Transcriptomic insights into photoperiodic regulation of goose reproduction: galanin emerges as a potential player.

[OBJECTIVE]: To characterize hypothalamic mRNA profiles under different photoperiods and identify key reproductive regulators based on the "ultralong-short-long" artificial photoperiodic reproduction model of practical production. [METHODS]: The triphasic photoperiodic regimens consisted of ultralong (L:D = 20 h:4 h), short (L:D = 6.5 h:17.5 h), and long (L:D = 12 h:12 h) photoperiods. At each phase of photoperiod (UP, SP and LP) treatment, three geese per group (n = 3) were selected for collection of blood, ovarian, and hypothalamic tissues. Hypothalamic samples subsequently processed for RNA-seq analysis. [RESULTS]: Ovarian volume and weight were significantly lower in UP and SP groups than in LP group, with ovaries remaining quiescent and containing only white follicles in UP and SP groups, whereas the LP group exhibited distinct hierarchical follicular development. Trend analysis was performed on total DEGs from both UP-vs-SP and SP-vs-LP comparisons, followed by KEGG enrichment analysis of the union set of genes exhibiting either positive-V or inverted-V expression patterns. Subsequently, we found that neuroactive ligand-receptor interaction pathway was highly responsive to photoperiodic changes, in which Galanin (GAL) neuropeptide was significantly altered, implying a possible involvement of GAL in photoperiod-mediated reproduction. [CONCLUSION]: This study expands the theory of central regulation of photoperiod-mediated avian reproductive activities, speculates on the possible important role of GAL neuropeptides, and provides new insights for optimizing lighting regimens in poultry production.