Cytoskeletal correlates of oocyte meiotic divisions

Abstract

Meiosis in oocytes is demanding, requiring chromosomes to be evenly segregated between daughter cells while the cytoplasm should be unequally shared to benefit the oocyte. Indeed, oocytes are extremely large cells compared to most somatic cells and divide twice asymmetrically, giving rise to tiny abortive daughter cells, at least in species that do not reproduce by parthenogenesis. The asymmetry of oocyte meiotic divisions allows preservation of maternal mRNAs, proteins, and nutrients in the cytoplasm, accumulated during the growth phase of oogenesis. In mammals, this asymmetry supports early embryonic development before implantation of the blastocyst in the female reproductive tract. We will review in this chapter how mouse oocytes have resolved the difficult task of dividing asymmetrically at the level of the cell’s cytoskeleton. First, chromosome alignment and subsequent segregation happens without centrosome-mediated spindle assembly; second, the positioning modules employed to ensure strong asymmetry based on the actin cytoskeleton.