LONG AND SHORT FORMS OF THE OVINE PROLACTIN RECEPTOR - CDNA CLONING AND GENOMIC ANALYSIS REVEAL THAT THE 2 FORMS ARISE BY DIFFERENT ALTERNATIVE SPLICING MECHANISMS IN RUMINANTS AND IN RODENTS

Prolactin is a pituitary hormone that binds to specific receptors in n umerous tissues. Depending on the size of their cytoplasmic domain, lo ng and short prolactin receptors (l-PR, s-PR) have been described. Up to now, s-PR were found in rodents only. We report here the cloning of full-length coding sequences for short and long ovine prolactin recep tors (s-oPR, l-oPR). The only difference between s- and l-oPR coding s equences was, respectively, the presence or absence of a 39 base pair insert at the beginning of the cytoplasmic domain, with two contiguous inframe stop codons at its 3' end. Sequence comparison revealed that the alternative splicing producing s- and l-oPR was different from tha t of rodents, although the resulting proteins were very similar. PCR e xperiments on ovine genomic DNA showed that the 39 base pair insert wa s directly linked to the downstream exon, and separated from the upstr eam exon by an 800 base pair intron. Thus, the alternative splicing us ed a single intron with one 5' and two 3' sites. The same organization was found in bovine and caprine genomes, suggesting that this feature is general in ruminants and different from rodents, which use mutuall y exclusive exons to produce s-PR and l-PR.