Fig. 6. Working hypothesis of the “dual GnRH model” in which two gonadotropins are regulated by two gonadotropin-releasing hormones, FSH-RH and LH-RH.

a The schematic of the present study identifies CCK as the hypothalamic FSH-RH, which stimulates the expression and release of FSH to induce folliculogenesis. After folliculogenesis is completed, GnRH (LH-RH)-induced LH induces final oocyte maturation followed by ovulation. b Illustration of the phylogenetic relationships indicating a transition of the models occurring during vertebrate evolution. We propose a “dual GnRH model” group in vertebrates, in addition to the canonical solo GnRH model group.