FIGURE 1.

The neuronal actin cytoskeleton and its regulation by external factors. (A) Overview of different actin structures present in pyramidal neurons: local F-actin enrichments called actin patches, longitudinal actin fibers, and a cortical periodic actin/spectrin lattice termed “actin rings” can be found throughout axon and in dendrites. (B) Dendritic spines contain branched F-actin in the head, and straight bundles as well as a periodic actin lattice in the neck. Directed transport of cargo from the soma to the dendrite is carried out via MTs, and can then be subjected to activity-dependent positioning at the base of activated spines in an F-actin and myosin-dependent manner. EV = endosomal vesicle, RNP = ribonucleoprotein, Mito = mitochondrium. (C) Dynamics of the dendritic actin cytoskeleton are influenced by external cues. Those include the transduction of external signals to the actin cytoskeleton via cell-surface receptors that couple to Rho-GEFs or ABPs, and Ca²⁺ signaling. The latter involves Ca²⁺ influx through glutamate receptors following synaptic stimulation (1), and Ca²⁺ release from internal stores, triggered for instance by BDNF-TrkB-signaling (2). Both pathways include the activation of Rho-GTPases (3), which act as “molecular switches” that govern a multitude of cellular functions. Diffusible factors, like Ca²⁺, Rho-GTPases, CaMKIIβ and other downstream effectors, can spread the signal from their activation site to the dendrite and to other spines (4). ER = endoplasmatic reticulum.