p140Sra-1 (specifically Rac1-associated protein) is a novel specific target for Rac1 small GTPase

The WAVE complex in developmental and adulthood brain disorders

Actin polymerization and depolymerization are fundamental cellular processes required not only for the embryonic and postnatal development of the brain but also for the maintenance of neuronal plasticity and survival in the adult and aging brain. The orchestrated organization of actin filaments is controlled by various actin regulatory proteins. Wiskott‒Aldrich syndrome protein-family verprolin-homologous protein (WAVE) members are key activators of ARP2/3 complex-mediated actin polymerization. WAVE proteins exist as heteropentameric complexes together with regulatory proteins, including CYFIP, NCKAP, ABI and BRK1. The activity of the WAVE complex is tightly regulated by extracellular cues and intracellular signaling to execute its roles in specific intracellular events in brain cells. Notably, dysregulation of the WAVE complex and WAVE complex-mediated cellular processes confers vulnerability to a variety of brain disorders. De novo mutations in WAVE genes and other components of the WAVE complex have been identified in patients with developmental disorders such as intellectual disability, epileptic seizures, schizophrenia, and/or autism spectrum disorder. In addition, alterations in the WAVE complex are implicated in the pathophysiology of Alzheimer's disease and Parkinson's disease, as well as in behavioral adaptations to psychostimulants or maladaptive feeding.

Hem1 inborn errors of immunity: waving goodbye to coordinated immunity in mice and humans

Inborn errors of immunity (IEI) are a group of diseases in humans that typically present as increased susceptibility to infections, autoimmunity, hyperinflammation, allergy, and in some cases malignancy. Among newly identified genes linked to IEIs include 3 independent reports of 9 individuals from 7 independent kindreds with severe primary immunodeficiency disease (PID) and autoimmunity due to loss-of-function mutations in the NCKAP1L gene encoding Hematopoietic protein 1 (HEM1). HEM1 is a hematopoietic cell specific component of the WASp family verprolin homologous (WAVE) regulatory complex (WRC), which acts downstream of multiple immune receptors to stimulate actin nucleation and polymerization of filamentous actin (F-actin). The polymerization and branching of F-actin is critical for creating force-generating cytoskeletal structures which drive most active cellular processes including migration, adhesion, immune synapse formation, and phagocytosis. Branched actin networks at the cell cortex have also been implicated in acting as a barrier to regulate inappropriate vesicle (e.g. cytokine) secretion and spontaneous antigen receptor crosslinking. Given the importance of the actin cytoskeleton in most or all hematopoietic cells, it is not surprising that HEM1 deficient children present with a complex clinical picture that involves overlapping features of immunodeficiency and autoimmunity. In this review, we will provide an overview of what is known about the molecular and cellular functions of HEM1 and the WRC in immune and other cells. We will describe the common clinicopathological features and immunophenotypes of HEM1 deficiency in humans and provide detailed comparative descriptions of what has been learned about Hem1 disruption using constitutive and immune cell-specific mouse knockout models. Finally, we discuss future perspectives and important areas for investigation regarding HEM1 and the WRC.

Disulfidptosis decoded: a journey through cell death mysteries, regulatory networks, disease paradigms and future directions

Cell death is an important part of the life cycle, serving as a foundation for both the orderly development and the maintenance of physiological equilibrium within organisms. This process is fundamental, as it eliminates senescent, impaired, or aberrant cells while also promoting tissue regeneration and immunological responses. A novel paradigm of programmed cell death, known as disulfidptosis, has recently emerged in the scientific circle. Disulfidptosis is defined as the accumulation of cystine by cancer cells with high expression of the solute carrier family 7 member 11 (SLC7A11) during glucose starvation. This accumulation causes extensive disulfide linkages between F-actins, resulting in their contraction and subsequent detachment from the cellular membrane, triggering cellular death. The RAC1-WRC axis is involved in this phenomenon. Disulfidptosis sparked growing interest due to its potential applications in a variety of pathologies, particularly oncology, neurodegenerative disorders, and metabolic anomalies. Nonetheless, the complexities of its regulatory pathways remain elusive, and its precise molecular targets have yet to be definitively identified. This manuscript aims to meticulously dissect the historical evolution, molecular underpinnings, regulatory frameworks, and potential implications of disulfidptosis in various disease contexts, illuminating its promise as a groundbreaking therapeutic pathway and target.

Cyfip2 controls the acoustic startle threshold through FMRP, actin polymerization, and GABAB receptor function

Animals process a constant stream of sensory input, and to survive they must detect and respond to dangerous stimuli while ignoring innocuous or irrelevant ones. Behavioral responses are elicited when certain properties of a stimulus such as its intensity or size reach a critical value, and such behavioral thresholds can be a simple and effective mechanism to filter sensory information. For example, the acoustic startle response is a conserved and stereotyped defensive behavior induced by sudden loud sounds, but dysregulation of the threshold to initiate this behavior can result in startle hypersensitivity that is associated with sensory processing disorders including schizophrenia and autism. Through a previous forward genetic screen for regulators of the startle threshold a nonsense mutation in Cytoplasmic Fragile X Messenger Ribonucleoprotein (FMRP)-interacting protein 2 (cyfip2) was found that causes startle hypersensitivity in zebrafish larvae, but the molecular mechanisms by which Cyfip2 establishes the acoustic startle threshold are unknown. Here we used conditional transgenic rescue and CRISPR/Cas9 to determine that Cyfip2 acts though both Rac1 and FMRP pathways, but not the closely related FXR1 or FXR2, to establish the acoustic startle threshold during early neurodevelopment. To identify proteins and pathways that may be downstream effectors of Rac1 and FMRP, we performed a candidate-based drug screen that indicated that Cyfip2 can also act acutely to maintain the startle threshold branched actin polymerization and N-methyl D-aspartate receptors (NMDARs). To complement this approach, we used unbiased discovery proteomics to determine that loss of Cyfip2 alters cytoskeletal and extracellular matrix components while also disrupting oxidative phosphorylation and GABA receptor signaling. Finally, we functionally validated our proteomics findings by showing that activating GABAB receptors, which like NMDARs are also FMRP targets, restores normal startle sensitivity in cyfip2 mutants. Together, these data reveal multiple mechanisms by which Cyfip2 regulates excitatory/inhibitory balance in the startle circuit to control the processing of acoustic information.

Intellectual Disability and Behavioral Deficits Linked to CYFIP1 Missense Variants Disrupting Actin Polymerization

BACKGROUND

15q11.2 deletions and duplications have been linked to autism spectrum disorder, schizophrenia, and intellectual disability. Recent evidence suggests that dysfunctional CYFIP1 (cytoplasmic FMR1 interacting protein 1) contributes to the clinical phenotypes observed in individuals with 15q11.2 deletion/duplication syndrome. CYFIP1 plays crucial roles in neuronal development and brain connectivity, promoting actin polymerization and regulating local protein synthesis. However, information about the impact of single nucleotide variants in CYFIP1 on neurodevelopmental disorders is limited.

METHODS

Here, we report a family with 2 probands exhibiting intellectual disability, autism spectrum disorder, spastic tetraparesis, and brain morphology defects and who carry biallelic missense point mutations in the CYFIP1 gene. We used skin fibroblasts from one of the probands, the parents, and typically developing individuals to investigate the effect of the variants on the functionality of CYFIP1. In addition, we generated Drosophila knockin mutants to address the effect of the variants in vivo and gain insight into the molecular mechanism that underlies the clinical phenotype.

RESULTS

Our study revealed that the 2 missense variants are in protein domains responsible for maintaining the interaction within the wave regulatory complex. Molecular and cellular analyses in skin fibroblasts from one proband showed deficits in actin polymerization. The fly model for these mutations exhibited abnormal brain morphology and F-actin loss and recapitulated the core behavioral symptoms, such as deficits in social interaction and motor coordination.

