Impaired leptin signaling causes subfertility in female zebrafish

Reproduction is an energetically costly event across vertebrates and tightly linked to nutritional status and en-ergy reserves. In mammals, the hormone leptin is considered as a link between energy homeostasis and repro-duction. However, its role in fish reproduction is still unclear. In this study, we investigated the possible role of leptin in the regulation of reproduction in zebrafish, using a loss of function leptin receptor (lepr) strain. Impaired leptin signaling resulted in severe reproductive deficiencies in female zebrafish. lepr mutant females laid significantly fewer eggs, with low fertilization rates compared to wild-type females. Folliculogenesis was not affected, but oocyte maturation and ovulation were disrupted in lepr mutants. Interestingly, the expression of luteinizing hormone beta (lhb) in the pituitary was significantly lower in mutant females. Analysis of candidate genes in the ovaries and isolated fully grown follicles revealed differential expression of genes involved in ste-roidogenesis, oocyte maturation and ovulation in the mutants, which are known to be regulated by LH signaling. Moreover, subfertility in lepr mutants could be partially restored by administration of human chorionic gonad-otropin. In conclusion, our results show that leptin deficiency does not affect early stages of follicular devel-opment, but leptin might be essential in later steps, such as in oocyte maturation and ovulation. To our knowledge, this is the first time that leptin is associated to reproductive deficiencies in zebrafish.

Automated summary

This study investigates the role of leptin in the regulation of reproduction in zebrafish. The results demonstrate that leptin is essential for oocyte maturation and ovulation in zebrafish, and deficiency of leptin leads to severe reproductive deficiencies in female zebrafish.