Abstract
The alternation of light and dark rhythm causes a series of physiological, biochemical and metabolic changes in animals, which also alters the growth and development of animals, and feeding, migration, reproduction and other behavioral activities. In recent years, many studies have reported the effects of long-term (more than 6 weeks) illumination on ovarian growth and development. In the present study, we observed the damage, repair and apoptosis of ovarian DNA in a short period of illumination. The results showed that, in short time (less than 2 weeks) illumination conditions, the 24-h light treatment caused the reduction of total ovarian follicle number and down-regulation of circadian clock related genes. Furthermore, the changed levels of serum sex hormones were also detected after 24-h light exposure, of which the concentrations of LH (luteinizing hormone), FSH (follicle-stimulating hormone) and E2 (estradiol) were increased, but the concentration of PROG (progesterone) was decreased. Moreover, 24-h light exposure increased the expression of DNA damage and repair related genes, the number of TUNEL and RAD51 positive cells. These results indicated that 24-h light exposure for 4, 8 and 12 days increased DNA damage and cell apoptosis, thereby affecting the development of ovary.
Highlights
It is well known that photoperiod affects the physiological behavior of animal by adjusting the daily and seasonal changes, and the animals develop specific adaptive periodic activities through rhythm oscillation [1,2,3,4]
The results showed that, compared with that in control group, 24-h light exposure significantly increased the levels of follicle-stimulating hormone (FSH) (Figure 2A), luteinizing hormone (LH) (Figure 2B) after 4- and 8-day treatment, and the level of E2 (Figure 2C) after 12-day treatment, significantly decreased PROG concentration (Figure 2D) after 8- and 12-day treatment
The reproductive cycle is related to the seasonal variation of the photoperiod [56,57,58], and the prolongation of the artificial photoperiod can affect ovarian development, which is based on the reflect of circadian rhythm to light [8,59,60]
Summary
It is well known that photoperiod affects the physiological behavior of animal by adjusting the daily and seasonal changes, and the animals develop specific adaptive periodic activities through rhythm oscillation [1,2,3,4]. Several biological clock genes important for the circadian rhythms have been identified, such as period genes (Per, Per2), cryptochrome genes (Cry, Cry2) and RAR-related orphan receptors genes (Rorα, Rorβ, Rorγ) [7,8,9]. Many previous studies have reported that compared with normal light cycle, both increasing the light and decreasing the light exposure can affect ovarian follicular development [41,42,43,44] These investigations suggest that photoperiod and other related signaling pathways affect the development of reproductive system, the secretion of sex hormones. The purpose of this investigation was to explore the effects of short period of illumination on DNA damage/repairment, and apoptosis in the mouse ovary
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