Polarized Cdc42 activation promotes polar body protrusion and asymmetric division in mouse oocytes

► Cdc42-GTP is polarized in the cortex overlying the spindle in mouse oocytes. ► Cdc42 activation is triggered by the Ran-GTP gradient emanating from chromatin. ► Polarized Cdc42-GTP recruits N-WASP to build F-actin-rich cortical protrusions. ► The Ran/Cdc42/N-WASP cascade is essential to second polar body protrusion. ► Cdc42 inhibition also induces central spindle defects in activated oocytes