Screening of nine candidate genes for autism on chromosome 2q reveals rare nonsynonymous variants in the cAMP-GEFII gene

Protein SUMOylation promotes cAMP-independent EPAC1 activation

Protein SUMOylation is a prevalent stress-response posttranslational modification crucial for maintaining cellular homeostasis. Herein, we report that protein SUMOylation modulates cellular signaling mediated by cAMP, an ancient and universal stress-response second messenger. We identify K561 as a primary SUMOylation site in exchange protein directly activated by cAMP (EPAC1) via site-specific mapping of SUMOylation using mass spectrometry. Sequence and site-directed mutagenesis analyses reveal that a functional SUMO-interacting motif in EPAC1 is required for the binding of SUMO-conjugating enzyme UBC9, formation of EPAC1 nuclear condensate, and EPAC1 cellular SUMOylation. Heat shock-induced SUMO modification of EPAC1 promotes Rap1/2 activation in a cAMP-independent manner. Structural modeling and molecular dynamics simulation studies demonstrate that SUMO substituent on K561 of EPAC1 promotes Rap1 interaction by increasing the buried surface area between the SUMOylated receptor and its effector. Our studies identify a functional SUMOylation site in EPAC1 and unveil a novel mechanism in which SUMOylation of EPAC1 leads to its autonomous activation. The findings of SUMOylation-mediated activation of EPAC1 not only provide new insights into our understanding of cellular regulation of EPAC1 but also will open up a new field of experimentation concerning the cross-talk between cAMP/EPAC1 signaling and protein SUMOylation, two major cellular stress response pathways, during cellular homeostasis.

Interactions between Ras and Rap signaling pathways during neurodevelopment in health and disease

The Ras family of small GTPases coordinates tissue development by modulating cell proliferation, cell-cell adhesion, and cellular morphology. Perturbations of any of these key steps alter nervous system development and are associated with neurological disorders. While the underlying causes are not known, genetic mutations in Ras and Rap GTPase signaling pathways have been identified in numerous neurodevelopmental disorders, including autism spectrum, neurofibromatosis, intellectual disability, epilepsy, and schizophrenia. Despite diverse clinical presentations, intersections between these two signaling pathways may provide a better understanding of how deviations in neurodevelopment give rise to neurological disorders. In this review, we focus on presynaptic and postsynaptic functions of Ras and Rap GTPases. We highlight various roles of these small GTPases during synapse formation and plasticity. Based on genomic analyses, we discuss how disease-related mutations in Ras and Rap signaling proteins may underlie human disorders. Finally, we discuss how recent observations have identified molecular interactions between these pathways and how these findings may provide insights into the mechanisms that underlie neurodevelopmental disorders.

Aberrant gene expression yet undiminished retinal ganglion cell genesis in iPSC-derived models of optic nerve hypoplasia

BACKGROUND

Optic nerve hypoplasia (ONH), the leading congenital cause of permanent blindness, is characterized by a retinal ganglion cell (RGC) deficit at birth. Multifactorial developmental events are hypothesized to underlie ONH and its frequently associated neurologic and endocrine abnormalities; however, environmental influences are unclear and genetic underpinnings are unexplored. This work investigates the genetic contribution to ONH RGC production and gene expression using patient induced pluripotent stem cell (iPSC)-derived retinal organoids (ROs).

MATERIALS AND METHODS

iPSCs produced from ONH patients and controls were differentiated to ROs. RGC genesis was assessed using immunofluorescence and flow cytometry. Flow-sorted BRN3+ cells were collected for RNA extraction for RNA-Sequencing. Differential gene expression was assessed using DESeq2 and edgeR. PANTHER was employed to identify statistically over-represented ontologies among the differentially expressed genes (DEGs). DEGs of high interest to ONH were distinguished by assessing function, mutational constraint, and prior identification in ONH, autism and neurodevelopmental disorder (NDD) studies.

RESULTS

RGC genesis and survival were similar in ONH and control ROs. Differential expression of 70 genes was identified in both DESeq2 and edgeR analyses, representing a ~ 4-fold higher percentage of DEGs than in randomized study participants. DEGs showed trends towards over-representation of validated NDD genes and ONH exome variant genes. Among the DEGs, RAPGEF4 and DMD had the greatest number of disease-relevant features.

CONCLUSIONS

ONH genetic background was not associated with impaired RGC genesis but was associated with DEGs exhibiting disease contribution potential. This constitutes some of the first evidence of a genetic contribution to ONH.

Protein SUMOylation promotes cAMP-independent EPAC1 activation

Exchange protein directly activated by cAMP (EPAC1) mediates the intracellular functions of a critical stress-response second messenger, cAMP. Herein, we report that EPAC1 is a cellular substrate of protein SUMOylation, a prevalent stress-response posttranslational modification. Site-specific mapping of SUMOylation by mass spectrometer leads to identifying K561 as a primary SUMOylation site in EPAC1. Sequence and site-directed mutagenesis analyses reveal a functional SUMO-interacting motif required for cellular SUMOylation of EPAC1. SUMO modification of EPAC1 mediates its heat shock-induced Rap1/2 activation in a cAMP-independent manner. Structural modeling and molecular dynamics simulation studies demonstrate that SUMO substituent on K561 of EPAC1 promotes Rap1 interaction by increasing the buried surface area between the SUMOylated receptor and its effector. Our studies identify a functional SUMOylation site in EPAC1 and unveil a novel mechanism in which SUMOylation of EPAC1 leads to its autonomous activation. The findings of SUMOylation-mediated activation of EPAC1 not only provide new insights into our understanding of cellular regulation of EPAC1 but also will open up a new field of experimentation concerning the cross-talk between cAMP/EPAC1 signaling and protein SUMOylation, two major cellular stress response pathways, during cellular homeostasis.

Molecular Mechanisms Involved in the Regulation of Neurodevelopment by miR-124

miR-124 is a miRNA predominantly expressed in the nervous system and accounts for more than a quarter of the total miRNAs in the brain. It regulates neurogenesis, neuronal differentiation, neuronal maturation, and synapse formation and is the most important miRNA in the brain. Furthermore, emerging evidence has suggested miR-124 may be associated with the pathogenesis of various neurodevelopmental and neuropsychiatric disorders. Here, we provide an overview of the role of miR-124 in neurodevelopment and the underling mechanisms, and finally, we prospect the significance of miR-124 research to the field of neuroscience.

