Characterization and messenger ribonucleic acid distribution of a cloned pituitary adenylate cyclase-activating polypeptide type I receptor in the frog Xenopus laevis brain

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been found t o modulate neuroendocrine functions in the frog brain and pituitary, but th e nucleotide sequence and brain distribution of messenger RNA (mRNA) for th e selective type I receptor for PACAP (PAC(1)) in the frog are still unknow n. Here, we report the isolation and characterization of a PAC(1) receptor complementary DNA (cDNA) clone from a frog (Xenopus laevis) tadpole brain c DNA Library. This cDNA encoded a 466-amino acid protein that has 74% homolo gy with human PAC(1) receptor and 48% homology to the frog vasoactive intes tinal peptide/PACAP receptor. Injection of in vitro synthesized mRNA of the cloned cDNA into Xenopus oocytes resulted in expression of selective high affinity PACAP receptors (K-d = 47 pM). IC50 values for PACAP-38; PACAP-27, and VIP were 27 pM, 110 pM and >1 mu M, respectively. These results indica ted that the cloned cDNA represents a Xenopus PACAP-preferring PAC(1) recep tor. Northern hybridization revealed that PAC(1) receptor mRNA was present at high levels in the brain. In situ hybridization showed that the PAC(1) r eceptor gene was expressed highly in the pallium, preoptic nucleus, and nuc leus of cerebellum, and moderately in the Purkinje cell layer of the cerebe llum. Moderate PAC(1) receptor mRNA signals were detected in the distal lob e of the pituitary. A knowledge of the molecular structure and expression p attern of the PAC(1) receptor will facilitate further investigation of the physiological roles of PAC(1) receptor in the frog brain.