Presynaptic CK2 promotes synapse organization and stability by targeting Ankyrin2

Missense mutation in the activation segment of the kinase CK2 models Okur-Chung neurodevelopmental disorder and alters the hippocampal glutamatergic synapse

Exome sequencing has enabled the identification of causative genes of monogenic forms of autism, amongst them, in 2016, CSNK2A1, the gene encoding the catalytic subunit of the kinase CK2, linking this kinase to Okur-Chung Neurodevelopmental Syndrome (OCNDS), a newly described neurodevelopmental condition with many symptoms resembling those of autism spectrum disorder. Thus far, no preclinical model of this condition exists. Here we describe a knock-in mouse model that harbors the K198R mutation in the activation segment of the α subunit of CK2. This region is a mutational hotspot, representing one-third of patients. These mice exhibit behavioral phenotypes that mirror patient symptoms. Homozygous knock-in mice die mid-gestation while heterozygous knock-in mice are born at half of the expected mendelian ratio and are smaller in weight and size than wildtype littermates. Heterozygous knock-in mice showed alterations in cognition and memory-assessing paradigms, enhanced stereotypies, altered circadian activity patterns, and nesting behavior. Phosphoproteome analysis from brain tissue revealed alterations in the phosphorylation status of major pre- and postsynaptic proteins of heterozygous knock-in mice. In congruence, we detect reduced synaptic maturation in hippocampal neurons and attenuated long-term potentiation in the hippocampus of knock-in mice. Taken together, heterozygous knock-in mice (CK2αK198R/+) exhibit significant face validity, presenting ASD-relevant phenotypes, synaptic deficits, and alterations in synaptic plasticity, all of which strongly validate this line as a mouse model of OCNDS.

Potential of extracellular vesicle cargo as molecular signals in Schizophrenia: a scoping review

The diagnosis of schizophrenia (SCZ) primarily relies on clinical history and mental status assessments by trained professionals. There has been a search for biomarkers to facilitate laboratory diagnosis. Since extracellular vesicles (EVs) communicate with brain cells and can easily cross blood-brain barrier, there is increased interest among experts to explore them as potential molecular signals for disease detection. A scoping review was conducted to provide a comprehensive summary of the existing literature to identify the differentially expressed molecular signals in EVs isolated from SCZ patients. The methodological framework outline provided by Arksey and O'Malley was employed to conduct this scoping review. A systematic search was conducted using a search string across four databases, ultimately leading to selection of 24 relevant studies. Over 1122 differentially expressed biomolecules were identified in EVs extracted from biological fluids and tissues that can be primarily categorized as RNAs, proteins, and metabolites. Among them, 83 biomolecules were identified as validated differentially expressed molecular signals, which included metabolites, circRNAs, lncRNAs, miRNAs, and proteins. These biomolecules were found to affect cellular receptors and intracellular pathways, neurotransmitters, mitochondrial functions, immune-related functions, and metabolic pathways, which could serve as potential biomarkers for SCZ diagnosis.

Stochastic RNA editing of the Complexin C-terminus within single neurons regulates neurotransmitter release

Neurotransmitter release requires assembly of the SNARE complex fusion machinery, with multiple SNARE-binding proteins regulating when and where synaptic vesicle fusion occurs. The presynaptic protein Complexin (Cpx) controls spontaneous and evoked neurotransmitter release by modulating SNARE complex zippering. Although the central SNARE-binding helix is essential, post-translational modifications to Cpx's C-terminal membrane-binding amphipathic helix regulate its ability to control synaptic vesicle fusion. Here, we demonstrate that RNA editing of the Cpx C-terminus modifies its ability to clamp SNARE-mediated fusion and alters presynaptic output. RNA editing of Cpx across single neurons is stochastic, generating up to eight edit variants that fine tune neurotransmitter release by altering the subcellular localization and clamping properties of the protein. Similar stochastic editing rules for other synaptic genes were observed, indicating editing variability at single adenosines and across multiple mRNAs generates unique synaptic proteomes within the same population of neurons to fine tune presynaptic output.

Stochastic RNA editing of the Complexin C-terminus within single neurons regulates neurotransmitter release

Neurotransmitter release requires assembly of the SNARE complex fusion machinery, with multiple SNARE-binding proteins regulating this process to control when and where synaptic vesicle fusion occurs. Complexin (Cpx) controls spontaneous and evoked neurotransmitter release by modulating SNARE complex zippering. Although the central SNARE-binding helix is essential, post-translational modifications to Cpx's C-terminal membrane-binding amphipathic helix modulate its activity. Here we demonstrate that RNA editing of the Cpx C-terminus regulates its ability to clamp SNARE-mediated fusion and alters presynaptic output. RNA editing of Cpx within single neurons is stochastic, generating up to eight edit variants that fine-tune neurotransmitter release by changing the subcellular localization and clamping properties of the protein. Similar editing rules for other synaptic genes were observed, indicating stochastic editing at single adenosines and across multiple mRNAs can generate unique synaptic proteomes within the same population of neurons to fine-tune presynaptic output.

