Oakley R A, Tosney K W
Neuroscience Program, University of Michigan, Ann Arbor 48109.
J Neurosci. 1993 Sep;13(9):3773-92. doi: 10.1523/JNEUROSCI.13-09-03773.1993.
In the chick embryo, the segmental pattern of motor outgrowth depends on guidance cues provided by sclerotome cells. Motor axons preferentially invade the anterior sclerotome but avoid the posterior sclerotome. To determine how motor growth cone motility is influenced by these cells, we used videomicroscopy to analyze the behavior of motor growth cones as they confronted identified sclerotome cells in vitro. After contact, motor growth cones invariably avoided posterior sclerotome cells by either branching or turning. Both types of avoidance behavior were initiated by a local inhibition of veil protrusion: veils failed to progress along the contacting filopodia. This inhibition was specific to veils since contact failed to alter the number of filopodia protruded. Moreover, motor growth cones turned away from posterior cells despite more persistent filopodial contacts with these cells than with the laminin substratum. In no case did contact with posterior cells cause a complete loss of growth cone motility or a complete collapse of growth cone structure. In contrast, motor growth cones exhibited a selective affinity for anterior cells, preferring the surfaces of these cells to the laminin substratum. Contact with anterior cells stimulated a generalized increase in protrusive activity: contact caused a net increase in the extension of veils and filopodia both locally and at sites distant from the site of contact. Contact also elicited a localized thickening of contacting processes, suggesting that contact with anterior cells promotes neurite consolidation. This behavior of motor growth cones in vitro suggests that both an inhibition of veil formation by posterior cells and an enhancement of motility and axon consolidation by anterior cells contribute to the preferential advance of motor axons into anterior sclerotome in vivo. We suggest that patterned outgrowth results from the juxtaposition of two contrasting environments that differentially influence growth cone motility.
在鸡胚中，运动神经元轴突生长的节段模式取决于由硬骨细胞提供的引导线索。运动神经元轴突优先侵入前硬骨细胞，但避开后硬骨细胞。为了确定运动生长锥的运动性如何受到这些细胞的影响，我们使用视频显微镜分析了运动生长锥在体外与已识别的硬骨细胞接触时的行为。接触后，运动生长锥总是通过分支或转向避开后硬骨细胞。这两种类型的回避行为都是由面纱状突起的局部抑制引发的：面纱状突起无法沿着接触的丝状伪足前进。这种抑制作用是面纱状突起特有的，因为接触并没有改变伸出的丝状伪足的数量。此外，尽管运动生长锥与后硬骨细胞的丝状伪足接触比与层粘连蛋白基质的接触更持久，但它们仍会从后硬骨细胞处转向。在任何情况下，与后硬骨细胞的接触都不会导致生长锥运动性完全丧失或生长锥结构完全塌陷。相反，运动生长锥对前硬骨细胞表现出选择性亲和力，相对于层粘连蛋白基质，它们更喜欢这些细胞的表面。与前硬骨细胞的接触刺激了突起活动的普遍增加：接触导致面纱状突起和丝状伪足在局部和远离接触部位的延伸净增加。接触还引发了接触部位的局部增厚，这表明与前硬骨细胞的接触促进了神经突的巩固。运动生长锥在体外的这种行为表明，后硬骨细胞对面纱状突起形成的抑制以及前硬骨细胞对运动性和轴突巩固的增强，都有助于运动神经元轴突在体内优先向硬骨细胞的前进。我们认为，有模式的生长是由两个对生长锥运动性有不同影响的对比环境并列造成的。
