Spatial patterns are ubiquitous in both physical and biological systems. We have recently discovered that mitotic chromosomes sequentially acquire two interesting morphological patterns along their structural axes [L. Chu et al., Mol. Cell, 10.1016/j.molcel.2020.07.002 (2020)]. First, axes of closely conjoined sister chromosomes acquire regular undulations comprising nearly planar arrays of sequential half-helices of similar size and alternating handedness, accompanied by periodic kinks. This pattern, which persists through all later stages, provides a case of the geometric form known as a “perversion.” Next, as sister chromosomes become distinct parallel units, their individual axes become linked by bridges, which are themselves miniature axes. These bridges are dramatically evenly spaced. Together, these effects comprise a unique instance of spatial patterning in a subcellular biological system. We present evidence that axis undulations and bridge arrays arise by a single continuous mechanically promoted progression, driven by stress within the chromosome axes. We further suggest that, after sister individualization, this same stress also promotes chromosome compaction by rendering the axes susceptible to the requisite molecular remodeling. Thus, by this scenario, the continuous presence of mechanical stress within the chromosome axes could potentially underlie the entire morphogenetic chromosomal program. Direct analogies with meiotic chromosomes suggest that the same effects could underlie interactions between homologous chromosomes as required for gametogenesis. Possible mechanical bases for generation of axis stress and resultant deformations are discussed. Together, these findings provide a perspective on the macroscopic changes of organized chromosomes.

空间模式在物理和生物系统中普遍存在。我们最近发现有丝分裂染色体沿着其结构轴顺序获得两种有趣的形态模式[L. Chu 等人， Mol。细胞，10.1016/j.molcel.2020.07.002（2020）]。首先，紧密相连的姐妹染色体的轴获得规则的波动，包括​​大小相似的连续半螺旋的近平面阵列和交替的旋向，并伴有周期性扭结。这种模式在所有后期阶段都持续存在，提供了一种被称为“倒错”的几何形式的例子。接下来，当姐妹染色体变成不同的平行单元时，它们各自的轴通过桥连接，而桥本身就是微型轴。这些桥的间距非常均匀。这些效应共同构成了亚细胞生物系统中空间模式的独特实例。我们提供的证据表明，轴波动和桥阵列是由染色体轴内压力驱动的单个连续机械促进进展引起的。我们进一步表明，在姐妹个体化之后，同样的压力也通过使轴易于进行必要的分子重塑来促进染色体压缩。因此，在这种情况下，染色体轴内持续存在的机械应力可能是整个形态发生染色体程序的基础。与减数分裂染色体的直接类比表明，相同的效应可能是配子发生所需的同源染色体之间相互作用的基础。讨论了产生轴应力和由此产生的变形的可能机械基础。 总之，这些发现为有组织的染色体的宏观变化提供了一个视角。