Joshi H C, Chu D, Buxbaum R E, Heidemann S R
J Cell Biol. 1985 Sep;101(3):697-705. doi: 10.1083/jcb.101.3.697.
We report in this article that the retraction of PC 12 neurites, unlike that of other cultured neurons, is due to tension within the neurite. Retraction is rapid and independent of metabolic energy. Transection of one arm of a branched neurite immediately causes the remaining arm to take up a new equilibrium position between attachment points. Similarly, detachment of one growth cone of a cell causes the cell body to move to a new equilibrium position between the remaining neurites. These observations provide direct evidence for the suspension of the cell soma among a network of tensioned neurites. We used retraction as an assay for neurite tension to examine the role of actin filaments and microtubules in neurite support and elongation. Our data suggest that microtubules (MTs) within PC 12 neurites are under compression, supporting tension within the actin network. Treatment of cells with drugs that disrupt actin networks, cytochalasin D or erythro-9-[3-(2-hydroxynonyl)]adenosine eliminates retraction regardless of the absence of MTs, lack of adhesion to the substratum, or integrity of the neurite. Conversely, stimulation of actin polymerization by injection of phalloidin causes retraction of neurites. Treatments that depolymerize MTs, nocodazole or cold, cause retraction of neurites, which suggests that microtubules support this tension, i.e., are under compression. Stabilization of MTs with taxol stabilizes neurites to retraction and under appropriate circumstances can drive neurite extension. Taxol-stimulated neurite extension is augmented by combined treatment with anti-actin drugs. This is consistent with the actin network's normally exerting a force opposite that of MT assembly. Cytochalasin and erythro-9-[3-(2-hydroxynonyl)] adenosine were found to increase slightly the dose of nocodazole required for MT depolymerization. This is consistent with the postulated balance of forces and also suggests that alteration of the compression borne by the microtubules could serve as a local regulator for MT polymerization during neurite outgrowth.
我们在本文中报告，与其他培养的神经元不同，PC12神经突的回缩是由于神经突内的张力所致。回缩迅速且与代谢能量无关。切断分支神经突的一个分支会立即导致其余分支在附着点之间占据新的平衡位置。同样，细胞的一个生长锥脱离会导致细胞体移动到其余神经突之间的新平衡位置。这些观察结果为细胞体悬浮于张紧的神经突网络中提供了直接证据。我们使用回缩作为神经突张力的检测方法，以研究肌动蛋白丝和微管在神经突支撑和伸长中的作用。我们的数据表明，PC12神经突内的微管处于压缩状态，支持肌动蛋白网络内的张力。用破坏肌动蛋白网络的药物细胞松弛素D或erythro-9-[3-(2-羟基壬基)]腺苷处理细胞，无论微管是否存在、对底物的粘附是否缺乏或神经突的完整性如何，都会消除回缩。相反，通过注射鬼笔环肽刺激肌动蛋白聚合会导致神经突回缩。使微管解聚的处理，如诺考达唑或低温，会导致神经突回缩，这表明微管支持这种张力，即处于压缩状态。用紫杉醇稳定微管可使神经突稳定以防回缩，在适当情况下可驱动神经突伸长。紫杉醇刺激的神经突伸长通过与抗肌动蛋白药物联合处理而增强。这与肌动蛋白网络通常施加与微管组装相反的力一致。发现细胞松弛素和erythro-9-[3-(2-羟基壬基)]腺苷会略微增加微管解聚所需的诺考达唑剂量。这与假定的力的平衡一致，也表明微管所承受的压缩变化可作为神经突生长过程中微管聚合的局部调节剂。
