Elevation of Kiss2 and its receptor gene expression in the brain and pituitary of grass puffer during the spawning season

Abstract

Kisspeptins are a family of neuropeptides encoded by Kiss1 and Kiss2 genes, and participate in neuroendocrine regulation of gonadotropin-releasing hormone (GnRH) secretion through activating their receptor, Kiss1r (or GPR54). Bioinformatic analyses have shown that there is a single gene for each kisspeptin (Kiss2) and its receptor (Kiss1r) in pufferfish, the function of which has yet to be elucidated. We cloned these two genes in grass puffer, which spawns on beach with semilunar cycles, and examined changes in their expression levels in the brain and pituitary at different reproductive stages over the spawning season. The Kiss2 precursor of 104 amino acid residues contains a putative kisspeptin peptide (SKFNLNPFGLRF). Kiss1r consists of 377 amino acid residues containing distinct characteristics of G-protein coupled receptors. Kiss2 and Kiss1r genes were expressed extensively in the brain, pituitary and gonads. The amounts of Kiss2 and Kiss1r mRNAs were significantly elevated during the spawning period in the brain and pituitary of both sexes. There were strong positive correlations between the amounts of Kiss2 and Kiss1r mRNAs in the brain and pituitary over the spawning season. Significant positive correlations were also observed between the amounts of Kiss2/Kiss1r mRNAs and GnRH1 mRNA in the brain. The present results indicate that the Kiss2/Kiss1r system most probably plays an important role in the regulation of reproductive function in the spawning period of grass puffer, possibly through the stimulation of GnRH1 secretion. Furthermore, Kiss2 may have a local action in the pituitary.