Actin waves could contribute to axonogenesis as the waves appear with higher frequencies in the early than later developmental stages in neurites that would become axons. In cultured hippocampal neurons, actin waves propagate from the base to the tip of the neurite once every half hour at a velocity of 3 µm/min ( Ruthel and Banker, 1999 Flynn et al., 2009). Initially, monomeric actin polymerizes to form F-actin that is further organized into higher-order dynamic assemblies like actin waves and trails ( Allard and Mogilner, 2013 Roy, 2016 Inagaki and Katsuno, 2017). In neurons, actin is essential for morphological changes such as neurite formation and growth cone navigation. The actin cytoskeleton, depending on cellular needs, shapes into various dimensions in a spatiotemporal manner. Hence, actin blob localization at future branching sites represents a dendrite-branching mechanism to account for highly diversified dendritic morphology. We identified the F-actin–severing protein Tsr/cofilin as a regulator of dynamic actin blobs and branching activity. Overstabilization of F-actin by the G15S mutant abolished actin blobs and dendrite branching. Interestingly, these actin blobs stalled at sites where new dendrites would branch out in minutes. A dynamic F-actin population that we named actin blobs propagated bidirectionally at an average velocity of 1 µm/min. By performing in vivo imaging of F-actin markers, we found that F-actin was highly dynamic and heterogeneously distributed in dendritic shafts with enrichment at terminal dendrites. However, the knowledge about actin dynamics in dendrites during these processes is limited.

Neuronal dendrites frequently undergo morphological changes by emanating, elongating, and withdrawing branches. The actin cytoskeleton provides structural stability and adaptability to the cell.

Dendrite branching