Characterization of protein production by bovine chorionic and allantoic membranes

Bovine allantoic (A) and chorionic (C) membranes from Days 29, 32, 36, and 40 of pregnancy were isolated by dissection and cultured in a modified minimum essential medium in the presence of L-[35S]methionine to characterize in vitro synthesis and release of proteins. Membranes were also cultured in the presence of the glycosylation inhibitor tunicamycin. Proteins synthesized and released into the medium were analyzed by two-dimensional polyacrylamide gel electrophoresis and fluorography of dried gels. Stained gels were used to analyze protein from allantoic fluids. Percent incorporation of the radiolabeled amino acid into nondialyzable protein was higher for A than for C (A = 8.0 +/- 1.2 vs. C = 6.4 +/- 0.5 per 200 mg tissue) but not significantly different. C released significantly more total protein (nonradioactive) into the medium (57.0 +/- 3 vs. 9.6 +/- 0.6 micrograms/ml). Of the 25 proteins analyzed, 19 appeared to be produced primarily by one membrane or the other. In general, C was the source of a number of basic-to-neutral glycosylated proteins and A was the source of a number of more acidic glycosylated proteins. Many but not all proteins synthesized by A were present in allantoic fluid. The present study is the first to characterize protein production by isolated chorionic and allantoic membranes and to demonstrate that both tissues contribute to the production of secretory conceptus proteins.