Key role of Rho GTPases in motor disorders associated with neurodevelopmental pathologies

Growing evidence suggests that Rho GTPases and molecules involved in their signaling pathways play a major role in the development of the central nervous system (CNS). Whole exome sequencing (WES) and de novo examination of mutations, including SNP (Single Nucleotide Polymorphism) in genes coding for the molecules of their signaling cascade, has allowed the recent discovery of dominant autosomic mutations and duplication or deletion of candidates in the field of neurodevelopmental diseases (NDD). Epidemiological studies show that the co-occurrence of several of these neurological pathologies may indeed be the rule. The regulators of Rho GTPases have often been considered for cognitive diseases such as intellectual disability (ID) and autism. But, in a remarkable way, mild to severe motor symptoms are now reported in autism and other cognitive NDD. Although a more abundant litterature reports the involvement of Rho GTPases and signaling partners in cognitive development, molecular investigations on their roles in central nervous system (CNS) development or degenerative CNS pathologies also reveal their role in embryonic and perinatal motor wiring through axon guidance and later in synaptic plasticity. Thus, Rho family small GTPases have been revealed to play a key role in brain functions including learning and memory but their precise role in motor development and associated symptoms in NDD has been poorly scoped so far, despite increasing clinical data highlighting the links between cognition and motor development. Indeed, early impairements in fine or gross motor performance is often an associated feature of NDDs, which then impact social communication, cognition, emotion, and behavior. We review here recent insights derived from clinical developmental neurobiology in the field of Rho GTPases and NDD (autism spectrum related disorder (ASD), ID, schizophrenia, hypotonia, spastic paraplegia, bipolar disorder and dyslexia), with a specific focus on genetic alterations affecting Rho GTPases that are involved in motor circuit development.

Meta-analysis of epigenome-wide association studies of major depressive disorder

Epigenetic mechanisms have been hypothesized to play a role in the etiology of major depressive disorder (MDD). In this study, we performed a meta-analysis between two case-control MDD cohorts to identify differentially methylated positions (DMPs) and differentially methylated regions (DMRs) in MDD. Using samples from two Cohorts (a total of 298 MDD cases and 63 controls with repeated samples, on average ~ 1.8 samples/subject), we performed an EWAS meta-analysis. Multiple cytosine-phosphate-guanine sites annotated to TNNT3 were associated with MDD reaching study-wide significance, including cg08337959 (p = 2.3 × 10^-11). Among DMPs with association p values less than 0.0001, pathways from REACTOME such as Ras activation upon Ca²⁺ influx through the NMDA receptor (p = 0.0001, p-adjusted = 0.05) and long-term potentiation (p = 0.0002, p-adjusted = 0.05) were enriched in this study. A total of 127 DMRs with Sidak-corrected p value < 0.05 were identified from the meta-analysis, including DMRs annotated to TNNT3 (chr11: 1948933 to 1949130 [6 probes], Sidak corrected P value = 4.32 × 10^-41), S100A13 (chr1: 153599479 to 153600972 [22 probes], Sidak corrected P value = 5.32 × 10^-18), NRXN1 (chr2: 50201413 to 50201505 [4 probes], Sidak corrected P value = 1.19 × 10^-11), IL17RA (chr22: 17564750 to 17565149, Sidak corrected P value = 9.31 × 10^-8), and NPFFR2 (chr4: 72897565 to 72898212, Sidak corrected P value = 8.19 × 10^-7). Using 2 Cohorts of depression case-control samples, we identified DMPs and DMRs associated with MDD. The molecular pathways implicated by these data include mechanisms involved in neuronal synaptic plasticity, calcium signaling, and inflammation, consistent with reports from previous genetic and protein biomarker studies indicating that these mechanisms are involved in the neurobiology of depression.

Deciphering complex rearrangements at the breakpoint of an apparently balanced reciprocal translocation t(4:18)(q31;q11.2)dn and at a cryptic deletion: Further evidence of TLL1 as a causative gene for atrial septal defect

When a de novo balanced reciprocal translocation is identified in patients with multiple congenital abnormalities, attempts are often made to infer the relationship between the phenotype of the patient and genes in the proximity of the breakpoint. Here, we report a patient with intellectual disability, atrial septal defect, syndactyly, and cleft lip and palate who had an "apparently balanced" de novo reciprocal translocation t(4:18)(q31;q11.2) as well as a 7-Mb cryptic deletion spanning the HOXD cluster on chromosome 2q31 that was unrelated to the reciprocal translocation. Further analysis using a nanopore long-read sequencer showed complex rearrangements on both derivative chromosomes 4 and 18 and the deleted chromosome 2. First, the TLL1 locus, which is associated with atrial septal defect, was disrupted by the rearrangement involving chromosome 4. Second, the deleted interval at 2q31 included the entire HOXD cluster, the deletion of which is known to cause toe syndactyly, and the DLX1 and DLX2 loci, which are responsible for cleft lip and palate. Among the haplo-sensitive genes within the deleted interval on 2q31, only the RAPGEF4 gene is known to be associated with an autistic phenotype. Hence, most of the clinical features of the patient could be ascribed to specific genomic rearrangements. We have shown the effectiveness of long-read sequencing in defining, in detail, the likely effects of an apparently balanced translocation and cryptic deletion. The results of the present analysis suggest the possibility of phenotypic prediction through a detailed analysis of structural abnormalities, including balanced translocations and deletions.

PXF-1 promotes synapse development at the neuromuscular junction in Caenorhabditis elegans

Guanine nucleotide exchange factors (GEFs) are a family of proteins that modulate small G protein signaling. Mutations in a subfamily of GEFs that act on Rap, known as RapGEFs, have been associated with neurological disorders, and knockout mice display impairments in neuronal activity. However, the precise functions of RapGEFs in the nervous system remain unclear. Here, we have used the Caenorhabditis elegans neuromuscular junction, to investigate how the RapGEF homolog, PXF-1, regulates synaptic function. We found that loss of function mutations in pxf-1 reduced cholinergic activity at the neuromuscular junction. We observed that PXF-1 is expressed in the nervous system, and its expression in neurons is sufficient to promote synaptic activity. In pxf-1 mutant animals, there is a reduction in the levels of synaptic vesicles in cholinergic motor neurons but no change in the overall synapse numbers. In addition to synaptic vesicles proteins, we also found that filamentous actin, a scaffold for nascent synapses, was reduced at developing cholinergic synapses in pxf-1 mutant animals. Our studies indicate that PXF-1 regulates neuromuscular function by promoting the formation of actin filaments to support the development of motor neuron synapses.

Epac1-/- and Epac2-/- mice exhibit deficient epithelial Na+ channel regulation and impaired urinary Na+ conservation

Exchange proteins directly activated by cAMP (Epacs) are abundantly expressed in the renal tubules. We used genetic and pharmacological tools in combination with balance, electrophysiological, and biochemical approaches to examine the role of Epac1 and Epac2 in renal sodium handling. We demonstrate that Epac1^–/– and Epac2^–/– mice exhibit a delayed anti-natriuresis to dietary sodium restriction despite augmented aldosterone levels. This was associated with a significantly lower response to the epithelial Na⁺ channel (ENaC) blocker amiloride, reduced ENaC activity in split-opened collecting ducts, and defective posttranslational processing of α and γENaC subunits in the KO mice fed with a Na⁺-deficient diet. Concomitant deletion of both isoforms led to a marginally greater natriuresis but further increased aldosterone levels. Epac2 blocker ESI-05 and Epac1&2 blocker ESI-09 decreased ENaC activity in Epac WT mice kept on the Na⁺-deficient diet but not on the regular diet. ESI-09 injections led to natriuresis in Epac WT mice on the Na⁺-deficient diet, which was caused by ENaC inhibition. In summary, our results demonstrate similar but nonredundant actions of Epac1 and Epac2 in stimulation of ENaC activity during variations in dietary salt intake. We speculate that inhibition of Epac signaling could be instrumental in treatment of hypertensive states associated with ENaC overactivation.

