The RhoGEF DOCK10 is essential for dendritic spine morphogenesis

In Cerebellar Atrophy of 12-Month-Old ATM-Null Mice, Transcriptome Upregulations Concern Most Neurotransmission and Neuropeptide Pathways, While Downregulations Affect Prominently Itpr1, Usp2 and Non-Coding RNA

The autosomal recessive disorder Ataxia-Telangiectasia is caused by a dysfunction of the stress response protein, ATM. In the nucleus of proliferating cells, ATM senses DNA double-strand breaks and coordinates their repair. This role explains T-cell dysfunction and tumour risk. However, it remains unclear whether this function is relevant for postmitotic neurons and underlies cerebellar atrophy, since ATM is cytoplasmic in postmitotic neurons. Here, we used ATM-null mice that survived early immune deficits via bone-marrow transplantation, and that reached initial neurodegeneration stages at 12 months of age. Global cerebellar transcriptomics demonstrated that ATM depletion triggered upregulations in most neurotransmission and neuropeptide systems. Downregulated transcripts were found for the ATM interactome component Usp2, many non-coding RNAs, ataxia genes Itpr1, Grid2, immediate early genes and immunity factors. Allelic splice changes affected prominently the neuropeptide machinery, e.g., Oprm1. Validation experiments with stressors were performed in human neuroblastoma cells, where ATM was localised only to cytoplasm, similar to the brain. Effect confirmation in SH-SY5Y cells occurred after ATM depletion and osmotic stress better than nutrient/oxidative stress, but not after ATM kinase inhibition or DNA stressor bleomycin. Overall, we provide pioneer observations from a faithful A-T mouse model, which suggest general changes in synaptic and dense-core vesicle stress adaptation.

Structural biology of DOCK-family guanine nucleotide exchange factors

DOCK proteins are a family of multi-domain guanine nucleotide exchange factors (GEFs) that activate the RHO GTPases CDC42 and RAC1, thereby regulating several RHO GTPase-dependent cellular processes. DOCK proteins are characterized by the catalytic DHR2 domain (DOCKDHR2 ), and a phosphatidylinositol(3,4,5)P3 -binding DHR1 domain (DOCKDHR1 ) that targets DOCK proteins to plasma membranes. DOCK-family GEFs are divided into four subfamilies (A to D) differing in their specificities for CDC42 and RAC1, and the composition of accessory signalling domains. Additionally, the DOCK-A and DOCK-B subfamilies are constitutively associated with ELMO proteins that auto-inhibit DOCK GEF activity. We review structural studies that have provided mechanistic insights into DOCK-protein functions. These studies revealed how a conserved nucleotide sensor in DOCKDHR2 catalyses nucleotide exchange, the basis for how different DOCK proteins activate specifically CDC42 and RAC1, and sometimes both, and how up-stream regulators relieve the ELMO-mediated auto-inhibition. We conclude by presenting a model for full-length DOCK9 of the DOCK-D subfamily. The involvement of DOCK GEFs in a range of diseases highlights the importance of gaining structural insights into these proteins to better understand and specifically target them.

Huntingtin coordinates dendritic spine morphology and function through cofilin-mediated control of the actin cytoskeleton

Compelling evidence indicates that in Huntington's disease (HD), mutation of huntingtin (HTT) alters several aspects of early brain development such as synaptogenesis. It is not clear to what extent the partial loss of wild-type HTT function contributes to these abnormalities. Here we investigate the function of HTT in the formation of spines. Although larger spines normally correlate with more synaptic activity, cell-autonomous depletion of HTT leads to enlarged spines but reduced excitatory synaptic function. We find that HTT is required for the proper turnover of endogenous actin and to recruit AMPA receptors at active synapses; loss of HTT leads to LIM kinase (LIMK) hyperactivation, which maintains cofilin in its inactive state. HTT therefore influences actin dynamics through the LIMK-cofilin pathway. Loss of HTT uncouples spine structure from synaptic function, which may contribute to the ultimate development of HD symptoms.

