Expression of the kisspeptin/gonadotropin-releasing hormone (GnRH) system in the brain of female Chinese sucker (Myxocyprinus asiaticus) at the onset of puberty

The kisspeptin-kisspeptin receptor (kissr)-gonadotropin-releasing hormone (GnRH) system plays a key role in regulating the onset of puberty in mammals. However, the role of this system in fish is still unclear. We examined the relative gene expression patterns for kiss1, kiss2, kissr2, sGnRH, and pjGnRH in all parts of the brains of Chinese sucker (Myxocyprinus asiaticus) females at the prepubertal and pubertal stages by using real-time PCR. We also analyzed the expression of kiss1 and GnRH1 via immunofluorescence. Two variants of kisspeptin; a variant of kissr (kissr2); and two variants of GnRH, pjGnRH (GnRH1), and sGnRH (GnRH3), were expressed in all parts of the brain. The mRNA expression of kiss1 was higher in the telencephalon, mesencephalon, and diencephalon at the pubertal stage than at the prepubertal stage, and the expression of kiss2 was higher in only the telencephalon. The expression of kissr2 was higher in all parts of the brain, except the medulla, at the pubertal stage than at the prepubertal stage. pjGnRH was highly expressed in all parts of the brain at the pubertal stage, whereas sGnRH expression showed no distinct changes, except in the epencephalon. Strong kiss1 and weak GnRH-1 immunoreactivity was observed in the pineal gland, lateral tuberal nucleus (NLT), and ventral part of the NLT in the diencephalon of the Chinese sucker females at the pubertal stage. Our results suggest that the kiss1-kissr2-pjGnRH system was expressed highly at the onset of pubertal female Chinese sucker.