The Rap1 small GTPase is a critical mediator of the effects of stress on prefrontal cortical dysfunction

The neural molecular and biochemical response to stress is a distinct physiological process, and multiple lines of evidence indicate that the prefrontal cortex (PFC) is particularly sensitive to, and afflicted by, exposure to stress. Largely through this PFC dysfunction, stress has a characterized role in facilitating cognitive impairment, which is often dissociable from its effects on non-cognitive behaviors. The Rap1 small GTPase pathway has emerged as a commonly disrupted intracellular target in neuropsychiatric conditions, whether it be via alterations in Rap1 expression or through alterations in the expression of direct and specific upstream Rap1 activators and inhibitors. Here we demonstrate that escalating, intermittent stress increases Rap1 in mouse PFC synapses, results in cognitive impairments, and reduces the preponderance of mature dendritic spines in PFC neurons. Using viral-mediated gene transfer, we reveal that the hyper-induction of Rap1 in the PFC is sufficient to drive stress-relevant cognitive and synaptic phenotypes. These findings point to Rap1 as a critical mediator of stress-driven neuronal and behavioral pathology and highlight a previously unrecognized involvement for Rap1 in novelty-driven PFC engagement.

Autophagy activity contributes to the impairment of social recognition in Epac2-/- mice

Autophagy is a lysosomal degradation pathway that regulates cellular homeostasis. It is constitutively active in neurons and controls the essential steps of neuronal development, leading to its dysfunction in neurodevelopmental disorders. Although mTOR-associated impaired autophagy has previously been reported in neurodevelopmental disorders, there is lack of information about the dysregulation of mTOR-independent autophagy in neurodevelopmental disorders. In this study, we investigated whether the loss of Epac2, involved in the mTOR-independent pathway, affects autophagy activity and whether the activity of autophagy is associated with social-behavioral phenotypes in mice with Epac2 deficiencies. We observed an accumulation of autophagosomes and a significant increase in autophagic flux in Epac2-deficient neurons, which had no effect on mTOR activity. Next, we examined whether an increase in autophagic activity contributed to the social behavior exhibited in Epac2^-/- mice. The social recognition deficit observed in Epac2^-/- mice recovered in double transgenic Epac2^-/-: Atg5^+/- mice. Our study suggests that excessive autophagy due to Epac2 deficiencies may contribute to social recognition defects through an mTOR-independent pathway.

The RNA-Binding Protein HuD Regulates Alternative Splicing and Alternative Polyadenylation in the Mouse Neocortex

The neuronal Hu/ELAV-like proteins HuB, HuC and HuD are a class of RNA-binding proteins that are crucial for proper development and maintenance of the nervous system. These proteins bind to AU-rich elements (AREs) in the untranslated regions (3'-UTRs) of target mRNAs regulating mRNA stability, transport and translation. In addition to these cytoplasmic functions, Hu proteins have been implicated in alternative splicing and alternative polyadenylation in the nucleus. The purpose of this study was to identify transcriptome-wide effects of HuD deletion on both of these nuclear events using RNA sequencing data obtained from the neocortex of Elavl4-/- (HuD KO) mice. HuD KO affected alternative splicing of 310 genes, including 17 validated HuD targets such as Cbx3, Cspp1, Snap25 and Gria2. In addition, deletion of HuD affected polyadenylation of 53 genes, with the majority of significantly altered mRNAs shifting towards usage of proximal polyadenylation signals (PAS), resulting in shorter 3'-UTRs. None of these genes overlapped with those showing alternative splicing events. Overall, HuD KO had a greater effect on alternative splicing than polyadenylation, with many of the affected genes implicated in several neuronal functions and neuropsychiatric disorders.

Epac: new emerging cAMP-binding protein

The well-known second messenger cyclic adenosine monophosphate (cAMP) regulates the morphology and physiology of neurons and thus higher cognitive brain functions. The discovery of exchange protein activated by cAMP (Epac) as a guanine nucleotide exchange factor for Rap GTPases has shed light on protein kinase A (PKA)-independent functions of cAMP signaling in neural tissues. Studies of cAMP-Epac-mediated signaling in neurons under normal and disease conditions also revealed its diverse contributions to neurodevelopment, synaptic remodeling, and neurotransmitter release, as well as learning, memory, and emotion. In this mini-review, the various roles of Epac isoforms, including Epac1 and Epac2, highly expressed in neural tissues are summarized, and controversies or issues are highlighted that need to be resolved to uncover the critical functions of Epac in neural tissues and the potential for a new therapeutic target of mental disorders.

Perseverative stereotypic behavior of Epac2 KO mice in a reward-based decision making task

Successfully navigating dynamic environments requires balancing the decision to stay at an optimal choice with that to switch to an alternative to acquire new knowledge. However, the genetic factors and cellular activity shaping this "stay or switch" action decision remains largely unidentified. Here we find that mice carrying a deletion of the exchange protein directly activated by cAMP 2 (Epac2) gene, a putative autism locus, exhibit perseverative "stay" behavior in a dynamic foraging task. Anatomical analysis found that the loss of Epac2 resulted in a significant decrease in the density of PV-expressing interneurons in the ventrolateral orbitofrontal cortex (OFC) and dorsal striatum (dSTR). Further, in vitro whole cell patch clamp recordings of PV⁺ GABAergic interneurons in the dSTR revealed altered neural activity in Epac2 KO mice in response to dopamine. Our findings highlight a potential role of Epac2 in structural changes and neural responses of PV-expressing GABAergic interneurons in the ventrolateral OFC and dSTR during value-based reinforcement learning and link Epac2 function to abnormal decision-making processes and perseverative behaviors seen in autism.

Small GTPases of the Ras and Rho Families Switch on/off Signaling Pathways in Neurodegenerative Diseases

Small guanosine triphosphatases (GTPases) of the Ras superfamily are key regulators of many key cellular events such as proliferation, differentiation, cell cycle regulation, migration, or apoptosis. To control these biological responses, GTPases activity is regulated by guanine nucleotide exchange factors (GEFs), GTPase activating proteins (GAPs), and in some small GTPases also guanine nucleotide dissociation inhibitors (GDIs). Moreover, small GTPases transduce signals by their downstream effector molecules. Many studies demonstrate that small GTPases of the Ras family are involved in neurodegeneration processes. Here, in this review, we focus on the signaling pathways controlled by these small protein superfamilies that culminate in neurodegenerative pathologies, such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). Specifically, we concentrate on the two most studied families of the Ras superfamily: the Ras and Rho families. We summarize the latest findings of small GTPases of the Ras and Rho families in neurodegeneration in order to highlight these small proteins as potential therapeutic targets capable of slowing down different neurodegenerative diseases.