Prenatal methadone exposure selectively alters protein expression in primary motor cortex: Implications for synaptic function

As problematic opioid use has reached epidemic levels over the past 2 decades, the annual prevalence of opioid use disorder (OUD) in pregnant women has also increased 333%. Yet, how opioids affect the developing brain of offspring from mothers experiencing OUD remains understudied and not fully understood. Animal models of prenatal opioid exposure have discovered many deficits in the offspring of prenatal opioid exposed mothers, such as delays in the development of sensorimotor function and long-term locomotive hyperactivity. In attempt to further understand these deficits and link them with protein changes driven by prenatal opioid exposure, we used a mouse model of prenatal methadone exposure (PME) and preformed an unbiased multi-omic analysis across many sensoriomotor brain regions known to interact with opioid exposure. The effects of PME exposure on the primary motor cortex (M1), primary somatosensory cortex (S1), the dorsomedial striatum (DMS), and dorsolateral striatum (DLS) were assessed using quantitative proteomics and phosphoproteomics. PME drove many changes in protein and phosphopeptide abundance across all brain regions sampled. Gene and gene ontology enrichments were used to assess how protein and phosphopeptide changes in each brain region were altered. Our findings showed that M1 was uniquely affected by PME in comparison to other brain regions. PME uniquely drove changes in M1 glutamatergic synapses and synaptic function. Immunohistochemical analysis also identified anatomical differences in M1 for upregulating the density of glutamatergic and downregulating the density of GABAergic synapses due to PME. Lastly, comparisons between M1 and non-M1 multi-omics revealed conserved brain wide changes in phosphopeptides associated with synaptic activity and assembly, but only specific protein changes in synapse activity and assembly were represented in M1. Together, our studies show that lasting changes in synaptic function driven by PME are largely represented by protein and anatomical changes in M1, which may serve as a starting point for future experimental and translational interventions that aim to reverse the adverse effects of PME on offspring.

Madm/NRBP1 mediates synaptic maintenance and neurodegeneration-induced presynaptic homeostatic potentiation

The precise regulation of synaptic connectivity and function is essential to maintain neuronal circuits. Here, we show that the Drosophila pseudo-kinase Madm/NRBP1 (Mlf-1-adapter-molecule/nuclear-receptor-binding protein 1) is required presynaptically to maintain synaptic stability and to coordinate synaptic growth and function. Presynaptic Madm mediates these functions by controlling cap-dependent translation via the target of rapamycin (TOR) effector 4E-BP/Thor (eukaryotic initiation factor 4E binding protein/Thor). Strikingly, at degenerating neuromuscular synapses, postsynaptic Madm induces a compensatory, transsynaptic signal that utilizes the presynaptic homeostatic potentiation (PHP) machinery to offset synaptic release deficits and to delay synaptic degeneration. Madm is not required for canonical PHP but induces a neurodegeneration-specific form of PHP and acts via the regulation of the cap-dependent translation regulators 4E-BP/Thor and S6-kinase. Consistently, postsynaptic induction of canonical PHP or TOR activation can compensate for postsynaptic Madm to alleviate functional and structural synaptic defects. Our results provide insights into the molecular mechanisms underlying neurodegeneration-induced PHP with potential neurotherapeutic applications.

Circulative Transmission of Cileviruses in Brevipalpus Mites May Involve the Paracellular Movement of Virions

Plant viruses transmitted by mites of the genus Brevipalpus are members of the genera Cilevirus, family Kitaviridae, or Dichorhavirus, family Rhabdoviridae. They produce non-systemic infections that typically display necrotic and/or chlorotic lesions around the inoculation loci. The cilevirus citrus leprosis virus C (CiLV-C) causes citrus leprosis, rated as one of the most destructive diseases affecting this crop in the Americas. CiLV-C is vectored in a persistent manner by the flat mite Brevipalpus yothersi. Upon the ingestion of viral particles with the content of the infected plant cell, virions must pass through the midgut epithelium and the anterior podocephalic gland of the mites. Following the duct from this gland, virions reach the salivary canal before their inoculation into a new plant cell through the stylet canal. It is still unclear whether CiLV-C multiplies in mite cells and what mechanisms contribute to its movement through mite tissues. In this study, based on direct observation of histological sections from viruliferous mites using the transmission electron microscope, we posit the hypothesis of the paracellular movement of CiLV-C in mites which may involve the manipulation of septate junctions. We detail the presence of viral particles aligned in the intercellular spaces between cells and the gastrovascular system of Brevipalpus mites. Accordingly, we propose putative genes that could control either active or passive paracellular circulation of viral particles inside the mites.

