[论文解读] Self Organized Criticality in the Neural Networks

M. N. Najafi|arXiv (Cornell University)|Jun 3, 2013

Neural Networks and Applications参考文献 1被引用 3

一句话总结

本研究鉴定出RhoD是哺乳动物细胞中纺锤状样延伸突起的关键调节因子，其在FGF2/4/8信号激活下通过mDia3C诱导肌动蛋白聚合，形成稳定且具有运动性的突起，可运输类似内体的囊泡并介导细胞间通讯。RhoD-mDia3C轴对于FGF诱导的突起形成及其功能至关重要。

ABSTRACT

The small GTPase RhoD regulates actin cytoskeleton to collapse actin stress fibers and focal adhesions, resulting in suppression of cell migration and cytokinesis. It also induces alignment of early endosomes along actin filaments and reduces their motility. We show here that a constitutively activated RhoD generated two types of actin-containing thin peripheral cellular protrusions distinct from Cdc42-induced filopodia. One was longer, almost straight, immotile, and sensitive to fixation, whereas the other was shorter, undulating, motile, and resistant to fixation. Moreover, cells expressing wild-type RhoD extended protrusions toward fibroblast growth factor (FGF) 2/4/8-coated beads. Stimulation of wild-type RhoD-expressing cells with these FGFs also caused formation of cellular protrusions. Nodules moved through the RhoD-induced longer protrusions, mainly toward the cell body. Exogenously expressed FGF receptor was associated with these moving nodules containing endosome-like vesicles. These results suggest that the protrusions are responsible for intercellular communication mediated by FGF and its receptor. Accordingly, the protrusions are morphologically and functionally equivalent to cytonemes. RhoD was activated by FGF2/4/8. Knockdown of RhoD interfered with FGF-induced protrusion formation. Activated RhoD specifically bound to mDia3C and facilitated actin polymerization together with mDia3C. mDia3C was localized to the tips or stems of the protrusions. In addition, constitutively activated mDia3C formed protrusions without RhoD or FGF stimulation. Knockdown of mDia3 obstructed RhoD-induced protrusion formation. These results imply that RhoD activated by FGF signaling forms cytoneme-like protrusions through activation of mDia3C, which induces actin filament formation.

研究动机与目标

• 研究RhoD在细胞迁移和胞质分裂过程中调节肌动蛋白细胞骨架动态的机制。
• 确定RhoD如何影响FGF信号响应下特殊肌动蛋白基底突起的形成与功能。
• 阐明RhoD通过与mDia3C相互作用调控突起形成的分子机制。

提出的方法

• 表达组成型激活的RhoD，诱导哺乳动物细胞中不同类型肌动蛋白含有的突起形成。
• 使用包被FGF的微珠刺激表达野生型RhoD的细胞，评估突起诱导情况。
• 通过活细胞成像和固定实验，表征突起的形态、运动性及稳定性。
• 采用共免疫沉淀和下拉实验检测RhoD与mDia3C的结合能力。
• 通过RNAi介导的RhoD或mDia3基因敲低，评估突起形成对功能的依赖性。
• 利用免疫荧光和共聚焦显微镜定位mDia3C在突起顶端和基部的位置。

实验结果

研究问题

• RQ1 RhoD如何调控与丝状伪足不同的肌动蛋白基底突起的形成？
• RQ2 FGF2/4/8在激活RhoD及诱导突起形成中发挥何种作用？
• RQ3 RhoD如何与mDia3C相互作用以促进突起中肌动蛋白的聚合？
• RQ4 RhoD诱导的突起在功能上是否等同于介导细胞间信号转导的纺锤状突起？
• RQ5 mDia3C在RhoD介导的突起形成中具有何种必要性？

主要发现

• 组成型激活的RhoD诱导出两种形态明显不同的肌动蛋白含突起：一种为较长、笔直、无运动性、固定后易丢失的突起，另一种为较短、波浪状、具有运动性、固定后仍保持的突起。
• 表达野生型RhoD的细胞会向包被FGF2/4/8的微珠延伸突起，且仅通过FGF刺激即可诱导突起形成。
• 含有类似内体囊泡的颗粒沿较长的RhoD诱导突起向细胞体方向移动，提示其具有运输功能。
• 外源表达的FGF受体与这些移动颗粒相关联，表明其具备功能性细胞间信号转导能力。
• 激活状态的RhoD特异性结合mDia3C，并与mDia3C协同促进肌动蛋白聚合。
• RhoD或mDia3的敲低会破坏突起形成，而单独表达组成型激活的mDia3C即可在无RhoD或FGF输入的情况下诱导突起形成。