Nerve growth cone lamellipodia contain two populations of actin filaments that differ in organization and polarity.
Nerve growth cone lamellipodia contain two populations of actin filaments that differ in organization and polarity.
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DOI：
10.1083/jcb.119.5.1219
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发表时间：
1992-12
期刊：
影响因子：
--
通讯作者：
Bridgman PC
中科院分区：
文献类型：
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作者：
Lewis AK;Bridgman PC
神经生长锥中肌动蛋白丝的组织和极性用负染色和冷冻蚀刻EM使用透化方案进行研究，当通过视频增强微分干涉对比显微镜观察培养的神经生长锥时，该透化方案在形态学上引起很少可检测的变化。片状伪足肌动蛋白细胞骨架由两个不同的亚群组成：一个是40 - 100 nm宽的丝束从前缘辐射，第二个是分支的短纤维填充在背侧和腹侧膜表面之间的体积。这两个种群共同形成了在扩张的板状伪足中看到的三维结构网络。肌动蛋白丝与腹侧膜表面的相互作用是通过膜相关蛋白沿肌动蛋白丝的长度方向沿着发生的。长束丝人口主要参与这些相互作用。两个种群的细丝尖端似乎只在前缘与膜相互作用;这种相互作用是由球形Triton不溶性材料介导的。肌动蛋白丝的极性由肌球蛋白S1或重肌球蛋白修饰决定。以前的报道表明，运动细胞中肌动蛋白丝的极性是均匀的，有倒刺的末端朝向前缘。我们观察到生长锥片状伪足内的肌动蛋白丝极性是不均匀的;虽然主要取向是有刺端朝向前缘（47 - 56%），但22 - 25%的肌动蛋白丝具有相反的取向，其尖端朝向前缘，19 - 31%平行于前缘。两个肌动蛋白丝群体显示出不同的极性配置文件：较长的长丝似乎主要是定向的，其倒刺端朝向前缘，而短的长丝似乎是随机取向。这两种丝状体的不同长度、组织和极性表明它们在稳定性和功能上不同。成束的长丝，这似乎是更位于腹侧，并与膜蛋白接触的人口，可能是更稳定的短分支丝的人口。长束丝的位置、组织和极性表明，它们可能是板状伪足扩张和由受体介导的底物粘附分子张力产生所必需的。
The organization and polarity of actin filaments in neuronal growth cones was studied with negative stain and freeze-etch EM using a permeabilization protocol that caused little detectable change in morphology when cultured nerve growth cones were observed by video- enhanced differential interference contrast microscopy. The lamellipodial actin cytoskeleton was composed of two distinct subpopulations: a population of 40-100-nm-wide filament bundles radiated from the leading edge, and a second population of branching short filaments filled the volume between the dorsal and ventral membrane surfaces. Together, the two populations formed the three- dimensional structural network seen within expanding lamellipodia. Interaction of the actin filaments with the ventral membrane surface occurred along the length of the filaments via membrane associated proteins. The long bundled filament population was primarily involved in these interactions. The filament tips of either population appeared to interact with the membrane only at the leading edge; this interaction was mediated by a globular Triton-insoluble material. Actin filament polarity was determined by decoration with myosin S1 or heavy meromyosin. Previous reports have suggested that the polarity of the actin filaments in motile cells is uniform, with the barbed ends toward the leading edge. We observed that the actin filament polarity within growth cone lamellipodia is not uniform; although the predominant orientation was with the barbed end toward the leading edge (47-56%), 22-25% of the filaments had the opposite orientation with their pointed ends toward the leading edge, and 19-31% ran parallel to the leading edge. The two actin filament populations display distinct polarity profiles: the longer filaments appear to be oriented predominantly with their barbed ends toward the leading edge, whereas the short filaments appear to be randomly oriented. The different length, organization and polarity of the two filament populations suggest that they differ in stability and function. The population of bundled long filaments, which appeared to be more ventrally located and in contact with membrane proteins, may be more stable than the population of short branched filaments. The location, organization, and polarity of the long bundled filaments suggest that they may be necessary for the expansion of lamellipodia and for the production of tension mediated by receptors to substrate adhesion molecules.