Cytoskeletal scaffolds in neuronal development

Neuronal polarization is one of the most studied topics in neuroscience. In less than seven days neurites sprout out from the neuron, explore the surrounding environment and mature in axon or dendrites. This process is possible because the neuronal cytoskeleton can rapidly modify its architecture changing neuronal shape and length. Among all, two main proteins are involved: tubulin that supports the neurite elongation and builds a solid frame, while actin supports pathfinding. In this period of important cytoskeletal changes, it is possible to observe the actin waves (AW) that are highly dynamic structures emerging at the neurite base which move up to its tip, causing a transient retraction of the growth cone (GC). Since their discovery in 1988, there have been only few studies about AWs, usually linked to the neurite outgrowth and axon elongation. In the present work, I used long term live cell imaging to investigate alternative roles of such cytoskeletal phenomena. I examined in details AWs and I concluded that they do not promote the neurite outgrowth and that neurites can elongate for hundreds of microns without the AWs. Super resolution nanoscopy indicates that myosin II shapes the GC like AWs structure. The highly concentrated myosin inside the wave can bend the tubulin that support the neurite provoking twists and kinks in the microtubular cytoskeleton. These tubulin twists (TT) cause the GC retraction and are completely abolished with the inhibition of myosin II, that compromises the AW morphology. My results indicate that myosin II has an important role in the AWs dynamics and can bend the tubulin in a way that was not previously observed. Finally, we suggested a role for AWs and TTs in GC exploration and in neurite maturation. Part of these results have already been published in Frontiers in Cellular Neuroscience in the article: Actin waves do not boost neurite outgrowth in the early stages of neuron maturation. We have a second manuscript in preparation entitled “Tubulin twists drive Growth Cone retraction and promote tubulin mixed polarity”.