Bird Alexander W, Hyman Anthony A
Max Planck Institute for Molecular Cell Biology and Genetics, 01307 Dresden, Germany.
J Cell Biol. 2008 Jul 28;182(2):289-300. doi: 10.1083/jcb.200802005.
To assemble mitotic spindles, cells nucleate microtubules from a variety of sources including chromosomes and centrosomes. We know little about how the regulation of microtubule nucleation contributes to spindle bipolarity and spindle size. The Aurora A kinase activator TPX2 is required for microtubule nucleation from chromosomes as well as for spindle bipolarity. We use bacterial artificial chromosome-based recombineering to introduce point mutants that block the interaction between TPX2 and Aurora A into human cells. TPX2 mutants have very short spindles but, surprisingly, are still bipolar and segregate chromosomes. Examination of microtubule nucleation during spindle assembly shows that microtubules fail to nucleate from chromosomes. Thus, chromosome nucleation is not essential for bipolarity during human cell mitosis when centrosomes are present. Rather, chromosome nucleation is involved in spindle pole separation and setting spindle length. A second Aurora A-independent function of TPX2 is required to bipolarize spindles.
为了组装有丝分裂纺锤体，细胞会从包括染色体和中心体在内的多种来源中形成微管。我们对微管成核的调控如何影响纺锤体双极性和纺锤体大小知之甚少。极光激酶A激活剂TPX2是染色体微管成核以及纺锤体双极性所必需的。我们利用基于细菌人工染色体的重组技术，将阻断TPX2与极光激酶A相互作用的点突变引入人类细胞。TPX2突变体的纺锤体非常短，但令人惊讶的是，它们仍然是双极的，并且能够分离染色体。在纺锤体组装过程中对微管成核的检查表明，微管无法从染色体上形成。因此，当存在中心体时，染色体成核对于人类细胞有丝分裂期间的双极性并非必不可少。相反，染色体成核参与纺锤体极分离和设定纺锤体长度。TPX2的第二个不依赖极光激酶A的功能是使纺锤体双极化所必需的。
