O'Connor T P, Bentley D
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
J Cell Biol. 1993 Nov;123(4):935-48. doi: 10.1083/jcb.123.4.935.
Directed outgrowth of neural processes must involve transmission of signals from the tips of filopodia to the central region of the growth cone. Here, we report on the distribution and dynamics of one possible element in this process, actin, in live growth cones which are reorienting in response to in situ guidance cues. In grasshopper embryonic limbs, pioneer growth cones respond to at least three types of guidance cues: a limb axis cue, intermediate target cells, and a circumferential band of epithelial cells. With time-lapse imaging of intracellularly injected rhodamine-phalloidin and rhodamine-actin, we monitored the distribution of actin during growth cone responses to these cues. In distal limb regions, accumulation of actin in filopodia and growth cone branches accompanies continued growth, while reduction of actin accompanies withdrawal. Where growth cones are reorienting to intermediate target cells, or along the circumferential epithelial band, actin selectively accumulates in the proximal regions of those filopodia that have contacted target cells or are extending along the band. Actin accumulations can be retrogradely transported along filopodia, and can extend into the central region of the growth cone. These results suggest that regulation and translocation of actin may be a significant element in growth cone steering.
神经突起的定向生长必定涉及从丝状伪足尖端到生长锥中心区域的信号传递。在此，我们报告了在响应原位引导线索而重新定向的活生长锥中，这一过程中一种可能的元素——肌动蛋白的分布和动态变化。在蝗虫胚胎肢体中，先驱生长锥对至少三种类型的引导线索做出反应：肢体轴线索、中间靶细胞以及上皮细胞的圆周带。通过对细胞内注射罗丹明 - 鬼笔环肽和罗丹明 - 肌动蛋白进行延时成像，我们监测了生长锥对这些线索做出反应时肌动蛋白的分布情况。在肢体远端区域，丝状伪足和生长锥分支中肌动蛋白的积累伴随着持续生长，而肌动蛋白的减少则伴随着回缩。当生长锥重新定向至中间靶细胞或沿着圆周上皮带时，肌动蛋白选择性地在那些已接触靶细胞或沿着带延伸的丝状伪足的近端区域积累。肌动蛋白积累物可沿丝状伪足逆行运输，并可延伸至生长锥的中心区域。这些结果表明，肌动蛋白的调节和转运可能是生长锥转向的一个重要因素。
