Mecha Miriam, Peña-Melián Angel L, Blanco Maria J
Departamento de Neurobiología Funcional y de Sistemas, Instituto Cajal, CSIC, Madrid, Spain.
Int J Dev Biol. 2010;54(4):691-8. doi: 10.1387/ijdb.082670mm.
The cerebellum is a highly conserved structure in the Central Nervous System (CNS) of vertebrates, and is involved in the coordination of voluntary motor behaviour. Supporting this function, the cerebellar cortex presents a layered structure which requires a precise spatial and temporal coordination of proliferation, migration and differentiation events. One of the characteristics of the developing cortex is the formation of the external granule cell layer (EGL) in the outermost part. The EGL is a highly proliferative transient layer which disappears when cells migrate inwards to form the inner granule cell layer. The balance between proliferation and migration leads to changes in EGL thickness, and might be related to "indentations" observed in the surface of the developing chick cerebellum. We have extended the observation of this feature to quail and mouse, supporting the idea that this phenomenon forms part of the mechanisms of cerebellar morphogenesis. Different factors involved in both mitotic activity and migration were analyzed in this study. Our results indicate that proliferation, more than formation of raphes for cell migration, is involved in the formation of indentations in the EGL. In addition, we show that vessels penetrating from the pial surface divide the EGL into regular regions at the time of the appearance of bulges and furrows. We conclude that indentations are the result of a coincidence in time of both the increase in thickness of the EGL and the establishment of the embryonic vascular pattern, which confers a characteristic transitory morphology to the surface of folia.
小脑是脊椎动物中枢神经系统（CNS）中高度保守的结构，参与自主运动行为的协调。为支持这一功能，小脑皮质呈现出一种分层结构，这需要增殖、迁移和分化事件在空间和时间上进行精确协调。发育中小脑皮质的特征之一是在最外层形成外颗粒细胞层（EGL）。EGL是一个高度增殖的过渡层，当细胞向内迁移形成内颗粒细胞层时，该层消失。增殖与迁移之间的平衡导致EGL厚度发生变化，这可能与发育中的鸡小脑表面观察到的“凹陷”有关。我们将这一特征的观察扩展到鹌鹑和小鼠，支持了这一现象是小脑形态发生机制一部分的观点。本研究分析了参与有丝分裂活动和迁移的不同因素。我们的结果表明，EGL中凹陷的形成涉及增殖，而非细胞迁移的缝隙形成。此外，我们表明，在凸起和沟出现时，从软膜表面穿透的血管将EGL分隔成规则区域。我们得出结论，凹陷是EGL厚度增加与胚胎血管模式建立在时间上巧合的结果，这赋予了小叶表面一种特有的过渡形态。
