Department of Molecular Biosciences, Program in Molecular, Cellular, and Developmental Biology, University of Kansas, Lawrence, KS, United States of America.
PLoS Genet. 2019 Jun 24;15(6):e1007960. doi: 10.1371/journal.pgen.1007960. eCollection 2019 Jun.
UNC-6/Netrin is a conserved axon guidance cue that directs growth cone migrations in the dorsal-ventral axis of C. elegans and in the vertebrate spinal cord. UNC-6/Netrin is expressed in ventral cells, and growth cones migrate ventrally toward or dorsally away from UNC-6/Netrin. Recent studies of growth cone behavior during outgrowth in vivo in C. elegans have led to a polarity/protrusion model in directed growth cone migration away from UNC-6/Netrin. In this model, UNC-6/Netrin first polarizes the growth cone via the UNC-5 receptor, leading to dorsally biased protrusion and F-actin accumulation. UNC-6/Netrin then regulates protrusion based on this polarity. The receptor UNC-40/DCC drives protrusion dorsally, away from the UNC-6/Netrin source, and the UNC-5 receptor inhibits protrusion ventrally, near the UNC-6/Netrin source, resulting in dorsal migration. UNC-5 inhibits protrusion in part by excluding microtubules from the growth cone, which are pro-protrusive. Here we report that the RHO-1/RhoA GTPase and its activator GEF RHGF-1 inhibit growth cone protrusion and MT accumulation in growth cones, similar to UNC-5. However, growth cone polarity of protrusion and F-actin were unaffected by RHO-1 and RHGF-1. Thus, RHO-1 signaling acts specifically as a negative regulator of protrusion and MT accumulation, and not polarity. Genetic interactions are consistent with RHO-1 and RHGF-1 acting with UNC-5, as well as with a parallel pathway, to regulate protrusion. The cytoskeletal interacting molecule UNC-33/CRMP was required for RHO-1 activity to inhibit MT accumulation, suggesting that UNC-33/CRMP might act downstream of RHO-1. In sum, these studies describe a new role of RHO-1 and RHGF-1 in regulation of growth cone protrusion by UNC-6/Netrin.
UNC-6/Netrin 是一种保守的轴突导向线索，它指导秀丽隐杆线虫的背腹轴和脊椎动物脊髓中的生长锥迁移。UNC-6/Netrin 在腹侧细胞中表达，生长锥向腹侧或背侧远离 UNC-6/Netrin 迁移。最近对秀丽隐杆线虫体内生长锥生长的研究导致了一个远离 UNC-6/Netrin 的定向生长锥迁移的极性/突起模型。在这个模型中，UNC-6/Netrin 通过 UNC-5 受体首先使生长锥极化，导致背侧偏向的突起和 F-肌动蛋白积累。UNC-6/Netrin 然后根据这种极性调节突起。受体 UNC-40/DCC 驱动突起向背侧，远离 UNC-6/Netrin 源，而 UNC-5 受体抑制靠近 UNC-6/Netrin 源的腹侧突起，导致背侧迁移。UNC-5 通过将微管从生长锥中排除来抑制突起，微管是促进突起的。在这里，我们报告 RHO-1/RhoA GTPase 及其激活因子 RHGF-1 抑制生长锥突起和生长锥中的微管积累，类似于 UNC-5。然而，生长锥突起和 F-肌动蛋白的极性不受 RHO-1 和 RHGF-1 的影响。因此，RHO-1 信号作为突起和微管积累的负调节剂特异性作用，而不是极性。遗传相互作用与 RHO-1 和 RHGF-1 与 UNC-5 以及平行途径一起作用以调节突起一致。细胞骨架相互作用分子 UNC-33/CRMP 是 RHO-1 活性抑制微管积累所必需的，这表明 UNC-33/CRMP 可能作为 RHO-1 的下游分子发挥作用。总之，这些研究描述了 RHO-1 和 RHGF-1 在 UNC-6/Netrin 调节生长锥突起中的新作用。
