EXAMINATION OF GUINEA-PIG LUTEINIZING-HORMONE-RELEASING HORMONE GENE REVEALS A UNIQUE DECAPEPTIDE AND EXISTENCE OF 2 TRANSCRIPTS IN THE BRAIN

We sequenced the complementary DNA (cDNA) encoding guinea pig LHRH fro m an expression library derived from the preoptic area-anterior hypoth alamus. Data from in situ hybridization and RNase protection assays ve rified that the cloned cDNA was complementary to guinea pig LHRH messe nger RNA. The architecture of the deduced precursor resembles that of LHRH precursors identified in other species. In contrast, the predicte d sequence of the decapeptide differs from mammalian LHRH by two amino acid substitutions in positions 2 and 7. This is a novel finding, bec ause the amino acid sequence that comprises LHRH decapeptide is identi cal in all mammals studied to date. Moreover, the predicted substituti on in amino acid position 2 is unique among vertebrates. A second obse rvation of potential significance is the existence of two subspecies o f LHRH messenger RNA differing only in the length of their 3' untransl ated regions. These two transcripts were verified by sequence analysis of positive clones from the cDNA library and by RNase protection anal ysis of preoptic area-anterior hypothalamus extracts, and their presen ce is consistent with the two polyadenylation signals identified in th e untranslated regions of the LHRH gene. Future studies will examine L HRH gene expression in guinea pigs, which like primates but unlike rat s, have a true luteal phase as a component of their reproductive cycle .