Neurite consolidation is an active process requiring constant repression of protrusive activity

Abstract

During development, neurons extend projections that pathfind to reach their appropriate targets. These projections are composed of two distinct domains: a highly dynamic growth cone and a stable neurite shaft, which is considered to be consolidated. Although the regulation of these domains is critical to the appropriate formation of neural networks, the molecular mechanisms that regulate neurite shape remain poorly understood. Here, we show that calpain protease activity localizes to the neurite shaft, where it is essential for the repression of protrusive activity by limiting cortactin levels and inhibiting actin polymerization. Correspondingly, inhibition of calpain by branching factors induces the formation of new growth cones along the neurite shaft through cAMP elevation. These findings demonstrate that neurite consolidation is an active process requiring constant repression of protrusive activity. We also show that sprouting is, at least in part, accomplished by turning off the mechanism of consolidation.

Reggies/Flotillins Regulate Retinal Axon Regeneration in the Zebrafish Optic Nerve and Differentiation of Hippocampal and N2a Neurons

“…Our present study shows cytoskeletal remodeling, necessary for axon growth by FAK, p38, Rho family GTPases (Takeda and Ichijo, 2002;Burridge and Wennerberg, 2004;Govek et al, 2005), and downstream targets such as the N-WASP, Arp2/3, cortactin complex, and cofilin. The Arp2/3 complex has been studied extensively in migrating cells and much less is known on its regulatory function during the differentiation of neurons, yet its components seem to be involved in neuritogenesis in vitro and are triggered by the regulated interaction of different Rho GTPases (Banzai et al, 2000;Pommereit and Wouters, 2007;Korobova and Svitkina, 2008;Mingorance-Le Meur and O'Connor, 2009). RhoA in general inhibits, whereas Rac1 and cdc42 stimulate, process outgrowth (for review, see Govek et al, 2005).…”

Augmented generation of protein fragments during wakefulness as the molecular cause of sleep: a hypothesis

“…Moreover, the maintenance of brain anatomy, including the suppression of sprouting in a stable neurite shaft, has been shown to be an active process mediated by the proteolytic activity of calpains (particularly calpain-2) throughout dendrites and axons, even in the absence of action potentials and accompanying Ca 2þ transients. 121 In other words, the preservation of normal morphologies and connections throughout the nervous system involves a constant generation of protein fragments, above and beyond their production during Ca 2þ transients at active synapses.…”

Involvement of Rho-family GTPases in axon branching

“…Arp2/3 subunits target to axonal actin patches, in both sensory and central nervous system neurons. 15,18 Inhibition of the Arp2/3 complex or upstream regulators decreases the formation of axonal actin patches, filopodia and branches. 15,18,19 Collectively, these studies identify Arp2/3 as a regulator of the earliest stages of axon branching.…”

“…15,18 Inhibition of the Arp2/3 complex or upstream regulators decreases the formation of axonal actin patches, filopodia and branches. 15,18,19 Collectively, these studies identify Arp2/3 as a regulator of the earliest stages of axon branching. It seems likely that additional actin nucleators (e.g., formins or cordon bleu) also contribute to the formation of actin patches, probably through the generation of mother filaments required by Arp2/3 to establish branch filament arrays.…”