Mora-Bermúdez Felipe, Gerlich Daniel, Ellenberg Jan
Gene Expression and Cell Biology Unit, European Molecular Biology Laboratory, Meyerhofstr. 1, 69117 Heidelberg, Germany.
Nat Cell Biol. 2007 Jul;9(7):822-31. doi: 10.1038/ncb1606. Epub 2007 Jun 10.
Eukaryotic cells must first compact their chromosomes before faithfully segregating them during cell division. Failure to do so can lead to segregation defects with pathological consequences, such as aneuploidy and cancer. Duplicated interphase chromosomes are, therefore, reorganized into tight rods before being separated and directed to the newly forming daughter cells. This vital reorganization of chromatin remains poorly understood. To address the dynamics of mitotic condensation of single chromosomes in intact cells, we developed quantitative assays based on confocal time-lapse microscopy of live mammalian cells stably expressing fluorescently tagged core histones. Surprisingly, maximal compaction was not reached in metaphase, but in late anaphase, after sister chromatid segregation. We show that anaphase compaction proceeds by a mechanism of axial shortening of the chromatid arms from telomere to centromere. Chromatid axial shortening was not affected in condensin-depleted cells, but depended instead on dynamic microtubules and Aurora kinase. Acute perturbation of this compaction resulted in failure to rescue segregation defects and in multilobed daughter nuclei, suggesting functions in chromosome segregation and nuclear architecture.
真核细胞在细胞分裂过程中忠实地分离染色体之前，必须先将其染色体压缩。若不这样做，可能会导致分离缺陷，并产生诸如非整倍体和癌症等病理后果。因此，复制后的间期染色体在被分离并导向新形成的子细胞之前，会被重新组织成紧密的棒状结构。染色质的这种重要重组过程仍鲜为人知。为了研究完整细胞中单个染色体有丝分裂凝聚的动态过程，我们基于对稳定表达荧光标记核心组蛋白的活哺乳动物细胞进行共聚焦延时显微镜观察，开发了定量分析方法。令人惊讶的是，最大压缩并非在中期达到，而是在后期姐妹染色单体分离之后的末期。我们发现后期压缩是通过染色单体臂从端粒到着丝粒的轴向缩短机制进行的。在凝聚素缺失的细胞中，染色单体轴向缩短不受影响，而是依赖于动态微管和极光激酶。这种压缩的急性扰动导致无法挽救分离缺陷，并产生多叶状子核，这表明其在染色体分离和核结构中发挥作用。
