Kisspeptin stimulates oocyte maturation, and food deprivation modulates the abundance of kisspeptin system in zebrafish gonads

Abstract

Kisspeptin is a hormone involved in the neuroendocrine control of reproduction in fish. We hypothesized that kisspeptin stimulates oocyte maturation and modulates other reproductive hormones in zebrafish; and the gonadal kisspeptin system in zebrafish is affected during energy unavailability. The main goals of this research were to test in vitro effects of kisspeptin on oocyte maturation and mRNA abundance in zebrafish ovarian follicles and determine how short-term feed restriction affects kisspeptin and its receptors in zebrafish testis and ovary. This study demonstrates the presence of kisspeptin and its receptors in zebrafish (Danio rerio) gonads and its direct action on ovarian follicles in vitro. Kisspeptin (10 ng/mL) induced oocyte maturation, as indicated by germinal vesicle break down at 18- and 24- hours post-treatment. Kisspeptin significantly increased the abundance of mRNAs encoding reproductive hormones and its receptors in zebrafish oocytes. This suggests that kisspeptin-10 affects ovarian functions by modulating other hormones. Reproduction is a process that requires energy. Therefore, whether energy availability affects the kisspeptin system in zebrafish gonads was determined. Food deprivation modulated kisspeptin expression differently in zebrafish testis and ovary. Kiss2 and kiss1ra were upregulated while kiss1rb was downregulated in the testis post-food deprivation. Meanwhile, no changes in kiss in the ovary were found after food deprivation. However, kiss1rb was downregulated in unfed fish at 3- and 7-days post-food deprivation. Overall, our results suggest sex- and tissue-specific changes in the gonadal abundance of the kisspeptin system in zebrafish. The fine tuning of reproduction during energy fluctuations in fish is likely mediated via changes in hormones, including kisspeptin as shown in this research.