Studies have shown that clock gene Cry1 may have important roles in the endocrine process of seasonal reproduction in mammals. In this study, Duolang sheep (non-seasonal reproduction sheep breed) and Chinese Merino (seasonal reproduction sheep breed) were used to determine the expression change of Cry1 in hypothala-mus-pituitary-ovary axis in different stage of estrous cycle by quantitative real-time PCR. The results showed that the Cry1 mRNA was expressed in all tested tissues, in which the expression levels in pineal gland and thyroid gland were higher than in other tissues. As far as different sheep breeds were concerned, the tissue expression profiles of Cry1 at different stage of estrous cycle were broadly similar. Besides hypothalamus, the expression levels of Cry1 in ovary, uterus, pineal gland, pituitary gland, and thyroid gland were all reached to peak in proestrus. The differences of expression change extent for Cry1 in vary, uterus, pineal gland, and pituitary gland in proestrus and oestrus were significant between different sheep breeds. The results suggested that Cry1 may play roles in switching on the estrus and seasonal reproduction.
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