Figure 1.

The regulation of mitochondrial DNA (mtDNA) copy number and mitochondria distribution during oocyte maturation. In primordial germ cells, the amount of mtDNA is very low. As oogenesis progresses, mtDNA copies increase significantly and then reach their maximum at the MII stage. There are two main points at which mtDNA copies go up very quickly: the first one is during the transition from the primordial to the primary follicle stage, and the second one is during the transition from GV to MII oocytes at the late antral follicle stage. In parallel as oogenesis progresses, ATP level also increases significantly as oocyte maturation requires a large amount of ATP for the subsequent transcription and translation. During the transition from GV to MII oocytes at the late antral follicle stage, the distribution of mitochondria changes significantly. They migrate from the center of the ooplasm to the pericortical region, distributing evenly through the whole ooplasm.