This study shows that Epac2, a cAMP-activated Rap-GEF, acts downstream of D1/D5 dopamine receptor signaling to regulate dendritic spines and synaptic transmission. The authors also show that rare mutations of the EPAC2 gene that are associated with autism cause defects in Epac2-mediated spine remodeling. Dynamic remodeling of spiny synapses is crucial for cortical circuit development, refinement and plasticity, whereas abnormal morphogenesis is associated with neuropsychiatric disorders. We found that activation of Epac2, a PKA-independent cAMP target and Rap guanine-nucleotide exchange factor (GEF), in cultured rat cortical neurons induced spine shrinkage, increased spine motility, removed synaptic GluR2/3-containing AMPA receptors and depressed excitatory transmission, whereas its inhibition promoted spine enlargement and stabilization. Epac2 was required for dopamine D1-like receptor–dependent spine shrinkage and GluR2 removal from spines. Epac2 interaction with neuroligin promoted its membrane recruitment and enhanced its GEF activity. Rare missense mutations in the EPAC2 (also known as RAPGEF4) gene, previously found in individuals with autism, affected basal and neuroligin-stimulated GEF activity, dendritic Rap signaling, synaptic protein distribution and spine morphology. Thus, we identify a previously unknown mechanism that promotes dynamic remodeling and depression of spiny synapses, disruption of which may contribute to some aspects of disease.

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Epac2 induces synapse remodeling and depression and its disease-associated forms alter spines.

Regulation of actin dynamics during structural plasticity of dendritic spines: Signaling messengers and actin-binding proteins

https://link.springer.com/content/pdf/10.1007%2Fs13311-015-0355-9.pdf

Therapeutic Strategies in Fragile X Syndrome: From Bench to Bedside and Back

This selective review examines the lack of an explanation for the sharply increasing prevalence of autism, and the lack of any synthesis of the proliferating theories of autism. The most controversial and most widely disseminated notion for increasing prevalence is the measles–mumps–rubella/thimerosal vaccine theory. Less controversial causes that have been proposed include changes in autism diagnostic criteria, increasing services for autism, and growing awareness of the disorder. Regardless of its causes, the increasing prevalence of autism has put pressure on the field of autism research to generate productive and predictive theories of autism. However, the heterogeneity of brain deficits, impaired behaviors, and genetic variants in autism have challenged researchers and theorists, and despite 45 years of research, no standard causal synthesis has emerged. Research going forward should assume that autism is an aggregation of myriad independent disorders of impaired sociality, social cognition, communication, and motor and cognitive skills.

Autism overflows: increasing prevalence and proliferating theories.

Deficits in social and communication behaviors are common features of a number of neurodevelopmental disorders. However, the molecular and cellular substrates of these higher order brain functions are not well understood. Here we report that specific alterations in social and communication behaviors in mice occur as a result of loss of the EPAC2 gene, which encodes a protein kinase A-independent cAMP target. Epac2-deficient mice exhibited robust deficits in social interactions and ultrasonic vocalizations, but displayed normal olfaction, working and reference memory, motor abilities, anxiety, and repetitive behaviors. Epac2-deficient mice displayed abnormal columnar organization in the anterior cingulate cortex, a region implicated in social behavior in humans, but not in somatosensory cortex. In vivo two-photon imaging revealed reduced dendritic spine motility and density on cortical neurons in Epac2-deficient mice, indicating deficits at the synaptic level. Together, these findings provide novel insight into the molecular and cellular substrates of social and communication behavior.

https://www.jneurosci.org/content/jneuro/32/34/11864.full.pdf

Jim Malter

Papers

The cyclic AMP phenotype of fragile X and autism.