CONCLUSIONS

Our findings suggest that the 2 CYFIP1 variants contribute to the clinical phenotype in the probands that reflects deficits in actin-mediated brain development processes.

Different dysregulations of CYFIP1 and CYFIP2 in distinct types of dementia

In humans, the cytoplasmic FMR1 interacting protein (CYFIP) family consists of two members, namely CYFIP1 and CYFIP2. Both CYFIP1 and CYFIP2 function in the WAVE regulatory complex (WRC), which regulates actin polymerization. Additionally, these two proteins form a posttranscriptional regulatory complex with the fragile X mental retardation protein (FMRP), which suppresses mRNA translation. Thus, CYFIP1 and CYFIP2 are important signalling regulators at synapses, and mutations in their genes are associated with neurodevelopmental and neuropsychiatric disorders, including intellectual disabilities. Moreover, dysregulation of the CYFIP protein family is involved in Alzheimer's disease (AD). However, the relevance of the CYFIP family in other dementias is largely unknown. Here, we compared CYFIP1/2 protein levels in the post-mortem hippocampus from patients with AD, dementia with Lewy bodies (DLB), vascular dementia (VaD) and frontotemporal lobar degeneration with TDP-43 pathology (FTLD-TDP). Consistent with previous findings, CYFIP2 was reduced in AD hippocampus. In DLB and VaD hippocampus, the protein level of CYFIP2 and CYFIP1 was unaltered. Finally, an increase in the protein level of both CYFIP1 and CYFIP2 was noted in FTLD-TDP hippocampus. These findings reveal that the protein levels of the CYFIP family is distinct in different types of dementia, suggesting that the pathogenesis of these neurodegenerative disorders has divergent impacts on hippocampal synaptic function.

The intrinsically disordered cytoplasmic tail of a dendrite branching receptor uses two distinct mechanisms to regulate the actin cytoskeleton

Dendrite morphogenesis is essential for neural circuit formation, yet the molecular mechanisms underlying complex dendrite branching remain elusive. Previous studies on the highly branched Caenorhabditis elegans PVD sensory neuron identified a membrane co-receptor complex that links extracellular signals to intracellular actin remodeling machinery, promoting high-order dendrite branching. In this complex, the claudin-like transmembrane protein HPO-30 recruits the WAVE regulatory complex (WRC) to dendrite branching sites, stimulating the Arp2/3 complex to polymerize actin. We report here our biochemical and structural analysis of this interaction, revealing that the intracellular domain (ICD) of HPO-30 is intrinsically disordered and employs two distinct mechanisms to regulate the actin cytoskeleton. First, HPO-30 ICD binding to the WRC requires dimerization and involves the entire ICD sequence, rather than a short linear peptide motif. This interaction enhances WRC activation by the GTPase Rac1. Second, HPO-30 ICD directly binds to the sides and barbed end of actin filaments. Binding to the barbed end requires ICD dimerization and inhibits both actin polymerization and depolymerization, resembling the actin capping protein CapZ. These dual functions provide an intriguing model of how membrane proteins can integrate distinct mechanisms to fine-tune local actin dynamics.

Local mRNA translation and cytoskeletal reorganization: Mechanisms that tune neuronal responses

Neurons are highly polarized cells with significantly long axonal and dendritic extensions that can reach distances up to hundreds of centimeters away from the cell bodies in higher vertebrates. Their successful formation, maintenance, and proper function highly depend on the coordination of intricate molecular networks that allow axons and dendrites to quickly process information, and respond to a continuous and diverse cascade of environmental stimuli, often without enough time for communication with the soma. Two seemingly unrelated processes, essential for these rapid responses, and thus neuronal homeostasis and plasticity, are local mRNA translation and cytoskeletal reorganization. The axonal cytoskeleton is characterized by high stability and great plasticity; two contradictory attributes that emerge from the powerful cytoskeletal rearrangement dynamics. Cytoskeletal reorganization is crucial during nervous system development and in adulthood, ensuring the establishment of proper neuronal shape and polarity, as well as regulating intracellular transport and synaptic functions. Local mRNA translation is another mechanism with a well-established role in the developing and adult nervous system. It is pivotal for axonal guidance and arborization, synaptic formation, and function and seems to be a key player in processes activated after neuronal damage. Perturbations in the regulatory pathways of local translation and cytoskeletal reorganization contribute to various pathologies with diverse clinical manifestations, ranging from intellectual disabilities (ID) to autism spectrum disorders (ASD) and schizophrenia (SCZ). Despite the fact that both processes are essential for the orchestration of pathways critical for proper axonal and dendritic function, the interplay between them remains elusive. Here we review our current knowledge on the molecular mechanisms and specific interaction networks that regulate and potentially coordinate these interconnected processes.

Lamellipodia-like actin networks in cells lacking WAVE regulatory complex

Cell migration frequently involves the formation of lamellipodia induced by Rac GTPases activating WAVE regulatory complex (WRC) to drive Arp2/3 complex-dependent actin assembly. Previous genome editing studies in B16-F1 melanoma cells solidified the view of an essential, linear pathway employing the aforementioned components. Here, disruption of the WRC subunit Nap1 (encoded by Nckap1) and its paralog Hem1 (encoded by Nckap1l) followed by serum and growth factor stimulation, or active GTPase expression, revealed a pathway to formation of Arp2/3 complex-dependent lamellipodia-like structures (LLS) that requires both Rac and Cdc42 GTPases, but not WRC. These phenotypes were independent of the WRC subunit eliminated and coincided with the lack of recruitment of Ena/VASP family actin polymerases. Moreover, aside from Ena/VASP proteins, LLS contained all lamellipodial regulators tested, including cortactin (also known as CTTN), the Ena/VASP ligand lamellipodin (also known as RAPH1) and FMNL subfamily formins. Rac-dependent but WRC-independent actin remodeling could also be triggered in NIH 3T3 fibroblasts by growth factor (HGF) treatment or by gram-positive Listeria monocytogenes usurping HGF receptor signaling for host cell invasion. Taken together, our studies thus establish the existence of a signaling axis to Arp2/3 complex-dependent actin remodeling at the cell periphery that operates without WRC and Ena/VASP.

Summary: Rac-dependent actin remodeling can occur in the absence of WAVE regulatory complex, triggered by active Cdc42. WAVE regulatory complex-independent actin structures harbor Arp2/3 complex but not VASP.

RNA and neuronal function: the importance of post-transcriptional regulation

The brain represents an organ with a particularly high diversity of genes that undergo post-transcriptional gene regulation through multiple mechanisms that affect RNA metabolism and, consequently, brain function. This vast regulatory process in the brain allows for a tight spatiotemporal control over protein expression, a necessary factor due to the unique morphologies of neurons. The numerous mechanisms of post-transcriptional regulation or translational control of gene expression in the brain include alternative splicing, RNA editing, mRNA stability and transport. A large number of trans-elements such as RNA-binding proteins and micro RNAs bind to specific cis-elements on transcripts to dictate the fate of mRNAs including its stability, localization, activation and degradation. Several trans-elements are exemplary regulators of translation, employing multiple cofactors and regulatory machinery so as to influence mRNA fate. Networks of regulatory trans-elements exert control over key neuronal processes such as neurogenesis, synaptic transmission and plasticity. Perturbations in these networks may directly or indirectly cause neuropsychiatric and neurodegenerative disorders. We will be reviewing multiple mechanisms of gene regulation by trans-elements occurring specifically in neurons.

