Abstract
The circadian rhythm is a biological rhythm that is closely related to the rhythmic expression of a series of clock genes. Results from several studies have indicated that clock genes are associated with the estrous cycle in female animals. Until now, the relationship between estrus cycle transition and clock gene expression in reproductive-axis-related tissues has remained unknown in Small-tailed Han (STH) sheep. This study was conducted to analyze the expression patterns of six canonical clock genes (Clock, BMAL1, Per1, Per2, Cry1, and Cry2) in the follicle phase and luteal phase of STH sheep. We found that all six genes were expressed in the brain, cerebellum, hypothalamus, pituitary, ovary, uterus, and oviduct in follicle and luteal phases. The results indicated that Clock expression was significantly higher in the cerebellum, hypothalamus, and uterus of the luteal phase than that of the follicle phase, whereas BMAL1 expression was significantly higher in the hypothalamus of the luteal phase than that of the follicle phase. Per1 expression was significantly higher in the brain, cerebellum, hypothalamus, and pituitary of the luteal phase than that of the follicle phase, and Per2 expression was significantly higher in the hypothalamus, pituitary, and uterus of the luteal phase than that of the follicle phase. Cry1 expression was significantly higher in the brain, cerebellum, and hypothalamus of the luteal phase than that of the follicle phase, whereas Cry2 expression was significantly higher in the pituitary of the luteal phase than that of the follicle phase. The clock gene expression in all tissues was different between follicle and luteal phases, but all clock gene mRNA levels were found to exhibit higher expression among seven tissues in the luteal phase. Our results suggest that estrous cycles may be associated with clock gene expression in the STH sheep. This is the first study to systematically analyze the expression patterns of clock genes of different estrous cycle in ewes, which could form a basis for further studies to develop the relationship between clock genes and the estrous cycle.
Highlights
Circadian rhythms are the nearly 24 h processes that allow an organism to coordinate appropriate physiological responses to the environmental light–dark changes associated with the rotation of the Earth (Goldstein and Smith, 2016)
Previous studies have shown that many aspects of the reproductive biology of males and females are regulated by the circadian rhythm (BrownGrant et al, 1977; Peterlin et al, 2019; Mills and Kuohung, 2019), including the estrus cycle, levels of luteinizing hormone (LH), ovulation, production and maturation of sperm, fertilization, insemination, and embryo implantation (Gray et al, 1978; Christian et al, 2005)
BMAL1 was expressed in seven tissues of the follicular and luteal phases in Small-tailed Han (STH) sheep, with the highest level being in the brain, followed by the hypothalamus, with a significant difference between the two tissues (P < 0.05)
Summary
Circadian rhythms are the nearly 24 h processes that allow an organism to coordinate appropriate physiological responses to the environmental light–dark changes associated with the rotation of the Earth (Goldstein and Smith, 2016). Previous studies have shown that many aspects of the reproductive biology of males and females are regulated by the circadian rhythm (BrownGrant et al, 1977; Peterlin et al, 2019; Mills and Kuohung, 2019), including the estrus cycle, levels of luteinizing hormone (LH), ovulation, production and maturation of sperm, fertilization, insemination, and embryo implantation (Gray et al, 1978; Christian et al, 2005). Studies in rodents have shown that ablation of the master circadian clock in the brain can block relevant clock output signals or disrupt the genes driving the circadian clock function at the cellular level, leading to pronounced deficits in ovulation and reproductive success (Gotlieb et al, 2020)
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