Differential expression patterns of PQRFamide peptide and its two receptor genes in the brain and pituitary of grass puffer during the reproductive cycle

Abstract

Pain-modulatory neuropeptides, PQRFamide (PQRFa) peptides, have recently been implicated in the regulation of reproduction in fish. As a first step toward investigating the role of PQRFa peptides on reproductive function in the grass puffer Takifugu niphobles, which is a semilunar spawner, we cloned genes encoding PQRFa peptide precursor (pqrfa) and its two types of receptors (pqrfa-r1 and pqrfa-r2), and examined changes in their expression levels in the brain and pituitary over several months during the reproductive cycle. The grass puffer PQRFa peptide precursor of 126 amino acid residues contains two putative PQRFa peptides, PQRFa-1 and PQRFa-2, which correspond to NPFF and NPAF in other vertebrates, respectively. The grass puffer PQRFa-R1 and PQRFa-R2 consist of 426 and 453 amino acid residues, respectively, and contain distinct characteristics of G-protein coupled receptors. These three genes were exclusively expressed in the brain and pituitary. The expression levels of pqrfa and pqrfa-r1 were significantly increased during the late stage of sexual maturation, but low in the spawning fish just after releasing sperms and eggs. Therefore, the grass puffer PQRFa peptide may have a role in the late stage of sexual maturation before spawning via PQRFa-R1. In contrast, the pqrfa-r2 expression showed maximum levels in the spawning fish and in the post-spawning period. The present results provide fundamental data suggesting that the grass puffer PQRFa peptide may have multiple roles in the control of reproduction that are dependent on the reproductive stages.