Molecular cloning and tissue distribution of pituitary adenylate cyclase activating polypeptide in the goldfish

Pituitary adenylate cyclase activating polypeptide (PACAP) is a novel member of the VIP/secretin peptide family and functions as a neurotransmitter/neuromodulator and nerve growth factor in mammals. Recently, we have shown that PACAP immunoreactivity is present in the goldfish pituitary and PACAP analogs are potent secretagogues of growth hormone release in goldfish pituitary cells, suggesting that PACAP may function as a hypophysiotropic factor in fish. To establish the structural identity of goldfish PACAP, a full-length cDNA of PACAP was obtained using a nested PCR approach and subsequent screening of a goldfish brain/pituitary cDNA library. This cDNA encodes a precursor protein of 175 a.a., with monobasic and dibasic enzyme-processing sites for cleavage of a 38 a.a. PACAP and a 45 a.a. GHRH-like peptide. The deduced a.a. sequence of this goldfish PACAP is highly homologous to that of catfish (92.1%), salmon.(89.5%), frog (92.1%), chicken (87.2%) and human PACAP (89.5%). Tissue distribution of PACAP mRNA in the goldfish was then examined using RT-PCR. PACAP expression was found mainly in the brain, pituitary, testes, gut and kidney, and to a less extent in the liver, heart and ovary, but not in the gill. In the brain, PACAP expression was detected in the telencephalon, hypothalamus, optic tectum, olfactory bulbs, cerebellum, medulla oblongata, and even in the spinal cord. A wide tissue distribution together with a highly conserved molecular structure suggest that PACAP may function as an important neuroendocrine factor for diverse biological functions in the goldfish.