Shintomi Keishi, Hirano Tatsuya
Chromosome Dynamics Laboratory, RIKEN Advanced Science Institute, Wako, Saitama 351-0198, Japan.
Genes Dev. 2009 Sep 15;23(18):2224-36. doi: 10.1101/gad.1844309. Epub 2009 Aug 20.
The cohesin complex establishes sister chromatid cohesion during S phase. In metazoan cells, most if not all cohesin dissociates from chromatin during mitotic prophase, leading to the formation of metaphase chromosomes with two cytologically discernible chromatids. This process, known as sister chromatid resolution, is believed to be a prerequisite for synchronous separation of sister chromatids in subsequent anaphase. To dissect this process at a mechanistic level, we set up an in vitro system. Sister chromatid resolution is severely impaired upon depletion of Wapl from Xenopus egg extracts. Exogenously added human Wapl can rescue these defects and, remarkably, it can do so in a very short time window of early mitosis. A similar set of observations is made for Pds5, a factor implicated previously in the stabilization of interphase cohesion. Characteristic amino acid motifs (the FGF motifs) in Wapl coordinate its physical and functional interactions with Pds5 and cohesin subunits. We propose that Wapl and Pds5 directly modulate conformational changes of cohesin to make it competent for dissociation from chromatin during prophase. Evidence is also presented that Sgo1 plays a hitherto underappreciated role in stabilizing cohesin along chromosome arms, which is antagonized by the mitotic kinases polo-like kinsase (Plk1) and aurora B.
黏连蛋白复合体在S期建立姐妹染色单体黏连。在多细胞动物细胞中，大多数（如果不是全部的话）黏连蛋白在有丝分裂前期从染色质上解离，导致形成具有两条在细胞学上可分辨染色单体的中期染色体。这个过程，称为姐妹染色单体分离，被认为是后续后期姐妹染色单体同步分离的先决条件。为了在机制层面剖析这个过程，我们建立了一个体外系统。从非洲爪蟾卵提取物中去除Wapl后，姐妹染色单体分离严重受损。外源添加的人Wapl可以挽救这些缺陷，而且，值得注意的是，它可以在有丝分裂早期的非常短的时间窗口内做到这一点。对于Pds5也有类似的观察结果，Pds5是先前与间期黏连稳定有关的一个因子。Wapl中的特征性氨基酸基序（FGF基序）协调其与Pds5和黏连蛋白亚基的物理和功能相互作用。我们提出，Wapl和Pds5直接调节黏连蛋白的构象变化，使其在前期能够从染色质上解离。也有证据表明，Sgo1在稳定沿染色体臂的黏连蛋白方面发挥了迄今未被充分认识的作用，而有丝分裂激酶波罗样激酶（Plk1）和极光B对其具有拮抗作用。
