Mesoscale macromolecular complexes and organelles, tens to hundreds of nanometers in size, crowd the eukaryotic cytoplasm. It is therefore unclear how mesoscale particles remain sufficiently mobile to regulate dynamic processes such as cell division. Here, we study mobility across dividing cells that contain densely packed, dynamic microtubules, comprising the metaphase spindle. In dividing human cells, we tracked 40 nm genetically encoded multimeric nanoparticles (GEMs), whose sizes are commensurate with the inter-filament spacing in metaphase spindles. Unexpectedly, the effective diffusivity of GEMs was similar inside the dense metaphase spindle and the surrounding cytoplasm. Eliminating microtubules or perturbing their polymerization dynamics decreased diffusivity by ~30%, suggesting that microtubule polymerization enhances random displacements to amplify diffusive-like motion. Our results suggest that microtubules effectively fluidize the mitotic cytoplasm to equalize mesoscale mobility across a densely packed, dynamic, non-uniform environment, thus spatially maintaining a key biophysical parameter that impacts biochemistry, ranging from metabolism to the nucleation of cytoskeletal filaments.

尺寸为数十至数百纳米的中尺度大分子复合物和细胞器挤满了真核细胞质。因此，尚不清楚中尺度粒子如何保持足够的移动性来调节细胞分裂等动态过程。在这里，我们研究了分裂细胞的迁移性，这些细胞含有密集的动态微管，包括中期纺锤体。在分裂的人类细胞中，我们追踪了 40 nm 基因编码的多聚纳米颗粒 (GEM)，其尺寸与中期纺锤体的丝间间距相称。出乎意料的是，GEM 在致密中期纺锤体和周围细胞质内的有效扩散率相似。消除微管或扰乱其聚​​合动力学可使扩散率降低约 30%，这表明微管聚合增强了随机位移，从而放大了类似扩散的运动。我们的结果表明，微管有效地使有丝分裂细胞质流化，以平衡密集、动态、不均匀环境中的中尺度流动性，从而在空间上维持影响生物化学的关键生物物理参数，从新陈代谢到细胞骨架丝的成核。