Filopodial protrusion driven by density-dependent Ena-TOCA-1 interactions.

Area of Science:

• Cell Biology
• Neuroscience
• Cytoskeleton Dynamics

Background:

• Filopodia are crucial actin-rich cellular protrusions in neuronal development.
• Membrane-binding adaptor proteins regulate filopodia by linking membrane interactions to actin regulators.
• F-BAR domain proteins, like TOCA-1, are key upstream regulators in these networks.

Purpose of the Study:

• To investigate the role of the F-BAR domain protein TOCA-1 (FNBP1L) in filopodial dynamics.
• To analyze the relationship between TOCA-1, Ena/VASP proteins, and filopodial protrusion in Xenopus retinal ganglion cells.

Main Methods:

• Quantitative analysis of TOCA-1 and filopodial dynamics in vivo.
• In vitro assessment of TOCA-1 density effects on Ena/VASP protein binding.
• Two-colour single-molecule localization microscopy (SMLM) to study TOCA-1 and Ena nanoscale association.
• Perturbation of Cdc42 activation using the small-molecule inhibitor CASIN.

Main Results:

• Increased TOCA-1 density enhances Ena/VASP protein binding in vitro.
• TOCA-1 accumulation and co-localization with Ena correlate with filopodial protrusion in vivo.
• TOCA-1 clusters, dependent on a functional SH3 domain and Cdc42 activation, promote filopodial protrusion.
• TOCA-1 and Ena exhibit nanoscale association.

Conclusions:

• TOCA-1 clusters function independently of membrane curvature to recruit and promote Ena activity.
• TOCA-1 plays a significant role in regulating filopodial protrusion via Ena/VASP recruitment.
• Cdc42 activation is essential for TOCA-1-mediated filopodial extension.