Characterization of kiss2/kissr2 system in largemouth bass (Micropterus salmoides) and Kiss2-10 peptide regulation of the hypothalamic-pituitary-gonadal axis

The kisspeptin system, which lies upstream of the hypothalamic-pituitary-gonadal (HPG) axis, is believed to function as a regulator of reproduction in teleosts. In this study, we isolated and characterized kiss2 and its receptor kissr2 in largemouth bass (Micropterus salmoides). The complete coding sequences of kiss2 and kissr2 were 375 and 1134 bp long and encoded precursor proteins 124 and 377 amino acid long, respectively. Real-time PCR showed that kiss2 and kissr2 were primarily expressed in the HPG axis. The expression profile of kiss2 and kissr2 varied with gonadal development, with the highest and lowest expression levels being detected during the immature and final maturation stages, respectively. Intraperitoneal injection of exogenous Kiss2-10 peptide increased the transcript levels of gnrh3, kissr2, fsh beta, lh beta, ar, and er2 within 24 h (p < 0.05), as well as plasma levels of 17 beta-estradiol and testosterone. Histological analysis indicated that chronic administration of exogenous Kiss2-10 peptide accelerated vitellogenesis in females and spermatogenesis in males. Further, in situ hybridization revealed that kiss2 is expressed in the ooplasm and vitelline envelope of oocytes and the spermatocytes of testes. In addition, experiments using gonad tissue primary cell cultures indicated that exogenous Kiss2-10 peptide stimulates the expression of reproduction-related genes. Collectively, our findings indicate that the kiss2/kissr2 system in largemouth bass is involved in regulating gonadal development through the HPG axis.