Small GTPases of the Ras and Rho Families Switch on/off Signaling Pathways in Neurodegenerative Diseases

Small guanosine triphosphatases (GTPases) of the Ras superfamily are key regulators of many key cellular events such as proliferation, differentiation, cell cycle regulation, migration, or apoptosis. To control these biological responses, GTPases activity is regulated by guanine nucleotide exchange factors (GEFs), GTPase activating proteins (GAPs), and in some small GTPases also guanine nucleotide dissociation inhibitors (GDIs). Moreover, small GTPases transduce signals by their downstream effector molecules. Many studies demonstrate that small GTPases of the Ras family are involved in neurodegeneration processes. Here, in this review, we focus on the signaling pathways controlled by these small protein superfamilies that culminate in neurodegenerative pathologies, such as Alzheimer's disease (AD) and Parkinson's disease (PD). Specifically, we concentrate on the two most studied families of the Ras superfamily: the Ras and Rho families. We summarize the latest findings of small GTPases of the Ras and Rho families in neurodegeneration in order to highlight these small proteins as potential therapeutic targets capable of slowing down different neurodegenerative diseases.

A peek into Epac physiology in the kidney

cAMP is a critical second messenger of numerous endocrine signals affecting water-electrolyte transport in the renal tubule. Exchange protein directly activated by cAMP (Epac) is a relatively recently discovered downstream effector of cAMP, having the same affinity to the second messenger as protein kinase A, the classical cAMP target. Two Epac isoforms, Epac1 and Epac2, are abundantly expressed in the renal epithelium, where they are thought to regulate water and electrolyte transport, particularly in the proximal tubule and collecting duct. Recent characterization of renal phenotype in mice lacking Epac1 and Epac2 revealed a critical role of the Epac signaling cascade in urinary concentration as well as in Na⁺ and urea excretion. In this review, we aim to critically summarize current knowledge of Epac relevance for renal function and to discuss the applicability of Epac-based strategies in the regulation of systemic water-electrolyte homeostasis.

Inherited and De Novo Genetic Risk for Autism Impacts Shared Networks

We performed a comprehensive assessment of rare inherited variation in autism spectrum disorder (ASD) by analyzing whole-genome sequences of 2,308 individuals from families with multiple affected children. We implicate 69 genes in ASD risk, including 24 passing genome-wide Bonferroni correction and 16 new ASD risk genes, most supported by rare inherited variants, a substantial extension of previous findings. Biological pathways enriched for genes harboring inherited variants represent cytoskeletal organization and ion transport, which are distinct from pathways implicated in previous studies. Nevertheless, the de novo and inherited genes contribute to a common protein-protein interaction network. We also identified structural variants (SVs) affecting non-coding regions, implicating recurrent deletions in the promoters of DLG2 and NR3C2. Loss of nr3c2 function in zebrafish disrupts sleep and social function, overlapping with human ASD-related phenotypes. These data support the utility of studying multiplex families in ASD and are available through the Hartwell Autism Research and Technology portal.

Loss of EPAC2 alters dendritic spine morphology and inhibitory synapse density

EPAC2 is a guanine nucleotide exchange factor that regulates GTPase activity of the small GTPase Rap and Ras and is highly enriched at synapses. Activation of EPAC2 has been shown to induce dendritic spine shrinkage and increase spine motility, effects that are necessary for synaptic plasticity. These morphological effects are dysregulated by rare mutations of Epac2 associated with autism spectrum disorders. In addition, EPAC2 destabilizes synapses through the removal of synaptic GluA2/3-containing AMPA receptors. Previous work has shown that Epac2 knockout mice (Epac2^−/−) display abnormal social interactions, as well as gross disorganization of the frontal cortex and abnormal spine motility in vivo. In this study we sought to further understand the cellular consequences of knocking out Epac2 on the development of neuronal and synaptic structure and organization of cortical neurons. Using primary cortical neurons generated from Epac2^+/+ or Epac2^−/− mice, we confirm that EPAC2 is required for cAMP-dependent spine shrinkage. Neurons from Epac2^−/− mice also displayed increased synaptic expression of GluA2/3-containing AMPA receptors, as well as of the adhesion protein N-cadherin. Intriguingly, analysis of excitatory and inhibitory synaptic proteins revealed that loss of EPAC2 resulted in altered expression of vesicular GABA transporter (VGAT) but not vesicular glutamate transporter 1 (VGluT1), indicating an altered ratio of excitatory and inhibitory synapses onto neurons. Finally, examination of cortical neurons located within the anterior cingulate cortex further revealed subtle deficits in the establishment of dendritic arborization in vivo. These data provide evidence that loss of EPAC2 enhances the stability of excitatory synapses and increases the number of inhibitory inputs.

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EPAC2 is required for cAMP-dependent spine remodeling.

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Loss of EPAC2 results in over-stabilized excitatory synapses.

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Loss of EPAC2 results in an increase in inhibitory input onto neurons.

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EPAC2 is required for correct dendritic arborization and spine formation in vivo.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Functional significance of rare neuroligin 1 variants found in autism

Genetic mutations contribute to the etiology of autism spectrum disorder (ASD), a common, heterogeneous neurodevelopmental disorder characterized by impairments in social interaction, communication, and repetitive and restricted patterns of behavior. Since neuroligin3 (NLGN3), a cell adhesion molecule at the neuronal synapse, was first identified as a risk gene for ASD, several additional variants in NLGN3 and NLGN4 were found in ASD patients. Moreover, synaptopathies are now known to cause several neuropsychiatric disorders including ASD. In humans, NLGNs consist of five family members, and neuroligin1 (NLGN1) is a major component forming a complex on excitatory glutamatergic synapses. However, the significance of NLGN1 in neuropsychiatric disorders remains unknown. Here, we systematically examine five missense variants of NLGN1 that were detected in ASD patients, and show molecular and cellular alterations caused by these variants. We show that a novel NLGN1 Pro89Leu (P89L) missense variant found in two ASD siblings leads to changes in cellular localization, protein degradation, and to the impairment of spine formation. Furthermore, we generated the knock-in P89L mice, and we show that the P89L heterozygote mice display abnormal social behavior, a core feature of ASD. These results, for the first time, implicate rare variants in NLGN1 as functionally significant and support that the NLGN synaptic pathway is of importance in the etiology of neuropsychiatric disorders.

Autism spectrum disorder (ASD) is a childhood disorder manifested by abnormal social behavior, interests, and activities. The genetic contribution to ASD is higher than in other psychiatric disorders such as schizophrenia and mood disorders. Here, we found a novel mutation in NLGN1, a gene encoding a synaptic protein, in patients with ASD. We also developed a mouse model with this mutation, and showed that the model mouse exhibits abnormal social behavior. These results suggest that a rare variant in NLGN1 is functionally significant and support that the NLGN synaptic pathway may be important in the etiology of neuropsychiatric disorders. This humanized mouse model recapitulates some of the symptoms of patients with ASD and will serve as a valuable tool for therapeutic development.

