The elevated clock genes involved in regulating the hormone secretion and follicular development during the laying period of geese.

The reproductive performance of geese is regulated by the hypothalamic-pituitary-ovarian (HPO) axis, which controls ovarian follicular development and hormone secretion, and ultimately determines egg production. In this study, Wanxi White geese at three reproductive stages (pre-laying, laying, and broody periods) were used to investigate the regulatory roles of circadian clock genes in follicular development. Results showed that follicular growth, serum levels of estradiol (E2), melatonin (MLT), and progesterone (P4) markedly increased during the laying period, whereas a higher number of atretic follicles was observed during the broody period. Correspondingly, expression of steroidogenesis-related genes (CYP11A1, CYP19A1, DHCR24, 3β-HSD and StAR) and melatonin synthesis-related gene (ASMT-1) was upregulated in the laying periods compared with pre-laying and broody periods. Moreover, expression of clock genes (CLOCK, PER2, CRY1, CRY2, ARNTL2A, EYA3 and NPAS2) was significantly higher in the hypothalamus during the laying period than that in the broody period. Notably, CLOCK, PER2, CRY1, CRY2 and DIO2 exhibited similar expression patterns in the hypothalamus and ovary across the three reproductive stages, suggesting that circadian clock genes may contribute to the coordination of hypothalamic and ovarian functions. In addition, genes involved in lipid metabolism and yolk precursor synthesis were markedly upregulated in both the liver and ovary during the laying period. Overall, the elevated expression of clock genes could play an important role in follicular development, hormone secretion, and the coordinating of hepatic lipid transport and yolk precursor formation, providing a theoretical basis for improving egg production and breeding strategies in Wanxi White geese.