GENETIC-REGULATION OF PLACENTAL FUNCTION - A QUANTITATIVE IN-SITU HYBRIDIZATION STUDY OF CALCIUM-BINDING PROTEIN (CALBINDIN-D-9K) AND CALCIUM-ATPASE MESSENGER-RNAS IN SHEEP PLACENTA

The calcium requirement of the ovine fetus increases progressively thr oughout pregnancy. The 9-kDa calcium binding protein (calbindin-D-9h; 9CBP) is considered to be a reliable marker for epithelia mediating ca lcium transport. This quantitative in situ hybridization study shows t hat the levels of 9CBP mRNA show a pregnancy stage-related increase wh ich correlates with fetal calcium demand only in maternal endometrial gland and fetal interplacentomal trophoblast epithelia. Levels of 9CBP mRNA in the placentome, which has by far the greater area of maternof etal contact, show no changes during pregnancy. mRNA for the CaATPase enzyme, a second requirement for calcium transport, is shown to be pre sent in epithelia in interplacentomal and placentomal regions but show s no change in concentration as pregnancy progresses. Results with the 9CBP and CaATPase mRNAs confirm our recent immunocytochemical results with ruminant placenta and indicate the basis for a cellular calcium transport system analogous to that in the enterocyte. The interplacent omal trophoblast system appears to be eminently suitable for investiga tions of details of the cellular mechanism and control of epithelial c alcium transport. (C) 1997 W. B. Saunders Company Ltd.