CK1α protects WAVE from degradation to regulate cell shape and motility in immune response

The WAVE regulatory complex (WRC) is the main activator of the Arp2/3 complex, promoting lamellipodial protrusions in migrating cells. The WRC is basally inactive but can be activated by Rac1 and phospholipids, and through phosphorylation. However, the in vivo relevance of the phosphorylation of WAVE proteins remains largely unknown. Here, we identified casein kinase I alpha (CK1α) as a regulator of WAVE, thereby controlling cell shape and cell motility in Drosophila macrophages. CK1α binds and phosphorylates WAVE in vitro. Phosphorylation of WAVE by CK1α appears not to be required for activation but, rather, regulates its stability. Pharmacologic inhibition of CK1α promotes ubiquitin-dependent degradation of WAVE. Consistently, loss of Ck1α but not ck2 function phenocopies the depletion of WAVE. Phosphorylation-deficient mutations in the CK1α consensus sequences within the VCA domain of WAVE can neither rescue mutant lethality nor lamellipodium defects. By contrast, phosphomimetic mutations rescue all cellular and developmental defects. Finally, RNAi-mediated suppression of 26S proteasome or E3 ligase complexes substantially rescues lamellipodia defects in CK1α-depleted macrophages. Therefore, we conclude that basal phosphorylation of WAVE by CK1α protects it from premature ubiquitin-dependent degradation, thus promoting WAVE function in vivo.

This article has an associated First Person interview with the first author of the paper.

Summary: We identified CK1α as a novel regulator of WAVE controlling cell shape and motility in immune response. Basal phosphorylation of WAVE by CK1α protects it from premature proteasomal degradation.

A multi-omic analysis of the dorsal striatum in an animal model of divergent genetic risk for alcohol use disorder

The development of selectively bred high and low alcohol-preferring mice (HAP and LAP, respectively) has allowed for an assessment of the polygenetic risk for pathological alcohol consumption and phenotypes associated with alcohol use disorder (AUD). Accumulating evidence indicates that the dorsal striatum (DS) is a central node in the neurocircuitry underlying addictive processes. Therefore, knowledge of differential gene, protein, and phosphorylated protein expression in the DS of HAP and LAP mice may foster new insights into how aberrant DS functioning may contribute to AUD-related phenotypes. To begin to elucidate these basal differences, a complementary and integrated analysis of DS tissue from alcohol-naïve male and female HAP and LAP mice was performed using RNA sequencing, quantitative proteomics, and phosphoproteomics. These datasets were subjected to a thorough analysis of gene ontology, pathway enrichment, and hub gene assessment. Analyses identified 2,108, 390, and 521 significant differentially expressed genes, proteins, and phosphopeptides, respectively between the two lines. Network analyses revealed an enrichment in the differential expression of genes, proteins, and phosphorylated proteins connected to cellular organization, cytoskeletal protein binding, and pathways involved in synaptic transmission and functioning. These findings suggest that the selective breeding to generate HAP and LAP mice may lead to a rearrangement of synaptic architecture which could alter DS neurotransmission and plasticity differentially between mouse lines. These rich datasets will serve as an excellent resource to inform future studies on how inherited differences in gene, protein, and phosphorylated protein expression contribute to AUD-related phenotypes.

Extracellular vesicles in patients in the acute phase of psychosis and after clinical improvement: an explorative study

Extracellular vesicles (EVs) are cell-derived structures that transport proteins, lipids and nucleic acids between cells, thereby affecting the phenotype of the recipient cell. As the content of EVs reflects the status of the originating cell, EVs can have potential as biomarkers. Identifying EVs, including their cells of origin and their cargo, may provide insights in the pathophysiology of psychosis. Here, we present an in-depth analysis and proteomics of EVs from peripheral blood in patients (n = 25) during and after the acute phase of psychosis. Concentration and protein content of EVs in psychotic patients were twofold higher than in 25 age- and sex-matched healthy controls (p < 0.001 for both concentration and protein content), and the diameter of EVs was larger in patients (p = 0.02). Properties of EVs did not differ significantly in blood sampled during and after the acute psychotic episode. Proteomic analyses on isolated EVs from individual patients revealed 1,853 proteins, whereof 45 were brain-elevated proteins. Of these, five proteins involved in regulation of plasticity of glutamatergic synapses were significantly different in psychotic patients compared to controls; neurogranin (NRGN), neuron-specific calcium-binding protein hippocalcin (HPCA), kalirin (KALRN), beta-adducin (ADD2) and ankyrin-2 (ANK2). To summarize, our results show that peripheral EVs in psychotic patients are different from those in healthy controls and point at alterations on the glutamatergic system. We suggest that EVs allow investigation of blood-borne brain-originating biological material and that their role as biomarkers in patients with psychotic disorders is worthy of further exploration.

