Mitigation of TDP-43 toxic phenotype by an RGNEF fragment in amyotrophic lateral sclerosis models.

Aggregation of the RNA-binding protein TAR DNA binding protein (TDP-43) is a hallmark of TDP-proteinopathies including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). As TDP-43 aggregation and dysregulation are causative of neuronal death, there is a special interest in targeting this protein as a therapeutic approach. Previously, we found that TDP-43 extensively co-aggregated with the dual function protein GEF (guanine exchange factor) and RNA-binding protein rho guanine nucleotide exchange factor (RGNEF) in ALS patients. Here, we show that an N-terminal fragment of RGNEF (NF242) interacts directly with the RNA recognition motifs of TDP-43 competing with RNA and that the IPT/TIG domain of NF242 is essential for this interaction. Genetic expression of NF242 in a fruit fly ALS model overexpressing TDP-43 suppressed the neuropathological phenotype increasing lifespan, abolishing motor defects and preventing neurodegeneration. Intracerebroventricular injections of AAV9/NF242 in a severe TDP-43 murine model (rNLS8) improved lifespan and motor phenotype, and decreased neuroinflammation markers. Our results demonstrate an innovative way to target TDP-43 proteinopathies using a protein fragment with a strong affinity for TDP-43 aggregates and a mechanism that includes competition with RNA sequestration, suggesting a promising therapeutic strategy for TDP-43 proteinopathies such as ALS and FTD.

A clustering of heterozygous missense variants in the crucial chromatin modifier WDR5 defines a new neurodevelopmental disorder.

WDR5 is a broadly studied, highly conserved key protein involved in a wide array of biological functions. Among these functions, WDR5 is a part of several protein complexes that affect gene regulation via post-translational modification of histones. We collected data from 11 unrelated individuals with six different rare de novo germline missense variants in WDR5; one identical variant was found in five individuals and another variant in two individuals. All individuals had neurodevelopmental disorders including speech/language delays (n = 11), intellectual disability (n = 9), epilepsy (n = 7), and autism spectrum disorder (n = 4). Additional phenotypic features included abnormal growth parameters (n = 7), heart anomalies (n = 2), and hearing loss (n = 2). Three-dimensional protein structures indicate that all the residues affected by these variants are located at the surface of one side of the WDR5 protein. It is predicted that five out of the six amino acid substitutions disrupt interactions of WDR5 with RbBP5 and/or KMT2A/C, as part of the COMPASS (complex proteins associated with Set1) family complexes. Our experimental approaches in Drosophila melanogaster and human cell lines show normal protein expression, localization, and protein-protein interactions for all tested variants. These results, together with the clustering of variants in a specific region of WDR5 and the absence of truncating variants so far, suggest that dominant-negative or gain-of-function mechanisms might be at play. All in all, we define a neurodevelopmental disorder associated with missense variants in WDR5 and a broad range of features. This finding highlights the important role of genes encoding COMPASS family proteins in neurodevelopmental disorders.

The epigenetic regulator G9a attenuates stress-induced resistance and metabolic transcriptional programs across different stressors and species.

BACKGROUND: Resistance and tolerance are two coexisting defense strategies for fighting infections. Resistance is mediated by signaling pathways that induce transcriptional activation of resistance factors that directly eliminate the pathogen. Tolerance refers to adaptations that limit the health impact of a given pathogen burden, without targeting the infectious agent. The key players governing immune tolerance are largely unknown. In Drosophila, the histone H3 lysine 9 (H3K9) methyltransferase G9a was shown to mediate tolerance to virus infection and oxidative stress (OS), suggesting that abiotic stresses like OS may also evoke tolerance mechanisms. In response to both virus and OS, stress resistance genes were overinduced in Drosophila G9a mutants, suggesting an intact but overactive stress response. We recently demonstrated that G9a promotes tolerance to OS by maintaining metabolic homeostasis and safeguarding energy availability, but it remained unclear if this mechanism also applies to viral infection, or is conserved in other species and stress responses. To address these questions, we analyzed publicly available datasets from Drosophila, mouse, and human in which global gene expression levels were measured in G9a-depleted conditions and controls at different time points upon stress exposure. RESULTS: In all investigated datasets, G9a attenuates the transcriptional stress responses that confer resistance against the encountered stressor. Comparative analysis of conserved G9a-dependent stress response genes suggests that G9a is an intimate part of the design principles of stress resistance, buffering the induction of promiscuous stress signaling pathways and stress-specific resistance factors. Importantly, we find stress-dependent downregulation of metabolic genes to also be dependent on G9a across all of the tested datasets. CONCLUSIONS: These results suggest that G9a sets the balance between activation of resistance genes and maintaining metabolic homeostasis, thereby ensuring optimal organismal performance during exposure to diverse types of stress across different species. We therefore propose G9a as a potentially conserved master regulator underlying the widely important, yet poorly understood, concept of stress tolerance.

