Novel fish hypothalamic neuropeptide: Cloning of a cDNA encoding the precursor polypeptide and identification and localization of the mature peptide

Recently, we identified novel avian and amphibian hypothalamic neuropeptides that inhibited gonadotropin release and stimulated growth hormone release. They were characterized by a similar structure including the C-terminal LPLRF-NH₂ motif. To clarify that the expression of these novel hypothalamic neuropeptides is a conserved property in vertebrates, we characterized a cDNA encoding a similar novel peptide, having LPLRF-NH₂ from the goldfish brain, by a combination of 3′ and 5′ rapid amplification of cDNA ends (RACE). The deduced peptide precursor consisted of 197 amino acid residues, encoding three putative peptide sequences that included -LPXRF (where X is L or Q) at their C-termini. Mass spectrometric analyses revealed that a tridecapeptide (SGTGLSATLPQRF-NH₂) was derived from the precursor in the brain as an endogenous ligand. Southern blotting analysis of reverse-transcriptase-mediated PCR products demonstrated a specific expression of the goldfish peptide gene in the diencephalon. In situ hybridization revealed the cellular localization of goldfish peptide mRNA in the nucleus posterioris periventricularis in the hypothalamus. Immunoreactive cell bodies were also restricted to the the nucleus posterioris periventricularis and the nervus terminalis and immunoreactive fibers were distributed in several brain regions including the nucleus lateralis tuberis pars posterioris and pituitary. Thus, the goldfish hypothalamus expresses a novel neuropeptide containing the C-terminal -LPQRF-NH₂ sequence, which may possess multiple regulatory functions and act, at least partly, on the pituitary to regulate pituitary hormone release.