Phosphorylation of Syntaxin-1a by casein kinase 2α regulates pre-synaptic vesicle exocytosis from the reserve pool

The t-soluble NSF-attachment protein receptor protein Syntaxin-1a (Stx-1a) is abundantly expressed at pre-synaptic terminals where it plays a critical role in the exocytosis of neurotransmitter-containing synaptic vesicles. Stx-1a is phosphorylated by Casein kinase 2α (CK2α) at Ser14, which has been proposed to regulate the interaction of Stx-1a and Munc-18 to control of synaptic vesicle priming. However, the role of CK2α in synaptic vesicle dynamics remains unclear. Here, we show that CK2α over-expression reduces evoked synaptic vesicle release. Furthermore, shRNA-mediated knockdown of CK2α in primary hippocampal neurons strongly enhanced vesicle exocytosis from the reserve pool, with no effect on the readily releasable pool of primed vesicles. In neurons in which endogenous Stx-1a was knocked down and replaced with a CK2α phosphorylation-deficient mutant, Stx-1a(D17A), vesicle exocytosis was also increased. These results reveal a previously unsuspected role of CK2α phosphorylation in specifically regulating the reserve synaptic vesicle pool, without changing the kinetics of release from the readily releasable pool.

Quantitative Phosphoproteomic Analysis in Alpha-Synuclein Transgenic Mice Reveals the Involvement of Aberrant p25/Cdk5 Signaling in Early-stage Parkinson's Disease

A30P and A53T mutations in the gene encoding alpha-synuclein-a presynaptic protein-are the most frequently identified genetic causes of Parkinson's disease (PD). Aberrant alpha-synuclein likely plays central roles in dopaminergic neuronal death and motor symptoms in PD. This study investigated the protein phosphorylation profile in early-stage PD through phosphoproteomic analyses of tissue samples from the substantia nigra pars compacta (SNpc) of 6-month-old alpha-synuclein transgenic mice (A30P/A53T double-mutant human alpha-synuclein; hm2α-SYN-39 strain). We identified 5351 phosphorylation sites in 2136 phosphoproteins. Of these, 357 upregulated sites in 245 proteins and 50 downregulated sites in 46 proteins were differentially phosphorylated between alpha-synuclein transgenic and wildtype mice. Bioinformatic analyses, including Gene Ontology, Kyoto Encyclopedia of Genes and Genomes pathway enrichment, and motif analyses, were used to elucidate the molecular and cellular mechanisms underlying double-mutant human alpha-synuclein overexpression. Scansite-based computational analysis and prediction of differentially quantitated phosphoproteins identified the neuronal protein cyclin-dependent kinase 5 (Cdk5) as the most significantly enriched kinase. Biochemical experiments suggested that the p25/Cdk5 pathway was activated in an MPP+-induced cell culture model and MPTP-induced mouse model. Moreover, Cdk5 could directly phosphorylate the Ank2 protein at Ser1889 in vitro. Therefore, quantitative phosphoproteomic using an alpha-synuclein transgenic mouse model offers a powerful approach for elucidating the protein phosphorylation mechanism underlying SNpc dopaminergic neuronal death in an animal model of PD.

Synaptic and Gene Regulatory Mechanisms in Schizophrenia, Autism, and 22q11.2 Copy Number Variant-Mediated Risk for Neuropsychiatric Disorders

BACKGROUND

22q11.2 copy number variants are among the most highly penetrant genetic risk variants for developmental neuropsychiatric disorders such as schizophrenia (SCZ) and autism spectrum disorder (ASD). However, the specific mechanisms through which they confer risk remain unclear.

METHODS

Using a functional genomics approach, we integrated transcriptomic data from the developing human brain, genome-wide association findings for SCZ and ASD, protein interaction data, and gene expression signatures from SCZ and ASD postmortem cortex to 1) organize genes into the developmental cellular and molecular systems within which they operate, 2) identify neurodevelopmental processes associated with polygenic risk for SCZ and ASD across the allelic frequency spectrum, and 3) elucidate pathways and individual genes through which 22q11.2 copy number variants may confer risk for each disorder.