Conditioned courtship suppression in Drosophila melanogaster.

Drosophila melanogaster males reduce courtship behaviour after mating failure. In the lab, such conditioned courtship suppression, aka 'courtship conditioning', serves as a complex learning and memory assay. Interestingly, variations in the courtship conditioning assay can establish different types of memory. Here, we review research investigating the underlying cellular and molecular mechanisms that allow male flies to form memories of previous mating failures.

Characterization of SETD1A haploinsufficiency in humans and Drosophila defines a novel neurodevelopmental syndrome.

Defects in histone methyltransferases (HMTs) are major contributing factors in neurodevelopmental disorders (NDDs). Heterozygous variants of SETD1A involved in histone H3 lysine 4 (H3K4) methylation were previously identified in individuals with schizophrenia. Here, we define the clinical features of the Mendelian syndrome associated with haploinsufficiency of SETD1A by investigating 15 predominantly pediatric individuals who all have de novo SETD1A variants. These individuals present with a core set of symptoms comprising global developmental delay and/or intellectual disability, subtle facial dysmorphisms, behavioral and psychiatric problems. We examined cellular phenotypes in three patient-derived lymphoblastoid cell lines with three variants: p.Gly535Alafs*12, c.4582-2_4582delAG, and p.Tyr1499Asp. These patient cell lines displayed DNA damage repair defects that were comparable to previously observed RNAi-mediated depletion of SETD1A. This suggested that these variants, including the p.Tyr1499Asp in the catalytic SET domain, behave as loss-of-function (LoF) alleles. Previous studies demonstrated a role for SETD1A in cell cycle control and differentiation. However, individuals with SETD1A variants do not show major structural brain defects or severe microcephaly, suggesting that defective proliferation and differentiation of neural progenitors is unlikely the single underlying cause of the disorder. We show here that the Drosophila melanogaster SETD1A orthologue is required in postmitotic neurons of the fly brain for normal memory, suggesting a role in post development neuronal function. Together, this study defines a neurodevelopmental disorder caused by dominant de novo LoF variants in SETD1A and further supports a role for H3K4 methyltransferases in the regulation of neuronal processes underlying normal cognitive functioning.

The histone methyltransferase G9a regulates tolerance to oxidative stress-induced energy consumption.

Stress responses are crucial processes that require activation of genetic programs that protect from the stressor. Stress responses are also energy consuming and can thus be deleterious to the organism. The mechanisms coordinating energy consumption during stress response in multicellular organisms are not well understood. Here, we show that loss of the epigenetic regulator G9a in Drosophila causes a shift in the transcriptional and metabolic responses to oxidative stress (OS) that leads to decreased survival time upon feeding the xenobiotic paraquat. During OS exposure, G9a mutants show overactivation of stress response genes, rapid depletion of glycogen, and inability to access lipid energy stores. The OS survival deficiency of G9a mutants can be rescued by a high-sugar diet. Control flies also show improved OS survival when fed a high-sugar diet, suggesting that energy availability is generally a limiting factor for OS tolerance. Directly limiting access to glycogen stores by knocking down glycogen phosphorylase recapitulates the OS-induced survival defects of G9a mutants. We propose that G9a mutants are sensitive to stress because they experience a net reduction in available energy due to (1) rapid glycogen use, (2) an inability to access lipid energy stores, and (3) an overinduced transcriptional response to stress that further exacerbates energy demands. This suggests that G9a acts as a critical regulatory hub between the transcriptional and metabolic responses to OS. Our findings, together with recent studies that established a role for G9a in hypoxia resistance in cancer cell lines, suggest that G9a is of wide importance in controlling the cellular and organismal response to multiple types of stress.