Targeting the WASF3 complex to suppress metastasis

Wiskott-Aldrich syndrome protein family members (WASF) regulate the dynamics of the actin cytoskeleton, which plays an instrumental role in cancer metastasis and invasion. WASF1/2/3 forms a hetero-pentameric complex with CYFIP1/2, NCKAP1/1 L, Abi1/2/3 and BRK1 called the WASF Regulatory Complex (WRC), which cooperatively regulates actin nucleation by WASF1/2/3. Activation of the WRC enables actin networking and provides the mechanical force required for the formation of lamellipodia and invadopodia. Although the WRC drives cell motility essential for several routine physiological functions, its aberrant deployment is observed in cancer metastasis and invasion. WASF3 expression is correlated with metastatic potential in several cancers and inversely correlates with overall progression-free survival. Therefore, disruption of the WRC may serve as a novel strategy for targeting metastasis. Given the complexity involved in the formation of the WRC which is largely comprised of large protein-protein interfaces, there are currently no inhibitors for WASF3. However, several constrained peptide mimics of the various protein-protein interaction interfaces within the WRC were found to successfully disrupt WASF3-mediated migration and invasion. This review explores the role of the WASF3 WRC in driving metastasis and how it may be selectively targeted for suppression of metastasis.

WASP family proteins: Molecular mechanisms and implications in human disease

Proteins of the Wiskott-Aldrich syndrome protein (WASP) family play a central role in regulating actin cytoskeletal dynamics in a wide range of cellular processes. Genetic mutations or misregulation of these proteins are tightly associated with many diseases. The WASP-family proteins act by transmitting various upstream signals to their conserved WH2-Central-Acidic (WCA) peptide sequence at the C-terminus, which in turn binds to the Arp2/3 complex to stimulate the formation of branched actin networks at membranes. Despite this common feature, the regulatory mechanisms and cellular functions of distinct WASP-family proteins are very different. Here, we summarize and clarify our current understanding of WASP-family proteins and how disruption of their functions is related to human disease.

Deregulated Rac1 Activity in Neural Crest Controls Cell Proliferation, Migration and Differentiation During Midbrain Development

Mutations in RAC1 allele are implicated in multiple brain tumors, indicating a rigorous control of Rac1 activity is required for neural tissue normal development and homeostasis. To understand how elevated Rac1 activity affects neural crest cells (NCCs) development, we have generated Rac1 ^CA ;Wnt1-Cre2 mice, in which a constitutively active Rac1 ^G12V mutant is expressed specifically in NCCs derivatives. Our results revealed that augmented Rac1 activity leads to enlarged midbrain and altered cell density, accompanied by increased NCCs proliferation rate and misrouted cell migration. Interestingly, our experimental data also showed that elevated Rac1 activity in NCCs disrupts regionalization of dopaminergic neuron progenitors in the ventral midbrain and impairs their differentiation. These findings shed light on the mechanisms of RAC1 mutation correlated brain tumor at the cellular and molecular level.

Cytoplasmic FMR1 interacting protein (CYFIP) family members and their function in neural development and disorders

In humans, the cytoplasmic FMR1 interacting protein (CYFIP) family is composed of CYFIP1 and CYFIP2. Despite their high similarity and shared interaction with many partners, CYFIP1 and CYFIP2 act at different points in cellular processes. CYFIP1 and CYFIP2 have different expression levels in human tissues, and knockout animals die at different time points of development. CYFIP1, similar to CYFIP2, acts in the WAVE regulatory complex (WRC) and plays a role in actin dynamics through the activation of the Arp2/3 complex and in a posttranscriptional regulatory complex with the fragile X mental retardation protein (FMRP). Previous reports have shown that CYFIP1 and CYFIP2 may play roles in posttranscriptional regulation in different ways. While CYFIP1 is involved in translation initiation via the 5'UTR, CYFIP2 may regulate mRNA expression via the 3'UTR. In addition, this CYFIP protein family is involved in neural development and maturation as well as in different neural disorders, such as intellectual disabilities, autistic spectrum disorders, and Alzheimer's disease. In this review, we map diverse studies regarding the functions, regulation, and implications of CYFIP proteins in a series of molecular pathways. We also highlight mutations and their structural effects both in functional studies and in neural diseases.

Phenotypic Diversity of 15q11.2 BP1-BP2 Deletion in Three Korean Families with Development Delay and/or Intellectual Disability: A Case Series and Literature Review

The 15q11.2 breakpoint (BP) 1-BP2 deletion syndrome is emerging as the most frequent pathogenic copy number variation in humans related to neurodevelopmental diseases, with changes in cognition, behavior, and brain morphology. Previous publications have reported that patients with 15q11.2 BP1-BP2 deletion showed intellectual disability (ID), speech impairment, developmental delay (DD), and/or behavioral problems. We describe three new cases, aged 3 or 6 years old and belonging to three unrelated Korean families, with a 350-kb 15q11.2 BP1-BP2 deletion of four highly conserved genes, namely, the TUBGCP5, CYFIP1, NIPA2, and NIPA1 genes. All of our cases presented with global DD and/or ID, and the severity ranged from mild to severe, but common facial dysmorphism and congenital malformations in previous reports were not characteristic. The 15q11.2 BP1-BP2 deletion was inherited from an unaffected parent in all cases. Our three cases, together with previous findings from the literature review, confirm some of the features earlier reported to be associated with 15q11.2 BP1-BP2 deletion and help to further delineate the phenotype associated with 15q11.2 deletion. Identification of more cases with 15q11.2 BP1-BP2 deletion will allow us to obtain a better understanding of the clinical phenotypes. Further explanation of the functions of the genes within the 15q11.2 BP1-BP2 region is required to resolve the pathogenic effects on neurodevelopment.

Aberrant Rac pathway signalling in glioblastoma

Glioblastoma is an aggressive and incurable form of brain cancer. Both mutation analysis in human glioblastoma and mouse modelling studies have shown that aberrant activation of the PI 3-kinase pathway is a central driver of glioblastoma malignancy. The small GTPase Rac is activated downstream of this pathway, mediating a subset of the effects of aberrant PI 3-kinase pathway activation. Here I discuss the current state of our knowledge on Rac activation mechanisms in glioblastoma. Current knowledge on roles for specific PI 3-kinase pathway responsive Rac guanine nucleotide exchange factors in glioblastoma is reviewed. Rac is best known for its role in promoting cell motility and invasion, but there is also evidence for roles in multiple other cellular processes with cancer relevance, including proliferation, differentiation, apoptosis, DNA damage responses, metabolism, angiogenesis and immunosuppression. I review what is known about the role of Rac in these processes in glioblastoma. Finally, I assess possible strategies to inhibit this pathway in glioblastoma through either direct inhibition of Rac or inhibition of upstream activators or downstream mediators of Rac signalling.

FMRP and CYFIP1 at the Synapse and Their Role in Psychiatric Vulnerability

There is increasing awareness of the role genetic risk variants have in mediating vulnerability to psychiatric disorders such as schizophrenia and autism. Many of these risk variants encode synaptic proteins, influencing biological pathways of the postsynaptic density and, ultimately, synaptic plasticity. Fragile-X mental retardation 1 (FMR1) and cytoplasmic fragile-X mental retardation protein (FMRP)-interacting protein 1 (CYFIP1) contain 2 such examples of highly penetrant risk variants and encode synaptic proteins with shared functional significance. In this review, we discuss the biological actions of FMRP and CYFIP1, including their regulation of (i) protein synthesis and specifically FMRP targets, (ii) dendritic and spine morphology, and (iii) forms of synaptic plasticity such as long-term depression. We draw upon a range of preclinical studies that have used genetic dosage models of FMR1 and CYFIP1 to determine their biological function. In parallel, we discuss how clinical studies of fragile X syndrome or 15q11.2 deletion patients have informed our understanding of FMRP and CYFIP1, and highlight the latest psychiatric genomic findings that continue to implicate FMRP and CYFIP1. Lastly, we assess the current limitations in our understanding of FMRP and CYFIP1 biology and how they must be addressed before mechanism-led therapeutic strategies can be developed for psychiatric disorders.

