Genetic studies of autism spectrum disorder (ASD) have revealed multigene variations that converge on synaptic dysfunction. DOCK4, a gene at 7q31.1 that encodes the Rac1 guanine nucleotide exchange factor Dock4, has been identified as a risk gene for ASD and other neuropsychiatric disorders. However, whether and how Dock4 disruption leads to ASD features through a synaptic mechanism remain unexplored. We generated and characterized a line of Dock4 knockout (KO) mice, which intriguingly displayed a series of ASD-like behaviors, including impaired social novelty preference, abnormal isolation-induced pup vocalizations, elevated anxiety, and perturbed object and spatial learning. Mice with conditional deletion of Dock4 in hippocampal CA1 recapitulated social preference deficit in KO mice. Examination in CA1 pyramidal neurons revealed that excitatory synaptic transmission was drastically attenuated in KO mice, accompanied by decreased spine density and synaptic content of AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid)-and NMDA (N-methyl-D-aspartate)-type glutamate receptors. Moreover, Dock4 deficiency markedly reduced Rac1 activity in the hippocampus, which resulted in downregulation of global protein synthesis and diminished expression of AMPA and NMDA receptor subunits. Notably, Rac1 replenishment in the hippocampal CA1 of Dock4 KO mice restored excitatory synaptic transmission and corrected impaired social deficits in these mice, and pharmacological activation of NMDA receptors also restored social novelty preference in Dock4 KO mice. Together, our findings uncover a previously unrecognized Dock4-Rac1-dependent mechanism involved in regulating hippocampal excitatory synaptic transmission and social behavior.
The Rho family GTPases are small G proteins that act as molecular switches shuttling between active and inactive forms. Rho GTPases are regulated by two classes of regulatory proteins, guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Rho GTPases transduce the upstream signals to downstream effectors, thus regulating diverse cellular processes, such as growth, migration, adhesion, and differentiation. In particular, Rho GTPases play essential roles in regulating neuronal morphology and function. Recent evidence suggests that dysfunction of Rho GTPase signaling contributes substantially to the pathogenesis of autism spectrum disorder (ASD). It has been found that 20 genes encoding Rho GTPase regulators and effectors are listed as ASD risk genes by Simons foundation autism research initiative (SFARI). This review summarizes the clinical evidence, protein structure, and protein expression pattern of these 20 genes. Moreover, ASD-related behavioral phenotypes in animal models of these genes are reviewed, and the therapeutic approaches that show successful treatment effects in these animal models are discussed.
Autism spectrum disorder (ASD) and dyslexia are both neurodevelopmental disorders with high prevalence in children. Both disorders have strong genetic basis, and share similar social communication deficits co-occurring with impairments of reading or language. However, whether these two disorders share common genetic risks remain elusive. DOCK4 (dedicator for cytokinesis 4), a guanine nucleotide exchange factor (GEF) for the small GTPase Rac1, is one of few genes that are associated with both ASD and dyslexia. Dock4 is important for neuronal development and social behaviors. Two DOCK4 variations, Exon27-52 deletion (protein product: Dock4-945VS) and a missense mutation at rs2074130 (protein product: Dock4-R853H), are associated with dyslexia and/or ASD with reading difficulties. The present study explores the molecular and cellular functions of these two DOCK4 variants on neuronal development, by comparing them with the wild-type Dock4 protein. Notably, it is revealed that both mutants of Dock4 showed decreased ability to activate not only Rac1, but also another small GTPase Rap1. Consistently, both mutants were dysfunctional for regulation of cell morphology and cytoskeleton. Using Neuro-2a cells and hippocampus neurons as models, we found that both mutants had compromised function in promoting neurite outgrowth and dendritic spine formation. Electrophysiological recordings further showed that R853H partially lost the ability to promote excitatory synaptic transmission, whereas 945VS totally lost the ability. Together, we identified R853 as a previously uncharacterized site for the regulation of the integrity of Dock4 function, and provides insights in understanding the common molecular pathophysiology of ASD and dyslexia.
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