Transient localization of the Arp2/3 complex initiates neuronal dendrite branching in vivo

Abstract

The formation of neuronal dendrite branches is fundamental for the wiring and function of the nervous system. Indeed, dendrite branching enhances the coverage of the neuron's receptive field and modulates the initial processing of incoming stimuli. Complex dendrite patterns are achieved in vivo through a dynamic process of de novo branch formation, branch extension and retraction. The first step towards branch formation is the generation of a dynamic filopodium-like branchlet. The mechanisms underlying the initiation of dendrite branchlets are therefore crucial to the shaping of dendrites. Through in vivo time-lapse imaging of the subcellular localization of actin during the process of branching of Drosophila larva sensory neurons, combined with genetic analysis and electron tomography, we have identified the Actin-related protein (Arp) 2/3 complex as the major actin nucleator involved in the initiation of dendrite branchlet formation, under the control of the activator WAVE and of the small GTPase Rac1. Transient recruitment of an Arp2/3 component marks the site of branchlet initiation in vivo. These data position the activation of Arp2/3 as an early hub for the initiation of branchlet formation.

Vinculin mediated axon growth requires interaction with actin but not talin

“…The actin cytoskeleton binds to a large array of actin-binding proteins, which regulate the structural changes in actin including polymerization and nucleation. The actin-related protein 2/3 (Arp2/3) complex is an important actin nucleator that binds to existing actin filaments and causes branching of actin filaments and neurites (Blanchoin et al, 2000;Mullins et al, 1998;Sturner et al, 2019). We hypothesized that Vcl-T-induced neurite branching is mediated by the Arp2/3 complex.…”

Distinct relations of microtubules and actin filaments with dendritic architecture

“…One study demonstrated moving actin blobs that stabilize at branch points (Nithianandam and Chien, 2018). Another study showed that the Arp2/3 complex driven nucleation of actin initiates branch formation from the F-act enriched location (Sturner et al, 2019). To test whether F-act enrichment occurs preferentially or exclusively in newly formed branches, we analyzed enrichment as a function of Strahler order.…”

“…All motile cells, including neurons, ubiquitously employ F-actin polymerization to drive plasma membrane protrusion, and actin-filled post-synaptic filipodia are involved in synaptogenesis (Ritzenthaler et al, 2000). F-actin polymerization is rate-controlled by nucleators such as Arp2/3 complex, which binds to monomeric actin to facilitate polymerization (Konietzny et al, 2017;Sturner et al, 2019) and enables F-actin polymer branching (Smith et al, 2013), and the formin family, which acts downstream of Rho-GTPases to nucleate unbranched F-actin (Konietzny et al, 2017). In addition to their recognized role in actin nucleation and polymerization (Breitsprecher and Goode, 2013;Chesarone et al, 2010;Kawabata Galbraith and Kengaku, 2019), formins have been also implicated in microtubule stabilization through Formin Homology domain induced acetylation (Thurston et al, 2012).…”

“…While actin polymerization has been shown to drive neurite outgrowth (Chia et al, 2016), contrasting experiments have indicated that actin waves at growth cones do not initiate elongation and neurite outgrowth can occur without F-actin at neurite tips (Mortal et al, 2017). Possibly stabilizing actin blobs are also found at branch points (Nithianandam and Chien, 2018) and nucleation events have been involved in this punctate expression of F-actin (Sturner et al, 2019). Since the local densities of microtubules and F-actin have never been quantified arbor-wide in large numbers of neurons, the multifarious relation between arbor architecture and cytoskeletal composition remains incompletely understood.…”

Deterministic and stochastic rules of branching govern dendritic morphogenesis of sensory neurons

“…Dendrite morphology is regulated cell-intrinsically by transcription factors [4][5][6][7][8] , cytoskeletal regulators [9][10][11][12][13][14][15] , components of endocytic pathway [16][17][18] and secretory pathway 19,20 all of which have been shown to either promote or reduce dendrite branching.…”