de Anda Froylan Calderon, Pollarolo Giulia, Da Silva Jorge Santos, Camoletto Paola G, Feiguin Fabian, Dotti Carlos G
Cavalieri Ottolenghi Scientific Institute, Universita degli Studi di Torino, 10043 Orbassano, Torino, Italy.
Nature. 2005 Aug 4;436(7051):704-8. doi: 10.1038/nature03811.
Neuronal polarization occurs shortly after mitosis. In neurons differentiating in vitro, axon formation follows the segregation of growth-promoting activities to only one of the multiple neurites that form after mitosis. It is unresolved whether such spatial restriction makes use of an intrinsic program, like during C. elegans embryo polarization, or is extrinsic and cue-mediated, as in migratory cells. Here we show that in hippocampal neurons in vitro, the axon consistently arises from the neurite that develops first after mitosis. Centrosomes, the Golgi apparatus and endosomes cluster together close to the area where the first neurite will form, which is in turn opposite from the plane of the last mitotic division. We show that the polarized activities of these organelles are necessary and sufficient for neuronal polarization: (1) polarized microtubule polymerization and membrane transport precedes first neurite formation, (2) neurons with more than one centrosome sprout more than one axon and (3) suppression of centrosome-mediated functions precludes polarization. We conclude that asymmetric centrosome-mediated dynamics in the early post-mitotic stage instruct neuronal polarity, implying that pre-mitotic mechanisms with a role in division orientation may in turn participate in this event.
神经元极化在有丝分裂后不久发生。在体外分化的神经元中，轴突形成遵循促生长活性仅分离至有丝分裂后形成的多个神经突中的一个。目前尚不清楚这种空间限制是利用了内在程序，如秀丽隐杆线虫胚胎极化过程中那样，还是如迁移细胞那样是外在的且由信号介导的。在这里我们表明，在体外培养的海马神经元中，轴突始终从有丝分裂后最早发育的神经突产生。中心体、高尔基体和内体聚集在靠近第一个神经突将形成的区域，该区域又与最后一次有丝分裂平面相对。我们表明，这些细胞器的极化活动对于神经元极化是必要且充分的：（1）极化的微管聚合和膜转运先于第一个神经突形成，（2）具有多个中心体的神经元会长出多个轴突，（3）抑制中心体介导的功能会阻止极化。我们得出结论，有丝分裂后早期阶段不对称的中心体介导的动态过程指导神经元极性，这意味着在分裂方向上起作用的有丝分裂前机制可能反过来参与这一事件。
