The Functional Role Of Mitochondria In Regulation Of Primordial Follicle Assembly

Primordial follicle assembly determines the lifetime supply of primordial follicles in the ovaries. In mammals, primordial follicle is formed by the enclosure of an individual oocyte with a single layer of granulosa cells in perinatal ovaries(Hirshfield, 1991). Despite of having been studied for many years, little knowledge was obtained about the regulation of primordial follicle assembly. Here, combining a screen of candidates identified through a mass spectrometry-based comparative proteomics analysis between mouse ovaries with and without primordial follicles, and large-scale RNAi knockdown in cultured mouse ovaries, Twenty-nine proteins were found regulating primordial follicle assembly. Surprisingly, we find that eight proteins (out of 29) are relevant to mitochondria. Also we find more abnormal mitochondria in oocytes and higher apoptosis of oocytes after knockdown of these mitochondrial proteins by RNAi knockdown in cultured mouse ovaries, leading to reduction of oocytes and primordial follicles. Moreover, we find SOD1G93A mutant mice show higher rate of abnormal mitochondria and oocytes apoptosis. These results show that a tightly regulated relationship between mitochondria and primordial follicle assembly. Additionally, we find oocytes in cyst during developmental process which contains more immature mitochondria and more cytochrome c than those in primordial follicles, suggesting mitochondria modulate oocyte loss during primordial follicle assembly through regulating oocyte apoptosis. In conclusion, this work is the first ever effort to evaluate the process of primordial follicle formation and to find that mitochondrial involvement in the primordial follicles assembly via regulation of oocyte apoptosis.