Individual components of the SWI/SNF chromatin remodelling complex have distinct roles in memory neurons of the Drosophila mushroom body.

Technology has led to rapid progress in the identification of genes involved in neurodevelopmental disorders such as intellectual disability (ID), but our functional understanding of the causative genes is lagging. Here, we show that the SWI/SNF chromatin remodelling complex is one of the most over-represented cellular components disrupted in ID. We investigated the role of individual subunits of this large protein complex using targeted RNA interference in post-mitotic memory-forming neurons of the Drosophila mushroom body (MB). Knockdown flies were tested for defects in MB morphology, short-term memory and long-term memory. Using this approach, we identified distinct roles for individual subunits of the Drosophila SWI/SNF complex. Bap60, Snr1 and E(y)3 are required for pruning of the MBγ neurons during pupal morphogenesis, while Brm and Osa are required for survival of MBγ axons during ageing. We used the courtship conditioning assay to test the effect of MB-specific SWI/SNF knockdown on short- and long-term memory. Several subunits, including Brm, Bap60, Snr1 and E(y)3, were required in the MB for both short- and long-term memory. In contrast, Osa knockdown only reduced long-term memory. Our results suggest that individual components of the SWI/SNF complex have different roles in the regulation of structural plasticity, survival and functionality of post-mitotic MB neurons. This study highlights the many possible processes that might be disrupted in SWI/SNF-related ID disorders. Our broad phenotypic characterization provides a starting point for understanding SWI/SNF-mediated gene regulatory mechanisms that are important for development and function of post-mitotic neurons.

A Syndromic Neurodevelopmental Disorder Caused by Mutations in SMARCD1, a Core SWI/SNF Subunit Needed for Context-Dependent Neuronal Gene Regulation in Flies.

Mutations in several genes encoding components of the SWI/SNF chromatin remodeling complex cause neurodevelopmental disorders (NDDs). Here, we report on five individuals with mutations in SMARCD1; the individuals present with developmental delay, intellectual disability, hypotonia, feeding difficulties, and small hands and feet. Trio exome sequencing proved the mutations to be de novo in four of the five individuals. Mutations in other SWI/SNF components cause Coffin-Siris syndrome, Nicolaides-Baraitser syndrome, or other syndromic and non-syndromic NDDs. Although the individuals presented here have dysmorphisms and some clinical overlap with these syndromes, they lack their typical facial dysmorphisms. To gain insight into the function of SMARCD1 in neurons, we investigated the Drosophila ortholog Bap60 in postmitotic memory-forming neurons of the adult Drosophila mushroom body (MB). Targeted knockdown of Bap60 in the MB of adult flies causes defects in long-term memory. Mushroom-body-specific transcriptome analysis revealed that Bap60 is required for context-dependent expression of genes involved in neuron function and development in juvenile flies when synaptic connections are actively being formed in response to experience. Taken together, we identify an NDD caused by SMARCD1 mutations and establish a role for the SMARCD1 ortholog Bap60 in the regulation of neurodevelopmental genes during a critical time window of juvenile adult brain development when neuronal circuits that are required for learning and memory are formed.

Conserved regulation of neurodevelopmental processes and behavior by FoxP in Drosophila.

FOXP proteins form a subfamily of evolutionarily conserved transcription factors involved in the development and functioning of several tissues, including the central nervous system. In humans, mutations in FOXP1 and FOXP2 have been implicated in cognitive deficits including intellectual disability and speech disorders. Drosophila exhibits a single ortholog, called FoxP, but due to a lack of characterized mutants, our understanding of the gene remains poor. Here we show that the dimerization property required for mammalian FOXP function is conserved in Drosophila. In flies, FoxP is enriched in the adult brain, showing strong expression in ~1000 neurons of cholinergic, glutamatergic and GABAergic nature. We generate Drosophila loss-of-function mutants and UAS-FoxP transgenic lines for ectopic expression, and use them to characterize FoxP function in the nervous system. At the cellular level, we demonstrate that Drosophila FoxP is required in larvae for synaptic morphogenesis at axonal terminals of the neuromuscular junction and for dendrite development of dorsal multidendritic sensory neurons. In the developing brain, we find that FoxP plays important roles in α-lobe mushroom body formation. Finally, at a behavioral level, we show that Drosophila FoxP is important for locomotion, habituation learning and social space behavior of adult flies. Our work shows that Drosophila FoxP is important for regulating several neurodevelopmental processes and behaviors that are related to human disease or vertebrate disease model phenotypes. This suggests a high degree of functional conservation with vertebrate FOXP orthologues and established flies as a model system for understanding FOXP related pathologies.

