Department of Biological Sciences, University of Notre Dame, 100 Galvin Life Science Center, Notre Dame, IN 46556, USA; Center for Stem Cells and Regenerative Medicine, University of Notre Dame, 101 Galvin Hall, Notre Dame, IN 46556, USA.
Department of Biological Sciences, University of Notre Dame, 100 Galvin Life Science Center, Notre Dame, IN 46556, USA; Center for Stem Cells and Regenerative Medicine, University of Notre Dame, 101 Galvin Hall, Notre Dame, IN 46556, USA.
Curr Biol. 2019 Aug 19;29(16):2652-2664.e4. doi: 10.1016/j.cub.2019.06.078. Epub 2019 Aug 1.
Synaptic vesicles are indispensable for neuronal communication in mature circuits. Synaptic vesicle biogenesis must be concurrent with axon navigation for synaptogenesis, but whether synaptic vesicles are functionally employed in circuit formation before synaptogenesis is poorly understood. Here, we use time-lapse imaging and transgenesis in zebrafish to visualize the role of synaptic-like vesicles in navigation of dorsal root ganglia pioneer axons. We identify that synaptic-like vesicles accumulate in the central growth cone as the pioneer axon breaches the spinal boundary at the dorsal root entry zone. Inhibition of vesicle release with cell-specific tetanus toxin expression results in pioneer axon pathfinding defects and altered spinal entry. We further show that the matrix metalloproteinase (MMP) mmp14a is required in pioneer axons to navigate across the boundary of the spinal cord and, with super-resolution microscopy, is positioned with synaptic vesicles at the boundary. Manipulations of concurrent actin reorganization reveal that actin remodeling drives vesicle release and subsequent MMP activity. Together, these data point to an indispensable role for synaptic-like vesicles at specific points in axon navigation as regulators of growth cone microenvironment.
突触小泡对于成熟回路中的神经元通讯是不可或缺的。突触小泡的生物发生必须与轴突导航同步进行，以促进突触发生，但在突触发生之前，突触小泡是否在回路形成中发挥功能尚不清楚。在这里，我们使用斑马鱼的延时成像和转基因技术来可视化突触样小泡在背根神经节先驱轴突导航中的作用。我们发现，突触样小泡在中央生长锥中积累，因为先驱轴突在背根进入区突破脊髓边界。用细胞特异性破伤风毒素表达抑制囊泡释放会导致先驱轴突寻路缺陷和脊髓进入改变。我们进一步表明，基质金属蛋白酶（MMP）mmp14a 在先驱轴突中是必需的，以跨越脊髓的边界，并且通过超分辨率显微镜，与突触小泡一起定位于边界。对并发肌动蛋白重排的操作表明，肌动蛋白重塑驱动囊泡释放和随后的 MMP 活性。总之，这些数据表明，突触样小泡在轴突导航的特定点作为生长锥微环境的调节剂，起着不可或缺的作用。