Dock10 Regulates Cardiac Function under Neurohormonal Stress

Dedicator of cytokinesis 10 (Dock10) is a guanine nucleotide exchange factor for Cdc42 and Rac1 that regulates the JNK (c-Jun N-terminal kinase) and p38 MAPK (mitogen-activated protein kinase) signaling cascades. In this study, we characterized the roles of Dock10 in the myocardium. In vitro: we ablated Dock10 in neonatal mouse floxed Dock10 cardiomyocytes (NMCMs) and cardiofibroblasts (NMCFs) by transduction with an adenovirus expressing Cre-recombinase. In vivo, we studied mice in which the Dock10 gene was constitutively and globally deleted (Dock10 KO) and mice with cardiac myocyte-specific Dock10 KO (Dock10 CKO) at baseline and in response to two weeks of Angiotensin II (Ang II) infusion. In vitro, Dock10 ablation differentially inhibited the α-adrenergic stimulation of p38 and JNK in NMCM and NMCF, respectively. In vivo, the stimulation of both signaling pathways was markedly attenuated in the heart. The Dock10 KO mice had normal body weight and cardiac size. However, echocardiography revealed mildly reduced systolic function, and IonOptix recordings demonstrated reduced contractility and elevated diastolic calcium levels in isolated cardiomyocytes. Remarkably, Dock10 KO, but not Dock10 CKO, exaggerated the pathological response to Ang II infusion. These data suggest that Dock10 regulates cardiac stress-related signaling. Although Dock10 can regulate MAPK signaling in both cardiomyocytes and cardiofibroblasts, the inhibition of pathological cardiac remodeling is not apparently due to the Dock10 signaling in the cardiomyocyte.

Brain-specific deletion of GIT1 impairs cognition and alters phosphorylation of synaptic protein networks implicated in schizophrenia susceptibility

Despite tremendous effort, the molecular and cellular basis of cognitive deficits in schizophrenia remain poorly understood. Recent progress in elucidating the genetic architecture of schizophrenia has highlighted the association of multiple loci and rare variants that may impact susceptibility. One key example, given their potential etiopathogenic and therapeutic relevance, is a set of genes that encode proteins that regulate excitatory glutamatergic synapses in brain. A critical next step is to delineate specifically how such genetic variation impacts synaptic plasticity and to determine if and how the encoded proteins interact biochemically with one another to control cognitive function in a convergent manner. Towards this goal, here we study the roles of GPCR-kinase interacting protein 1 (GIT1), a synaptic scaffolding and signaling protein with damaging coding variants found in schizophrenia patients, as well as copy number variants found in patients with neurodevelopmental disorders. We generated conditional neural-selective GIT1 knockout mice and found that these mice have deficits in fear conditioning memory recall and spatial memory, as well as reduced cortical neuron dendritic spine density. Using global quantitative phospho-proteomics, we revealed that GIT1 deletion in brain perturbs specific networks of GIT1-interacting synaptic proteins. Importantly, several schizophrenia and neurodevelopmental disorder risk genes are present within these networks. We propose that GIT1 regulates the phosphorylation of a network of synaptic proteins and other critical regulators of neuroplasticity, and that perturbation of these networks may contribute specifically to cognitive deficits observed in schizophrenia and neurodevelopmental disorders.

Combination of Genomic and Transcriptomic Approaches Highlights Vascular and Circadian Clock Components in Multiple Sclerosis

Aiming at exploring vascular components in multiple sclerosis (MS) with brain outflow disturbance, we combined transcriptome analysis in MS internal jugular vein (IJV) wall with WES in MS families with vertical transmission of disease. Main results were the differential expression in IJV wall of 16 MS-GWAS genes and of seven genes (GRIN2A, GRIN2B, IL20RB, IL26, PER3, PITX2, and PPARGC1A) not previously indicated by GWAS but encoding for proteins functionally interacting with MS candidate gene products. Strikingly, 22/23 genes have been previously associated with vascular or neuronal traits/diseases, nine encoded for transcriptional factors/regulators and six (CAMK2G, GRIN2A, GRIN2B, N1RD1, PER3, PPARGC1A) for circadian entrainment/rhythm components. Among the WES low-frequency (MAF ≤ 0.04) SNPs (n = 7) filtered in the 16 genes, the NR1D1 rs17616365 showed significantly different MAF in the Network for Italian Genomes affected cohort than in the 1000 Genome Project Tuscany samples. This pattern was also detected in five nonintronic variants (GRIN2B rs1805482, PER3 rs2640909, PPARGC1A rs2970847, rs8192678, and rs3755863) in genes coding for functional partners. Overall, the study proposes specific markers and low-frequency variants that might help (i) to understand perturbed biological processes in vascular tissues contributing to MS disease, and (ii) to characterize MS susceptibility genes for functional association with disease-pathways.

New Functions of Vav Family Proteins in Cardiovascular Biology, Skeletal Muscle, and the Nervous System

Simple Summary

In this review, we provide information on the role of Vav proteins, a group of signaling molecules that act as both Rho GTPase activators and adaptor molecules, in the cardiovascular system, skeletal muscle, and the nervous system. We also describe how these functions impact in other physiological and pathological processes such as sympathoregulation, blood pressure regulation, systemic metabolism, and metabolic syndrome.