RESULTS

Polygenic risk for SCZ and ASD converged on partially overlapping neurodevelopmental modules involved in synaptic function and transcriptional regulation, with ASD risk variants additionally enriched for modules involved in neuronal differentiation during fetal development. The 22q11.2 locus formed a large protein network during development that disproportionately affected SCZ-associated and ASD-associated neurodevelopmental modules, including loading highly onto synaptic and gene regulatory pathways. SEPT5, PI4KA, and SNAP29 genes are candidate drivers of 22q11.2 synaptic pathology relevant to SCZ and ASD, and DGCR8 and HIRA are candidate drivers of disease-relevant alterations in gene regulation.

CONCLUSIONS

This approach offers a powerful framework to identify neurodevelopmental processes affected by diverse risk variants for SCZ and ASD and elucidate mechanisms through which highly penetrant, multigene copy number variants contribute to disease risk.

SerThr-PhosphoProteome of Brain from Aged PINK1-KO+A53T-SNCA Mice Reveals pT1928-MAP1B and pS3781-ANK2 Deficits, as Hub between Autophagy and Synapse Changes

Hereditary Parkinson’s disease (PD) can be triggered by an autosomal dominant overdose of alpha-Synuclein (SNCA) as stressor or the autosomal recessive deficiency of PINK1 Serine/Threonine-phosphorylation activity as stress-response. We demonstrated the combination of PINK1-knockout with overexpression of SNCA^A53T in double mutant (DM) mice to exacerbate locomotor deficits and to reduce lifespan. To survey posttranslational modifications of proteins underlying the pathology, brain hemispheres of old DM mice underwent quantitative label-free global proteomic mass spectrometry, focused on Ser/Thr-phosphorylations. As an exceptionally strong effect, we detected >300-fold reductions of phosphoThr1928 in MAP1B, a microtubule-associated protein, and a similar reduction of phosphoSer3781 in ANK2, an interactor of microtubules. MAP1B depletion is known to trigger perturbations of microtubular mitochondria trafficking, neurite extension, and synaptic function, so it was noteworthy that relevantly decreased phosphorylation was also detected for other microtubule and microfilament factors, namely MAP2^S1801, MARK1^S394, MAP1A^T1794, KIF1A^S1537, 4.1N^S541, 4.1G^S86, and ADD2^S528. While the MAP1B heavy chain supports regeneration and growth cones, its light chain assists DAPK1-mediated autophagy. Interestingly, relevant phosphorylation decreases of DAPK2^S299, VPS13D^S2429, and VPS13C^S2480 in the DM brain affected regulators of autophagy, which are implicated in PD. Overall, significant downregulations were enriched for PFAM C2 domains, other kinases, and synaptic transmission factors upon automated bioinformatics, while upregulations were not enriched for selective motifs or pathways. Validation experiments confirmed the change of LC3 processing as reflection of excessive autophagy in DM brain, and dependence of ANK2/MAP1B expression on PINK1 levels. Our new data provide independent confirmation in a mouse model with combined PARK1/PARK4/PARK6 pathology that MAP1B/ANK2 phosphorylation events are implicated in Parkinsonian neurodegeneration. These findings expand on previous observations in Drosophila melanogaster that the MAP1B ortholog futsch in the presynapse is a primary target of the PARK8 protein LRRK2, and on a report that MAP1B is a component of the pathological Lewy body aggregates in PD patient brains. Similarly, ANK2 gene locus variants are associated with the risk of PD, ANK2 interacts with PINK1/Parkin-target proteins such as MIRO1 or ATP1A2, and ANK2-derived peptides are potent inhibitors of autophagy.

Alzheimer's Disease Associated Genes Ankyrin and Tau Cause Shortened Lifespan and Memory Loss in Drosophila

Alzheimer's disease (AD) is the most common form of dementia and is characterized by intracellular neurofibrillary tangles of hyperphosphorylated Tau, including the 0N4R isoform and accumulation of extracellular amyloid beta (Aβ) plaques. However, less than 5% of AD cases are familial, with many additional risk factors contributing to AD including aging, lifestyle, the environment and epigenetics. Recent epigenome-wide association studies (EWAS) of AD have identified a number of loci that are differentially methylated in the AD cortex. Indeed, hypermethylation and reduced expression of the Ankyrin 1 (ANK1) gene in AD has been reported in the cortex in numerous different post-mortem brain cohorts. Little is known about the normal function of ANK1 in the healthy brain, nor the role it may play in AD. We have generated Drosophila models to allow us to functionally characterize Drosophila Ank2, the ortholog of human ANK1 and to determine its interaction with human Tau and Aβ. We show expression of human Tau 0N4R or the oligomerizing Aβ 42 amino acid peptide caused shortened lifespan, degeneration, disrupted movement, memory loss, and decreased excitability of memory neurons with co-expression tending to make the pathology worse. We find that Drosophila with reduced neuronal Ank2 expression have shortened lifespan, reduced locomotion, reduced memory and reduced neuronal excitability similar to flies overexpressing either human Tau 0N4R or Aβ42. Therefore, we show that the mis-expression of Ank2 can drive disease relevant processes and phenocopy some features of AD. Therefore, we propose targeting human ANK1 may have therapeutic potential. This represents the first study to characterize an AD-relevant gene nominated from EWAS.

