Gregory W A, Edmondson J C, Hatten M E, Mason C A
Department of Pharmacology, New York University Medical Center, New York 10016.
J Neurosci. 1988 May;8(5):1728-38. doi: 10.1523/JNEUROSCI.08-05-01728.1988.
In developing mammalian brain, many neurons migrate to their final position by moving in direct apposition to radially oriented glial cells. Glial-guided migration can be visualized in microcultures of mouse cerebellar cells by the combined use of cellular antigen markers and high resolution time-lapse video microscopy (Hatten et al., 1984; Edmondson and Hatten, 1987). Such studies have demonstrated the behavior of migrating cells and revealed a motile leading process on the migrating neuron that resembles an axonal growth cone and grows along extended glial fibers. To study the fine structural details of the migrating neuron and its neuron-glial apposition, we identified and monitored neurons in microcultures with video microscopy and examined the cytology and cellular contacts of the same cells with transmission electron microscopy. The cytology of the soma and leading process of migrating cells closely matches that described for granule cells in intact brain (Rakic, 1971). Newly observed structures include the presence of longitudinally oriented microtubules extending from a basal body in the soma into the leading process, and microfilament-rich filopodia arising from the soma and leading process. The most striking feature of actively migrating neurons is a specialized junction between the neuronal cell soma and apposing glial fibers. At this junction, here termed "interstitial density," the extracellular space is dilated to 20 nm and filamentous material in the intracellular cleft either spans the cleft or runs parallel to the cell membranes. Some interstitial fibrils are contiguous with, or are transmembranous extensions of, submembranous cytoskeletal elements that attach to microtubules. Interstitial junctions were not found between neurons that did not translocate in the observation period before fixation. Instead, stationary cells formed desmosomes (puncta and macula adhaerentia) at appositions with glial processes.
在发育中的哺乳动物大脑中，许多神经元通过与放射状排列的神经胶质细胞直接相邻移动，迁移到它们的最终位置。通过联合使用细胞抗原标记物和高分辨率延时视频显微镜，可以在小鼠小脑细胞的微培养物中观察到神经胶质引导的迁移（哈滕等人，1984年；埃德蒙森和哈滕，1987年）。此类研究已经证明了迁移细胞的行为，并揭示了迁移神经元上一个能动的前端突起，它类似于轴突生长锥，并沿着伸展的神经胶质纤维生长。为了研究迁移神经元及其与神经胶质细胞相邻处的精细结构细节，我们用视频显微镜识别并监测了微培养物中的神经元，并用透射电子显微镜检查了相同细胞的细胞学和细胞接触情况。迁移细胞的胞体和前端突起的细胞学特征与完整大脑中颗粒细胞的描述密切匹配（拉基奇，1971年）。新观察到的结构包括从胞体中的基体延伸到前端突起的纵向排列的微管，以及从胞体和前端突起产生的富含微丝的丝状伪足。活跃迁移的神经元最显著的特征是神经元细胞胞体与相邻神经胶质纤维之间的一种特殊连接。在这个连接部位，这里称为“间隙密度”，细胞外间隙扩大到20纳米，细胞内裂隙中的丝状物质要么横跨裂隙，要么与细胞膜平行排列。一些间隙纤维与附着在微管上的膜下细胞骨架元件相连或为其跨膜延伸。在固定前观察期内未发生移位的神经元之间未发现间隙连接。相反，静止细胞在与神经胶质突起相邻处形成了桥粒（点状和斑状粘着）。
