Abstract
Dendritic spines are actin-rich protrusions that establish excitatory synaptic contacts with surrounding neurons. Reorganization of the actin cytoskeleton is critical for the development and plasticity of dendritic spines, which is the basis for learning and memory. Rho family GTPases are emerging as important modulators of spines and synapses, predominantly through their ability to regulate actin dynamics. Much less is known, however, about the function of guanine nucleotide exchange factors (GEFs), which activate these GTPases, in spine and synapse development. In this study we show that the Rho family GEF Asef2 is found at synaptic sites, where it promotes dendritic spine and synapse formation. Knockdown of endogenous Asef2 with shRNAs impairs spine and synapse formation, whereas exogenous expression of Asef2 causes an increase in spine and synapse density. This effect of Asef2 on spines and synapses is abrogated by expression of GEF activity-deficient Asef2 mutants or by knockdown of Rac, suggesting that Asef2-Rac signaling mediates spine development. Because Asef2 interacts with the F-actin-binding protein spinophilin, which localizes to spines, we investigated the role of spinophilin in Asef2-promoted spine formation. Spinophilin recruits Asef2 to spines, and knockdown of spinophilin hinders spine and synapse formation in Asef2-expressing neurons. Furthermore, inhibition of N-methyl-d-aspartate receptor (NMDA) activity blocks spinophilin-mediated localization of Asef2 to spines. These results collectively point to spinophilin-Asef2-Rac signaling as a novel mechanism for the development of dendritic spines and synapses.
Highlights
The role of Rho family guanine nucleotide exchange factors (GEFs) in dendritic spine formation is currently not well understood
In this study we show that the Rho family GEF Asef2 is found at synaptic sites, where it promotes dendritic spine and synapse formation
The function of Rho family GEFs in spine development represents an increasingly exciting area of study given that not much is currently known about the contribution of these proteins to spine and synapse formation
Summary
The role of Rho family GEFs in dendritic spine formation is currently not well understood. Results: The Rho family GEF Asef promotes spine and synapse formation through activation of Rac and spinophilin-mediated localization to spines. In this study we show that the Rho family GEF Asef is found at synaptic sites, where it promotes dendritic spine and synapse formation. Inhibition of N-methyl-D-aspartate receptor (NMDA) activity blocks spinophilin-mediated localization of Asef to spines These results collectively point to spinophilin-Asef2-Rac signaling as a novel mechanism for the development of dendritic spines and synapses. Spinophilin knock-out mice display defects in associative learning [43], further emphasizing the importance of this protein in regulating synaptic function Spinophilin could mediate these effects on spines and synapses at least in part through its interaction with proteins such as Asef. These results indicate that spinophilin-Asef2-Rac signaling is important in spine and synapse development
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