Photoperiod regulate gonad development via kisspeptin/kissr in hypothalamus and saccus vasculosus of Atlantic salmon (Salmo salar)

Liang Chi,Qinghua Liu,Ying Liu,Xian Li,Andrew Wolfe

doi:10.1371/journal.pone.0169569

Liang Chi, Qinghua Liu + Show 3 more

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https://doi.org/10.1371/journal.pone.0169569

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Abstract

Atlantic salmon exhibit seasonal reproduction. However, the mechanisms governing this are still unclear. Generally speaking, kisspeptin has been recognized as a regulator of reproduction. Here, we report a relationship between kisspeptin, GnRH and photoperiod in Atlantic salmon. The results demonstrated that the expression of the Atlantic salmon kisspeptin-receptor (skissr) was not always consistent with the expression pattern of Atlantic salmon GnRH3 (sGnRH3) during all developmental processes. Kisspeptin may exert its influence primarily in the early and later stages of gonad development by promoting the secretion of sGnRH3. Meanwhile, the expression levels of kissr were higher in fish with gonads at stage II and stage V under the long-day photoperiod regime than under the short-day regime. In addition, both skissr and sGnRH3 were also expressed in the saccus vasculosus (SV), an organ only found in fish. The SV might be a seasonal sensor regulating reproduction in addition to the hypothalamus (Hyp).

Highlights

Seasonal reproduction is an important adaptive trait for animals living outside the tropics and photoperiod is undoubtedly one of the most effective environmental signals available to living organisms, including fish [1, 2]
The mRNA expressions of skissr and salmon GnRH3 (sGnRH3) were detected in the different regions of the Atlantic salmon brain using qPCR (Quantitative real-time PCR) with β-actin mRNA as a reference gene
The results showed that the both sGnRH3 and skissr transcripts were primarily expressed in the diencephalon

Summary

Introduction

Seasonal reproduction is an important adaptive trait for animals living outside the tropics and photoperiod (day length) is undoubtedly one of the most effective environmental signals available to living organisms, including fish [1, 2]. Photoperiod is the only environmental factor which provides a reliable indicator of the time of year and so enables reproduction and growth processes to be expressed at the most appropriate date [3]. It is widely accepted that seasonally changing photoperiods provide the proximate environmental signal for the initiation and co-ordination of gonad development in most temperate fish [4]. The synchronization of reproduction with photoperiod is mediated by melatonin which is secreted by the pineal organ[5, 6]. Do not possess a distinct PT, and the signal transduction pathway for their reproduction remains unclear [12]

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