Department of Pathology and Laboratory Medicine, Robert Wood Johnson Medical School, University of Medicine and Dentistry New Jersey, Piscataway, New Jersey, United States of America.
PLoS Genet. 2012;8(8):e1002863. doi: 10.1371/journal.pgen.1002863. Epub 2012 Aug 2.
Many cells in a developing embryo, including neurons and their axons and growth cones, must integrate multiple guidance cues to undergo directed growth and migration. The UNC-6/netrin, SLT-1/slit, and VAB-2/Ephrin guidance cues, and their receptors, UNC-40/DCC, SAX-3/Robo, and VAB-1/Eph, are known to be major regulators of cellular growth and migration. One important area of research is identifying the molecules that interpret this guidance information downstream of the guidance receptors to reorganize the actin cytoskeleton. However, how guidance cues regulate the actin cytoskeleton is not well understood. We report here that UNC-40/DCC, SAX-3/Robo, and VAB-1/Eph differentially regulate the abundance and subcellular localization of the WAVE/SCAR actin nucleation complex and its activator, Rac1/CED-10, in the Caenorhabditis elegans embryonic epidermis. Loss of any of these three pathways results in embryos that fail embryonic morphogenesis. Similar defects in epidermal enclosure have been observed when CED-10/Rac1 or the WAVE/SCAR actin nucleation complex are missing during embryonic development in C. elegans. Genetic and molecular experiments demonstrate that in fact, these three axonal guidance proteins differentially regulate the levels and membrane enrichment of the WAVE/SCAR complex and its activator, Rac1/CED-10, in the epidermis. Live imaging of filamentous actin (F-actin) in embryos developing in the absence of individual guidance receptors shows that high levels of F-actin are not essential for polarized cell migrations, but that properly polarized distribution of F-actin is essential. These results suggest that proper membrane recruitment and activation of CED-10/Rac1 and of WAVE/SCAR by signals at the plasma membrane result in polarized F-actin that permits directed movements and suggest how multiple guidance cues can result in distinct changes in actin nucleation during morphogenesis.
许多胚胎中的细胞，包括神经元及其轴突和生长锥，必须整合多种导向线索才能进行定向生长和迁移。UNC-6/netrin、SLT-1/slit 和 VAB-2/Ephrin 导向线索及其受体 UNC-40/DCC、SAX-3/Robo 和 VAB-1/Eph 是细胞生长和迁移的主要调节因子。一个重要的研究领域是确定在导向受体下游解释这种导向信息的分子，以重新组织肌动蛋白细胞骨架。然而，导向线索如何调节肌动蛋白细胞骨架还不是很清楚。我们在这里报告 UNC-40/DCC、SAX-3/Robo 和 VAB-1/Eph 差异调节 WAVE/SCAR 肌动蛋白成核复合物及其激活因子 Rac1/CED-10 在秀丽隐杆线虫胚胎表皮中的丰度和亚细胞定位。这三种途径中的任何一种缺失都会导致胚胎形态发生失败。在秀丽隐杆线虫胚胎发育过程中缺失 CED-10/Rac1 或 WAVE/SCAR 肌动蛋白成核复合物时，表皮包封也会出现类似的缺陷。遗传和分子实验表明，事实上，这三种轴突导向蛋白差异调节 WAVE/SCAR 复合物及其激活因子 Rac1/CED-10 在表皮中的水平和膜富集。在单个导向受体缺失的情况下发育的胚胎中丝状肌动蛋白 (F-actin) 的实时成像表明，高水平的 F-actin 对于极化细胞迁移不是必需的，但 F-actin 的正确极化分布是必需的。这些结果表明，信号在质膜处适当募集和激活 CED-10/Rac1 和 WAVE/SCAR 会导致极化的 F-actin，从而允许定向运动，并表明多个导向线索如何在形态发生过程中导致肌动蛋白成核的不同变化。
