Actin cytoskeleton dynamics in mammalian oocyte meiosis

During mitosis, cells undergo symmetrical cell division, while oocyte meiotic maturation undergoes two consecutive, asymmetric divisions that generate a totipotent haploid oocyte and two small polar bodies not involved in DNA replication. This specialized division allows most maternal components to be maintained in the oocytes for early embryo development. Nuclear positioning, germinal vesicle breakdown, spindle migration, spindle rotation, chromosome segregation, and polar body extrusion are the most critical cellular processes during oocyte meiosis I and II, and a growing number of studies primarily using the mouse oocyte model revealed that actin filaments were critical for these processes, especially for spindle migration. Several important molecules have been reported to be involved in these processes. One family of molecules are the small GTPases, such as Rho GTPases, Ran GTPases, and Rab GTPases and another are the actin nucleators, such as the formin family and the Arp2/3 complex. The present review summarizes recent progress made regarding the roles of actin filaments in the asymmetric oocyte division. Actin filaments widely involve into multiple cellular processes such as nuclear positioning, germinal vesicle breakdown, spindle migration, chromosome segregation, spindle rotation and polar body extrusion in oocyte mammalian meiosis.