ULTRASTRUCTURE AND PROTEIN-SYNTHESIS OF BOVINE AMNION

Morphology of the bovine amnion was studied by light microscopy, scann ing and transmission electron microscopy throughout pregnancy. Early i n gestation, amniotic epithelial cells were squamous with few microvil li and numerous cytoplasmic organelles. Late in gestation, cells were cuboidal with numerous microvilli, wide intercellular spaces, and few cytoplasmic organelles. Amnion contained many plaque-like projections. Amniotic plaques appeared to be formed by mitosis of normal epithelia l cells. The ultrastructure of plaques was similar to mammalian epider mis. In addition, protein synthesis and secretion in vitro by amniotic tissues from Days 40, 70, 90 and 160 of pregnancy was characterized. Metabolically labeled proteins released into culture medium were analy zed by two-dimensional polyacrylamide gel electrophoresis and fluorogr aphy. Patterns of protein production by the amnion remained relatively unchanged from Days 40 through 160. A low molecular mass protein (23 kDa; pl 5.3-6.1) produced by amnion and present in amniotic fluid was identified as retinol-binding protein (RBP) by immune precipitation wi th antiserum to bovine placental RBP. Immunocytochemical analysis loca lized the protein in amniotic epithelial cells and cells of amniotic p laques. Results of the study suggest that morphological changes of bov ine amnion during the course of pregnancy may reflect functional chang es in the amnion. Moreover, proteins synthesized by bovine amnion, suc h as RBP, may function in embryonic development.