Finely-Fabricated Nanomaterials to Reveal Curvature Roles in Neuronal Network Formation

Abstract

In the vertebrate central nervous system, exploratory filopodia transiently form on dendritic branches to sample the neuronal environment and initiate new trans-neuronal contacts. While much is known about the molecules that control filopodia extension and subsequent maturation into functional synapses, the mechanisms that regulate initiation of these dynamic, actin-rich structures have remained elusive.Using nanomaterials that deform the plasma membrane of neurons, correlative light-electron microscopy (CLEM) and quantitative live cell microscopy, we find that filopodia initiation is suppressed by recruitment of ArhGAP44 to actin-patches that seed filopodia in dendritic branches. Recruitment is mediated by binding of a membrane curvature-sensing ArhGAP44 N-BAR domain to convoluted plasma membrane sections that were deformed inward by acto-myosin mediated contractile forces. A GAP domain in the enriched ArhGAP44 triggers local Rac-GTP hydrolysis, thus reducing local actin polymerization required for filopodia formation. ArhGAP44 expression increases as the neuronal network is established and the frequency of exploratory filopodia formation is diminished, suggesting that ArhGAP44 may facilitate the transition of neurons from a dynamic exploratory mode to a mature more static state, a hallmark of nervous system development.Together, our data reveals a local and receptor-independent auto-regulatory mechanism that limits initiation of exploratory filopodia in neurons via protein recruitment to nanoscale membrane deformations.