A long-standing conundrum is how mitotic chromosomes can compact, as required for clean separation to daughter cells, while maintaining close parallel alignment of sister chromatids. Pursuit of this question, by high resolution 3D fluorescence imaging of living and fixed mammalian cells, has led to three discoveries. First, we show that the structural axes of separated sister chromatids are linked by evenly spaced “mini-axis” bridges. Second, when chromosomes first emerge as discrete units, at prophase, they are organized as co-oriented sister linear loop arrays emanating from a conjoined axis. We show that this same basic organization persists throughout mitosis, without helical coiling. Third, from prophase onward, chromosomes are deformed into sequential arrays of half-helical segments of alternating handedness (perversions), accompanied by correlated kinks. These arrays fluctuate dynamically over <15 s timescales. Together these discoveries redefine the foundation for thinking about the evolution of mitotic chromosomes as they prepare for anaphase segregation.

一个长期存在的难题是有丝分裂染色体如何压缩，这是干净分离子细胞所需的，同时保持姐妹染色单体的紧密平行排列。通过对活的和固定的哺乳动物细胞进行高分辨率 3D 荧光成像来解决这个问题，已经导致了三个发现。首先，我们表明分离的姐妹染色单体的结构轴通过均匀间隔的“迷你轴”桥连接。其次，当染色体首次作为离散单元出现时，在前期，它们被组织为从连体轴发出的同向姐妹线性环阵列。我们表明这个相同的基本组织在整个有丝分裂过程中持续存在，没有螺旋卷曲。第三，从前期开始，染色体变形为交替的手性（变态）半螺旋片段的连续阵列，伴随着相关的扭结。这些阵列在 <15 秒的时间尺度内动态波动。这些发现一起重新定义了思考有丝分裂染色体在准备后期分离时进化的基础。