Tuttle R, Schlaggar B L, Braisted J E, O'Leary D D
Molecular Neurobiology Laboratory, Salk Institute, La Jolla, California 92037, USA.
J Neurosci. 1995 Apr;15(4):3039-52. doi: 10.1523/JNEUROSCI.15-04-03039.1995.
We have tested the hypothesis that maturation-dependent changes in the cortical plate affect the spatiotemporal growth patterns of developing thalamocortical and corticocortical axonal projections. Given a choice between alternating lanes of embryonic (E18-19) and neonatal (P0-1) rat cortical plate membranes, embryonic (E18-19) thalamic and cortical neurites prefer to extend on neonatal membranes. Thalamic and cortical explants do extend neurites on uniform carpets of E19 cortical plate membranes, but the outgrowth is consistently greater on uniform carpets of P1 cortical plate membranes. These experiments demonstrate a maturation-dependent enhancement in the ability of cortical plate to support neurite growth from thalamic and cortical explants. In contrast, retinal and cerebellar neurites, which do not grow into cortex in vivo, generally grew poorly on these membranes, suggesting a degree of specificity to the neurite growth response. Immunohistochemical analysis of developing cortex suggests that several extracellular matrix (ECM) and cell adhesion molecules are upregulated in cortical plate. However, immunocharacterization of membrane carpets for these same ECM and cell adhesion molecules suggests that the growth preferences of thalamic and cortical neurites in vitro are predominantly influenced by membrane-anchored, rather than ECM, molecules. Western analysis of E19 and P1 cortical plate membranes supports this conclusion, and indicates that the membrane-anchored cell adhesion molecules L1 and N-CAM are more abundant in the P1 cortical plate membrane preparation. Experiments in which cortical plate membranes were treated to remove molecules sensitive to phosphatidylinositol (PI)-specific phospholipase C demonstrate that neurite growth promoters present in E19 cortical plate membranes are predominantly PI linked, whereas those present in P1 membranes are predominantly non-PI linked. These findings indicate that the neurite growth preferences are mediated, at least in part, by an upregulation of neurite growth-promoting molecules in developing cortical plate that are not PI linked. Taken together, these findings suggest that a maturation-dependent upregulation of neurite growth-promoting molecules on cortical plate cells controls the invasion of the cortical plate by thalamocortical and corticocortical axons.
皮质板中依赖成熟度的变化会影响发育中的丘脑皮质和皮质皮质轴突投射的时空生长模式。在胚胎期（E18 - 19）和新生期（P0 - 1）大鼠皮质板膜的交替泳道之间进行选择时，胚胎期（E18 - 19）的丘脑和皮质神经突更倾向于在新生期膜上延伸。丘脑和皮质外植体确实能在E19皮质板膜的均匀铺层上延伸神经突，但在P1皮质板膜的均匀铺层上生长始终更旺盛。这些实验证明了皮质板支持丘脑和皮质外植体神经突生长的能力存在依赖成熟度的增强。相比之下，在体内不会长入皮质的视网膜和小脑神经突，在这些膜上通常生长不佳，这表明神经突生长反应具有一定程度的特异性。对发育中的皮质进行免疫组织化学分析表明，几种细胞外基质（ECM）和细胞黏附分子在皮质板中上调。然而，对这些相同的ECM和细胞黏附分子的膜铺层进行免疫鉴定表明，丘脑和皮质神经突在体外的生长偏好主要受膜锚定分子而非ECM分子的影响。对E19和P1皮质板膜的蛋白质印迹分析支持这一结论，并表明膜锚定细胞黏附分子L1和N - CAM在P1皮质板膜制剂中更为丰富。用对磷脂酰肌醇（PI）特异性磷脂酶C敏感的分子处理皮质板膜的实验表明，E19皮质板膜中存在的神经突生长促进剂主要是PI连接的，而P1膜中存在的则主要是非PI连接的。这些发现表明，神经突生长偏好至少部分是由发育中的皮质板中不与PI连接的神经突生长促进分子的上调介导的。综上所述，这些发现表明，皮质板细胞上依赖成熟度的神经突生长促进分子上调控制着丘脑皮质和皮质皮质轴突对皮质板的侵入。
