EARLY GESTATIONAL EXPRESSION OF RETINOL-BINDING PROTEIN MESSENGER-RNABY THE OVINE CONCEPTUS AND ENDOMETRIUM

Communication between the mother and the early developing embryo is me diated by a variety of signals secreted by either the uterus or the em bryo to elicit a response from the other. These signals include prosta glandins, proteins, and steroids. Recently, retinol-binding protein (R BP) has been described as a product of both the conceptus and endometr ium in several species. Utilizing a cDNA clone to bovine RBP, we have described RBP mRNA expression in the endometrium, early conceptus, and extraembryonic membranes of sheep. Endometrial RBP mRNA expression di d not differ between samples collected on day 13 of the estrous cycle and early pregnancy, In cyclic animals, RBP mRNA expression decreased two-fold between days 13 and 16, presumably a result of luteal regress ion and the consequential withdrawal of progesterone. In pregnant anim als, endometrial RBP mRNA expression likewise decreased between days 1 3 and 16 and remained at this reduced level through day 30, despite th e presence of a functional corpus luteum. Initiation of embryonic RBP expression appeared to coincide with early stages of blastocyst elonga tion at day 13. Levels of expression increased dramatically with conce ptus development, peaked on day 23, and declined afterwards. Results f rom restriction enzyme analysis of genomic DNA indicated that RBP was encoded by a single gene per haploid genome. Differences in the tempor al and tissue-specific expression of the protein, despite the apparent utilization of a single gene, suggest complex regulation of RBP gene expression. (C) 1994 Wiley-Liss, Inc.