Abstract
Primordial follicle pool provides all available oocytes throughout the whole reproductive life span. Abnormal regulation in primordial follicle assembly leads to abnormal size of primordial follicle pool, even causes infertility. Here, miR-378-3p was proved to regulate mouse primordial follicle assembly both in vivo and in vitro. The expression of miR-378-3p significantly increased in mice ovaries from 17.5 dpc (days post coitum) up to 3 dpp (day post partum) compared with the expression of 16.5 dpc ovaries, which suggested that miR-378-3p was involved in primordial follicle assembly. To uncover the underlying mechanism, newborn mice ovaries were cultured in vitro in the presence of rapamycin and 3-methyladenine, which showed that the expression of miR-378-3p changed together with the percentage of primordial follicle. Moreover, during the normal process of primordial follicle assembly between 17.6 dpc and 3 dpp, autophagy is activated, while, apoptosis is inhibited. The in vivo results showed that newborn mice starved for 1.5 days showing the increased miR-378-3p, activated autophagy and inhibited apoptosis in the ovaries, had more percentage of primordial follicles. Over-expression of miR-378-3p using miR-378-3p agomir caused increased percentage of primordial follicle, increased level of autophagy, and decreased level of apoptosis. Knockdown of miR-378-3p by miR-378-3p antiagomir had the opposite results. Using pmirGLO Dual-Luciferase miRNA Target Expression system, we confirmed both PDK1 and Caspase9 were targets of miR-378-3p, which suggested that miR-378-3p activated autophagy by targeting PDK1 and inhibited apoptosis by targeting Caspase9. MiR-378-3p could be used as a biomarker of diseases caused by abnormal size of primordial follicle pool for diagnosis, prevention, or therapy.
Highlights
In mammals, the establishment of primordial follicle pool is an important process, which provides all available oocytes throughout the whole reproductive life span[1,2,3]
At 17.5 dpc germ cell cysts break down and primordial follicle assembly begin. miRNA qRT-PCR was performed to evaluate the expression of miR-378-3p during these processes
The results showed that the expression of miR-378-3p significantly increased in the ovaries from 17.5 dpc up to 3 dpp compared with that of 16.5 dpc (Fig. 1a), which suggested a role of miR-378-3p in germ cell cyst break down and primordial follicle assembly
Summary
The establishment of primordial follicle pool is an important process, which provides all available oocytes throughout the whole reproductive life span[1,2,3]. After migrating to the genital ridges, undergo mitosis with incomplete cytokinesis, closely associated clusters of syncytic germ cells are gathered to form germ cell cyst[4,5]. The abnormal primordial follicle assembly leads to diseases of female reproductive system even causes infertility[7]. During the process of germ cell cyst breakdown and primordial follicle assembly, approximately two-thirds of germ cells undergo loss before or shortly after birth in mice[8,9]. Most previous studies reported that programmed cell death named cell apoptosis accounted for the germ cell loss during this process[8,10,11].
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