| Kisspeptin (Kiss or Kp), a novel physiologically active peptide encoded by the KISS1/Kiss1 gene, activates its cognate receptor KissR (also known as GPR54) in various target tissues to exert disparate functions, including inhibition of tumor metastasis and control of reproductive function. The KISS1 gene was originally isolated from human melanoma and breast cancer cells, and kisspeptin was initially called metastin in consideration of its suppressive effects on tumor growth and metastasis. With the exception of the platypus, a mammalian monotreme, which has two forms of kisspeptin genes (Kiss1 and Kiss2), there is only one ligand, Kiss1, and its receptor, Kiss1R in placental mammals. However, this situation is different and even complex in non-mammalian species. Three kiss/kissr genes were described in amphibians, while searches in the chicken genome databases failed to identify these paralogous genes. To date, multiple forms of kiss/kissr genes have been identified in many teleosts, including Cypriniformes, Perciforms, Pleuronectiforms, Tetraodontiforms, Beloniforms, Scorpaeniformes, Salmoniformes and Gadiformes. A dual kisspeptin system, kiss1/kiss1r and kiss2/kiss2r, have been detected in medaka, zebrafish, goldfish, chub mackerel, striped bass, and European sea bass, while only kiss2/kiss2r was identified in orange-spotted grouper, grass puffer, Nile tilapia, Atlantic halibut, Senegalese sole, and half-smooth tongue sole. In addition, the physiological relevance and functions of the Kiss/KissR system for the neuroendocrine regulation of reproduction remains to be established in fish. It should be noted that the mechanisms underlying the actions of Kiss on the hypothalamo-pituitary-gonadal (HPG) axis are still far from being fully understood. Given the multiple forms of kiss and kissr genes obtained in teleosts, the regulation of fish reproduction by the Kiss system is even complex. This review briefly summarized the progress of research on Kiss and its receptors, with special emphasis on the physiological functions of Kiss in fish, the signaling transduction pathways as well as the regulation of kiss/kissr gene expression. We hope that this review will contribute to future studies. |