Modelling Learning and Memory in Drosophila to Understand Intellectual Disabilities

Neurodevelopmental disorders (NDDs) include a large number of conditions such as Fragile  X  syndrome, autism spectrum disorders and Down syndrome, among others. They are characterized by limitations in adaptive and social behaviors, as well as intellectual disability (ID). Whole-exome and whole-genome sequencing studies have highlighted a large number of NDD/ID risk genes. To dissect the genetic causes and underlying biological pathways, in vivo experimental validation of the effects of these mutations is needed. The fruit fly, Drosophila melanogaster, is an ideal model to study NDDs, with highly tractable genetics, combined with simple behavioral and circuit assays, permitting rapid medium-throughput screening of NDD/ID risk genes. Here, we review studies where the use of well-established assays to study mechanisms of learning and memory in Drosophila has permitted insights into molecular mechanisms underlying IDs. We discuss how technologies in the fly model, combined with a high degree of molecular and physiological conservation between flies and mammals, highlight the Drosophila system as an ideal model to study neurodevelopmental disorders, from genetics to behavior.

The first quarter of the C-terminal domain of Abelson regulates the WAVE regulatory complex and Enabled in axon guidance

Background

Abelson tyrosine kinase (Abl) plays a key role in axon guidance in linking guidance receptors to actin dynamics. The long C-terminal domain (CTD) of Drosophila Abl is important for this role, and previous work identified the ‘first quarter’ (1Q) of the CTD as essential. Here, we link the physical interactions of 1Q binding partners to Abl’s function in axon guidance.

Methods

Protein binding partners of 1Q were identified by GST pulldown and mass spectrometry, and validated using axon guidance assays in the embryonic nerve cord and motoneurons. The role of 1Q was assessed genetically, utilizing a battery of Abl transgenes in combination with mutation or overexpression of the genes of pulled down proteins, and their partners in actin dynamics. The set of Abl transgenes had the following regions deleted: all of 1Q, each half of 1Q (‘eighths’, 1E and 2E) or a PxxP motif in 2E, which may bind SH3 domains.

Results

GST pulldown identified Hem and Sra-1 as binding partners of 1Q, and our genetic analyses show that both proteins function with Abl in axon guidance, with Sra-1 likely interacting with 1Q. As Hem and Sra-1 are part of the actin-polymerizing WAVE regulatory complex (WRC), we extended our analyses to Abi and Trio, which interact with Abl and WRC members. Overall, the 1Q region (and especially 2E and its PxxP motif) are important for Abl’s ability to work with WRC in axon guidance. These areas are also important for Abl’s ability to function with the actin regulator Enabled. In comparison, 1E contributes to Abl function with the WRC at the midline, but less so with Enabled.

Conclusions

The 1Q region, and especially the 2E region with its PxxP motif, links Abl with the WRC, its regulators Trio and Abi, and the actin regulator Ena. Removing 1E has specific effects suggesting it may help modulate Abl’s interaction with the WRC or Ena. Thus, the 1Q region of Abl plays a key role in regulating actin dynamics during axon guidance.

RAC1-Dependent ORAI1 Translocation to the Leading Edge Supports Lamellipodia Formation and Directional Persistence

Tumor invasion requires efficient cell migration, which is achieved by the generation of persistent and polarized lamellipodia. The generation of lamellipodia is supported by actin dynamics at the leading edge where a complex of proteins known as the WAVE regulatory complex (WRC) promotes the required assembly of actin filaments to push the front of the cell ahead. By using an U2OS osteosarcoma cell line with high metastatic potential, proven by a xenotransplant in zebrafish larvae, we have studied the role of the plasma membrane Ca²⁺ channel ORAI1 in this process. We have found that epidermal growth factor (EGF) triggered an enrichment of ORAI1 at the leading edge, where colocalized with cortactin (CTTN) and other members of the WRC, such as CYFIP1 and ARP2/3. ORAI1-CTTN co-precipitation was sensitive to the inhibition of the small GTPase RAC1, an upstream activator of the WRC. RAC1 potentiated ORAI1 translocation to the leading edge, increasing the availability of surface ORAI1 and increasing the plasma membrane ruffling. The role of ORAI1 at the leading edge was studied in genetically engineered U2OS cells lacking ORAI1 expression that helped us to prove the key role of this Ca²⁺ channel on lamellipodia formation, lamellipodial persistence, and cell directness, which are required for tumor cell invasiveness in vivo.

Autism and Schizophrenia-Associated CYFIP1 Regulates the Balance of Synaptic Excitation and Inhibition

Altered excitatory/inhibitory (E/I) balance is implicated in neuropsychiatric and neurodevelopmental disorders, but the underlying genetic etiology remains poorly understood. Copy number variations in CYFIP1 are associated with autism, schizophrenia, and intellectual disability, but its role in regulating synaptic inhibition or E/I balance remains unclear. We show that CYFIP1, and the paralog CYFIP2, are enriched at inhibitory postsynaptic sites. While CYFIP1 or CYFIP2 upregulation increases excitatory synapse number and the frequency of miniature excitatory postsynaptic currents (mEPSCs), it has the opposite effect at inhibitory synapses, decreasing their size and the amplitude of miniature inhibitory postsynaptic currents (mIPSCs). Contrary to CYFIP1 upregulation, its loss in vivo, upon conditional knockout in neocortical principal cells, increases expression of postsynaptic GABA_A receptor β2/3-subunits and neuroligin 3, enhancing synaptic inhibition. Thus, CYFIP1 dosage can bi-directionally impact inhibitory synaptic structure and function, potentially leading to altered E/I balance and circuit dysfunction in CYFIP1-associated neurological disorders.

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CYFIP1 and CYFIP2 are enriched at inhibitory synapses.

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CYFIP1 upregulation differentially disrupts inhibitory and excitatory synapses.

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Conditional loss of CYFIP1 alters neuroligin 3 and GABA_AR β-subunits expression.

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Loss of CYFIP1 increases inhibitory synaptic clusters and hence mIPSC amplitude.

Rho GTPase Regulators and Effectors in Autism Spectrum Disorders: Animal Models and Insights for Therapeutics

The Rho family GTPases are small G proteins that act as molecular switches shuttling between active and inactive forms. Rho GTPases are regulated by two classes of regulatory proteins, guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Rho GTPases transduce the upstream signals to downstream effectors, thus regulating diverse cellular processes, such as growth, migration, adhesion, and differentiation. In particular, Rho GTPases play essential roles in regulating neuronal morphology and function. Recent evidence suggests that dysfunction of Rho GTPase signaling contributes substantially to the pathogenesis of autism spectrum disorder (ASD). It has been found that 20 genes encoding Rho GTPase regulators and effectors are listed as ASD risk genes by Simons foundation autism research initiative (SFARI). This review summarizes the clinical evidence, protein structure, and protein expression pattern of these 20 genes. Moreover, ASD-related behavioral phenotypes in animal models of these genes are reviewed, and the therapeutic approaches that show successful treatment effects in these animal models are discussed.

Epigenome-wide association study for perceived discrimination among sub-Saharan African migrants in Europe - the RODAM study

Sub-Saharan African (SSA) migrants in Europe experience psychosocial stressors, such as perceived discrimination (PD). The effect of such a stressor on health could potentially be mediated via epigenetics. In this study we performed an epigenome-wide association study (EWAS) to assess the association between levels of PD with genome-wide DNA methylation profiles in SSA migrants. The Illumina 450 K DNA-methylation array was used on whole blood samples of 340 Ghanaian adults residing in three European cities from the cross-sectional Research on Obesity and Diabetes among African Migrants (RODAM) study. PD was assessed using sum scores of the Everyday Discrimination Scale (EDS). Differentially methylated positions and regions (DMPs and DMRs) were identified through linear regression analysis. Two hypo-methylated DMPs, namely cg13986138 (CYFIP1) and cg10316525(ANKRD63), were found to be associated with PD. DMR analysis identified 47 regions associated with the PD. To the best of our knowledge, this survey is the first EWAS for PD in first generation SSA migrants. We identified two DMPs associated with PD. Whether these associations underlie a consequence or causal effect within the scope of biological functionality needs additional research.