Abstract

Vav proteins act as tyrosine phosphorylation-regulated guanosine nucleotide exchange factors for Rho GTPases and as molecular scaffolds. In mammals, this family of signaling proteins is composed of three members (Vav1, Vav2, Vav3) that work downstream of protein tyrosine kinases in a wide variety of cellular processes. Recent work with genetically modified mouse models has revealed that these proteins play key signaling roles in vascular smooth and skeletal muscle cells, specific neuronal subtypes, and glia cells. These functions, in turn, ensure the proper regulation of blood pressure levels, skeletal muscle mass, axonal wiring, and fiber myelination events as well as systemic metabolic balance. The study of these mice has also led to the discovery of new physiological interconnection among tissues that contribute to the ontogeny and progression of different pathologies such as, for example, hypertension, cardiovascular disease, and metabolic syndrome. Here, we provide an integrated view of all these new Vav family-dependent signaling and physiological functions.

Variable Distribution of DOCK-D Proteins between Cytosol and Nucleoplasm in Cell Lines, Effect of Interleukin-4 on DOCK10 in B-Cell Lymphoid Neoplasms, and Validation of a New DOCK10 Antiserum for Immunofluorescence Studies

Dedicator-of-cytokinesis (DOCK), a family of guanine-nucleotide exchange factors (GEFs), comprises four subfamilies, named from A to D. DOCK-D comprises DOCK9, DOCK10, and DOCK11. The GEF activity involves translocation from the cytoplasm to the plasma membrane (PM), as assessed by the transfection of tagged proteins. However, the cellular localization of endogenous DOCK proteins is poorly understood. In this paper, to gain a better understanding of the role of the DOCK-D proteins, we studied their distribution between cytosol and nucleoplasm in 11 cell lines. DOCK-D proteins were distributed with variable cytosolic or nuclear predominance, although the latter was common for DOCK9 and DOCK11. These results suggest that the DOCK-D proteins may perform new nuclear functions, which remain to be discovered. Furthermore, we found that DOCK10 levels are increased by interleukin-4 (IL-4) in B-cell lymphoid neoplasms other than chronic lymphocytic leukemia (CLL) such as mantle cell lymphoma and diffuse large B-cell lymphoma. We also found evidence for an induction of the cytosolic levels of DOCK10 by IL-4 in CLL. Finally, we obtained a valid DOCK10 antiserum for immunofluorescence (IF) microscopy that, as an antibody against the hemagglutinin (HA) tag, marked PM ruffles and filopodia in HeLa cells with inducible expression of HA-DOCK10.

The roles of Cdc42 and Rac1 in the formation of plasma membrane protrusions in cancer epithelial HeLa cells

The inducible model of clones generated from the cervical cancer epithelial HeLa cell line has shown the role of DOCK10 as a guanine-nucleotide exchange factor for Rho GTPases Cdc42 and Rac1 and as an inducer of filopodia and plasma membrane (PM) ruffles. In this model, constitutively active (CA) mutants of Cdc42 and Rac1 promote filopodia and ruffles, respectively, as in other models. DOCK9 also induces filopodia and ruffles, although ruffling activity is less prominent. By exploiting this model further, the aim of this work is to provide a more complete understanding of the role of Cdc42 and Rac1, and their interactions with DOCK10 and DOCK9, in regulation of PM protrusions. New clones have been generated from HeLa, including single clones expressing one form of wild-type (WT) or dominant negative (DN) Cdc42 or Rac1, and double clones co-expressing one of them together with either DOCK10 or DOCK9. Expression of WT- and DN-Cdc42 induced filopodia. WT-Cdc42 and, especially, DN-Cdc42 also gave rise to veil protrusions, which were neutralized by DOCK10. Moreover, DN-Cdc42 stimulated the emergence of ruffles, further increased by DOCK10, and WT-Cdc42 also augmented ruffles in presence of DOCK9 and DOCK10. WT-Rac1 greatly increased PM blebbing, as did DN-Rac1 more moderately. In both cases, blebs were enhanced by DOCK10. DN-Rac1 and CA-Rac1 moderately raised filopodia, and DOCK10 and DOCK9 had opposed effects on filopodia (up and down, respectively) in presence of WT-Rac1. As conclusions, we highlight that Cdc42 promotes filopodia regardless of its conformational state, and Rac1 induces blebs in conformations other than CA, especially WT-Rac1, in the inducible HeLa clones. The model could be useful to learn more about the mechanisms underlying PM protrusions.

Effects of CXCL12 isoforms in a pancreatic pre-tumour cellular model: Microarray analysis

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of death among cancers, it is characterized by poor prognosis and strong chemoresistance. In the PDAC microenvironment, stromal cells release different extracellular components, including CXCL12. The CXCL12 is a chemokine promoting the communication between tumour and stromal cells. Six different splicing isoforms of CXCL12 are known (α, β, γ, δ, ε, θ) but their role in PDAC has not yet been characterized.

AIM

To investigate the specific role of α, β, and γ CXCL12 isoforms in PDAC onset.

