The mechanisms of MTOCs maturation in human and mouse oocytes.

The microtubule organizing centers (MTOCs) of human and mouse oocytes are essential for meiotic spindle assembly and for ensuring precise chromosome segregations. Previous studies mainly focus on investigating MTOCs changes in metaphase I oocyte. However, the detailed dynamic changes and underlying mechanisms of the MTOCs in germinal vesicle (GV) oocytes-a stage that early events of MTOC maturation happened- remain unclear. Here we explored the dynamics of MTOCs maturation in human and mouse GV oocytes and found that MTOCs maturation is a largely conserved process, consisting of two tightly coupled processes referred to as MTOCs activation and migration. We found that cytoskeleton associated protein 5 (CKAP5) and transforming acidic coiled-coil containing protein 3 (TACC3) play key roles in MTOCs maturation in oocytes. The activation of the MTOCs is a prerequisite for migration initiation, and the migration of the MTOCs is facilitated by dynein/dynactin in oocytes. The disruption of MTOC maturation resulted in spindle assembly failure. Importantly, impaired MTOCs maturation is associated with the physiological aging of oocytes. This study provides a comprehensive understanding of MTOCs dynamics in human and mouse oocytes.