The mRNA expression patterns of kisspeptins, GnRHs, and gonadotropins in the brain and pituitary gland of a tropical damselfish, Chrysiptera cyanea, during the reproductive cycle
The sapphire devil (Chrysiptera cyanea) is a tropical damselfish that undergoes active reproduction under long-day conditions. To elucidate the physiological regulation of the brain–pituitary–gonadal axis in female sapphire devil, we cloned and characterized the genes of two kisspeptins (kiss1 and kiss2), three gonadotropin-releasing hormones (gnrh1, gnrh2, gnrh3), and the β-subunit of two gonadotropins (fshβ and lhβ) and investigated the gene expression changes during ovarian development. Quantitative polymerase chain reaction analyses in various brain parts revealed high expression levels of kiss1, kiss2, and gnrh2 in the diencephalon; gnrh2 and gnrh3 in the telencephalon; and fshβ and lhβ in the pituitary. In situ hybridization (ISH) analyses revealed positive signals of kiss1 in the dorsal and ventral habenular nucleus and of kiss2 in the dorsal and ventral parts of the nucleus of the lateral recess. This analysis showed gnrh1 expression in the preoptic area (POA), suggesting that GnRH1 plays a stimulating role in the secretion of gonadotropins from the pituitary of the sapphire devil. High transcription levels of kiss1, kiss2, gnrh1, gnrh2, fshβ, and lhβ were observed in the brain during the late vitellogenic stage, suggesting their involvement in the physiological processes of vitellogenesis. Immersion of fish in estradiol-17β (E2)-containing seawater resulted in increased expression of kiss2 and gnrh1 in their brains. This study showed that kiss-expressing neurons in the diencephalon are influenced by E2, leading to upregulation of gnrh1 in the POA and of fshβ and lhβ in the pituitary during vitellogenesis.
KeywordsCoral reef Damselfish Gonadotropin-releasing hormone In situ hybridization Kisspeptin Real-time PCR Estradiol Vitellogenesis
We gratefully thank to staff of Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus, Okinawa, Japan, for use of facilities. This study was supported in part by a Grant-in-Aid for Scientific Research (B) (KAKENHI, Grant number 16H05796) from the Japan Society for the Promotion of Science (JSPS) to AT and Heiwa Nakajima Foundation to AT.
Compliance with ethical standards
All experiments were conducted in compliance with the guidelines of the Animal Care and Use Committee of the University of the Ryukyus and the regulations for the care and use of laboratory animals in Japan (#25-2014).
Conflict of interest
The authors declare that they have no conflict of interest.
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