METHODS

We used hTERT-HPNE E6/E7/KRasG12D (Human Pancreatic Nestin-Expressing) cell line as a pancreatic pre-tumour model and exposed it to the α, β, and γ CXCL12 isoforms. The altered expression profiles were assessed by microarray analyses and confirmed by Real-Time polymerase chain reaction. The functional enrichment analyses have been performed by Enrichr tool to highlight Gene Ontology enriched terms. In addition, wound healing assays have been carried out to assess the phenotypic changes, in terms of migration ability, induced by the α, β, and γ CXCL12 isoforms.

RESULTS

Microarray analysis of hTERT-HPNE cells treated with the three different CXCL12 isoforms highlighted that the expression of only a few genes was altered. Moreover, the α and β isoforms showed an alteration in expression of different genes, whereas γ isoform affected the expression of genes also common with α and β isoforms. The β isoform altered the expression of genes mainly involved in cell cycle regulation. In addition, all isoforms affected the expression of genes associated to cell migration, adhesion and cytoskeleton. In vitro cell migration assay confirmed that CXCL12 enhanced the migration ability of hTERT-HPNE cells. Among the CXCL12 splicing isoforms, the γ isoform showed higher induction of migration than α and β isoforms.

CONCLUSION

Our data suggests an involvement and different roles of CXCL12 isoforms in PDAC onset. However, more investigations are needed to confirm these preliminary observations.

The distinct roles of calcium in rapid control of neuronal glycolysis and the tricarboxylic acid cycle

When neurons engage in intense periods of activity, the consequent increase in energy demand can be met by the coordinated activation of glycolysis, the tricarboxylic acid (TCA) cycle, and oxidative phosphorylation. However, the trigger for glycolytic activation is unknown and the role for Ca2+ in the mitochondrial responses has been debated. Using genetically encoded fluorescent biosensors and NAD(P)H autofluorescence imaging in acute hippocampal slices, here we find that Ca2+ uptake into the mitochondria is responsible for the buildup of mitochondrial NADH, probably through Ca2+ activation of dehydrogenases in the TCA cycle. In the cytosol, we do not observe a role for the Ca2+/calmodulin signaling pathway, or AMPK, in mediating the rise in glycolytic NADH in response to acute stimulation. Aerobic glycolysis in neurons is triggered mainly by the energy demand resulting from either Na+ or Ca2+ extrusion, and in mouse dentate granule cells, Ca2+ creates the majority of this demand.

Sculpting Dendritic Spines during Initiation and Maintenance of Neuropathic Pain

Accumulating evidence has established a firm role for synaptic plasticity in the pathogenesis of neuropathic pain. Recent advances have highlighted the importance of dendritic spine remodeling in driving synaptic plasticity within the CNS. Identifying the molecular players underlying neuropathic pain induced structural and functional maladaptation is therefore critical to understanding its pathophysiology. This process of dynamic reorganization happens in unique phases that have diverse pathologic underpinnings in the initiation and maintenance of neuropathic pain. Recent evidence suggests that pharmacological targeting of specific proteins during distinct phases of neuropathic pain development produces enhanced antinociception. These findings outline a potential new paradigm for targeted treatment and the development of novel therapies for neuropathic pain. We present a concise review of the role of dendritic spines in neuropathic pain and outline the potential for modulation of spine dynamics by targeting two proteins, srGAP3 and Rac1, critically involved in the regulation of the actin cytoskeleton.

Structure of the DOCK2-ELMO1 complex provides insights into regulation of the auto-inhibited state

DOCK (dedicator of cytokinesis) proteins are multidomain guanine nucleotide exchange factors (GEFs) for RHO GTPases that regulate intracellular actin dynamics. DOCK proteins share catalytic (DOCKDHR2) and membrane-associated (DOCKDHR1) domains. The structurally-related DOCK1 and DOCK2 GEFs are specific for RAC, and require ELMO (engulfment and cell motility) proteins for function. The N-terminal RAS-binding domain (RBD) of ELMO (ELMORBD) interacts with RHOG to modulate DOCK1/2 activity. Here, we determine the cryo-EM structures of DOCK2-ELMO1 alone, and as a ternary complex with RAC1, together with the crystal structure of a RHOG-ELMO2RBD complex. The binary DOCK2-ELMO1 complex adopts a closed, auto-inhibited conformation. Relief of auto-inhibition to an active, open state, due to a conformational change of the ELMO1 subunit, exposes binding sites for RAC1 on DOCK2DHR2, and RHOG and BAI GPCRs on ELMO1. Our structure explains how up-stream effectors, including DOCK2 and ELMO1 phosphorylation, destabilise the auto-inhibited state to promote an active GEF.

