Snow Diane M, Smith Jeffrey D, Cunningham Andrew T, McFarlin Jessica, Goshorn Eric C
The University of Kentucky, Department of Anatomy and Neurobiology, Lexington, KY 40536-0298, USA.
Exp Neurol. 2003 Aug;182(2):310-21. doi: 10.1016/s0014-4886(03)00034-7.
In the developing or regenerating nervous system, migrating growth cones are exposed to regulatory molecules that positively and/or negatively affect guidance. Chondroitin sulfate proteoglycans (CSPGs) are complex macromolecules that are typically negative regulators of growth cone migration in vivo and in vitro. However, in certain cases, neurites sometimes traverse regions expressing relatively high levels of CSPGs, seemingly a paradox. In our continuing efforts to characterize CSPG inhibition in vitro, we manipulated the ratio of CSPGs to growth-promoting laminin-1 to produce a substratum that supports outgrowth of a subpopulation of dorsal root ganglia (DRG) neurites, while still being inhibitory to other populations of DRG neurons [Exp. Neurol. 109 (1990), 111; J. Neurobiol. 51 (2002), 285]. This model comprises a useful tool in the analysis of mechanisms of growth cone guidance and is particularly useful to analyze how CSPGs can be inhibitory under some conditions, and growth permissive under others. We grew embryonic (E9-10) chicken DRG neurons on nervous system-isolated, substratum-bound CSPGs at a concentration that supports an intermittent pattern of outgrowth, alternating with regions adsorbed with growth-promoting laminin-1 alone, and analyzed outgrowth behaviors qualitatively and quantitatively. A novel finding of the study was that DRG neurites that elongated onto CSPGs were predominantly fasciculated, but immediately returned to a defasciculated state upon contact with laminin-1. Further, cursory inspection suggests that outgrowth onto CSPGs may be initially accomplished by pioneer axons, along which subsequent axons migrate. The outgrowth patterns characterized in vitro may accurately reflect outgrowth in vivo in locations where inhibitory CSPGs and growth-promoting molecules are coexpressed, e.g., in the developing retina where fasciculated outgrowth may be instrumental in the guidance of retinal ganglion cells from the periphery to the optic fissure.
在发育或再生的神经系统中，迁移的生长锥会接触到对导向产生正向和/或负向影响的调节分子。硫酸软骨素蛋白聚糖（CSPG）是复杂的大分子，在体内和体外通常是生长锥迁移的负调节因子。然而，在某些情况下，神经突有时会穿过表达相对高水平CSPG的区域，这似乎是一个矛盾现象。在我们持续表征体外CSPG抑制作用的过程中，我们调整了CSPG与促进生长的层粘连蛋白-1的比例，以产生一种支持背根神经节（DRG）神经突亚群生长的基质，同时仍对其他DRG神经元群体具有抑制作用[《实验神经病学》109（1990），111；《神经生物学杂志》51（2002），285]。该模型是分析生长锥导向机制的有用工具，对于分析CSPG在某些条件下如何具有抑制作用而在其他条件下又允许生长尤为有用。我们将胚胎（E9 - 10）期鸡的DRG神经元培养在分离自神经系统、与基质结合的CSPG上，其浓度支持间歇性生长模式，与仅吸附有促进生长的层粘连蛋白-1的区域交替出现，并对生长行为进行定性和定量分析。该研究的一个新发现是，延伸到CSPG上的DRG神经突主要是成束的，但在与层粘连蛋白-1接触后会立即恢复到解束状态。此外，初步观察表明，在CSPG上的生长最初可能是由先驱轴突完成的，后续轴突沿着这些先驱轴突迁移。体外表征的生长模式可能准确反映了体内抑制性CSPG和促进生长分子共表达的位置的生长情况，例如在发育中的视网膜中，成束生长可能有助于视网膜神经节细胞从周边向视裂的导向。