PDE11A regulates social behaviors and is a key mechanism by which social experience sculpts the brain

Despite the fact that appropriate social behaviors are vital to thriving in one's environment, little is understood of the molecular mechanisms controlling social behaviors or how social experience sculpts these signaling pathways. Here, we determine if Phosphodiesterase 11A (PDE11A), an enzyme that is enriched in the ventral hippocampal formation (VHIPP) and that breaks down cAMP and cGMP, regulates social behaviors. PDE11 wild-type (WT), heterozygous (HT), and knockout (KO) mice were tested in various social approach assays and gene expression differences were measured by RNA sequencing. The effect of social isolation on PDE11A4 compartmentalization and subsequent social interactions and social memory was also assessed. Deletion of PDE11A triggered age- and sex-dependent deficits in social approach in specific social contexts but not others. Mice appear to detect altered social behaviors of PDE11A KO mice, because C57BL/6J mice prefer to spend time with a sex-matched PDE11A WT vs. its KO littermate; whereas, a PDE11A KO prefers to spend time with a novel PDE11A KO vs. its WT littermate. Not only is PDE11A required for intact social interactions, we found that 1month of social isolation vs. group housing decreased PDE11A4 protein expression specifically within the membrane fraction of VHIPP. This isolation-induced decrease in PDE11A4 expression appears functional because social isolation impairs subsequent social approach behavior and social memory in a PDE11A genotype-dependent manner. Pathway analyses following RNA sequencing suggests PDE11A is a key regulator of the oxytocin pathway and membrane signaling, consistent with its pivotal role in regulating social behavior.

Impairments in dendrite morphogenesis as etiology for neurodevelopmental disorders and implications for therapeutic treatments

Dendrite morphology is pivotal for neural circuitry functioning. While the causative relationship between small-scale dendrite morphological abnormalities (shape, density of dendritic spines) and neurodevelopmental disorders is well established, such relationship remains elusive for larger-scale dendrite morphological impairments (size, shape, branching pattern of dendritic trees). Here, we summarize published data on dendrite morphological irregularities in human patients and animal models for neurodevelopmental disorders, with focus on autism and schizophrenia. We next discuss high-risk genes for these disorders and their role in dendrite morphogenesis. We finally overview recent developments in therapeutic attempts and we discuss how they relate to dendrite morphology. We find that both autism and schizophrenia are accompanied by dendritic arbor morphological irregularities, and that majority of their high-risk genes regulate dendrite morphogenesis. Thus, we present a compelling argument that, along with smaller-scale morphological impairments in dendrites (spines and synapse), irregularities in larger-scale dendrite morphology (arbor shape, size) may be an important part of neurodevelopmental disorders' etiology. We suggest that this should not be ignored when developing future therapeutic treatments.

Correspondence between Resting-State Activity and Brain Gene Expression

The relationship between functional brain activity and gene expression has not been fully explored in the human brain. Here, we identify significant correlations between gene expression in the brain and functional activity by comparing fractional amplitude of low-frequency fluctuations (fALFF) from two independent human fMRI resting-state datasets to regional cortical gene expression from a newly generated RNA-seq dataset and two additional gene expression datasets to obtain robust and reproducible correlations. We find significantly more genes correlated with fALFF than expected by chance and identify specific genes correlated with the imaging signals in multiple expression datasets in the default mode network. Together, these data support a population-level relationship between regional steady-state brain gene expression and resting-state brain activity.

Control of Dendritic Spine Morphological and Functional Plasticity by Small GTPases

Structural plasticity of excitatory synapses is a vital component of neuronal development, synaptic plasticity, and behaviour. Abnormal development or regulation of excitatory synapses has also been strongly implicated in many neurodevelopmental, psychiatric, and neurodegenerative disorders. In the mammalian forebrain, the majority of excitatory synapses are located on dendritic spines, specialized dendritic protrusions that are enriched in actin. Research over recent years has begun to unravel the complexities involved in the regulation of dendritic spine structure. The small GTPase family of proteins have emerged as key regulators of structural plasticity, linking extracellular signals with the modulation of dendritic spines, which potentially underlies their ability to influence cognition. Here we review a number of studies that examine how small GTPases are activated and regulated in neurons and furthermore how they can impact actin dynamics, and thus dendritic spine morphology. Elucidating this signalling process is critical for furthering our understanding of the basic mechanisms by which information is encoded in neural circuits but may also provide insight into novel targets for the development of effective therapies to treat cognitive dysfunction seen in a range of neurological disorders.

PSD-Zip70 Deficiency Causes Prefrontal Hypofunction Associated with Glutamatergic Synapse Maturation Defects by Dysregulation of Rap2 Activity

Dysregulation of synapse formation and plasticity is closely related to the pathophysiology of psychiatric and neurodevelopmental disorders. The prefrontal cortex (PFC) is particularly important for executive functions such as working memory, cognition, and emotional control, which are impaired in the disorders. PSD-Zip70 (Lzts1/FEZ1) is a postsynaptic density (PSD) protein predominantly expressed in the frontal cortex, olfactory bulb, striatum, and hippocampus. Here we found that PSD-Zip70 knock-out (PSD-Zip70KO) mice exhibit working memory and cognitive defects, and enhanced anxiety-like behaviors. These abnormal behaviors are caused by impaired glutamatergic synapse transmission accompanied by tiny-headed immature dendritic spines in the PFC, due to aberrant Rap2 activation, which has roles in synapse formation and plasticity. PSD-Zip70 modulates the Rap2 activity by interacting with SPAR (spine-associated RapGAP) and PDZ-GEF1 (RapGEF) in the postsynapse. Furthermore, suppression of the aberrant Rap2 activation in the PFC rescued the behavioral defects in PSD-Zip70KO mice. Our data demonstrate a critical role for PSD-Zip70 in Rap2-dependent spine synapse development in the PFC and underscore the importance of this regulation in PFC-dependent behaviors.

SIGNIFICANCE STATEMENT

PSD-Zip70 deficiency causes behavioral defects in working memory and cognition, and enhanced anxiety due to prefrontal hypofunction. This study revealed that PSD-Zip70 plays essential roles in glutamatergic synapse maturation via modulation of the Rap2 activity in the PFC. PSD-Zip70 interacts with both SPAR (spine-associated RapGAP) and PDZ-GEF1 (RapGEF) and modulates the Rap2 activity in postsynaptic sites. Our results provide a novel Rap2-specific regulatory mechanism in synaptic maturation involving PSD-Zip70.

