Changes in goose hypothalamus under different photocycles: RNA-Seq reveals new pathways and molecules.

Reproduction in avian species is regulated by light, and the hypothalamus is the most important regulator of the response to light signals. The objective of this study was to identify the key molecules and signaling pathways in the hypothalamus that regulate reproduction in birds based on the photoperiod. Yangzhou geese kept in a closed goose barn were selected for transcriptome sequencing. The light program during rearing was as follows: a short photoperiod (light[L]: dark[D]=6.5 h:17.5 h) for 60 days, followed by a prolonged photoperiod (L:D = 11.5 h:12.5 h). Samples were collected on the 38th day of the short photoperiod (SP), the 20th (LPS), 73rd (LPP), and 135th (LPF) days of the long photoperiod. Hypothalamus were collected to screen for key avian reproduction-related genes and signaling pathways affected by the photoperiod using RNA sequencing (RNA-seq) analysis. In the SP group, the testis gradually enlarged and mature sperm were observed in the curved seminiferous tubules after a prolonged photoperiod. Meanwhile, the concentrations of testosterone (T), follicle-stimulating hormone (FSH) and luteinizing hormone (LH) increased in the blood. The RNA-seq results revealed that compared with the SP group, the LPS group showed 24 significantly upregulated genes, and 9 significantly downregulated genes. Compared with the LPS, the LPP group showed 7 significantly upregulated genes, and 27 significantly downregulated genes. Compared with the LPP group, the LPF group showed 7 significantly upregulated genes, and 5 significantly downregulated genes. Differentially expressed genes were mainly enriched in neuroactive ligand-receptor interaction, ovarian steroidogenesis, thyroid hormone synthesis, GnRH secretion, and GnRH signaling pathway, etc. Key genes, including GAL, GnRH, UCN3, CGA and CYP19A1, were identified. This study extends the theory of the central regulation of avian reproductive activity by light.