Biallelic missense variants in ZBTB11 can cause intellectual disability in humans

Exploring genes and pathways underlying intellectual disability (ID) provides insight into brain development and function, clarifying the complex puzzle of how cognition develops. As part of ongoing systematic studies to identify candidate ID genes, linkage analysis and next-generation sequencing revealed Zinc Finger and BTB Domain Containing 11 (ZBTB11) as a novel candidate ID gene. ZBTB11 encodes a little-studied transcription regulator, and the two identified missense variants in this study are predicted to disrupt canonical Zn2+-binding residues of its C2H2 zinc finger domain, leading to possible altered DNA binding. Using HEK293T cells transfected with wild-type and mutant GFP-ZBTB11 constructs, we found the ZBTB11 mutants being excluded from the nucleolus, where the wild-type recombinant protein is predominantly localized. Pathway analysis applied to ChIP-seq data deposited in the ENCODE database supports the localization of ZBTB11 in nucleoli, highlighting associated pathways such as ribosomal RNA synthesis, ribosomal assembly, RNA modification and stress sensing, and provides a direct link between subcellular ZBTB11 location and its function. Furthermore, given the report of prominent brain and spinal cord degeneration in a zebrafish Zbtb11 mutant, we investigated ZBTB11-ortholog knockdown in Drosophila melanogaster brain by targeting RNAi using the UAS/Gal4 system. The observed approximate reduction to a third of the mushroom body size-possibly through neuronal reduction or degeneration-may affect neuronal circuits in the brain that are required for adaptive behavior, specifying the role of this gene in the nervous system. In conclusion, we report two ID families segregating ZBTB11 biallelic mutations disrupting Zn2+-binding motifs and provide functional evidence linking ZBTB11 dysfunction to this phenotype.

Ankyrins: Roles in synaptic biology and pathology

Ankyrins are broadly expressed adaptors that organize diverse membrane proteins into specialized domains and link them to the sub-membranous cytoskeleton. In neurons, ankyrins are known to have essential roles in organizing the axon initial segment and nodes of Ranvier. However, recent studies have revealed novel functions for ankyrins at synapses, where they organize and stabilize neurotransmitter receptors, modulate dendritic spine morphology and control adhesion to the presynaptic site. Ankyrin genes have also been highly associated with a range of neurodevelopmental and psychiatric diseases, including bipolar disorder, schizophrenia and autism, which all demonstrate overlap in their genetics, mechanisms and phenotypes. This review discusses the novel synaptic functions of ankyrin proteins in neurons, and places these exciting findings in the context of ANK genes as key neuropsychiatric disorder risk-factors.

Microtubule organization in presynaptic boutons relies on the formin DAAM

Regulation of the cytoskeleton is fundamental to the development and function of synaptic terminals, such as neuromuscular junctions. Despite the identification of numerous proteins that regulate synaptic actin and microtubule dynamics, the mechanisms of cytoskeletal control during terminal arbor formation have remained largely elusive. Here, we show that DAAM, a member of the formin family of cytoskeleton organizing factors, is an important presynaptic regulator of neuromuscular junction development in Drosophila We demonstrate that the actin filament assembly activity of DAAM plays a negligible role in terminal formation; rather, DAAM is necessary for synaptic microtubule organization. Genetic interaction studies consistently link DAAM with the Wg/Ank2/Futsch module of microtubule regulation and bouton formation. Finally, we provide evidence that DAAM is tightly associated with the synaptic active zone scaffold, and electrophysiological data point to a role in the modulation of synaptic vesicle release. Based on these results, we propose that DAAM is an important cytoskeletal effector element of the Wg/Ank2 pathway involved in the determination of basic synaptic structures, and, additionally, that DAAM may couple the active zone scaffold to the presynaptic cytoskeleton.

