Cloning and expression of GnRH2 gene in spotted sea bass ( Lateolabrax maculatus ) under different photoperiods

Gonadotropin-releasing hormone ( GnRH ) is a pivotal neuropeptide in the regulation of vertebrate reproduction, orchestrating the release of gonadotropins from the pituitary gland. This study focuses on the subtype GnRH2 and its regulatory response to different photoperiods, a known environmental cue affecting reproductive cycles in spotted sea bass ( Lateolabrax maculatus ). In the present study, we successfully isolated and cloned a subtype of GnRH ( GnRH2 ) from L. maculatus . Bioinformatics analysis indicated that LmGnRH2 gene is highly conserved evolutionarily. The expression of LmGnRH2 mRNA was found to be widespread across various tissues, with higher expression levels in the hypothalamus, pituitary, saccus vasculosus (SV), and gonads. The expression level of LmGnRH2 was correlated with the stages of gonadal development. An ascending trend in the expression of LmGnRH2 was observed in the hypothalamus, pituitary, SV and gonads from the stages I to V, peaking during the period of highest reproductive activity (stage V). Photoperiodic experiments in vivo have demonstrated that the expression levels of LmGnRH2 were augmented in response to short -day conditions (8 h of light, 16 h of darkness, 8L:16D) within the hypothalamus, pituitary, SV and gonads, compared to control photoperiod (12L:12D). In addition, photoperiod of 16L:8D also showed elevated LmGnRH2 expression in the hypothalamus, SV and gonads. Notably, the expression of LmGnRH2 was notably higher in the pituitary and gonads compared to extended photoperiod treatments under shortened photoperiod conditions. The regulatory effects on LmGnRH2 expression under varying photoperiods has also been observed in the hypothalamus, pituitary, and SV in vitro. These findings suggest that reduced light exposure can upregulate the expression of LmGnRH2 , which may in turn positively influence the gonadal development in L. maculatus . These results provide a foundation for further investigation into the mechanisms underlying the photoperiodic regulation in L. maculatus .