Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ, 08544, USA.
Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, 08544, USA.
Nat Commun. 2023 Jun 21;14(1):3696. doi: 10.1038/s41467-023-39041-z.
Microtubules are generated at centrosomes, chromosomes, and within spindles during cell division. Whereas microtubule nucleation at the centrosome is well characterized, much remains unknown about where, when, and how microtubules are nucleated at chromosomes. To address these questions, we reconstitute microtubule nucleation from purified chromosomes in meiotic Xenopus egg extract and find that chromosomes alone can form spindles. We visualize microtubule nucleation near chromosomes using total internal reflection fluorescence microscopy to find that this occurs through branching microtubule nucleation. By inhibiting molecular motors, we find that the organization of the resultant polar branched networks is consistent with a theoretical model where the effectors for branching nucleation are released by chromosomes, forming a concentration gradient that spatially biases branching microtbule nucleation. In the presence of motors, these branched networks are ultimately organized into functional spindles, where the number of emergent spindle poles scales with the number of chromosomes and total chromatin area.
微管在细胞分裂过程中在中心体、染色体和纺锤体中生成。虽然中心体处的微管核化已经得到很好的描述，但对于染色体处的微管核化在何处、何时以及如何发生，仍有很多未知。为了解决这些问题，我们在减数分裂的爪蟾卵提取物中从纯化的染色体中重新组装微管核化，发现仅染色体本身就可以形成纺锤体。我们使用全内反射荧光显微镜来观察染色体附近的微管核化，发现这是通过分支微管核化发生的。通过抑制分子马达，我们发现所得的极性分支网络的组织与分支核化的效应物由染色体释放的理论模型一致，形成了空间偏向分支微管核化的浓度梯度。在有马达的情况下，这些分支网络最终被组织成功能性的纺锤体，其中出现的纺锤体极的数量与染色体的数量和总染色质面积成比例。
