Endocrinology, Vol 129, 126-132, Copyright © 1991 by Endocrine Society

ARTICLES

Characterization of protein production by ovine placental membranes: identification of a placental retinol-binding protein

KH Liu, RG Brewton, GA Baumbach and JD Godkin
Department of Animal Science, University of Tennessee, Knoxville 37901.

Ovine chorion, allantois, and amnion from days 23, 26, 28, 35, 45, 53, 62, and 72 and yolk sac from day 23 of pregnancy were isolated by dissection and cultured for 24 h in modified minimum essential medium in the presence of [35S] methionine to characterize in vitro synthesis and release of proteins. Proteins synthesized and released into medium were analyzed by two-dimensional polyacrylamide gel electrophoresis and fluorography. Patterns of protein production by these isolated membranes remained relatively unchanged from days 23-72 with the exception of the products of yolk sac, which regress by day 35 of pregnancy. In general, chorion was the source of a number of basic-to- neutral proteins; allantois and amnion were the sources of more acidic proteins; and yolk sac was the source of serum-like proteins. A major low mol wt acidic protein, D4, was produced by all membranes and present in fetal membrane fluids. Protein D4 consisted of three isoelectric variants (isoelectric point 5.3-6.1) with identical mol wts (23,000 +/- 800) and was shown to react immunologically with antibovine placental retinol-binding protein (RBP) serum. Hence, protein D4 is a putative ovine placental RBP. The present study is the first to characterize and compare protein production by isolated ovine chorionic, allantoic, amniotic, and yolk sac membranes from day 23 through midpregnancy and identify the major low mol wt acidic protein produced by each membrane as a placental RBP.

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