The roles of kisspeptin in the mechanism underlying reproductive functions in mammals.

Kisspeptin, identified as a natural ligand of GPR54 in 2001, is now considered as a master regulator of puberty and subsequent reproductive functions in mammals. Our previous studies using Kissl knockout (KO) rats clearly demonstrated the indispensable role of kisspeptin in gonadotropin-releasing hormone (GnRH)/gonadotropin secretion. In addition, behavioral analyses of Kiss/ KO rats revealed an organizational effect of kisspeptin on neural circuits controlling sexual behaviors. Our studies using transgenic mice carrying a region-specific Kissl enhancer-driven reporter gene provided a clue as to the mechanism by which estrogen regulates Kissl expression in hypothalamic kisspeptin neurons. Analyses of Kissl expression and gonadotropin secretion during the pubertal transition shed light on the mechanism triggering GnRH/gonadotropin secretion at the onset of puberty in rats. Here, we summarize data obtained from the aforementioned studies and revisit the physiological roles of kisspeptin in the mechanism underlying reproductive functions in mammals.