Zhang Xuan, Ma Chunqi, Miller Ann L, Katbi Hadia Arabi, Bement William M, Liu X Johné
Ottawa Health Research Institute, Ottawa Hospital, 725 Parkdale Avenue, Ottawa, ON K1Y 4E9, Canada.
Department of Zoology, University of Wisconsin-Madison, 1117 West Johnson Street, Madison, WI 53706, USA.
Dev Cell. 2008 Sep;15(3):386-400. doi: 10.1016/j.devcel.2008.07.005.
Vertebrate oocyte maturation is an extreme form of asymmetric cell division, producing a mature egg alongside a diminutive polar body. Critical to this process is the attachment of one spindle pole to the oocyte cortex prior to anaphase. We report here that asymmetric spindle pole attachment and anaphase initiation are required for localized cortical activation of Cdc42, which in turn defines the surface of the impending polar body. The Cdc42 activity zone overlaps with dynamic F-actin and is circumscribed by a RhoA-based actomyosin contractile ring. During cytokinesis, constriction of the RhoA contractile ring is accompanied by Cdc42-mediated membrane outpocketing such that one spindle pole and one set of chromosomes are pulled into the Cdc42 enclosure. Unexpectedly, the guanine nucleotide exchange factor Ect2, which is necessary for contractile ring formation, does not colocalize with active RhoA. Polar body emission thus requires a classical RhoA contractile ring and Cdc42-mediated membrane protrusion.
脊椎动物卵母细胞成熟是不对称细胞分裂的一种极端形式，会产生一个成熟卵子以及一个微小的极体。对这一过程至关重要的是在后期之前一个纺锤体极附着到卵母细胞皮质上。我们在此报告，不对称纺锤体极附着和后期起始对于Cdc42的局部皮质激活是必需的，而Cdc42反过来又界定了即将形成的极体的表面。Cdc42活性区与动态F-肌动蛋白重叠，并由基于RhoA的肌动球蛋白收缩环所限定。在胞质分裂期间，RhoA收缩环的收缩伴随着Cdc42介导的膜外突，从而使一个纺锤体极和一组染色体被拉进Cdc42包被中。出乎意料的是，对于收缩环形成所必需的鸟嘌呤核苷酸交换因子Ect2并不与活性RhoA共定位。因此，极体排出需要经典的RhoA收缩环和Cdc42介导的膜突出。
