Davis L, Dou P, DeWit M, Kater S B
Program in Neuronal Growth and Development, Colorado State University, Fort Collins 80523.
J Neurosci. 1992 Dec;12(12):4867-77. doi: 10.1523/JNEUROSCI.12-12-04867.1992.
This study investigates the capacity of neuronal growth cones to synthesize protein locally and independently of their cell body. Isolated growth cones were prepared from cultures of neurons from the snail Helisoma by transecting neurites proximal to the growth cone. The capacity for protein synthesis was tested by radiolabeling cultures with 3H-leucine and analyzing the resultant autoradiograms. Isolated growth cones displayed incorporation of 3H-leucine that was inhibited by treatment with the protein synthesis inhibitors anisomycin and pactamycin, indicating that ribosomal-dependent translation occurs in growth cones. Ultrastructural analyses of growth cones demonstrated the presence of polyribosomes, the machinery for protein synthesis. The density of polyribosomes varied between growth cones, even between different growth cones on the same neuron, suggesting that growth cones express a range of protein synthetic capabilities. That different types of growth cones possess differing capabilities for protein synthesis is suggested in autoradiograms of 3H-leucine incorporation by the growth cones of axonal and nonaxonal neurites; incorporation was radically reduced in axonal growth cones in comparison with non-axonal growth cones. Finally, growth cones that were isolated for 2 d prior to radiolabeling incorporate 3H-leucine in a eukaryotic ribosomal-dependent manner, suggesting that the capacity for translation is long-lived in growth cones. Taken together, these studies reveal a capacity for protein synthesis confined totally to the neuronal growth cone proper. The synthesis of proteins in growth cones could afford a mechanism for the alteration of growth cone structure or function. This is in accord with the view that growth cones participate autonomously, to at least some extent, in the processes of synaptogenesis and the construction of neuronal architecture.
本研究调查了神经元生长锥在局部独立于其细胞体合成蛋白质的能力。通过在靠近生长锥的位置横切神经突，从蜗牛Helisoma的神经元培养物中制备分离的生长锥。用3H-亮氨酸对培养物进行放射性标记，并分析所得的放射自显影片，以此测试蛋白质合成能力。分离的生长锥显示出3H-亮氨酸的掺入，而蛋白质合成抑制剂茴香霉素和放线菌酮的处理可抑制这种掺入，这表明核糖体依赖性翻译发生在生长锥中。对生长锥的超微结构分析表明存在多核糖体，即蛋白质合成机制。多核糖体的密度在不同生长锥之间有所不同，甚至在同一神经元的不同生长锥之间也存在差异，这表明生长锥具有一系列蛋白质合成能力。轴突和非轴突神经突的生长锥对3H-亮氨酸掺入的放射自显影片表明，不同类型的生长锥具有不同的蛋白质合成能力；与非轴突生长锥相比，轴突生长锥中的掺入量大幅降低。最后，在放射性标记前分离2天的生长锥以真核核糖体依赖性方式掺入3H-亮氨酸，这表明生长锥中的翻译能力具有较长寿命。综上所述，这些研究揭示了完全局限于神经元生长锥本身的蛋白质合成能力。生长锥中蛋白质的合成可能为生长锥结构或功能的改变提供一种机制。这与生长锥至少在一定程度上自主参与突触发生和神经元结构构建过程的观点一致。
