Strukov Yuri G, Belmont A S
Biophysics Program, University of Illinois, Urbana-Champaign, Illinois, USA.
Biophys J. 2009 Feb 18;96(4):1617-28. doi: 10.1016/j.bpj.2008.10.051.
Mitotic chromosome structure and pathways of mitotic condensation remain unknown. The limited amount of structural data on mitotic chromosome structure makes it impossible to distinguish between several mutually conflicting models. Here we used a Chinese hamster ovary cell line with three different lac operator-tagged vector insertions distributed over an approximately 1 microm chromosome arm region to determine positioning reproducibility, long-range correlation in large-scale chromatin folding, and sister chromatid symmetry in minimally perturbed, metaphase chromosomes. The three-dimensional positions of these lac operator-tagged spots, stained with lac repressor, were measured in isolated metaphase chromosomes relative to the central chromatid axes labeled with antibodies to topoisomerase II. Longitudinal, but not axial, positioning of spots was reproducible but showed intrinsic variability, up to approximately 300 nm, between sister chromatids. Spot positions on the same chromatid were uncorrelated, and no correlation or symmetry between the positions of corresponding spots on sister chromatids was detectable, showing the absence of highly ordered, long-range chromatin folding over tens of mega-basepairs. Our observations are in agreement with the absence of any regular, reproducible helical, last level of chromosome folding, but remain consistent with any hierarchical folding model in which irregularity in folding exists at one or multiple levels.
有丝分裂染色体的结构以及有丝分裂凝聚的途径仍然未知。关于有丝分裂染色体结构的有限结构数据，使得区分几种相互冲突的模型变得不可能。在这里，我们使用了一种中国仓鼠卵巢细胞系，其有三个不同的带有乳糖操纵子标签的载体插入片段，分布在大约1微米的染色体臂区域，来确定定位的可重复性、大规模染色质折叠中的长程相关性以及在微扰的中期染色体中的姐妹染色单体对称性。用乳糖阻遏物染色的这些带有乳糖操纵子标签的位点的三维位置，在分离的中期染色体中相对于用拓扑异构酶II抗体标记的中央染色单体轴进行测量。位点的纵向定位（而非轴向定位）是可重复的，但在姐妹染色单体之间显示出高达约300纳米的内在变异性。同一染色单体上的位点位置不相关，并且在姐妹染色单体上相应位点的位置之间未检测到相关性或对称性，这表明在数十兆碱基对的范围内不存在高度有序的长程染色质折叠。我们的观察结果与不存在任何规则的、可重复的螺旋状的、染色体折叠的最后一级相一致，但与任何在一个或多个层次存在折叠不规则性的层次折叠模型仍然一致。
