Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 560-8531, Japan.
J Neurosci. 2010 Nov 10;30(45):15221-7. doi: 10.1523/JNEUROSCI.1527-10.2010.
Mature neurons polarize by extending an axon and dendrites. In vitro studies of dissociated neurons have demonstrated that axons are initiated from a nonpolarized stage. Dissociated hippocampal neurons form four to five minor neurites shortly after plating but then one of them starts to elongate rapidly to become the future axon, whereas the rest constitutes the dendrites at later stages. However, neuroepithelial cells as well as migrating neurons in vivo are already polarized, raising the possibility that mature neurons inherit the polarities of immature neurons of neuroepithelial or migrating neurons. Here we show that the axon of interneurons in mouse cortical explant emerges from a morphologically nonpolarized shape. The morphological maturation of cortical interneurons labeled by electroporation at an embryonic stage was analyzed by time-lapse imaging during the perinatal stage. In contrast to earlier stages, most interneurons at this stage show sea urchin-like nonpolarized shapes with alternately extending and retracting short processes. Abruptly, one of these processes extends to give rise to an outstandingly long axon-like process. Given that the interneurons exhibit typical polarized shapes during embryonic development, the present results suggest that axon-dendrite polarity develops from a nonpolarized intermediate stage.
成熟神经元通过延伸轴突和树突来极化。体外分离神经元的研究表明，轴突是从非极化阶段开始的。分离的海马神经元在接种后不久就会形成四到五个小突起，但其中一个会迅速伸长成为未来的轴突，而其余的则在后期成为树突。然而，神经上皮细胞以及体内迁移的神经元已经是极化的，这就提出了一个可能性，即成熟神经元继承了神经上皮或迁移神经元的不成熟神经元的极性。在这里，我们展示了小鼠皮质外植体中中间神经元的轴突从形态上的非极化形状中出现。通过在胚胎期进行电穿孔标记，对皮质中间神经元在围产期的形态成熟进行了延时成像分析。与早期阶段相比，在这个阶段，大多数中间神经元呈现出棘皮动物样的非极化形状，交替地延伸和缩回短突起。突然，其中一个突起延伸，形成一个非常长的轴突样突起。鉴于中间神经元在胚胎发育过程中表现出典型的极化形状，本研究结果表明，轴突-树突极性是从非极化的中间阶段发展而来的。