The regulation of DOCK family proteins on T and B cells

The dedicator of cytokinesis (DOCK) family proteins consist of 11 members, each of which contains 2 domains, DOCK homology region (DHR)-1 and DHR-2, and as guanine nucleotide exchange factors, they mediate activation of small GTPases. Both DOCK2 and DOCK8 deficiencies in humans can cause severe combined immunodeficiency, but they have different characteristics. DOCK8 defect mainly causes high IgE, allergic disease, refractory skin virus infection, and increased incidence of malignant tumor, whereas DOCK2 defect mainly causes early-onset, invasive infection with less atopy and increased IgE. However, the underlying molecular mechanisms causing the disease remain unclear. This paper discusses the role of DOCK family proteins in regulating B and T cells, including development, survival, migration, activation, immune tolerance, and immune functions. Moreover, related signal pathways or molecule mechanisms are also described in this review. A greater understanding of DOCK family proteins and their regulation of lymphocyte functions may facilitate the development of new therapeutics for immunodeficient patients and improve their prognosis.

Expression of DOCK10.1 protein revealed with a specific antiserum: insights into regulation of first exon isoforms of DOCK10

DOCK10, a guanine-nucleotide exchange factor (GEF) for Rho GTPases, represents the example of a gene that gives rise to alternative first exon mRNA isoforms, named DOCK10.1 and DOCK10.2. Expression of human DOCK10.2 protein in cell lines, and its induction by interleukin-4 (IL-4) in normal B lymphocytes and chronic lymphocytic leukemia (CLL) cells, were previously demonstrated using an antiserum raised against a peptide encoded by sequences from exon 1.2. Here, expression of human DOCK10.1 protein was demonstrated using an antiserum raised against a peptide encoded by sequences from exon 1.1. Specificity of the DOCK10.1 and DOCK10.2 antisera for their respective isoforms was demonstrated using transfected human 293 T cells. Their specificity for endogenous DOCK10 was strongly suggested by the high significance of the correlations between the levels of their expected signals at the molecular size of 250 kDa and the levels of DOCK10.1 and DOCK10.2 mRNAs, respectively, in human hematopoietic cell lines. Specificity of the DOCK10.1 antiserum for DOCK10 was also demostrated in mouse using the DOCK10 knockout model. The DOCK10.1 protein was induced by IL-4 in CLL cells, which demonstrates that the mechanism by which IL-4 regulates DOCK10 is not isoform-specific. Last, to get insights into differential regulation of the DOCK10 isoforms, their protein levels in cell lines were compared with their gene expression profiles retrieved from the Cancer Cell Line Encyclopedia (CCLE), leading to the identification of BCL3 and KLF12 as potential transcriptional regulators of DOCK10.1 and DOCK10.2, respectively.

The role of DOCK10 in the regulation of the transcriptome and aging

DOCK10, a guanine-nucleotide exchange factor (GEF) for Rac1 and Cdc42 Rho GTPases whose expression is induced by interleukin-4 (IL-4) in B cells, is involved in B cell development and function according to recent studies performed in Dock10-knockout (KO) mice. To investigate whether DOCK10 is involved in regulation of the transcriptome, changes in the gene expression profiles (GEPs) were studied by microarray in three cellular models: DOCK10 expression induced by doxycycline (dox) withdrawal in a stable inducible HeLa clone, DOCK10 expression induced by transient transfection of 293T cells, and wild type (WT) versus KO mouse spleen B cells (SBC). In all three systems, DOCK10 expression determined moderate differences in the GEPs, which were functionally interpreted by gene set enrichment analysis (GSEA). Common signatures significantly associated to expression of DOCK10 were found in all three systems, including the upregulated targets of HOXA5 and the SWI/SNF complex, and EGF signaling. In SBC, Dock10 expression was associated to enrichment of gene sets of Cmyb, integrin, IL-4, Wnt, Rac1, and Cdc42 pathways, and of cellular components such as the immunological synapse and the cell leading edge. Transcription of genes involved in these pathways likely acts as a feedforward mechanism downstream of activation of Rac1 and Cdc42 mediated by DOCK10. Interestingly, a senescence gene set was found significantly associated to WT SBC. To test whether DOCK10 is related to aging, we set out to analyse the survival of the mouse colony, which led to the finding that Dock10-KO mice lived longer than WT mice. Moreover, Dock10-KO mice showed slower loss of their coat during aging. These results indicate a role for Dock10 in senescence. These novel roles of DOCK10 in the regulation of the transcriptome and aging deserve further exploration.

Advantages of Single-Nucleus over Single-Cell RNA Sequencing of Adult Kidney: Rare Cell Types and Novel Cell States Revealed in Fibrosis

BACKGROUND

A challenge for single-cell genomic studies in kidney and other solid tissues is generating a high-quality single-cell suspension that contains rare or difficult-to-dissociate cell types and is free of both RNA degradation and artifactual transcriptional stress responses.

