title: Photoperiodic Modulation of Circadian Clock and Reproductive Axis Gene Expression in the Pre-Pubertal European Sea Bass Brain.
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.
authors.affiliation: Comparative Endocrinology and Integrative Biology group, Centre of Marine Sciences (CCMAR), University of Algarve, Campus de Gambelas, Faro, Portugal.
authors.forename: Rute S T
authors.initials: RS
authors.lastname: Martins
authors.affiliation: Department of Fish Physiology and Biotechnology, Instituto de Acuicultura de Torre la Sal, Consejo Superior de Investigaciones Científicas (CSIC), Torre la Sal, Castellón, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Gomez
authors.affiliation: Department of Fish Physiology and Biotechnology, Instituto de Acuicultura de Torre la Sal, Consejo Superior de Investigaciones Científicas (CSIC), Torre la Sal, Castellón, Spain.
authors.forename: Silvia
authors.initials: S
authors.lastname: Zanuy
authors.affiliation: Department of Fish Physiology and Biotechnology, Instituto de Acuicultura de Torre la Sal, Consejo Superior de Investigaciones Científicas (CSIC), Torre la Sal, Castellón, Spain.
authors.forename: Manuel
authors.initials: M
authors.lastname: Carrillo
authors.affiliation: Comparative Endocrinology and Integrative Biology group, Centre of Marine Sciences (CCMAR), University of Algarve, Campus de Gambelas, Faro, Portugal.
authors.forename: Adelino V M
authors.initials: AV
authors.lastname: Canário
mesh_terms: D000818:Animals; D001492:Bass / Q000378:metabolism*; D001921:Brain / Q000378:metabolism*; D057906:Circadian Clocks / Q000502:physiology*; D005260:Female; D029941:Fish Proteins / Q000096:biosynthesis*; D005786:Gene Expression Regulation / Q000502:physiology*; D008297:Male; D009419:Nerve Tissue Proteins / Q000096:biosynthesis*; D017440:Photoperiod
chemical_list: D029941:Fish Proteins; D009419:Nerve Tissue Proteins