Perez R G, Halfter W
Department of Neurobiology, Anatomy, and Cell Science, University of Pittsburgh, Pennsylvania 15261.
Dev Biol. 1993 Mar;156(1):278-92. doi: 10.1006/dbio.1993.1076.
The distribution of the extracellular matrix protein tenascin was studied in the developing chick visual system to determine its possible regulatory role in retinotectal development. Little tenascin was present in the retinal optic fiber layer, and the optic nerve and tract, but was abundant in the stratum opticum of the tectum, the target of retinal axons in the brain. A high concentration of tenascin was found in areas bordering the developing visual pathway, such as the optic disc, the outer surface of the optic nerve, and the supraoptic commissure. In vitro studies showed that tenascin did not promote neurite outgrowth of retinal axons. When optic axons were confronted with a tenascin substrate in culture, they did not grow onto the tenascin suggesting that this protein inhibited optic axon outgrowth. Furthermore, the addition of tenascin to retinal explants in collagen gels slowed the growth rate of optic axons by as much as 50%. The distribution of tenascin in vivo and its inhibitory function in several in vitro systems suggest that this protein acts as a modulator of axonal growth in vivo. Tenascin may act as a barrier at specific sites along the visual pathway, and at the target, may slow the rate of axon outgrowth, and ultimately act as a stop molecule. The growth inhibitory activity of tenascin in retinal and tectal synaptic layers may also serve to stabilize synapses once appropriate connections have been made.
为了确定细胞外基质蛋白腱生蛋白在视网膜顶盖发育中可能的调节作用，研究人员对发育中的鸡视觉系统中腱生蛋白的分布进行了研究。在视网膜视神经纤维层、视神经和视束中，腱生蛋白含量很少，但在顶盖的视层（大脑中视网膜轴突的靶区）中含量丰富。在与发育中的视觉通路相邻的区域，如视盘、视神经外表面和视上连合，发现了高浓度的腱生蛋白。体外研究表明，腱生蛋白不会促进视网膜轴突的神经突生长。当在培养中使视神经轴突与腱生蛋白底物接触时，它们不会生长到腱生蛋白上，这表明这种蛋白抑制视神经轴突生长。此外，在胶原凝胶中将腱生蛋白添加到视网膜外植体中，可使视神经轴突的生长速度减慢多达50%。腱生蛋白在体内的分布及其在多个体外系统中的抑制功能表明，这种蛋白在体内充当轴突生长的调节剂。腱生蛋白可能在视觉通路的特定部位充当屏障，并且在靶区可能减缓轴突生长速度，并最终充当终止分子。一旦建立了适当的连接，腱生蛋白在视网膜和顶盖突触层中的生长抑制活性也可能有助于稳定突触。
