Photoperiodic Modulation of Circadian Clock and Reproductive Axis Gene Expression in the Pre-Pubertal European Sea Bass Brain

PLoS One. 2015 Dec 7;10(12):e0144158. doi: 10.1371/journal.pone.0144158. eCollection 2015.

Abstract

The acquisition of reproductive competence requires the activation of the brain-pituitary-gonad (BPG) axis, which in most vertebrates, including fishes, is initiated by changes in photoperiod. In the European sea bass long-term exposure to continuous light (LL) alters the rhythm of reproductive hormones, delays spermatogenesis and reduces the incidence of precocious males. In contrast, an early shift from long to short photoperiod (AP) accelerates spermatogenesis. However, how photoperiod affects key genes in the brain to trigger the onset of puberty is still largely unknown. Here, we investigated if the integration of the light stimulus by clock proteins is sufficient to activate key genes that trigger the BPG axis in the European sea bass. We found that the clock genes clock, npas2, bmal1 and the BPG genes gnrh, kiss and kissr share conserved transcription factor frameworks in their promoters, suggesting co-regulation. Other gene promoters of the BGP axis were also predicted to be co-regulated by the same frameworks. Co-regulation was confirmed through gene expression analysis of brains from males exposed to LL or AP photoperiod compared to natural conditions: LL fish had suppressed gnrh1, kiss2, galr1b and esr1, while AP fish had stimulated npas2, gnrh1, gnrh2, kiss2, kiss1rb and galr1b compared to NP. It is concluded that fish exposed to different photoperiods present significant expression differences in some clock and reproductive axis related genes well before the first detectable endocrine and morphological responses of the BPG axis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bass / metabolism*
  • Brain / metabolism*
  • Circadian Clocks / physiology*
  • Female
  • Fish Proteins / biosynthesis*
  • Gene Expression Regulation / physiology*
  • Male
  • Nerve Tissue Proteins / biosynthesis*
  • Photoperiod

Substances

  • Fish Proteins
  • Nerve Tissue Proteins

Grant support

The research leading to these results was funded by European Community's Seventh Framework Programme (FP7/ 2007- 2013) under grant agreement n° 222719 - LIFECYCLE and by the Foundation for Science and Technology of Portugal (FCT), through project PEst-C/MAR/LA0015/2011 and Prometeo II/2014/051 from the Valencian Regional Goverment and CSD 2007-0002 (AQUAGENOMICS) Spanish Ministry of Science and Innovation (MICINN). RSTM was funded by the Foundation for Science and Technology of Portugal (FCT) under fellowship (SFRH/BPD/66742/2009). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.