Watson D F, Hoffman P N, Fittro K P, Griffin J W
Department of Neurology, Johns Hopkins Hospital, Baltimore, MD 21205.
Brain Res. 1989 Jan 16;477(1-2):225-32. doi: 10.1016/0006-8993(89)91410-8.
The rate of axonal transport of tubulin and of neurofilament proteins was measured in mature, non-growing, axons of rat lumbar ventral roots and sciatic nerves. A progressive decrease in the velocity of transport was observed along the course of the axons. The rate of advance of the 'front' of labeled neurofilaments decreased from 1.40 +/- 0.07 mm/day proximally to 0.64 +/- 0.04 mm/day distally. The rate for tubulin decreased from 3.10 +/- 0.13 proximally to 1.01 +/- 0.04 mm/day distally. These results demonstrate that a gradient of the velocity of cytoskeletal transport along axons is not a specific adaptation for radial growth of axons, as previously suggested. Local degradation of excess cytoskeletal proteins may permit axons to accommodate a net slowing of cytoskeletal transport without accumulation of neurofilaments or microtubules. Alternatively, the transport kinetics of radiolabeled proteins may be influenced by mixing of labeled and unlabeled cytoskeletal proteins within the axoplasm; in this case, a slowing of the movement of the labeled proteins may not reflect net slowing of transport of the total pool of cytoskeletal proteins.
在大鼠腰腹根和坐骨神经的成熟、非生长轴突中，测量了微管蛋白和神经丝蛋白的轴突运输速率。沿轴突行程观察到运输速度逐渐降低。标记神经丝“前沿”的推进速率从近端的1.40±0.07毫米/天降至远端的0.64±0.04毫米/天。微管蛋白的速率从近端的3.10±0.13降至远端的1.01±0.04毫米/天。这些结果表明，轴突上细胞骨架运输速度的梯度并非如先前所认为的那样是轴突径向生长的特定适应性变化。过量细胞骨架蛋白的局部降解可能使轴突在不积累神经丝或微管的情况下适应细胞骨架运输的净减慢。或者，放射性标记蛋白的运输动力学可能受轴浆内标记和未标记细胞骨架蛋白混合的影响；在这种情况下，标记蛋白运动的减慢可能并不反映细胞骨架蛋白总库运输的净减慢。
