Sequence and expression of a cDNA encoding both pituitary adenylate cyclase activating polypeptide and growth hormone-releasing hormone-like peptide in channel catfish (Ictalurus punctatus)

Abstract

In nonmammalian vertebrates, pituitary adenylate cyclase activating polypeptide (PACAP) and a putative growth hormone-releasing hormone (GHRH-like peptide) are encoded by a single mRNA transcript. Both PACAP and GHRH have been implicated in the control of fish growth. Although the gene encoding PACAP and GHRH-like peptide (GHRHLP) has been cloned in other fishes, characterization of this gene in the commercially important channel catfish (Ictalurus punctatus) has not been previously reported. In this study, the GHRHLP/PACAP cDNA was cloned from channel catfish hypothalamic tissue and a brain cDNA library. Two cDNA variants of the GHRHLP/PACAP precursor gene were identified as a result of alternative splicing, a long form encoding both PACAP and GHRHLP and a short form encoding only PACAP. Both the long and the short forms of the GHRHLP/PACAP precursor cDNA were identified in channel catfish brain, pituitary, fat, gastrointestinal tract, ovary, testes, and muscle by RT-PCR detection. This study is the first to demonstrate mRNA expression of this gene in fat or skeletal muscle of fish. By characterizing the GHRHLP/PACAP gene and its distribution in channel catfish, we have developed essential tools to investigate the roles of these peptides in the regulation of catfish growth.