Role of EPAC in cAMP-Mediated Actions in Adrenocortical Cells

Adrenocorticotropic hormone regulates adrenal steroidogenesis mainly via the intracellular signaling molecule cAMP. The effects of cAMP are principally relayed by activating protein kinase A (PKA) and the more recently discovered exchange proteins directly activated by cAMP 1 and 2 (EPAC1 and EPAC2). While the intracellular roles of PKA have been extensively studied in steroidogenic tissues, those of EPACs are only emerging. EPAC1 and EPAC2 are encoded by the genes RAPGEF3 and RAPGEF4, respectively. Whereas EPAC1 is ubiquitously expressed, the expression of EPAC2 is more restricted, and typically found in endocrine tissues. Alternative promoter usage of RAPGEF4 gives rise to three different isoforms of EPAC2 that vary in their N-termini (EPAC2A, EPAC2B, and EPAC2C) and that exhibit distinct expression patterns. EPAC2A is expressed in the brain and pancreas, EPAC2B in steroidogenic cells of the adrenal gland and testis, and EPAC2C has until now only been found in the liver. In this review, we discuss current knowledge on EPAC expression and function with focus on the known roles of EPAC in adrenal gland physiology.

Structure and functional roles of Epac2 (Rapgef4)

Epac (exchange protein activated by cyclic-AMP) 2 is a direct target of 3'-5'-cyclic adenosine monophosphate (cAMP) and is involved in cAMP-mediated signal transduction through activation of the Ras-like small GTPase Rap. Crystallographic analyses revealed that activation of Epac2 by cAMP is accompanied by dynamic structural changes. Epac2 is expressed mainly in brain, neuroendocrine and endocrine tissues, and is involved in diverse cellular functions in the tissues. In this review, we summarize the structure and function of Epac2. We also discuss the physiological and pathophysiological roles of Epac2, and the possibility of Epac2 as a therapeutic target.

Molecular underpinnings of prefrontal cortex development in rodents provide insights into the etiology of neurodevelopmental disorders

The prefrontal cortex (PFC), seat of the highest-order cognitive functions, constitutes a conglomerate of highly specialized brain areas and has been implicated to have a role in the onset and installation of various neurodevelopmental disorders. The development of a properly functioning PFC is directed by transcription factors, guidance cues and other regulatory molecules and requires the intricate and temporal orchestration of a number of developmental processes. Disturbance or failure of any of these processes causing neurodevelopmental abnormalities within the PFC may contribute to several of the cognitive deficits seen in patients with neurodevelopmental disorders. In this review, we elaborate on the specific processes underlying prefrontal development, such as induction and patterning of the prefrontal area, proliferation, migration and axonal guidance of medial prefrontal progenitors, and their eventual efferent and afferent connections. We furthermore integrate for the first time the available knowledge from genome-wide studies that have revealed genes linked to neurodevelopmental disorders with experimental molecular evidence in rodents. The integrated data suggest that the pathogenic variants in the neurodevelopmental disorder-associated genes induce prefrontal cytoarchitectonical impairments. This enhances our understanding of the molecular mechanisms of prefrontal (mis)development underlying the four major neurodevelopmental disorders in humans, that is, intellectual disability, autism spectrum disorders, attention deficit hyperactivity disorder and schizophrenia, and may thus provide clues for the development of novel therapies.

Deletion of Rapgef6, a candidate schizophrenia susceptibility gene, disrupts amygdala function in mice

In human genetic studies of schizophrenia, we uncovered copy-number variants in RAPGEF6 and RAPGEF2 genes. To discern the effects of RAPGEF6 deletion in humans, we investigated the behavior and neural functions of a mouse lacking Rapgef6. Rapgef6 deletion resulted in impaired amygdala function measured as reduced fear conditioning and anxiolysis. Hippocampal-dependent spatial memory and prefrontal cortex-dependent working memory tasks were intact. Neural activation measured by cFOS phosphorylation demonstrated a reduction in hippocampal and amygdala activation after fear conditioning, while neural morphology assessment uncovered reduced spine density and primary dendrite number in pyramidal neurons of the CA3 hippocampal region of knockout mice. Electrophysiological analysis showed enhanced long-term potentiation at cortico-amygdala synapses. Rapgef6 deletion mice were most impaired in hippocampal and amygdalar function, brain regions implicated in schizophrenia pathophysiology. The results provide a deeper understanding of the role of the amygdala in schizophrenia and suggest that RAPGEF6 may be a novel therapeutic target in schizophrenia.

De novo TBR1 mutations in sporadic autism disrupt protein functions

Next-generation sequencing recently revealed that recurrent disruptive mutations in a few genes may account for 1% of sporadic autism cases. Coupling these novel genetic data to empirical assays of protein function can illuminate crucial molecular networks. Here we demonstrate the power of the approach, performing the first functional analyses of TBR1 variants identified in sporadic autism. De novo truncating and missense mutations disrupt multiple aspects of TBR1 function, including subcellular localization, interactions with co-regulators and transcriptional repression. Missense mutations inherited from unaffected parents did not disturb function in our assays. We show that TBR1 homodimerizes, that it interacts with FOXP2, a transcription factor implicated in speech/language disorders, and that this interaction is disrupted by pathogenic mutations affecting either protein. These findings support the hypothesis that de novo mutations in sporadic autism have severe functional consequences. Moreover, they uncover neurogenetic mechanisms that bridge different neurodevelopmental disorders involving language deficits.

The role of glutamate and its receptors in autism and the use of glutamate receptor antagonists in treatment

Glutamate is the major excitatory neurotransmitter in the brain and may be a key neurotransmitter involved in autism. Literature pertaining to glutamate and autism or related disorders (e.g., Fragile X syndrome) is reviewed in this article. Interest in glutamatergic dysfunction in autism is high due to increasing convergent evidence implicating the system in the disorder from peripheral biomarkers, neuroimaging, protein expression, genetics and animal models. Currently, there are no pharmaceutical interventions approved for autism that address glutamate deficits in the disorder. New treatments related to glutamatergic neurotransmission, however, are emerging. In addition, older glutamate-modulating medications with approved indications for use in other disorders are being investigated for re-tasking as treatments for autism. This review presents evidence in support of glutamate abnormalities in autism and the potential for translation into new treatments for the disorder.

Single nucleotide polymorphism rs6716901 in SLC25A12 gene is associated with Asperger syndrome

BACKGROUND

Autism Spectrum Conditions (ASC) are a group of developmental conditions which affect communication, social interactions and behaviour. Mitochondrial oxidative dysfunction has been suggested as a mechanism of autism based on the results of multiple genetic association and expression studies. SLC25A12 is a gene encoding a calcium-binding carrier protein that localizes to the mitochondria and is involved in the exchange of aspartate for glutamate in the inner membrane of the mitochondria regulating the cytosolic redox state. rs2056202 SNP in this gene has previously been associated with ASC. SNPs rs6716901 and rs3765166 analysed in this study have not been previously explored in association with AS.

METHODS

We genotyped three SNPs (rs2056202, rs3765166, and rs6716901) in SLC25A12 in n?=?117 individuals with Asperger syndrome (AS) and n?=?426 controls, all of Caucasian ancestry.

RESULTS

rs6716901 showed significant association with AS (P?=?0.008) after correcting for multiple testing. We did not replicate the previously identified association between rs2056202 and AS in our sample. Similarly, rs3765166 (P?=?0.11) showed no significant association with AS.

CONCLUSION

The present study, in combination with previous studies, provides evidence for SLC25A12 as involved in the etiology of AS. Further cellular and molecular studies are required to elucidate the role of this gene in ASC.

