Expression and cellular localization of retinol-binding protein messenger ribonucleic acid in bovine blastocysts and extraembryonic membranes

Abstract

A cDNA clone encoding retinol-binding protein (RBP) was isolated from a bovine conceptus cDNA library by use of an antiserum specific for bovine 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 RBP 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-bcRBP serum and in situ hybridization with 35S-labeled bcRBP-700 cDNA. Strong immunostaining for RBP and hybridization signals for RBP mRNA were observed in trophectoderm of tubular but not spherical Day 13 blastocysts. RBP mRNA was localized in epithelial cells lining the chorion, allantois, and amnion at Day 45 of pregnancy. In addition, RBP mRNA was detected in cotyledons, the sites of chorionic attachment to the uterine endometrium and physiological exchange between the embryo and its mother. Expression of RBP in expanding conceptuses, developing extraembryonic membranes, and sites of fetal-maternal attachment suggests that the extraembryonic membranes regulate retinol transport and availability within the conceptus.