BILIARY GLYCOPROTEIN-1 EXPRESSION DURING EMBRYOGENESIS - CORRELATION WITH EVENTS OF EPITHELIAL DIFFERENTIATION, MESENCHYMAL-EPITHELIAL INTERACTIONS, ABSORPTION, AND MYOGENESIS

Biliary glycoprotein (Bgp1), a carcinoembryonic antigen-related family member of the immunoglobulin superfamily, is involved in normal and n eoplastic events. Analysis of Bgp1 expression throughout post-implanta tion mouse embryogenesis using reverse transcription-polymerase chain reactions, immunostaining with anti-Bgp1 monoclonal antibodies, and in situ hybridization with specific Bgp1 cDNA fragments revealed that Bg p1 may be involved in a number of specific embryonic processes. Immuno blot analysis of Bgp1 deletion mutant proteins indicated that distingu ishable epitopes of the molecule were preferentially identified by the three Bgp1 antibodies used in this study. This distinction is support ed by our immunolocalization studies during mouse embryogenesis in whi ch the three antibodies revealed specific patterns of Bgp1 expression. Bgp1 is not expressed in early post-implantation embryos (7.5 dpc), b ut is found in the placenta and extra-embryonic tissues (decidual endo thelial cells, giant trophoblasts, yolk sac visceral endoderm, and end ometrial glands) at this time. The primitive gut epithelium and surfac e ectoderm were the first embryonic tissues to express Bgp1. Significa nt Bgp1 expression was also observed later during epithelial-mesenchym al interactions (skin, meninges, lung, kidney, salivary glands, pancre as). A unique epitope of Bgp1, detectable by the monoclonal antibody C C1, was also associated with mesenchymal expression and was prominent during myogenesis (secondary myotube formation) at sites of terminal d ifferentiation. These studies suggest multiple roles for isoforms and glycoforms of the Bgp1 proteins localized in specific sites during pre natal development. (C) 1996 Wiley-Liss, Inc.