Identification of a cDNA encoding a novel amphibian growth hormone-releasing peptide and localization of its transcript

Recently, we identified in the bullfrog brairi a novel neuropeptide with a C-terminal Leu-Pro-Leu-Arg-Phe-NH₂ sequence. This amphibian neuropeptide was shown to stimulate growth hormone (GH) release in vitro and in vivo and so was designated frog GH-releasiug peptide (fGRP). In this study, we cloned a cDNA encoding fGRP from the bullfrog brain by a combinatiou of 3′ and 5′ rapid amplification of cDNA ends (RACE). The deduced fGRP precursor consisted of 221 amino acid residues, encoding one fGRP and three putative fCRP-related peptides that included Leu-Pro-Xaa-Arg-Phe-NH₂ (Xaa = Leu or Gln) at their C-termini. All these peptide sequences were flanked by a glycine C-terminal amidation signal and a single basic amino acid on each end as an endoproteolytic site. Northern blot analysis detected a single band of approximately 1.0 kb, indicating that no alternatively spliced forms were present. Such an apparent migration was in agreement with the estimated length of the cDNA, 902 bp. In situ hybridization further revealed the cellular localization of fGRP mRNA in the suprachiasmatic nucleus in the hypothalamus. In addition to fGRP, its related peptides may be hypothalamic factors involved in pituitary hormone secretion.