PAK1 regulates spindle microtubule organization during oocyte meiotic maturation

P21-activated kinase 1 (PAK1), an effector of Rho GTPase Rac 1 and Cdc42, is required for mitotic progression. However, its functions in meiosis are unclear. In the present study, we examined the expression, localization and function of PAK1 during mouse oocyte meiotic maturation and found that PAK1 was mainly associated with the meiotic spindle microtubules. Taxol treatment resulted in localization of PAK1 on spindle and aster microtubules, while nocodazole treatment induced the dispersion of PAK1 protein into the cytoplasm. Loss-of-function of PAK1 by both inhibitor treatment and morpholino oligonucleotide injection caused disorganized spindles, decreased polar body extrusion and misaligned chromosomes. In addition, inhibition of PAK1 resulted in abnormal localization of mitogen-activated protein kinase kinase (MEK). Taken together, our results suggest that PAK1 plays an important role in spindle assembly and chromosome alignment during mouse oocyte meiotic maturation.