Dendritic spines: the locus of structural and functional plasticity

The introduction of high-resolution time lapse imaging and molecular biological tools has changed dramatically the rate of progress towards the understanding of the complex structure-function relations in synapses of central spiny neurons. Standing issues, including the sequence of molecular and structural processes leading to formation, morphological change, and longevity of dendritic spines, as well as the functions of dendritic spines in neurological/psychiatric diseases are being addressed in a growing number of recent studies. There are still unsettled issues with respect to spine formation and plasticity: Are spines formed first, followed by synapse formation, or are synapses formed first, followed by emergence of a spine? What are the immediate and long-lasting changes in spine properties following exposure to plasticity-producing stimulation? Is spine volume/shape indicative of its function? These and other issues are addressed in this review, which highlights the complexity of molecular pathways involved in regulation of spine structure and function, and which contributes to the understanding of central synaptic interactions in health and disease.

Genetic aspects of autism spectrum disorders: insights from animal models

Autism spectrum disorders (ASDs) are a complex neurodevelopmental disorder that display a triad of core behavioral deficits including restricted interests, often accompanied by repetitive behavior, deficits in language and communication, and an inability to engage in reciprocal social interactions. ASD is among the most heritable disorders but is not a simple disorder with a singular pathology and has a rather complex etiology. It is interesting to note that perturbations in synaptic growth, development, and stability underlie a variety of neuropsychiatric disorders, including ASD, schizophrenia, epilepsy, and intellectual disability. Biological characterization of an increasing repertoire of synaptic mutants in various model organisms indicates synaptic dysfunction as causal in the pathophysiology of ASD. Our understanding of the genes and genetic pathways that contribute toward the formation, stabilization, and maintenance of functional synapses coupled with an in-depth phenotypic analysis of the cellular and behavioral characteristics is therefore essential to unraveling the pathogenesis of these disorders. In this review, we discuss the genetic aspects of ASD emphasizing on the well conserved set of genes and genetic pathways implicated in this disorder, many of which contribute to synapse assembly and maintenance across species. We also review how fundamental research using animal models is providing key insights into the various facets of human ASD.

A genome-wide survey of transgenerational genetic effects in autism

Effects of parental genotype or parent-offspring genetic interaction are well established in model organisms for a variety of traits. However, these transgenerational genetic models are rarely studied in humans. We have utilized an autism case-control study with 735 mother-child pairs to perform genome-wide screening for maternal genetic effects and maternal-offspring genetic interaction. We used simple models of single locus parent-child interaction and identified suggestive results (P<10⁻⁴) that cannot be explained by main effects, but no genome-wide significant signals. Some of these maternal and maternal-child associations were in or adjacent to autism candidate genes including: PCDH9, FOXP1, GABRB3, NRXN1, RELN, MACROD2, FHIT, RORA, CNTN4, CNTNAP2, FAM135B, LAMA1, NFIA, NLGN4X, RAPGEF4, and SDK1. We attempted validation of potential autism association under maternal-specific models using maternal-paternal comparison in family-based GWAS datasets. Our results suggest that further study of parental genetic effects and parent-child interaction in autism is warranted.

Neuronal autophagy and neurodevelopmental disorders

Neurodevelopmental disorders include a wide range of diseases such as autism spectrum disorders and mental retardation. Mutations in several genes that regulate neural development and synapse function have been identified in neurodevelopmental disorders. Interestingly, some affected genes and pathways in these diseases are associated with the autophagy pathway. Autophagy is a complex, bulky degradative process that involves the sequestration of cellular proteins, RNA, lipids, and cellular organelles into lysosomes. Despite recent progress in elucidating the genetics and molecular pathogenesis of these disorders, little is known about the pathogenic mechanisms and autophagy-related pathways involved in common neurodevelopmental disorders. Therefore, in this review, we focus on the current understanding of neuronal autophagy as well as recent findings on genetics and the roles of autophagy pathway in common neurodevelopmental disorders.

Structural plasticity of dendritic spines: the underlying mechanisms and its dysregulation in brain disorders

Dendritic spines are specialized structures on neuronal processes where the majority of excitatory synapses are localized. Spines are highly dynamic, and their stabilization and morphology are influenced by synaptic activity. This extrinsic regulation of spine morphogenesis underlies experience-dependent brain development and information storage within the brain circuitry. In this review, we summarize recent findings that demonstrate the phenomenon of activity-dependent structural plasticity and the molecular mechanisms by which synaptic activity sculpt neuronal connections. Impaired structural plasticity is associated with perturbed brain function in neurodevelopmental disorders such as autism. Information from the mechanistic studies therefore provides important insights into the design of therapeutic strategies for these brain disorders.

EPAC inhibition of SUR1 receptor increases glutamate release and seizure vulnerability

EPAC (Exchange Proteins Activated by cAMP) regulates glutamate transmitter release in the central neurons, but a role underlying this regulation has yet to be identified. Here we show that EPAC binds directly to the intracellular loop of an ATP-sensitive potassium (KATP) channel type-1 sulfonylurea receptor (SUR1) receptor consisting of amino acids 859-881 (SUR1(859-881)). Ablation of EPAC or expression of SUR1(859-881), which intercepts EPAC-SUR1 binding, increases the open probability of KATP channels consisting of the Kir6.1 subunit and SUR1. Opening of KATP channels inhibits glutamate release and reduces seizure vulnerability in adult mice. Therefore, EPAC interaction with SUR1 controls seizure susceptibility and possibly acts via regulation of glutamate release.

Exchange protein directly activated by cAMP (epac): a multidomain cAMP mediator in the regulation of diverse biological functions

Since the discovery nearly 60 years ago, cAMP is envisioned as one of the most universal and versatile second messengers. The tremendous feature of cAMP to tightly control highly diverse physiologic processes, including calcium homeostasis, metabolism, secretion, muscle contraction, cell fate, and gene transcription, is reflected by the award of five Nobel prizes. The discovery of Epac (exchange protein directly activated by cAMP) has ignited a new surge of cAMP-related research and has depicted novel cAMP properties independent of protein kinase A and cyclic nucleotide-gated channels. The multidomain architecture of Epac determines its activity state and allows cell-type specific protein-protein and protein-lipid interactions that control fine-tuning of pivotal biologic responses through the "old" second messenger cAMP. Compartmentalization of cAMP in space and time, maintained by A-kinase anchoring proteins, phosphodiesterases, and β-arrestins, contributes to the Epac signalosome of small GTPases, phospholipases, mitogen- and lipid-activated kinases, and transcription factors. These novel cAMP sensors seem to implement certain unexpected signaling properties of cAMP and thereby to permit delicate adaptations of biologic responses. Agonists and antagonists selective for Epac are developed and will support further studies on the biologic net outcome of the activation of Epac. This will increase our current knowledge on the pathophysiology of devastating diseases, such as diabetes, cognitive impairment, renal and heart failure, (pulmonary) hypertension, asthma, and chronic obstructive pulmonary disease. Further insights into the cAMP dynamics executed by the Epac signalosome will help to optimize the pharmacological treatment of these diseases.

