Cytolinker Gas2L1 regulates axon morphology through microtubule-modulated actin stabilization

Abstract
Crosstalk between the actin and microtubule cytoskeletons underlies cellular morphogenesis. Interactions between actin filaments and microtubules are particularly important for establishing the complex polarized morphology of neurons. Here, we characterised the neuronal function of Growth Arrest Specific 2-like 1 (Gas2L1), a protein that can directly bind to actin, microtubules and microtubule plus-end-tracking End Binding proteins. We found that Gas2L1 promotes axon branching, but restricts axon elongation in cultured hippocampal neurons. Using pull-down experiments and in vitro reconstitution assays, in which purified Gas2L1 was combined with actin and dynamic microtubules, we demonstrated that Gas2L1 is autoinhibited. This autoinhibition is relieved by simultaneous binding to actin filaments and microtubules. In neurons, Gas2L1 primarily localizes to the actin cytoskeleton and functions as an actin stabilizer. The ability of Gas2L1 to interact with microtubules directs its actin-stabilizing activity to the axon. We propose that Gas2L1 acts as an actin regulator, the function of which is spatially modulated by microtubules.