The Functions And The Related Mechanisms Of MiR-7a2 In The Reproductive System Of Female Mouse

It is known that microRNAs involve in regulating the cellular functions and pathophysiologic processes by inhibiting translation or promoting mRNA degradation at the post-transcriptional level.microRNA-7(miR-7)is an evolutionally conserved microRNA.It has been reported that mouse miR-7 includes three subtypes:miR-7al,miR-7a2 and miR-7b,which are involved in multiple physiological functions,such as insulin synthesis.However,the specific functions of miR-7 in reproductive system are still unclear.The purposes of this study were to explore the functions of miR-7 in the reproductive system of female mice by using miR-7 knockout mouse model established in our laboratory.The main results of this study include the following items:1.The In Situ Hybridization was used to detect the expression of miR-7 in the mouse ovary.The results show that all the granulosa cells express miR-7,suggesting that miR-7 plays important roles in the reproductive functions of mice.2.The results of fertility tests show that miR-7al or miR-7b knockout had no significant effect on female mice fecundity,while miR-7a2 knockout resulted in the infertility of female mice with no obvious estrous cycle and low plugging rate.3.The results of the ovary histology examination at different developmental stages show that miR-7a2 deletion did not lead to the obvious defects in the ovaries of prepubertal female mice.However,the large antral follicles and corpus luteums were not observed in adult miR-7a2 knockout mouse ovaries,although the numbers of primordial and atretic follicles significantly increased.Moreover,the apoptosis of follicle granulosa cells increased significantly.These results indicate that miR-7a2 knockout affects the follicle development in mouse ovary.4.The levels of gonadotrophins were assayed,and the results show that miR-7a2 knockout remarkably decreased the expressions of the pituitary follicle-stimulating hormone(FSH)and luteinizing hormone(LH).In addition,sharply decreased serum FSH and LH levels were also detected by using ELISA,although the miR-7a2 knockout did not have significant effect on the expressions of the LH and FSH receptors in the ovary.Further,we did the superovulation test and results show that the ovulation could be resumed in the miR-7a2 knockout female mice,and the oocytes obtained were similar to that of wild type in the oocyte number and morphology.These indicates that the reductions of gonadotropin synthesis and secretion resulted from miR-7a2 knockout were the main cause of abnormal ovarian development in female mice.5.The results of the uterine histology examination show that after miR-7 a2 knockout,the uterine endometriums got thinner,and fewer curled luminal epitheliums were observed,although the uterine morphogenesis in prepubertal miR-7a2 knockout mice seemed to be normal.In addition,immunofluorescence labeled proliferative or glandular cells show that miR-7a2 knockout did not affect the uterine cell proliferation and gland formation in prepubertal mice,but miR-7a2 is required in adult mice for the uterine cell proliferation and gland formations.These results indicate that deficiency of miR-7a2 could lead to defects in adult mouse uterus.6.The implantation of estrogen sustained-release tablets to the 3-week old miR-7a2 knockout female mice enhanced the proliferation of uterine epithelia,and the number of uterine glands significantly increased.These suggest that lack of estrogen is the primary cause of abnormal uterine development in adult miR-7a2 knockout mice.In conclusion,miR-7a2 is involved in the process of folliculogenesis and ovulation in female mice by influencing the synthesis and secretion of FSH and LH.And miR-7a2 is necessary for the acquirement and maintenance of female fertility.Meanwhile,miR-7a2 has no obvious effect in the prepubertal uterine development in mice.