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 present in those tissues. Primers were designed from the bovine PRLR cDNA sequence 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 tcRNA isolated from days 3, 7, 10, 13 and 16 of the estrous cycle revealed that PRLR mRNA was present in these tissues. However, two RT-PCR products were generated from both tissues. The two RT-PCR products did not differ between the two tissue sources in sequence, and were designated 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 until nucleotide (nt) 420 at which point a 39 bp insertion occurs. This insertion occurs between Homology Boxes 1 and 2 within the cytoplasmic domain of the receptor, resulting in an 11 amino acid divergent sequence, followed by two stop codons. Ribonuclease-protection assay revealed 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 adult ovary, and that one form (oPRLR-2) is predicted to encode a truncated PRLR.
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