Rac1 Signaling: From Intestinal Homeostasis to Colorectal Cancer Metastasis

The small GTPase Rac1 has been implicated in a variety of dynamic cell biological processes, including cell proliferation, cell survival, cell-cell contacts, epithelial mesenchymal transition (EMT), cell motility, and invasiveness. These processes are orchestrated through the fine tuning of Rac1 activity by upstream cell surface receptors and effectors that regulate the cycling Rac1-GDP (off state)/Rac1-GTP (on state), but also through the tuning of Rac1 accumulation, activity, and subcellular localization by post translational modifications or recruitment into molecular scaffolds. Another level of regulation involves Rac1 transcripts stability and splicing. Downstream, Rac1 initiates a series of signaling networks, including regulatory complex of actin cytoskeleton remodeling, activation of protein kinases (PAKs, MAPKs) and transcription factors (NFkB, Wnt/β-catenin/TCF, STAT3, Snail), production of reactive oxygen species (NADPH oxidase holoenzymes, mitochondrial ROS). Thus, this GTPase, its regulators, and effector systems might be involved at different steps of the neoplastic progression from dysplasia to the metastatic cascade. After briefly placing Rac1 and its effector systems in the more general context of intestinal homeostasis and in wound healing after intestinal injury, the present review mainly focuses on the several levels of Rac1 signaling pathway dysregulation in colorectal carcinogenesis, their biological significance, and their clinical impact.

FMRP ribonucleoprotein complexes and RNA homeostasis

The Fragile Mental Retardation 1 gene (FMR1), at Xq27.3, encodes the fragile mental retardation protein (FMRP), and displays in its 5'-untranslated region a series of polymorphic CGG triplet repeats that may undergo dynamic mutation. Fragile X syndrome (FXS) is the leading cause of inherited intellectual disability among men, and is most frequently due to FMR1 full mutation and consequent transcription repression. FMR1 premutations may associate with at least two other clinical conditions, named fragile X-associated primary ovarian insufficiency (FXPOI) and tremor and ataxia syndrome (FXTAS). While FXPOI and FXTAS appear to be mediated by FMR1 mRNA accumulation, relative reduction of FMRP, and triplet repeat translation, FXS is due to the lack of the RNA-binding protein FMRP. Besides its function as mRNA translation repressor in neuronal and stem/progenitor cells, RNA editing roles have been assigned to FMRP. In this review, we provide a brief description of FMR1 transcribed microsatellite and associated clinical disorders, and discuss FMRP molecular roles in ribonucleoprotein complex assembly and trafficking, as well as aspects of RNA homeostasis affected in FXS cells.

Evidence for a Contribution of the Nlgn3/Cyfip1/Fmr1 Pathway in the Pathophysiology of Autism Spectrum Disorders

Autism Spectrum Disorders (ASD) are characterized by heterogeneity both in their presentation and their genetic aetiology. In order to discover points of convergence common to different cases of ASD, attempts were made to identify the biological pathways genes associated with ASD contribute to. Many of these genes were found to play a role in neuronal and synaptic development and function. Among these genes are FMR1, CYFIP1 and NLGN3, all present at the synapse and reliably linked to ASD. In this review, we evaluate the evidence for the contribution of these genes to the same biological pathway responsible for the regulation of structural and physiological plasticity. Alterations in dendritic spine density and turnover, as well as long-term depression (LTD), were found in mouse models of mutations of all three genes. This overlap in the phenotypes associated with these mouse models likely arises from the molecular interaction between the protein products of FMR1, CYFIP1, and NLG3. A number of other proteins linked to ASD are also likely to participate in these pathways, resulting in further downstream effects. Overall, a synaptic pathway centered around FMR1, CYFIP1, and NLG3 is likely to contribute to the phenotypes associated with structural and physiological plasticity characteristic of ASD.

Arf GTPase interplay with Rho GTPases in regulation of the actin cytoskeleton

The Arf and Rho subfamilies of small GTPases are nucleotide-dependent molecular switches that act as master regulators of vesicular trafficking and the actin cytoskeleton organization. Small GTPases control cell processes with high fidelity by acting through distinct repertoires of binding partners called effectors. While we understand a great deal about how these GTPases act individually, relatively little is known about how they cooperate, especially in the control of effectors. This review highlights how Arf GTPases collaborate with Rac1 to regulate actin cytoskeleton dynamics at the membrane via recruiting and activating the Wave Regulatory Complex (WRC), a Rho effector that underpins lamellipodia formation and macropinocytosis. This provides insight into Arf regulation of the actin cytoskeleton, while putting the spotlight on small GTPase cooperation with emerging evidence of its importance in fundamental cell biology and interactions with pathogenic bacteria.

Domain-Specific Cognitive Impairments in Humans and Flies With Reduced CYFIP1 Dosage

BACKGROUND

Deletions encompassing a four-gene region on chromosome 15 (BP1-BP2 at 15q11.2), seen at a population frequency of 1 in 500, are associated with increased risk for schizophrenia, epilepsy, and other common neurodevelopmental disorders. However, little is known in terms of how these common deletions impact cognition.

METHODS

We used a Web-based tool to characterize cognitive function in a novel cohort of adult carriers and their noncarrier family members. Results from 31 carrier and 38 noncarrier parents from 40 families were compared with control data from 6530 individuals who self-registered on the Lumosity platform and opted in to participate in research. We then examined aspects of sensory and cognitive function in flies harboring a mutation in Cyfip, the homologue of one of the genes within the deletion. For the fly studies, 10 or more groups of 50 individuals per genotype were included.

RESULTS

Our human studies revealed profound deficits in grammatical reasoning, arithmetic reasoning, and working memory in BP1-BP2 deletion carriers. No such deficits were observed in noncarrier spouses. Our fly studies revealed deficits in associative and nonassociative learning despite intact sensory perception.

CONCLUSIONS

Our results provide new insights into outcomes associated with BP1-BP2 deletions and call for a discussion on how to appropriately communicate these findings to unaffected carriers. Findings also highlight the utility of an online tool in characterizing cognitive function in a geographically distributed population.

The autism- and schizophrenia-associated protein CYFIP1 regulates bilateral brain connectivity and behaviour

Copy-number variants of the CYFIP1 gene in humans have been linked to autism spectrum disorders (ASD) and schizophrenia (SCZ), two neuropsychiatric disorders characterized by defects in brain connectivity. Here, we show that CYFIP1 plays an important role in brain functional connectivity and callosal functions. We find that Cyfip1-heterozygous mice have reduced functional connectivity and defects in white matter architecture, similar to phenotypes found in patients with ASD, SCZ and other neuropsychiatric disorders. Cyfip1-deficient mice also present decreased myelination in the callosal axons, altered presynaptic function, and impaired bilateral connectivity. Finally, Cyfip1 deficiency leads to abnormalities in motor coordination, sensorimotor gating and sensory perception, which are also known neuropsychiatric disorder-related symptoms. These results show that Cyfip1 haploinsufficiency compromises brain connectivity and function, which might explain its genetic association to neuropsychiatric disorders.

