In recent years, brain kisspeptin system has been shown to be involved in diverse reproductive function, including sexual differentiation in vertebrates. Our previous reports demonstrated that the chub mackerel (Scomber japonicus) brain expresses two kisspeptin (kiss1, kiss2), two kisspeptin receptor (kissr1, kissr2) and three gonadotropin-releasing hormone (gnrh1, gnrh2, gnrh3) genes. In the present study, using quantitative real-time PCR (qRT-PCR) assays, we analysed expression changes of these genes during early development (0-30 dphs) and gonadal sex differentiation periods (37-60 dphs). Absolute expression level of kiss-kissr-gnrh in the whole head was higher between 0 and 15 dphs, in comparison to later developmental periods. Histological analyses revealed presence of sexually differentiated males and females with testicular and ovarian features at 37, 45, and 60 dphs. In both males and females, kiss2, kissr1, and kissr2 levels were higher at 37 dph, in comparison to 45 and 60 dphs, with kiss1 showing no significant differences. Levels of all three gnrh mRNAs were higher at 45 dph, in comparison to 60 dph. Changes in the expression level of kiss-kissr-gnrh mRNAs in different brain regions of sexually differentiated males and females indicated differences in their regional distribution. These results suggest possible involvement of Kiss-KissR-GnRH systems during early development and gonadal sex differentiation in the chub mackerel.
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