Dynamics of nerve cell growth cone : Role of actin binding protein.

发育中的神经细胞的生长锥从它们的前缘投射出丝状足，它们的动态与轴突的伸长和寻径有关。在丝状伪足内部是一束束的F-肌动蛋白，其顶端区域有带刺的(或首先生长的)末端，而底部区域有尖端(或生长缓慢的)末端。然而，丝状足的动力学的确切机制仍然不清楚。丝状伪足中的一种肌动蛋白捆绑蛋白Fasin的敲除导致了培养神经元中丝状伪足的丢失，提示Fascin是肌动蛋白束形成的关键分子。在此，我们发现，在体外，法辛结合的F-肌动蛋白与丝状基座中的F-肌动蛋白具有相同的取向。此外，在肌球蛋白II和肌球蛋白V上，束蛋白/肌动蛋白束可以像单个F-肌动蛋白一样平稳滑动。当肌球蛋白浓度较高时，束蛋白/肌动蛋白束从尖端解体，这种动力学与体内观察到的非常相似。由于肌球蛋白II和肌球蛋白V定位于丝状伪足，我们的结果提示，这些蛋白可能驱动丝状伪足肌动蛋白束向后，并导致丝状伪足基底区的解体。

Growth cone of developing nerve cell projects filopodia from their leading edge, and their dynamics have been implicated in elongation and pathfinding of axon. Inside filopodia are the bundles of F-actin with barbed (or first growing) ends in its tip region, and pointed (or slow growing) ends in the basal region. Precise mechanism of the dynamics of filopodia, however, is still unclear. Knockout of fascin, an actin bundling protein in filopodia, caused the loss of filopodia in cultured neuron, suggesting that fascin is a key player to form actin bundles. Here, we showed that orientation of F-actin bundled by fascin in vitro were the same as those in filopodium. Furthermore, fascin/actin bundles could slide smoothly as fast as individual F-actin on myosin II and myosin V.At higher concentration of myosins, fascin/actin bundles disassemble from the pointed end, the dynamics quite similar to that observed in vivo. Because myosin II and myosin V localize in filopodia, our results suggest that these proteins may drive the filopodial actin bundles backward, and cause the disassembly at basal region of filopodia.