Stem Cells to Inform the Neurobiology of Mental Illness

The inception of human-induced pluripotent stem cell (hiPSCs) technology has provided an exciting platform upon which the modelling and treatment of human neurodevelopmental and neuropsychiatric disorders may be expedited. Although the genetic architecture of these disorders is far more complex than previously imagined, many key loci have at last been identified. This has allowed in vivo and in vitro technologies to be refined to model specific high-penetrant genetic loci involved in both disorders. Animal models of neurodevelopmental disorders, such as schizophrenia and autism spectrum disorders, show limitations in recapitulating the full complexity and heterogeneity of human neurodevelopmental disease states. Indeed, patient-derived hiPSCs offer distinct advantages over classical animal models in the study of human neuropathologies. Here we have discussed the current, relative translational merit of hiPSCs in investigating human neurodevelopmental and neuropsychiatric disorders with a specific emphasis on the utility of such systems to aid in the identification of biomarkers. We have highlighted the promises and pitfalls of reprogramming cell fate for the study of these disorders and provide recommendations for future directions in this field in order to overcome current limitations. Ultimately, this will aid in the development of effective clinical strategies for diverse patient populations affected by these disorders with the aim of also leading to biomarker identification.

Using mouse transgenic and human stem cell technologies to model genetic mutations associated with schizophrenia and autism

Solid progress has occurred over the last decade in our understanding of the molecular genetic basis of neurodevelopmental disorders, and of schizophrenia and autism in particular. Although the genetic architecture of both disorders is far more complex than previously imagined, many key loci have at last been identified. This has allowed in vivo and in vitro technologies to be refined to model specific high-penetrant genetic loci involved in both disorders. Using the DISC1/NDE1 and CYFIP1/EIF4E loci as exemplars, we explore the opportunities and challenges of using animal models and human-induced pluripotent stem cell technologies to further understand/treat and potentially reverse the worst consequences of these debilitating disorders.

This article is part of a discussion meeting issue ‘Of mice and mental health: facilitating dialogue between basic and clinical neuroscientists’.

Dendritic spine actin cytoskeleton in autism spectrum disorder

Dendritic spines are small actin-rich protrusions from neuronal dendrites that form the postsynaptic part of most excitatory synapses. Changes in the shape and size of dendritic spines correlate with the functional changes in excitatory synapses and are heavily dependent on the remodeling of the underlying actin cytoskeleton. Recent evidence implicates synapses at dendritic spines as important substrates of pathogenesis in neuropsychiatric disorders, including autism spectrum disorder (ASD). Although synaptic perturbations are not the only alterations relevant for these diseases, understanding the molecular underpinnings of the spine and synapse pathology may provide insight into their etiologies and could reveal new drug targets. In this review, we will discuss recent findings of defective actin regulation in dendritic spines associated with ASD.

Wild-type p53 upregulates an early onset breast cancer-associated gene GAS7 to suppress metastasis via GAS7-CYFIP1-mediated signaling pathway

The early onset breast cancer patients (age ≤ 40) often display higher incidence of axillary lymph node metastasis, and poorer five-year survival than the late-onset patients. To identify the genes and molecules associated with poor prognosis of early onset breast cancer, we examined gene expression profiles from paired breast normal/tumor tissues, and coupled with Gene Ontology and public data base analysis. Our data showed that the expression of GAS7b gene was lower in the early onset breast cancer patients as compared to the elder patients. We found that GAS7 was associated with CYFIP1 and WAVE2 complex to suppress breast cancer metastasis via blocking CYFIP1 and Rac1 protein interaction, actin polymerization, and β1-integrin/FAK/Src signaling. We further demonstrated that p53 directly regulated GAS7 gene expression, which was inversely correlated with p53 mutations in breast cancer specimens. Our study uncover a novel regulatory mechanism of p53 in early onset breast cancer progression through GAS7-CYFIP1-mediated signaling pathways.

CNV biology in neurodevelopmental disorders

Copy number variants (CNVs), characterized in recent years by cutting-edge technology, add complexity to our knowledge of the human genome. CNVs contribute not only to human diversity but also to different kinds of diseases including neurodevelopmental delay, autism spectrum disorder and neuropsychiatric diseases. Interestingly, many pathogenic CNVs are shared among these diseases. Studies suggest that pathophysiology of disease may not be simply attributed to a single driver gene within a CNV but also that multifactorial effects may be important. Gene expression and the resulting phenotypes may also be affected by epigenetic alteration and chromosomal structural changes. Combined with human genetics and systems biology, integrative research by multi-dimensional approaches using animal and cell models of CNVs are expected to further understanding of pathophysiological mechanisms of neurodevelopmental disorders and neuropsychiatric disorders.

Differential functions of WAVE regulatory complex subunits in the regulation of actin-driven processes

The WAVE regulatory complex (WRC) links upstream Rho-family GTPase signaling to the activation of the ARP2/3 complex in different organisms. WRC-induced and ARP2/3 complex-mediated actin nucleation beneath the plasma membrane is critical for actin assembly in the leading edge to drive efficient cell migration. The WRC is a stable heteropentamer composed of SCAR/WAVE, Abi, Nap, Pir and the small polypeptide Brk1/Hspc300. Functional interference with individual subunits of the complex frequently results in diminished amounts of the remaining polypeptides of the WRC complex, implying the complex to act as molecular entity. However, Abi was also found to associate with mammalian N-WASP, formins, Eps8/SOS1 or VASP, indicating additional functions of individual WRC subunits in eukaryotic cells. To address this issue systematically, we inactivated all WRC subunits, either alone or in combination with VASP in Dictyostelium cells and quantified the protein content of the remaining subunits in respective WRC knockouts. The individual mutants displayed highly differential phenotypes concerning various parameters, including cell morphology, motility, cytokinesis or multicellular development, corroborating the view of additional roles for individual subunits, beyond their established function in WRC-mediated Arp2/3 complex activation. Finally, our data uncover the interaction of the actin polymerase VASP with WRC-embedded Abi to mediate VASP accumulation in cell protrusions, driving efficient cell migration.

CYFIP1 is directly controlled by NOTCH1 and down-regulated in cutaneous squamous cell carcinoma

Squamous cell carcinoma of the skin (SCC) represents one of the most common cancers in the general population and is associated with a substantial risk of metastasis. Previous work uncovered the functional role of CYFIP1 in epithelial tumors as an invasion inhibitor. It was down-regulated in some cancers and correlated with the metastatic properties of these malignant cells. We investigated its role and expression mechanisms in SCC. We analyzed the expression of CYFIP1 in patient derived SCC, primary keratinocytes and SCC cell lines, and correlated it to the differentiation and NOTCH1 levels. We analyzed the effects of Notch1 manipulation on CYFIP1 expression and confirmed the biding of Notch1 to the CYFIP1 promoter. CYFIP1 expression was down-regulated in SCC and correlated inversely with histological differentiation of tumors. As keratinocyte differentiation depends on Notch1 signaling, we investigated the influence of Notch1 on CYFIP1 expression. CYFIP1 mRNA was highly increased in human Notch1-overexpressing keratinocytes. Further manipulation of the Notch1 pathway in keratinocytes impacted CYFIP1 levels and chromatin immunoprecipitation assay confirmed the direct binding of Notch1 to the CYFIP1 promoter. CYFIP1 may be a link between loss of differentiation and invasive potential in malignant keratinocytes of cutaneous squamous cell carcinoma.

A conformational change within the WAVE2 complex regulates its degradation following cellular activation

WASp family Verprolin-homologous protein-2 (WAVE2), a member of the Wiskott-Aldrich syndrome protein (WASp) family of actin nucleation promoting factors, is a central regulator of actin cytoskeleton polymerization and dynamics. Multiple signaling pathways operate via WAVE2 to promote the actin-nucleating activity of the actin-related protein 2/3 (Arp2/3) complex. WAVE2 exists as a part of a pentameric protein complex known as the WAVE regulatory complex (WRC), which is unstable in the absence of its individual proteins. While the involvement of WAVE2 in actin polymerization has been well documented, its negative regulation mechanism is poorly characterized to date. Here, we demonstrate that WAVE2 undergoes ubiquitylation in a T-cell activation dependent manner, followed by proteasomal degradation. The WAVE2 ubiquitylation site was mapped to lysine 45, located at the N-terminus where WAVE2 binds to the WRC. Using Förster resonance energy transfer (FRET), we reveal that the autoinhibitory conformation of the WRC maintains the stability of WAVE2 in resting cells; the release of autoinhibition following T-cell activation facilitates the exposure of WAVE2 to ubiquitylation, leading to its degradation. The dynamic conformational structures of WAVE2 during cellular activation dictate its degradation.

