Cloning and differential expression pattern of pituitary adenylyl cyclase-activating polypeptide and the PACAP-specific receptor in darkbarbel catfish Pelteobagrus vachelli

Pituitary adenylyl cyclase-activating polypeptide (PACAP) can mediate growth hormone and gonadotropin release in teleost pituitary via PACAP receptors. In this study, the full-length cDNAs encoding PACAP and PACAP-related peptide (PRP) and the PACAP-specific receptor (PAC1-R) were cloned from the brain of darkbarbel catfish Pelteobagrus vachelli. The PRP-PACAP cDNA had two variants expressed by alternative splicing: a long form encoding both PRP and PACAP and a short form encoding PACAP only. Our data showed that the exon skipping on the PACAP transcripts was a possible mechanism regulating the expression ratio of PACAP to PRP in non-mammalian vertebrates. Based on multi-sequence alignments and phylogenetic analysis, the catfish PACAP and PAC1-R were highly conserved during evolution. Real-time quantitative PCR revealed that the PACAP-short and PAC1-R tanscripts were mainly expressed in the brain and gonad of darkbarbel catfish, though a small amount of mRNAs was also found in other tissues. Immunofluorescent staining studies showed wide distribution and high levels of PAC1-R in the catfish brain, suggesting that the PAC1-R form may play a central role in growth hormone release. The expressions of PACAP and PAC1-R in gonads and the occurrence of PACAP-immunoreactive material in testis suggest that PACAP may act as a paracrine/autocrine factor for gonad development.