METHODS

We compared single-cell RNA sequencing (scRNA-seq) using the DropSeq platform with single-nucleus RNA sequencing (snRNA-seq) using sNuc-DropSeq, DroNc-seq, and 10X Chromium platforms on adult mouse kidney. We validated snRNA-seq on fibrotic kidney from mice 14 days after unilateral ureteral obstruction (UUO) surgery.

RESULTS

A total of 11,391 transcriptomes were generated in the comparison phase. We identified ten clusters in the scRNA-seq dataset, but glomerular cell types were absent, and one cluster consisted primarily of artifactual dissociation-induced stress response genes. By contrast, snRNA-seq from all three platforms captured a diversity of kidney cell types that were not represented in the scRNA-seq dataset, including glomerular podocytes, mesangial cells, and endothelial cells. No stress response genes were detected. Our snRNA-seq protocol yielded 20-fold more podocytes compared with published scRNA-seq datasets (2.4% versus 0.12%, respectively). Unexpectedly, single-cell and single-nucleus platforms had equivalent gene detection sensitivity. For validation, analysis of frozen day 14 UUO kidney revealed rare juxtaglomerular cells, novel activated proximal tubule and fibroblast cell states, and previously unidentified tubulointerstitial signaling pathways.

CONCLUSIONS

snRNA-seq achieves comparable gene detection to scRNA-seq in adult kidney, and it also has substantial advantages, including reduced dissociation bias, compatibility with frozen samples, elimination of dissociation-induced transcriptional stress responses, and successful performance on inflamed fibrotic kidney.

Rho GTPases in Intellectual Disability: From Genetics to Therapeutic Opportunities

Rho-class small GTPases are implicated in basic cellular processes at nearly all brain developmental steps, from neurogenesis and migration to axon guidance and synaptic plasticity. GTPases are key signal transducing enzymes that link extracellular cues to the neuronal responses required for the construction of neuronal networks, as well as for synaptic function and plasticity. Rho GTPases are highly regulated by a complex set of activating (GEFs) and inactivating (GAPs) partners, via protein:protein interactions (PPI). Misregulated RhoA, Rac1/Rac3 and cdc42 activity has been linked with intellectual disability (ID) and other neurodevelopmental conditions that comprise ID. All genetic evidences indicate that in these disorders the RhoA pathway is hyperactive while the Rac1 and cdc42 pathways are consistently hypoactive. Adopting cultured neurons for in vitro testing and specific animal models of ID for in vivo examination, the endophenotypes associated with these conditions are emerging and include altered neuronal networking, unbalanced excitation/inhibition and altered synaptic activity and plasticity. As we approach a clearer definition of these phenotype(s) and the role of hyper- and hypo-active GTPases in the construction of neuronal networks, there is an increasing possibility that selective inhibitors and activators might be designed via PPI, or identified by screening, that counteract the misregulation of small GTPases and result in alleviation of the cognitive condition. Here we review all knowledge in support of this possibility.

DOCK9 induces membrane ruffles and Rac1 activity in cancer HeLa epithelial cells

Dedicator-of-cytokinesis (DOCK) proteins are a family of guanine-nucleotide exchange factors (GEF) for Rho GTPases. The DOCK-D homology subfamily comprises DOCK9, DOCK10, and DOCK11. DOCK9 and DOCK11 are GEFs for Cdc42 and induce filopodia, while DOCK10 is a dual GEF for Cdc42 and Rac1 and induces filopodia and ruffles. We provide data showing that DOCK9, the only one of the DOCK-D members that is not considered hematopoietic, is nevertheless expressed at high levels in T lymphocytes, as do DOCK10 and DOCK11, although unlike these, it is not expressed in B lymphocytes. To investigate DOCK9 function, we have created a stable HeLa clone with inducible expression of HA-DOCK9. Induction of expression of HA-DOCK9 produced loss of elongation and polygonal shape of HeLa cells. Regarding membrane protrusions, HA-DOCK9 prominently induced filopodia, but also an increase of membrane ruffles. The latter was consistent with an increase in the levels of activation of Rac1, suggesting that DOCK9 carries a secondary ability to induce ruffles through activation of Rac1.

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DOCK9 is expressed in T cells but, unlike DOCK10 and DOCK11, not in B cells.

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Clones with inducible expression of DOCK9 were created from HeLa cancer cell line.

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DOCK9 induced filopodia, membrane ruffles, and loss of cell elongation.

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DOCK9 induced activation of Rac1.

