Meiosis and oogenesis

How does the follicle coordinate meiosis progression? The ovarian follicle is an integrated system in which follicular cells regulate oocyte progression into meiosis. Oocytes are large cells that divide asymmetrically to preserve stores for future embryonic development. To do this, they must coordinate asymmetric spindle positioning with cell cycle progression and chromosome segregation. In mammals, the luteinizing hormone signaling induces a drop in cyclic guanosine monophosphate (cGMP) levels in the granulosa cells surrounding the oocyte. As discussed by Laurinda Jaffe, this drop in cGMP is due to a decrease in guanylyl cyclase-B activity in these cells. As a consequence, the phosphodiesterase PDE3A activity is no longer inhibited in oocytes, leading to a drop in cAMP levels and thus triggering a drop in protein kinase A activity and subsequent activation of cyclin B/ cyclin-dependent kinase 1 (CDK1), a prerequisite for meiotic resumption. Takeo Kishimoto presented evidence that robust meiotic resumption in starfish oocytes not only requires cyclin B/ CDK1 activation but also depends on Greatwall kinase activity.