Dysfunctional mTORC1 Signaling: A Convergent Mechanism between Syndromic and Nonsyndromic Forms of Autism Spectrum Disorder?

Whereas autism spectrum disorder (ASD) exhibits striking heterogeneity in genetics and clinical presentation, dysfunction of mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway has been identified as a molecular feature common to several well-characterized syndromes with high prevalence of ASD. Additionally, recent findings have also implicated mTORC1 signaling abnormalities in a subset of nonsyndromic ASD, suggesting that defective mTORC1 pathway may be a potential converging mechanism in ASD pathology across different etiologies. However, the mechanistic evidence for a causal link between aberrant mTORC1 pathway activity and ASD neurobehavioral features varies depending on the ASD form involved. In this review, we first discuss six monogenic ASD-related syndromes, including both classical and potentially novel mTORopathies, highlighting their contribution to our understanding of the neurobiological mechanisms underlying ASD, and then we discuss existing evidence suggesting that aberrant mTORC1 signaling may also play a role in nonsyndromic ASD.

New insights into the regulatory function of CYFIP1 in the context of WAVE- and FMRP-containing complexes

Cytoplasmic FMRP interacting protein 1 (CYFIP1) is a candidate gene for intellectual disability (ID), autism, schizophrenia and epilepsy. It is a member of a family of proteins that is highly conserved during evolution, sharing high homology with its Drosophila homolog, dCYFIP. CYFIP1 interacts with the Fragile X mental retardation protein (FMRP, encoded by the FMR1 gene), whose absence causes Fragile X syndrome, and with the translation initiation factor eIF4E. It is a member of the WAVE regulatory complex (WRC), thus representing a link between translational regulation and the actin cytoskeleton. Here, we present data showing a correlation between mRNA levels of CYFIP1 and other members of the WRC. This suggests a tight regulation of the levels of the WRC members, not only by post-translational mechanisms, as previously hypothesized. Moreover, we studied the impact of loss of function of both CYFIP1 and FMRP on neuronal growth and differentiation in two animal models - fly and mouse. We show that these two proteins antagonize each other's function not only during neuromuscular junction growth in the fly but also during new neuronal differentiation in the olfactory bulb of adult mice. Mechanistically, FMRP and CYFIP1 modulate mTor signaling in an antagonistic manner, likely via independent pathways, supporting the results obtained in mouse as well as in fly at the morphological level. Collectively, our results illustrate a new model to explain the cellular roles of FMRP and CYFIP1 and the molecular significance of their interaction.

Inhibition of WAVE Regulatory Complex Activation by a Bacterial Virulence Effector Counteracts Pathogen Phagocytosis

To establish pathogenicity, bacteria must evade phagocytosis directed by remodeling of the actin cytoskeleton. We show that macrophages facilitate pathogen phagocytosis through actin polymerization mediated by the WAVE regulatory complex (WRC), small GTPases Arf and Rac1, and the Arf1 activator ARNO. To establish extracellular infections, enteropathogenic (EPEC) and enterohaemorrhagic (EHEC) Escherichia coli hijack the actin cytoskeleton by injecting virulence effectors into the host cell. Here, we find that the virulence effector EspG counteracts WRC-dependent phagocytosis, enabling EPEC and EHEC to remain extracellular. By reconstituting membrane-associated actin polymerization, we find that EspG disabled WRC activation through two mechanisms: EspG interaction with Arf6 blocked signaling to ARNO while EspG binding of Arf1 impeded collaboration with Rac1, thereby inhibiting WRC recruitment and activation. Investigating the mode of EspG interference revealed sites in Arf1 required for WRC activation and a mechanism facilitating pathogen evasion of innate host defenses.

Direct interaction between exocyst and Wave complexes promotes cell protrusions and motility

Coordination between membrane trafficking and actin polymerization is fundamental in cell migration, but a dynamic view of the underlying molecular mechanisms is still missing. The Rac1 GTPase controls actin polymerization at protrusions by interacting with its effector, the Wave regulatory complex (WRC). The exocyst complex, which functions in polarized exocytosis, has been involved in the regulation of cell motility. Here, we show a physical and functional connection between exocyst and WRC. Purified components of exocyst and WRC directly associate in vitro, and interactions interfaces are identified. The exocyst-WRC interaction is confirmed in cells by co-immunoprecipitation and is shown to occur independently of the Arp2/3 complex. Disruption of the exocyst-WRC interaction leads to impaired migration. By using time-lapse microscopy coupled to image correlation analysis, we visualized the trafficking of the WRC towards the front of the cell in nascent protrusions. The exocyst is necessary for WRC recruitment at the leading edge and for resulting cell edge movements. This direct link between the exocyst and WRC provides a new mechanistic insight into the spatio-temporal regulation of cell migration.

Homologs of SCAR/WAVE complex components are required for epidermal cell morphogenesis in rice

Filamentous actins (F-actins) play a vital role in epidermal cell morphogenesis. However, a limited number of studies have examined actin-dependent leaf epidermal cell morphogenesis events in rice. In this study, two recessive mutants were isolated: less pronounced lobe epidermal cell2-1 (lpl2-1) and lpl3-1, whose leaf and stem epidermis developed a smooth surface, with fewer serrated pavement cell (PC) lobes, and decreased papillae. The lpl2-1 also exhibited irregular stomata patterns, reduced plant height, and short panicles and roots. Molecular genetic studies demonstrated that LPL2 and LPL3 encode the PIROGI/Specifically Rac1-associated protein 1 (PIR/SRA1)-like and NCK-associated protein 1 (NAP1)-like proteins, respectively, two components of the suppressor of cAMP receptor/Wiskott-Aldrich syndrome protein-family verprolin-homologous protein (SCAR/WAVE) regulatory complex involved in actin nucleation and function. Epidermal cells exhibited abnormal arrangement of F-actins in both lpl2 and lpl3 expanding leaves. Moreover, the distorted trichomes of Arabidopsis pir could be partially restored by an overexpression of LPL2 A yeast two-hybrid assay revealed that LPL2 can directly interact with LPL3 in vitro Collectively, the results indicate that LPL2 and LPL3 are two functionally conserved homologs of the SCAR/WAVE complex components, and that they play an important role in controlling epidermal cell morphogenesis in rice by organising F-actin.

A Common CYFIP1 Variant at the 15q11.2 Disease Locus Is Associated with Structural Variation at the Language-Related Left Supramarginal Gyrus

Copy number variants (CNVs) at the Breakpoint 1 to Breakpoint 2 region at 15q11.2 (BP1-2) are associated with language-related difficulties and increased risk for developmental disorders in which language is compromised. Towards underlying mechanisms, we investigated relationships between single nucleotide polymorphisms (SNPs) across the region and quantitative measures of human brain structure obtained by magnetic resonance imaging of healthy subjects. We report an association between rs4778298, a common variant at CYFIP1, and inter-individual variation in surface area across the left supramarginal gyrus (lh.SMG), a cortical structure implicated in speech and language in independent discovery (n = 100) and validation cohorts (n = 2621). In silico analyses determined that this same variant, and others nearby, is also associated with differences in levels of CYFIP1 mRNA in human brain. One of these nearby polymorphisms is predicted to disrupt a consensus binding site for FOXP2, a transcription factor implicated in speech and language. Consistent with a model where FOXP2 regulates CYFIP1 levels and in turn influences lh.SMG surface area, analysis of publically available expression data identified a relationship between expression of FOXP2 and CYFIP1 mRNA in human brain. We propose that altered CYFIP1 dosage, through aberrant patterning of the lh.SMG, may contribute to language-related difficulties associated with BP1-2 CNVs. More generally, this approach may be useful in clarifying the contribution of individual genes at CNV risk loci.

