Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
J Cell Biol. 2011 Jun 27;193(7):1167-80. doi: 10.1083/jcb.201103138.
Sister chromatid cohesion provides the mechanistic basis, together with spindle microtubules, for generating tension between bioriented chromosomes in metaphase. Pericentric chromatin forms an intramolecular loop that protrudes bidirectionally from the sister chromatid axis. The centromere lies on the surface of the chromosome at the apex of each loop. The cohesin and condensin structural maintenance of chromosomes (SMC) protein complexes are concentrated within the pericentric chromatin, but whether they contribute to tension-generating mechanisms is not known. To understand how pericentric chromatin is packaged and resists tension, we map the position of cohesin (SMC3), condensin (SMC4), and pericentric LacO arrays within the spindle. Condensin lies proximal to the spindle axis and is responsible for axial compaction of pericentric chromatin. Cohesin is radially displaced from the spindle axis and confines pericentric chromatin. Pericentric cohesin and condensin contribute to spindle length regulation and dynamics in metaphase. Together with the intramolecular centromere loop, these SMC complexes constitute a molecular spring that balances spindle microtubule force in metaphase.
姐妹染色单体黏合为纺锤体微管提供了机械基础，共同作用于中期时使同源染色体间产生张力。着丝粒周围染色质形成分子内环，从姐妹染色单体轴双向伸出。着丝粒位于每条环的顶点，即染色体表面。黏合蛋白和凝聚素结构维持染色体（SMC）蛋白复合物集中在着丝粒周围染色质内，但它们是否有助于张力产生机制尚不清楚。为了了解着丝粒周围染色质是如何包装和抵抗张力的，我们在纺锤体中定位了黏合蛋白（SMC3）、凝聚素（SMC4）和着丝粒 LacO 阵列的位置。凝聚素位于纺锤体轴附近，负责着丝粒周围染色质的轴向压缩。黏合蛋白从纺锤体轴径向位移，并限制着丝粒周围染色质。着丝粒黏合蛋白和凝聚素有助于调节纺锤体长度和中期的动力学。与分子内着丝粒环一起，这些 SMC 复合物构成了一个分子弹簧，在中期平衡纺锤体微管力。
