2 FORMS OF THE PROLACTIN RECEPTOR MESSENGER-RIBONUCLEIC-ACID ARE PRESENT IN OVINE FETAL LIVER AND ADULT OVARY

Previous binding studies indicated that there is little to no specific prolactin binding in ovine fetal liver and adult ovary. Therefore, we sought to determine if ovine prolactin receptor (PRLR) mRNA is presen t in those tissues. Primers were designed from the bovine PRLR cDNA se quence for use in reverse transcriptase-polymerase chain reaction (RT- PCR). RT-PCR analysis of ovine fetal liver total cellular RNA (tcRNA) isolated from days 60, 90, 105, 120 and 135 of gestation, and luteal t cRNA isolated from days 3, 7, 10, 13 and 16 of the estrous cycle revea led that PRLR mRNA was present in these tissues. However, two RT-PCR p roducts were generated from both tissues. The two RT-PCR products did not differ between the two tissue sources in sequence, and were design ated oPRLR-1 and oPRLR-2. Ovine PRLR-1 is 513 bp in length and is 96.4 % identical to the bovine cDNA. Ovine PRLR-2 is identical to oPRLR-1 u ntil nucleotide (nt) 420 at which point a 39 bp insertion occurs. This insertion occurs between Homology Boxes 1 and 2 within the cytoplasmi c domain of the receptor, resulting in an 11 amino acid divergent sequ ence, followed by two stop codons. Ribonuclease-protection assay revea led that oPRLR-1 mRNA is the most abundant in these tissues. Our data indicate that two forms of oPRLR mRNA are present in fetal liver and a dult ovary, and that one form (oPRLR-2) is predicted to encode a trunc ated PRLR.