Link to bioRxiv paper:
http://biorxiv.org/cgi/content/short/2023.01.04.522504v1?rss=1

Authors: Blake, T. C. A., Fox, H. M., Urbancic, V., Wolowczyk, A., Allgeyer, E. S., Mason, J., Gallop, J. L.

Abstract:
Filopodia are narrow actin-rich protrusions with important roles in neuronal development. The neuronally-enriched TOCA-1/CIP4 family of F-BAR and SH3 domain adaptor proteins have emerged as upstream regulators that link membrane interactions to actin binding proteins in lamellipodia and filopodia, including WAVE and N-WASP nucleation promoting factors and formins. Here, we demonstrate a direct interaction between TOCA-1 and Ena/VASP actin filament elongators that is mediated by clustered SH3 domain interactions. Using Xenopus retinal gangion cell axonal growth cones, where Ena/VASP proteins have a native role in filopodia extension, we show that TOCA-1 localises to filopodia and lamellipodia with a retrograde flow of puncta and correlates with filopodial protrusion. Two-colour single molecule localization microscopy of TOCA-1 and Ena supports their nanoscale association. TOCA-1 clusters coalesce at advancing lamellipodia and filopodia and operate synergistically with Ena to promote filopodial protrusion dependent on a functional SH3 domain. In analogous yet distinct ways to lamellipodin and IRSp53, we propose that transient TOCA-1 clusters recruit and promote Ena activity to orchestrate filopodial protrusion.

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