Lamellipodia are crucial for haptotactic sensing and response

Haptotaxis is the process by which cells respond to gradients of substrate-bound cues, such as extracellular matrix proteins (ECM); however, the cellular mechanism of this response remains poorly understood and has mainly been studied by comparing cell behavior on uniform ECMs with different concentrations of components. To study haptotaxis in response to gradients, we utilized microfluidic chambers to generate gradients of the ECM protein fibronectin, and imaged the cell migration response. Lamellipodia are fan-shaped protrusions that are common in migrating cells. Here, we define a new function for lamellipodia and the cellular mechanism required for haptotaxis - differential actin and lamellipodial protrusion dynamics lead to biased cell migration. Modest differences in lamellipodial dynamics occurring over time periods of seconds to minutes are summed over hours to produce differential whole cell movement towards higher concentrations of fibronectin. We identify a specific subset of lamellipodia regulators as being crucial for haptotaxis. Numerous studies have linked components of this pathway to cancer metastasis and, consistent with this, we find that expression of the oncogenic Rac1 P29S mutation abrogates haptotaxis. Finally, we show that haptotaxis also operates through this pathway in 3D environments.

Temporal-specific roles of Rac1 during vascular development and retinal angiogenesis

Angiogenesis, the formation of new blood vessels by remodeling and growth of pre-existing vessels, is a highly orchestrated process that requires a tight balance between pro-angiogenic and anti-angiogenic factors and the integration of their corresponding signaling networks. The family of Rho GTPases, including RhoA, Rac1, and Cdc42, play a central role in many cell biological processes that involve cytoskeletal changes and cell movement. Specifically for Rac1, we have shown that excision of Rac1 using a Tie2-Cre animal line results in embryonic lethality in midgestation (embryonic day (E) 9.5), with multiple vascular defects. However, Tie2-Cre can be also expressed during vasculogenesis, prior to angiogenesis, and is active in some hematopoietic precursors that can affect vessel formation. To circumvent these limitations, we have now conditionally deleted Rac1 in a temporally controlled and endothelial-restricted fashion using Cdh5(PAC)-iCreERT2 transgenic mice. In this highly controlled experimental in vivo system, we now show that Rac1 is required for embryonic vascular integrity and angiogenesis, and for the formation of superficial and deep vascular networks in the post-natal developing retina, the latter involving a novel specific function for Rac1 in vertical blood vessel sprouting. Aligned with these findings, we show that RAC1 is spatially involved in endothelial cell migration, invasion, and radial sprouting activities in 3D collagen matrix in vitro models. Hence, Rac1 and its downstream molecules may represent potential anti-angiogeneic therapeutic targets for the treatment of many human diseases that involve aberrant neovascularization and blood vessel overgrowth.

Increased CYFIP1 dosage alters cellular and dendritic morphology and dysregulates mTOR

Rare maternally inherited duplications at 15q11-13 are observed in ~1% of individuals with an autism spectrum disorder (ASD), making it among the most common causes of ASD. 15q11-13 comprises a complex region, and as this copy number variation encompasses many genes, it is important to explore individual genotype-phenotype relationships. Cytoplasmic FMR1-interacting protein 1 (CYFIP1) is of particular interest because of its interaction with Fragile X mental retardation protein (FMRP), its upregulation in transformed lymphoblastoid cell lines from patients with duplications at 15q11-13 and ASD and the presence of smaller overlapping deletions of CYFIP1 in patients with schizophrenia and intellectual disability. Here, we confirm that CYFIP1 is upregulated in transformed lymphoblastoid cell lines and demonstrate its upregulation in the post-mortem brain from 15q11-13 duplication patients for the first time. To investigate how increased CYFIP1 dosage might predispose to neurodevelopmental disease, we studied the consequence of its overexpression in multiple systems. We show that overexpression of CYFIP1 results in morphological abnormalities including cellular hypertrophy in SY5Y cells and differentiated mouse neuronal progenitors. We validate these results in vivo by generating a BAC transgenic mouse, which overexpresses Cyfip1 under the endogenous promotor, observing an increase in the proportion of mature dendritic spines and dendritic spine density. Gene expression profiling on embryonic day 15 suggested the dysregulation of mammalian target of rapamycin (mTOR) signaling, which was confirmed at the protein level. Importantly, similar evidence of mTOR-related dysregulation was seen in brains from 15q11-13 duplication patients with ASD. Finally, treatment of differentiated mouse neuronal progenitors with an mTOR inhibitor (rapamycin) rescued the morphological abnormalities resulting from CYFIP1 overexpression. Together, these data show that CYFIP1 overexpression results in specific cellular phenotypes and implicate modulation by mTOR signaling, further emphasizing its role as a potential convergent pathway in some forms of ASD.

Up-regulated cytoplasmic FMRP-interacting protein 1 in intractable temporal lobe epilepsy patients and a rat model

Cytoplasmic FMRP-interacting protein 1 (CYFIP1) is a multifunctional protein which expresses highly at excitatory synapses and can locally regulate actin cytoskeletal dynamics, spine morphology and synaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor lateral diffusion. Altered synaptic actin plays a role in the pathogenesis of epilepsy. The aim of this study was to investigate the expression pattern of CYFIP1 in temporal lobe epilepsy (TLE). Protein and mRNA expression levels were compared in temporal lobe tissue from patients with TLE versus trauma patients without TLE using quantitative real-time polymerase chain reaction (qRT-PCR), double-label immunofluorescence and Western blot analysis. We have further determined the expression pattern of Cyfip1 mRNA and protein in the hippocampus and adjacent cortex of a common rat model of TLE, lithium-pilocarpine treatment, compared to control rats. CYFIP1 expression was significantly up-regulated in the temporal neocortex of patients with intractable TLE and pilocarpine-treated rats compared to control groups. CYFIP1 localizes to the cytoplasm of neurons, and is not expressed in the astrocytes. Furthermore, CYFIP1 expression levels increased significantly in the two months after pilocarpine treatment, which corresponds to the period of epileptogenesis. Thus, our results indicate that CYFIP1 may be involved in the pathogenesis of TLE.

Whole exome sequencing in females with autism implicates novel and candidate genes

Classical autism or autistic disorder belongs to a group of genetically heterogeneous conditions known as Autism Spectrum Disorders (ASD). Heritability is estimated as high as 90% for ASD with a recently reported compilation of 629 clinically relevant candidate and known genes. We chose to undertake a descriptive next generation whole exome sequencing case study of 30 well-characterized Caucasian females with autism (average age, 7.7 ± 2.6 years; age range, 5 to 16 years) from multiplex families. Genomic DNA was used for whole exome sequencing via paired-end next generation sequencing approach and X chromosome inactivation status. The list of putative disease causing genes was developed from primary selection criteria using machine learning-derived classification score and other predictive parameters (GERP2, PolyPhen2, and SIFT). We narrowed the variant list to 10 to 20 genes and screened for biological significance including neural development, function and known neurological disorders. Seventy-eight genes identified met selection criteria ranging from 1 to 9 filtered variants per female. Five females presented with functional variants of X-linked genes (IL1RAPL1, PIR, GABRQ, GPRASP2, SYTL4) with cadherin, protocadherin and ankyrin repeat gene families most commonly altered (e.g., CDH6, FAT2, PCDH8, CTNNA3, ANKRD11). Other genes related to neurogenesis and neuronal migration (e.g., SEMA3F, MIDN), were also identified.