Murdoch Childrens Research Institute, Royal Children's Hospital, Melbourne, Victoria 3052, Australia.
J Cell Sci. 2012 Mar 15;125(Pt 6):1591-604. doi: 10.1242/jcs.097790. Epub 2012 Feb 17.
In vertebrates, two condensin complexes exist, condensin I and condensin II, which have differing but unresolved roles in organizing mitotic chromosomes. To dissect accurately the role of each complex in mitosis, we have made and studied the first vertebrate conditional knockouts of the genes encoding condensin I subunit CAP-H and condensin II subunit CAP-D3 in chicken DT40 cells. Live-cell imaging reveals highly distinct segregation defects. CAP-D3 (condensin II) knockout results in masses of chromatin-containing anaphase bridges. CAP-H (condensin I)-knockout anaphases have a more subtle defect, with chromatids showing fine chromatin fibres that are associated with failure of cytokinesis and cell death. Super-resolution microscopy reveals that condensin-I-depleted mitotic chromosomes are wider and shorter, with a diffuse chromosome scaffold, whereas condensin-II-depleted chromosomes retain a more defined scaffold, with chromosomes more stretched and seemingly lacking in axial rigidity. We conclude that condensin II is required primarily to provide rigidity by establishing an initial chromosome axis around which condensin I can arrange loops of chromatin.
在脊椎动物中，存在两种凝聚素复合物，即凝聚素 I 和凝聚素 II，它们在有丝分裂染色体的组织中具有不同但尚未解决的作用。为了准确剖析每个复合物在有丝分裂中的作用，我们在鸡 DT40 细胞中制造并研究了第一个脊椎动物条件性敲除编码凝聚素 I 亚基 CAP-H 和凝聚素 II 亚基 CAP-D3 的基因。活细胞成像揭示了高度不同的分离缺陷。CAP-D3（凝聚素 II）敲除导致含有染色质的后期桥的大量聚集。CAP-H（凝聚素 I）敲除的后期具有更微妙的缺陷，染色单体显示出与胞质分裂失败和细胞死亡相关的精细染色质纤维。超分辨率显微镜显示，耗尽凝聚素-I 的有丝分裂染色体更宽更短，具有弥散的染色体支架，而耗尽凝聚素-II 的染色体保留更明确的支架，染色体更伸展，似乎缺乏轴向刚性。我们得出结论，凝聚素 II 主要通过围绕其构建初始染色体轴来提供刚性，从而使凝聚素 I 能够排列染色质环。
