Lamoureux P, Zheng J, Buxbaum R E, Heidemann S R
Department of Physiology, Michigan State University, East Lansing 48824-1101.
J Cell Biol. 1992 Aug;118(3):655-61. doi: 10.1083/jcb.118.3.655.
We have examined the relationship between tension, an intrinsic stimulator of axonal elongation, and the culture substrate, an extrinsic regulator of axonal elongation. Chick sensory neurons were cultured on three substrata: (a) plain tissue culture plastic; (b) plastic treated with collagen type IV; and (c) plastic treated with laminin. Calibrated glass needles were used to increase the tension loads on growing neurites. We found that growth cones on all substrata failed to detach when subjected to two to threefold and in some cases 5-10-fold greater tensions than their self-imposed rest tension. We conclude that adhesion to the substrate does not limit the tension exerted by growth cones. These data argue against a "tug-of-war" model for substrate-mediated guidance of growth cones. Neurite elongation was experimentally induced by towing neurites with a force-calibrated glass needle. On all substrata, towed elongation rate was proportional to applied tension above a threshold tension. The proportionality between elongation rate and tension can be regarded as the growth sensitivity of the neurite to tension, i.e., its growth rate per unit tension. On this basis, towed growth on all substrata can be described by the simple linear equation: elongation rate = sensitivity x (applied tension - tension threshold) The numerical values of tension thresholds and neurite sensitivities varied widely among different neurites. On all substrata, thresholds varied from near zero to greater than 200 mudynes, with some tendency for thresholds to cluster between 100 and 150 mudynes. Similarly, the tension sensitivity of neurites varied between 0.5 and 5.0 microns/h/mudyne. The lack of significant differences among sensitivity or threshold values on the various substrata suggest to use that the substratum does not affect the internal "set points" of the neurite for its response to tension. The growth cone of chick sensory neurons is known to pull on its neurite. The simplest cytomechanical model would assume that both growth cone-mediated elongation and towed growth are identical as far as tension input and elongation rate are concerned. We used the equation above and mean values for thresholds and sensitivity from towing experiments to predict the mean growth cone-mediated elongation rate based on mean rest tensions. These predictions are consistent with the observed mean values.
我们研究了轴突伸长的内在刺激因素——张力与轴突伸长的外在调节因素——培养底物之间的关系。将鸡感觉神经元培养在三种底物上：(a) 普通组织培养塑料；(b) 用IV型胶原处理过的塑料；(c) 用层粘连蛋白处理过的塑料。使用校准过的玻璃针来增加生长中神经突上的张力负荷。我们发现，当施加的张力比其自身施加的静息张力大两到三倍，在某些情况下大5 - 10倍时，所有底物上的生长锥都不会脱离。我们得出结论，与底物的黏附并不限制生长锥施加的张力。这些数据反驳了底物介导生长锥导向的“拔河”模型。通过用校准过力的玻璃针牵引神经突，实验性地诱导神经突伸长。在所有底物上，牵引伸长率与高于阈值张力的施加张力成正比。伸长率与张力之间的比例关系可被视为神经突对张力的生长敏感性，即其单位张力下的生长速率。在此基础上，所有底物上的牵引生长都可以用简单的线性方程来描述：伸长率 = 敏感性×(施加张力 - 张力阈值) 不同神经突的张力阈值和神经突敏感性的数值差异很大。在所有底物上，阈值从接近零到大于200微达因不等，阈值有一些聚集在100到150微达因之间的趋势。同样，神经突的张力敏感性在0.5到5.0微米/小时/微达因之间变化。不同底物上的敏感性或阈值数值缺乏显著差异表明，底物不会影响神经突对张力反应的内部“设定点”。已知鸡感觉神经元的生长锥会牵拉其神经突。最简单的细胞力学模型会假定，就张力输入和伸长率而言，生长锥介导的伸长和牵引生长是相同的。我们使用上述方程以及牵引实验中阈值和敏感性的平均值，根据平均静息张力来预测平均生长锥介导的伸长率。这些预测与观察到的平均值一致。