Drosophila melanogaster White Mutant w1118 Undergo Retinal Degeneration

Key scientific discoveries have resulted from genetic studies of Drosophila melanogaster, using a multitude of transgenic fly strains, the majority of which are constructed in a genetic background containing mutations in the white gene. Here we report that white mutant flies from w1118 strain undergo retinal degeneration. We observed also that w1118 mutants have progressive loss of climbing ability, shortened life span, as well as impaired resistance to various forms of stress. Retinal degeneration was abolished by transgenic expression of mini-white+ in the white null background w1118 . We conclude that beyond the classical eye-color phenotype, mutations in Drosophila white gene could impair several biological functions affecting parameters like mobility, life span and stress tolerance. Consequently, we suggest caution and attentiveness during the interpretation of old experiments employing white mutant flies and when planning new ones, especially within the research field of neurodegeneration and neuroprotection. We also encourage that the use of w1118 strain as a wild-type control should be avoided.

Impact of protein kinase CK2 inhibitors on proliferation and differentiation of neural stem cells

BACKGROUND

Protein kinases play central roles in cell and tissue development. Protein kinase CK2, an ubiquitously expressed serine/threonine kinase has severe impacts on embryo- and spermatogenesis. Since its role in neurogenesis has so far only been investigated in very few studies, we analysed the role of CK2 in neural stem cells by using two specific inhibitors.

METHODS

Neural stem cells were isolated from the subventricular zone of neonatal mice, using a neurosphere approach. Proliferation of the neurospheres, as well as their differentiation was investigated with and without inhibition of CK2. Changes in proliferation were assessed by counting the number and measuring the diameter of the neurospheres. Furthermore, the absolute cell numbers within the neurospheres were estimated. Differentiation was induced by retinoic acid in single cells after dissociation of the neurospheres. CK2 was inhibited at consecutive time points after induction of the differentiation process.

RESULTS

CK2 inhibition reduced the amount and size of proliferating neurospheres dose dependently. Adding the CK2 inhibitor CX-4945 at the start of differentiation we observed a dose-dependent effect of CX-4945 on cell viability and glia cell differentiation. Adding quinalizarin, a second CK2 inhibitor, at the start of differentiation led to an elevated level of apoptosis, which was accompanied by a reduced neural differentiation. Adding the CK2 inhibitors at 72 h after the start of differentiation had no effect on stem cell differentiation. Conclusion: Inhibition of CK2 influences early gliogenesis in a time point and concentration dependent manner.

GENERAL SIGNIFICANCE

The use of a CK2 inhibitor significantly affects the neural stem cell niche.

SlgA, encoded by the homolog of the human schizophrenia-associated gene PRODH, acts in clock neurons to regulate Drosophila aggression

Mutations in the proline dehydrogenase gene PRODH are linked to behavioral alterations in schizophrenia and as part of DiGeorge and velo-cardio-facial syndromes, but the role of PRODH in their etiology remains unclear. Here, we establish a Drosophila model to study the role of PRODH in behavioral disorders. We determine the distribution of the Drosophila PRODH homolog slgA in the brain and show that knockdown and overexpression of human PRODH and slgA in the lateral neurons ventral (LNv) lead to altered aggressive behavior. SlgA acts in an isoform-specific manner and is regulated by casein kinase II (CkII). Our data suggest that these effects are, at least partially, due to effects on mitochondrial function. We thus show that precise regulation of proline metabolism is essential to drive normal behavior and we identify Drosophila aggression as a model behavior relevant for the study of the mechanisms that are impaired in neuropsychiatric disorders.

Editors' choice: A Drosophila model to study the role of PRODH, a schizophrenia-associated gene, in behavioral disorders.

Drosophila Protein Kinase CK2: Genetics, Regulatory Complexity and Emerging Roles during Development

CK2 is a Ser/Thr protein kinase that is highly conserved amongst all eukaryotes. It is a well-known oncogenic kinase that regulates vital cell autonomous functions and animal development. Genetic studies in the fruit fly Drosophila are providing unique insights into the roles of CK2 in cell signaling, embryogenesis, organogenesis, neurogenesis, and the circadian clock, and are revealing hitherto unknown complexities in CK2 functions and regulation. Here, we review Drosophila CK2 with respect to its structure, subunit diversity, potential mechanisms of regulation, developmental abnormalities linked to mutations in the gene encoding CK2 subunits, and emerging roles in multiple aspects of eye development. We examine the Drosophila CK2 "interaction map" and the eye-specific "transcriptome" databases, which raise the prospect that this protein kinase has many additional targets in the developing eye. We discuss the possibility that CK2 functions during early retinal neurogenesis in Drosophila and mammals bear greater similarity than has been recognized, and that this conservation may extend to other developmental programs. Together, these studies underscore the immense power of the Drosophila model organism to provide new insights and avenues to further investigate developmentally relevant targets of this protein kinase.