Directional Migration in Esophageal Squamous Cell Carcinoma (ESCC) is Epigenetically Regulated by SET Nuclear Oncogene, a Member of the Inhibitor of Histone Acetyltransferase Complex

Directional cell migration is of fundamental importance to a variety of biological events, including metastasis of malignant cells. Herein, we specifically investigated SET oncoprotein, a subunit of the recently identified inhibitor of acetyltransferases (INHAT) complex and identified its role in the establishment of front-rear cell polarity and directional migration in Esophageal Squamous Cell Carcinoma (ESCC). We further define the molecular circuits that govern these processes by showing that SET modulated DOCK7/RAC1 and cofilin signaling events. Moreover, a detailed analysis of the spatial distribution of RAC1 and cofilin allowed us to decipher the synergistical contributions of the two in coordinating the advancing dynamics by measuring architectures, polarities, and cytoskeletal organizations of the lamellipodia leading edges. In further investigations in vivo, we identified their unique role at multiple levels of the invasive cascade for SET cell and indicate the necessity for their functional balance to enable efficient invasion as well. Additionally, SET epigenetically repressed miR-30c expression by deacetylating histones H2B and H4 on its promoter, which was functionally important for the biological effects of SET in our cell-context. Finally, we corroborated our findings in vivo by evaluating the clinical relevance of SET signaling in the metastatic burden in mice and a large series of patients with ESCC at diagnosis, observing it's significance in predicting metastasis formation. Our findings uncovered a novel signaling network initiated by SET that epigenetically modulated ESCC properties and suggest that targeting the regulatory axis might be a promising strategy to inhibit migration and metastasis.

Maturation, Refinement, and Serotonergic Modulation of Cerebellar Cortical Circuits in Normal Development and in Murine Models of Autism

The formation of the complex cerebellar cortical circuits follows different phases, with initial synaptogenesis and subsequent processes of refinement guided by a variety of mechanisms. The regularity of the cellular and synaptic organization of the cerebellar cortex allowed detailed studies of the structural plasticity mechanisms underlying the formation of new synapses and retraction of redundant ones. For the attainment of the monoinnervation of the Purkinje cell by a single climbing fiber, several signals are involved, including electrical activity, contact signals, homosynaptic and heterosynaptic interaction, calcium transients, postsynaptic receptors, and transduction pathways. An important role in this developmental program is played by serotonergic projections that, acting on temporally and spatially regulated postsynaptic receptors, induce and modulate the phases of synaptic formation and maturation. In the adult cerebellar cortex, many developmental mechanisms persist but play different roles, such as supporting synaptic plasticity during learning and formation of cerebellar memory traces. A dysfunction at any stage of this process can lead to disorders of cerebellar origin, which include autism spectrum disorders but are not limited to motor deficits. Recent evidence in animal models links impairment of Purkinje cell function with autism-like symptoms including sociability deficits, stereotyped movements, and interspecific communication by vocalization.

Regulation of Rho GTPase proteins during spine structural plasticity for the control of local dendritic plasticity

While it is generally appreciated that learning involves the structural rearrangement of neuronal circuits, the underlying orchestration of molecular events that drives these changes is not as well understood. Recent studies on the spatiotemporal organization of synaptic signaling events have provided new insights into the biochemical underpinnings of various expressions of structural neuronal plasticity, as well as the functional consequences that emerge because of the particular behavior of the molecules involved. In particular, activity patterns of and interplay among a class of morphogenic signaling proteins, the Rho GTPases, and their downstream signals, are found to be critical for linking neuronal activity with various forms of neuronal plasticity. We review recent findings on this topic and discuss their physiological implications.

Deletion of Dock10 in B Cells Results in Normal Development but a Mild Deficiency upon In Vivo and In Vitro Stimulations

We sought to identify genes necessary to induce cytoskeletal change in B cells. Using gene expression microarray, we compared B cells stimulated with interleukin-4 (IL-4) and anti-CD40 antibodies that induce B cell spreading, cell motility, tight aggregates, and extensive microvilli with B cells stimulated with lipopolysaccharide that lack these cytoskeletal changes. We identified 84 genes with 10-fold or greater expression in anti-CD40 + IL-4 stimulated B cells, one of these encoded the guanine nucleotide exchange factor (GEF) dedicator of cytokinesis 10 (Dock10). IL-4 selectively induced Dock10 expression in B cells. Using lacZ expression to monitor Dock10 promoter activity, we found that Dock10 was expressed at all stages during B cell development. However, specific deletion of Dock10 in B cells was associated with a mild phenotype with normal B cell development and normal B cell spreading, polarization, motility, chemotaxis, aggregation, and Ig class switching. Dock10-deficient B cells showed lower proliferation in response to anti-CD40 and IL-4 stimulation. Moreover, the IgG response to soluble antigen in vivo was lower when Dock10 was specifically deleted in B cells. Together, we found that most B cell responses were intact in the absence of Dock10. However, specific deletion of Dock10 in B cells was associated with a mild reduction in B cell activation in vitro and in vivo.

