EXPRESSION AND CELLULAR-LOCALIZATION OF RETINOL-BINDING PROTEIN MESSENGER-RIBONUCLEIC-ACID IN BOVINE BLASTOCYSTS AND EXTRAEMBRYONIC MEMBRANES

A cDNA clone encoding retinol-binding protein (RBP) was isolated from a bovine conceptus cDNA library by use of an antiserum specific for bo vine conceptus RBP (bcRBP). The RBP cDNA clone, designated bcRBP-700, is 732 bp in length and codes for a protein whose predicted amino acid sequence is identical to that of bovine plasma RBP. The size of the R BP mRNA transcript in bovine chorioallantois was approximately 1.4 kb as determined by Northern blot analysis. Expression of the protein and its mRNA in expanding bovine conceptuses (Day 13) and extraembryonic membranes (Day 45) was determined by immunocytochemistry with anti-bcR BP serum and in situ hybridization with S-35-labeled bcRBP-700 cDNA. S trong immunostaining for RBP and hybridization signals for RBP mRNA we re observed in trophectoderm of tubular but not spherical Day 13 blast ocysts. RBP mRNA was localized in epithelial cells lining the chorion, allantois, and amnion at Day 45 of pregnancy. In addition, RBP mRNA w as detected in cotyledons, the sites of chorionic attachment to the ut erine endometrium and physiological exchange between the embryo and it s mother. Expression of RBP in expanding conceptuses, developing extra embryonic membranes, and sites of fetal-maternal attachment suggests t hat the extraembryonic membranes regulate retinol transport and availa bility within the conceptus.