MicroRNA-101 Regulates Multiple Developmental Programs to Constrain Excitation in Adult Neural Networks

A critical feature of neural networks is that they balance excitation and inhibition to prevent pathological dysfunction. How this is achieved is largely unknown, although deficits in the balance contribute to many neurological disorders. We show here that a microRNA (miR-101) is a key orchestrator of this essential feature, shaping the developing network to constrain excitation in the adult. Transient early blockade of miR-101 induces long-lasting hyper-excitability and persistent memory deficits. Using target site blockers in vivo, we identify multiple developmental programs regulated in parallel by miR-101 to achieve balanced networks. Repression of one target, NKCC1, initiates the switch in γ-aminobutyric acid (GABA) signaling, limits early spontaneous activity, and constrains dendritic growth. Kif1a and Ank2 are targeted to prevent excessive synapse formation. Simultaneous de-repression of these three targets completely phenocopies major dysfunctions produced by miR-101 blockade. Our results provide new mechanistic insight into brain development and suggest novel candidates for therapeutic intervention.

The Presynaptic Microtubule Cytoskeleton in Physiological and Pathological Conditions: Lessons from Drosophila Fragile X Syndrome and Hereditary Spastic Paraplegias

The capacity of the nervous system to generate neuronal networks relies on the establishment and maintenance of synaptic contacts. Synapses are composed of functionally different presynaptic and postsynaptic compartments. An appropriate synaptic architecture is required to provide the structural basis that supports synaptic transmission, a process involving changes in cytoskeletal dynamics. Actin microfilaments are the main cytoskeletal components present at both presynaptic and postsynaptic terminals in glutamatergic synapses. However, in the last few years it has been demonstrated that microtubules (MTs) transiently invade dendritic spines, promoting their maturation. Nevertheless, the presence and functions of MTs at the presynaptic site are still a matter of debate. Early electron microscopy (EM) studies revealed that MTs are present in the presynaptic terminals of the central nervous system (CNS) where they interact with synaptic vesicles (SVs) and reach the active zone. These observations have been reproduced by several EM protocols; however, there is empirical heterogeneity in detecting presynaptic MTs, since they appear to be both labile and unstable. Moreover, increasing evidence derived from studies in the fruit fly neuromuscular junction proposes different roles for MTs in regulating presynaptic function in physiological and pathological conditions. In this review, we summarize the main findings that support the presence and roles of MTs at presynaptic terminals, integrating descriptive and biochemical analyses, and studies performed in invertebrate genetic models.

Transmission, Development, and Plasticity of Synapses

Chemical synapses are sites of contact and information transfer between a neuron and its partner cell. Each synapse is a specialized junction, where the presynaptic cell assembles machinery for the release of neurotransmitter, and the postsynaptic cell assembles components to receive and integrate this signal. Synapses also exhibit plasticity, during which synaptic function and/or structure are modified in response to activity. With a robust panel of genetic, imaging, and electrophysiology approaches, and strong evolutionary conservation of molecular components, Drosophila has emerged as an essential model system for investigating the mechanisms underlying synaptic assembly, function, and plasticity. We will discuss techniques for studying synapses in Drosophila, with a focus on the larval neuromuscular junction (NMJ), a well-established model glutamatergic synapse. Vesicle fusion, which underlies synaptic release of neurotransmitters, has been well characterized at this synapse. In addition, studies of synaptic assembly and organization of active zones and postsynaptic densities have revealed pathways that coordinate those events across the synaptic cleft. We will also review modes of synaptic growth and plasticity at the fly NMJ, and discuss how pre- and postsynaptic cells communicate to regulate plasticity in response to activity.

Hierarchical microtubule organization controls axon caliber and transport and determines synaptic structure and stability

The dimensions of axons and synaptic terminals determine cell-intrinsic properties of neurons; however, the cellular mechanisms selectively controlling establishment and maintenance of neuronal compartments remain poorly understood. Here, we show that two giant Drosophila Ankyrin2 isoforms, Ank2-L and Ank2-XL, and the MAP1B homolog Futsch form a membrane-associated microtubule-organizing complex that determines axonal diameter, supports axonal transport, and provides independent control of synaptic dimensions and stability. Ank2-L controls microtubule and synaptic stability upstream of Ank2-XL that selectively controls microtubule organization. Synergistically with Futsch, Ank2-XL provides three-dimensional microtubule organization and is required to establish appropriate synaptic dimensions and release properties. In axons, the Ank2-XL/Futsch complex establishes evenly spaced, grid-like microtubule organization and determines axonal diameter in the absence of neurofilaments. Reduced microtubule spacing limits anterograde transport velocities of mitochondria and synaptic vesicles. Our data identify control of microtubule architecture as a central mechanism to selectively control neuronal dimensions, functional properties, and connectivity.