remained unchanged. Immunohistochemical analysis of first
trimester tissues demonstrated intense gp46 staining in mononucleated
villous and estravillous cytotrophoblasts, decidual cells and in the
villous connective tissue stroma. Syncytiotrophoblast in the same tiss
ues also exhibited gp46 staining but at a reduced intensity. In chorio
nic villi of term placentae, faint gp46 staining was only observed in
the syncytiotrophoblast layer. However, as in the first trimester plac
entae, intense labelling was evident in the estravillous cytotrophobla
sts and decidual cells of these tissues. These results suggest a devel
opmental regulation of gp46 expression at the fetal-maternal interface
during pregnancy and suggest a possible functional link between gp46
and collagen type IV during gestation. (C) 1997 W. B. Saunders Company
Ltd.