Focal adhesion kinase regulates actin nucleation and neuronal filopodia formation during axonal growth

Abstract

The establishment of neural circuits depends on the ability of axonal growth cones to sense their surrounding environment en route to their target. To achieve this, a coordinated rearrangement of cytoskeleton in response to extracellular cues is essential. Although previous studies have identified different chemotropic and adhesion molecules that influence axonal development, the molecular mechanism by which these signals control the cytoskeleton remains poorly understood. Here, we show that in vivo conditional ablation of the focal adhesion kinase gene (Fak) from mouse hippocampal pyramidal cells impairs axon outgrowth and growth cone morphology during development, which leads to functional defects in neuronal connectivity. Time-lapse recordings and in vitro FRAP analysis indicate that filopodia motility is altered in growth cones lacking FAK, probably owing to deficient actin turnover. We reveal the intracellular pathway that underlies this process and describe how phosphorylation of the actin nucleation-promoting factor N-WASP is required for FAK-dependent filopodia formation. Our study reveals a novel mechanism through which FAK controls filopodia formation and actin nucleation during axonal development.

Substrate Topography Determines Neuronal Polarization and Growth In Vitro

“…Tyrosine phosphorylation is considered as one of the key steps in signal transduction and regulation of enzymatic activity and is required in a wide range of signaling pathways such as integrin signaling and focal adhesion kinase mediated actin nucleation [33]–[35]. Hence, we investigated the relationship between this biochemical modification and pillar-induced growth.…”

“…This is the case for e.g. paxillin [34], [49], for the actin nucleation-promoting factor N-WASP [33], and for different sites of focal adhesion kinase phosphorylated by Src [49]. These processes can also work in concert, initiated by mechanical tension that activates for instance mechanosensitive ion channels by the force neurites are exerting on the pillars while elongating [40].…”

Optimising parameters for the differentiation of SH-SY5Y cells to study cell adhesion and cell migration

“…FAK has previously been reported to localise in the growth cone [10] and has been implicated in mediating the response to attractive and repulsive cues as growth cones migrate to their specific target (reviewed by Chacón and Fazzari [11]). FAK is important in axon outgrowth as it controls filopodia formation and actin nucleation through the phosphorylation of N-WASP [12]. High levels of FAK are expressed in the hippocampus and this protein has been shown to be important in long term memory storage [13-15].…”

Building Blocks of Functioning Brain: Cytoskeletal Dynamics in Neuronal Development

“…Although many studies have established the function of NPFs in motility and cell shape change in nonneuronal cells, very little is known about NPFs in neuron morphology establishment. Suetsugu et al suggest that a balance between WASP phosphorylation and degradation is essential to neurite extension and required for axonal growth-cone filopodia formation (Chacon et al, 2012; Suetsugu et al, 2002). Junction-mediating and regulatory protein (JMY) promotes actin polymerization either by functioning as an NPF for the Arp2/3 complex or through its tandem-monomer-binding property independent of Arp2/3 activity.…”