Growth cone-like waves transport actin and promote axonogenesis and neurite branching.

Axonogenesis involves a shift from uniform delivery of materials to all neurites to preferential delivery to the putative axon, supporting its more rapid extension. Waves, growth cone-like structures that propagate down the length of neurites, were shown previously to correlate with neurite growth in dissociated cultured hippocampal neurons. Waves are similar to growth cones in their structure, composition and dynamics. Here, we report that waves form in all undifferentiated neurites, but occur more frequently in the future axon during initial neuronal polarization. Moreover, wave frequency and their impact on neurite growth are altered in neurons treated with stimuli that enhance axonogenesis. Coincident with wave arrival, growth cones enlarge and undergo a marked increase in dynamics. Through their engorgement of filopodia along the neurite shaft, waves can induce de novo neurite branching. Actin in waves maintains much of its cohesiveness during transport whereas actin in non-wave regions of the neurite rapidly diffuses as measured by live cell imaging of photoactivated GFP-actin and photoconversion of Dendra-actin. Thus, waves represent an alternative axonal transport mechanism for actin. Waves also occur in neurons in organotypic hippocampal slices where they propagate along neurites in the dentate gyrus and the CA regions and induce branching. Taken together, our results indicate that waves are physiologically relevant and contribute to axon growth and branching via the transport of actin and by increasing growth cone dynamics.

轴突发生涉及从向所有神经突均匀输送物质转变为优先向假定的轴突输送物质，以支持其更快速的延伸。波，这种沿神经突长度传播的类似生长锥的结构，先前已表明与离散培养的海马神经元中的神经突生长相关。波在结构、组成和动力学方面与生长锥相似。在此，我们报道波在所有未分化的神经突中形成，但在初始神经元极化过程中在未来的轴突中更频繁地出现。此外，在接受增强轴突发生的刺激处理的神经元中，波的频率及其对神经突生长的影响发生改变。与波的到达同时，生长锥增大并在动力学方面显著增加。通过使丝状伪足在神经突轴上充血，波可诱导神经突新生分支。通过对光活化的绿色荧光蛋白 - 肌动蛋白的活细胞成像以及Dendra - 肌动蛋白的光转化测量，波中的肌动蛋白在运输过程中保持其大部分的内聚力，而神经突非波区域的肌动蛋白则迅速扩散。因此，波代表了一种肌动蛋白的替代轴突运输机制。波也出现在器官型海马切片的神经元中，它们沿齿状回和CA区的神经突传播并诱导分支。综上所述，我们的结果表明波具有生理相关性，并通过肌动蛋白的运输以及增加生长锥动力学来促进轴突生长和分支。