Focal Rings and Filopodial Emergence in Neuronal Growth Cones

图斯尼，k.w.， K. Balazovich和M. Steketee，密歇根大学安娜堡分校MCDB系和神经科学项目，丝状足是一种感觉和运动结构，对生长锥的运动和引导至关重要。如果没有丝状伪足，生长锥可以前进，但不能对引导信号做出反应，丝状伪足的尖端专门用于信号接收，并且单个丝状伪足尖端粘附到提示上可以改变运动的离散元素以及轴突轨迹。通过相关的光学记录、电子显微镜和免疫标记对单个丝状足进行分析，以阐明丝状足粘连在运动和引导中的作用。我们报告说，与普遍的看法相反，所有的基材粘连不是平等的。单个丝状足在三个部位发生粘连，这些粘连在功能上有明显的不同。舌尖粘连足以发出信号。基底粘连位于丝足基部和内部肌动蛋白束，与一种新的细胞器“焦环”有关，并在丝足的出现和动力学中起作用。轴粘连位于丝状轴上，缺乏焦环，并控制层状（“面纱”）推进的程度。当存在时，轴粘连抑制面纱前进。面纱不受基底粘连的影响，但在遇到轴粘连时停止前进。面纱容易沿着缺乏轴粘连的丝状伪足前进，但不沿着显示轴粘连的丝状伪足前进。这种关系不是由于面纱在前进时去除粘连。减少抗体黏附降低丝状足与轴黏附的比例，并协调增加膜的推进。特别有趣的是，引导线索可以通过瞄准轴粘连起作用。当丝状尖端接触到抑制性线索时，信号诱导轴粘连并协调消除面纱前进，而与允许性线索接触则阻止轴粘连并协调促进面纱前进。以轴粘连为目标的线索，会产生轴突前进的系统性改变，从而调节轴突轨迹。因此，个体生长锥丝状足发育出三种功能不同的粘连，可以帮助调节运动和导航。这些粘接剂也有结构和成分上的区别。例如，基粘连和轴粘连与Rho GTPases的关联不同，基粘连与Rac1的关联不同，轴粘连与Cdc42的关联不同。我们目前正在测试一种假设，即Rac1和Cdc42控制运动的一种方式是通过选择性地诱导功能不同的粘连。由NIH-21308和NSF-0212326资助。

0212326TosneyAxon Guidance & Neural Plasticity Oral preferred, Poster is OK THREE FUNCTIONALLY DISTINCT ADHESIONS IN FILOPODIA Tosney, K.W., K. Balazovich and M. Steketee, MCDB Department and Neuroscience Program, University of Michigan, Ann Arbor, MI 48109 Filopodia are sensory and motile structures, vital for the motility and guidance of growth cones. Growth cones can advance but cannot respond to guidance cues if bereft of filopodia, the tips of their filopodia are specialized for signal reception, and adhesion of just a single filopodial tip to a cue can alter discrete elements of motility as well as axonal trajectory. Individual filopodia were analyzed with correlated optical recording, electron microscopy and immunolabeling, to elucidate the role of filopodial adhesions in motility and guidance. We report that, contrary to common belief, all substrate adhesions are not created equal. Individual filopodia develop adhesions at three sites, and these adhesions differ distinctively in function. Tip adhesions suffice to signal. Basal adhesions lie at filopodial bases and along internal actin bundles, associate with a novel organelle, the "focal ring," and function in filopodial emergence and dynamics. Shaft adhesions lie along filopodial shafts, lack a focal ring, and control the extent of lamellar ("veil") advance. When present, shaft adhesions inhibit veil advance. Veils are unaffected by basal adhesions, but stop advancing as they encountered shaft adhesions. Veils readily advance along filopodia lacking shaft adhesions, but not along filopodia displaying shaft adhesions. This relationship is not due to veils removing adhesions as they advance. Reducing adhesion with antibodies decreases the proportion of filopodia with shaft adhesions and coordinately increases veil advance. Of particular interest, guidance cues can act by targeting shaft adhesions. When a filopodial tip contacts an inhibitory cue, the signal induces shaft adhesions and coordinately abolishes veil advance, whereas contact with a permissive cue prohibits shaft adhesions and coordinately promotes veil advance. Cues that target shaft adhesions produce systematic changes in veil advance and thereby modulate axonal trajectory. Individual growth cone filopodia thus develop three functionally distinct adhesions that can help regulate both motility and navigation. These adhesions also have structural and compositional distinctions. For instance, basal and shaft adhesions differentially associate with Rho GTPases, basal adhesions with Rac1 and shaft adhesions with Cdc42. We are currently testing the hypothesis that one way in which Rac1 and Cdc42 control motility is by selectively inducing adhesions that differ in function. Supported by NIH-21308 and NSF-0212326.