Characterization of Bovine Conceptus Proteins Produced during the Peri- and Postattachment Periods of Early Pregnancy1

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Abstract
Bovine conceptuses removed from the uterus during the peri- and postattachment periods of placentation (Days 17-24 and 26-38, respectively) were cultured in a modified minimum essential medium in the presence of L-[3H]leucine to characterize in vitro synthesis of proteins released into the medium. Patterns of protein production were analyzed by two-dimensional polyacrylamide gel electrophoresis followed by fluorography of dried gels. Four groups of low molecular weight acidic proteins (LMWAP) were observed to be synthesized during the peri- and postattachment periods. The number and relative concentration of these changed with development. One group (A) consisted of three major and two or more minor isoelectric species (pI .simeq. 5.8-6.8); these were the major synthesized proteins observed from Days 17-22. The major polypeptides of Group A were present at all time points examined through Day 38 and, in several preparations, appeared as doublets (Mr .simeq. 22,000 and 24,000) through Day 29 but not thereafter. Group A polypeptides from Day 19 and 36 conceptus cultures were demonstrated by immunoblot analysis to cross-react with antiserum produced against ovine trophoblast protein-1 (oTP-1). A second group of proteins (A1) and a single protein (B) in the 20,000-24,000 Mr range were observed between Days 17 and 22. These were acidic relative to Group A and were not detected after Day 22. A fourth group (C) of LMWAP (Mr .simeq. 14,000-18,000) was first observed around Day 21 and appeared to increase relative to Group A through Day 29. One protein from this group, C3, was the predominant LMWAP at Day 38. Production of numerous proteins in the 30,000-70,000 Mr range (Group E) was first observed between Days 21 and 24. Three of these.sbd.E7, E8, and E9.sbd.were acidic (pI .simeq. 5.0-5.8), with apparent molecular weights between 30,000 and 45,000, and became prominent secretory products around Day 29 and times thereafter. A very large (Mr > 20,000) acidic (pI < 4.5) protein was present from Day 17 through at least Day 29, and several large (Mr .gtoreq. 10,000) were observed around Day 24 and afterwards. Group A proteins have been referred to as bovine trophoblast protein-1 (bTP-1) and implicated in events associated with maternal recognition of pregnancy. The present study is the first to demonstrate continued production of these products beyond Day 24, and to report qualitative changes observed in bovine conceptus protein synthesis during the early postattachment period.