Synaptic scaffolding protein, nArgBP2, plays a role in dendritic spine formation by controlling actin cytoskeleton

Abstract

Dendritic spines are small actin-rich protrusions that function to receive the excitatory synaptic transmission, which is crucially related to the synaptic plasticity. Hundreds of proteins take part in synaptic activity, consisting of networks in a small dendritic spine with spine head volumes ranging 0.01 µm3 to 0.8 µm3. Representatively, WAVE regulatory complex is well-known as mediating upstream signal Rac1 to the activation of the Arp2/3 complex, arranging actin cytoskeleton. In relation to SH3 interactor, WAVE cooperates with nArgBP2 and other adaptor proteins. However, our understanding of nArgBP2 is limited, and properties of nArgBP2 are merely inferred from non-neuronal cell biology. nArgBP2 is a neuronal specific splice variant of ArgBP2 and an adaptor protein of Ponsin/ArgBP2/Vinexin family, and is enriched postsynaptically. nArgBP2 has a sorbin homology (SoHo) domain in the N-terminal region, a zinc finger in the middle, and three src homology (SH) 3 domains in the C-terminal region. Via its SH3 domains, nArgBP2 interacts with SAPAP, dynamin, synaptojanin, and WAVE isoforms. RNA interference-mediated knock-down of nArgBP2 has a strong effect in dendritic spines of developmental hippocampal neurons. In the developing stage, nArgBP2 knock-down shows a distinct reduction in the number of dendritic spines, but enhances the number of filopodia. Rescue experiments show that knock-down effects are recovered in terms of the number of dendritic spines in the developing stage. When knocking down nArgBP2 in the mature stage, there are no changes in the number of dendritic spines. From live cell imaging, knocking down of nArgBP2 alters shapes and motility of dendritic spines in the developing stage. FRAP (fluorescence recovery after photobleaching) experiments prove that the mobile fraction of actin is increased in the depletion of nArgBP2. In conclusion, nArgBP2 plays a role in dendritic spine formation in the developing stage, organizing synaptic architecture through actin cytoskeleton.