Social, communication, and cortical structural impairments in Epac2-deficient mice

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.

Gene Expression Profiling of Tuberculous Meningitis Co-infected with HIV

Tuberculous meningitis (TBM) is a fatal form of Mycobacterium tuberculosis infection of the central nervous system (CNS). The similarities in the clinical and radiological findings in TBM cases with or without HIV make the diagnosis very challenging. Identification of genes, which are differentially expressed in brain tissues of HIV positive and HIV negative TBM patients, would enable better understanding of the molecular aspects of the infection and would also serve as an initial platform to evaluate potential biomarkers. Here, we report the identification of 796 differentially regulated genes in brain tissues of TBM patients co-infected with HIV using oligonucleotide DNA microarrays. We also performed immunohistochemical validation and confirmed the abundance of four gene products-glial fibrillary acidic protein (GFAP), serpin peptidase inhibitor, clade A member 3 (SERPINA3), thymidine phosphorylase (TYMP/ECGF1) and heat shock 70 kDa protein 8 (HSPA8). Our study paves the way for understanding the mechanism of TBM in HIV positive patients and for further validation of potential disease biomarkers.

Novel candidate genes and regions for childhood apraxia of speech identified by array comparative genomic hybridization

PURPOSE

The goal of this study was to identify new candidate genes and genomic copy-number variations associated with a rare, severe, and persistent speech disorder termed childhood apraxia of speech. Childhood apraxia of speech is the speech disorder segregating with a mutation in FOXP2 in a multigenerational London pedigree widely studied for its role in the development of speech-language in humans.

METHODS

A total of 24 participants who were suspected to have childhood apraxia of speech were assessed using a comprehensive protocol that samples speech in challenging contexts. All participants met clinical-research criteria for childhood apraxia of speech. Array comparative genomic hybridization analyses were completed using a customized 385K Nimblegen array (Roche Nimblegen, Madison, WI) with increased coverage of genes and regions previously associated with childhood apraxia of speech.

RESULTS

A total of 16 copy-number variations with potential consequences for speech-language development were detected in 12 or half of the 24 participants. The copy-number variations occurred on 10 chromosomes, 3 of which had two to four candidate regions. Several participants were identified with copy-number variations in two to three regions. In addition, one participant had a heterozygous FOXP2 mutation and a copy-number variation on chromosome 2, and one participant had a 16p11.2 microdeletion and copy-number variations on chromosomes 13 and 14.

CONCLUSION

Findings support the likelihood of heterogeneous genomic pathways associated with childhood apraxia of speech.

An autism-associated variant of Epac2 reveals a role for Ras/Epac2 signaling in controlling basal dendrite maintenance in mice

The architecture of dendritic arbors determines circuit connectivity, receptive fields, and computational properties of neurons, and dendritic structure is impaired in several psychiatric disorders. While apical and basal dendritic compartments of pyramidal neurons are functionally specialized and differentially regulated, little is known about mechanisms that selectively maintain basal dendrites. Here we identified a role for the Ras/Epac2 pathway in maintaining basal dendrite complexity of cortical neurons. Epac2 is a guanine nucleotide exchange factor (GEF) for the Ras-like small GTPase Rap, and it is highly enriched in the adult mouse brain. We found that in vivo Epac2 knockdown in layer 2/3 cortical neurons via in utero electroporation reduced basal dendritic architecture, and that Epac2 knockdown in mature cortical neurons in vitro mimicked this effect. Overexpression of an Epac2 rare coding variant, found in human subjects diagnosed with autism, also impaired basal dendritic morphology. This mutation disrupted Epac2's interaction with Ras, and inhibition of Ras selectively interfered with basal dendrite maintenance. Finally, we observed that components of the Ras/Epac2/Rap pathway exhibited differential abundance in the basal versus apical dendritic compartments. These findings define a role for Epac2 in enabling crosstalk between Ras and Rap signaling in maintaining basal dendrite complexity, and exemplify how rare coding variants, in addition to their disease relevance, can provide insight into cellular mechanisms relevant for brain connectivity.

Transcriptional co-regulation of neuronal migration and laminar identity in the neocortex

The cerebral neocortex is segregated into six horizontal layers, each containing unique populations of molecularly and functionally distinct excitatory projection (pyramidal) neurons and inhibitory interneurons. Development of the neocortex requires the orchestrated execution of a series of crucial processes, including the migration of young neurons into appropriate positions within the nascent neocortex, and the acquisition of layer-specific neuronal identities and axonal projections. Here, we discuss emerging evidence supporting the notion that the migration and final laminar positioning of cortical neurons are also co-regulated by cell type- and layer-specific transcription factors that play concomitant roles in determining the molecular identity and axonal connectivity of these neurons. These transcriptional programs thus provide direct links between the mechanisms controlling the laminar position and identity of cortical neurons.

EPAC null mutation impairs learning and social interactions via aberrant regulation of miR-124 and Zif268 translation

EPAC proteins are the guanine nucleotide exchange factors that act as the intracellular receptors for cyclic AMP. Two variants of EPAC genes including EPAC1 and EPAC2 are cloned and are widely expressed throughout the brain. But, their functions in the brain remain unknown. Here, we genetically delete EPAC1 (EPAC1(-/-)), EPAC2 (EPAC2(-/-)), or both EPAC1 and EPAC2 genes (EPAC(-/-)) in the forebrain of mice. We show that EPAC null mutation impairs long-term potentiation (LTP) and that this impairment is paralleled with the severe deficits in spatial learning and social interactions and is mediated in a direct manner by miR-124 transcription and Zif268 translation. Knockdown of miR-124 restores Zif268 and hence reverses all aspects of the EPAC(-/-) phenotypes, whereas expression of miR-124 or knockdown of Zif268 reproduces the effects of EPAC null mutation. Thus, EPAC proteins control miR-124 transcription in the brain for processing spatial learning and social interactions.

Deconstructing signal transduction pathways that regulate the actin cytoskeleton in dendritic spines

Dendritic spines are the sites of most excitatory synapses in the central nervous system. Recent studies have shown that spines function independently of each other, and they are currently the smallest known processing units in the brain. Spines exist in an array of morphologies, and spine structure helps dictate synaptic function. Dendritic spines are rich in actin, and actin rearrangements are critical regulators of spine morphology and density. In this review, we discuss the importance of actin in regulating dendritic spine morphogenesis, and discuss the upstream signal transduction pathways that either foster or inhibit actin polymerization. The understanding of actin regulatory pathways is best conceptualized as a hierarchical network in which molecules function in discrete levels defined by their molecular distance to actin. To this end, we focus on several classes of molecules, including guanine nucleotide exchange factors, small GTPases, small GTPase effectors, and actin binding proteins. We discuss how individual proteins in these molecular classes impact spine morphogenesis, and reveal the biochemical interactions in these networks that are responsible for shaping actin polymerization. Finally, we discuss the importance of these actin regulatory pathways in neuropsychiatric disorders.