RhoGTPases at the synapse: An embarrassment of choice

Activity-dependent modifications in the strength of excitatory synapses are considered to be major cellular mechanisms that contribute to the plasticity of neuronal networks underlying learning and memory. Key mechanisms for the regulation of synaptic efficacy involve the dynamic changes in size and number of dendritic spines, as well as the synaptic incorporation and removal of AMPA-type glutamate receptors (AMPAr). As key regulators of the actin cytoskeleton, the Rho subfamily of GTP-binding proteins play a critical role in synaptic development and plasticity. They shuttle between the active GTP-bound form and the inactive GDP-bound form under the regulation of dedicated guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). More than 80 human GEFs and 70 GAPs have been identified, most of which are expressed in the brain with a specific spatial and temporal expression pattern. However, the function of most GEFs and GAPs in the brain has not been elucidated. In this review, we highlight the novel neuronal function of the synaptic RhoGAP ARHGAP12 and the ID-associated RhoGEF TRIO and further propose 3 possible approaches of neurons utilizing Rho GTPase regulatory proteins to accurately modulate synaptic function.

A dual role for the RhoGEF Ephexin5 in regulation of dendritic spine outgrowth

The outgrowth of new dendritic spines is closely linked to the formation of new synapses, and is thought to be a vital component of the experience-dependent circuit plasticity that supports learning. Here, we examined the role of the RhoGEF Ephexin5 in driving activity-dependent spine outgrowth. We found that reducing Ephexin5 levels increased spine outgrowth, and increasing Ephexin5 levels decreased spine outgrowth in a GEF-dependent manner, suggesting that Ephexin5 acts as an inhibitor of spine outgrowth. Notably, we found that increased neural activity led to a proteasome-dependent reduction in the levels of Ephexin5 in neuronal dendrites, which could facilitate the enhanced spine outgrowth observed following increased neural activity. Surprisingly, we also found that Ephexin5-GFP levels were elevated on the dendrite at sites of future new spines, prior to new spine outgrowth. Moreover, lowering neuronal Ephexin5 levels inhibited new spine outgrowth in response to both global increases in neural activity and local glutamatergic stimulation of the dendrite, suggesting that Ephexin5 is necessary for activity-dependent spine outgrowth. Our data support a model in which Ephexin5 serves a dual role in spinogenesis, acting both as a brake on overall spine outgrowth and as a necessary component in the site-specific formation of new spines.

Single-cell RNAseq reveals cell adhesion molecule profiles in electrophysiologically defined neurons

In brain, signaling mediated by cell adhesion molecules defines the identity and functional properties of synapses. The specificity of presynaptic and postsynaptic interactions that is presumably mediated by cell adhesion molecules suggests that there exists a logic that could explain neuronal connectivity at the molecular level. Despite its importance, however, the nature of such logic is poorly understood, and even basic parameters, such as the number, identity, and single-cell expression profiles of candidate synaptic cell adhesion molecules, are not known. Here, we devised a comprehensive list of genes involved in cell adhesion, and used single-cell RNA sequencing (RNAseq) to analyze their expression in electrophysiologically defined interneurons and projection neurons. We compared the cell type-specific expression of these genes with that of genes involved in transmembrane ion conductances (i.e., channels), exocytosis, and rho/rac signaling, which regulates the actin cytoskeleton. Using these data, we identified two independent, developmentally regulated networks of interacting genes encoding molecules involved in cell adhesion, exocytosis, and signal transduction. Our approach provides a framework for a presumed cell adhesion and signaling code in neurons, enables correlating electrophysiological with molecular properties of neurons, and suggests avenues toward understanding synaptic specificity.

Dock10 regulates CD23 expression and sustains B-cell lymphopoiesis in secondary lymphoid tissue

Dock10, a guanine nucleotide exchange factor for the Rho GTPases Rac1 and Cdc42, affects cell morphology, membrane protrusive activity, and cell movement. Dock10 is prominently expressed in lymphoid tissue and upregulated by IL-4 in B cells. To investigate the physiological role of Dock10, WT mice and Dock10 KO mice were used. KO mice showed decreased numbers of B cells in spleen, both follicular B cells and marginal zone B cells, and in peripheral blood, but not in bone marrow. The antiapoptotic effect of IL-4 in vitro, the migratory response to CXCL13 or CCL21 in vitro, and the whole genome expression profile were intact in spleen B cells from KO mice. CD23, the low-affinity receptor for immunoglobulin E, was overexpressed on follicular B cells from KO mice, suggesting that Dock10 negatively regulates membrane CD23 expression. Negative regulation of CD23 expression by Dock10 could play a role in B cell maturation and function.