Mushroom Body Specific Transcriptome Analysis Reveals Dynamic Regulation of Learning and Memory Genes After Acquisition of Long-Term Courtship Memory in Drosophila.

The formation and recall of long-term memory (LTM) requires neuron activity-induced gene expression. Transcriptome analysis has been used to identify genes that have altered expression after memory acquisition, however, we still have an incomplete picture of the transcriptional changes that are required for LTM formation. The complex spatial and temporal dynamics of memory formation creates significant challenges in defining memory-relevant gene expression changes. The Drosophila mushroom body (MB) is a signaling hub in the insect brain that integrates sensory information to form memories across several different experimental memory paradigms. Here, we performed transcriptome analysis in the MB at two time points after the acquisition of LTM: 1 hr and 24 hr. The MB transcriptome was compared to biologically paired whole head (WH) transcriptomes. In both, we identified more transcript level changes at 1 hr after memory acquisition (WH = 322, MB = 302) than at 24 hr (WH = 23, MB = 20). WH samples showed downregulation of developmental genes and upregulation of sensory response genes. In contrast, MB samples showed vastly different changes in transcripts involved in biological processes that are specifically related to LTM. MB-downregulated genes were highly enriched for metabolic function. MB-upregulated genes were highly enriched for known learning and memory processes, including calcium-mediated neurotransmitter release and cAMP signaling. The neuron activity inducible genes Hr38 and sr were also specifically induced in the MB. These results highlight the importance of sampling time and cell type in capturing biologically relevant transcript level changes involved in learning and memory. Our data suggests that MB cells transiently upregulate known memory-related pathways after memory acquisition and provides a critical frame of reference for further investigation into the role of MB-specific gene regulation in memory.

Optimal RNA isolation method and primer design to detect gene knockdown by qPCR when validating Drosophila transgenic RNAi lines.

OBJECTIVE: RNA interference is employed extensively in Drosophila research to study gene function within a specific cell-type or tissue. Thousands of transgenic Drosophila lines have been generated to express double stranded RNA for gene knockdown; however, no standardized method exists for quantifying their knockdown efficiency. Since antibodies are not available for many proteins, quantitative real-time PCR is often used. Here, we explore how primer design and RNA isolation method can influence detection of gene knockdown using qPCR. RESULTS: We tested differences in detected gene knockdown efficiency when using purified polyadenylated mRNA or total RNA as templates for cDNA synthesis. We also tested two different primer locations for each gene: one to amplify a region 5' of the RNAi cut site, and one to amplify a region 3' of the cut site. Consistently, the strongest gene knockdown was detected when qPCR was performed using 5' primer sets in combination with mRNA-derived cDNA. Our results indicate that detection of undegraded mRNA cleavage fragments can result in underestimation of true knockdown efficiency for a RNAi construct. Purification of polyadenylated mRNA, combined with primers designed to amplify the non-polyadenylated 5' mRNA cleavage fragment can avoid this problem.

Identification of a novel synaptic protein, TMTC3, involved in periventricular nodular heterotopia with intellectual disability and epilepsy.

Defects in neuronal migration cause brain malformations, which are associated with intellectual disability (ID) and epilepsy. Using exome sequencing, we identified compound heterozygous variants (p.Arg71His and p. Leu729ThrfsTer6) in TMTC3, encoding transmembrane and tetratricopeptide repeat containing 3, in four siblings with nocturnal seizures and ID. Three of the four siblings have periventricular nodular heterotopia (PVNH), a common brain malformation caused by failure of neurons to migrate from the ventricular zone to the cortex. Expression analysis using patient-derived cells confirmed reduced TMTC3 transcript levels and loss of the TMTC3 protein compared to parental and control cells. As TMTC3 function is currently unexplored in the brain, we gathered support for a neurobiological role for TMTC3 by generating flies with post-mitotic neuron-specific knockdown of the highly conserved Drosophila melanogaster TMTC3 ortholog, CG4050/tmtc3. Neuron-specific knockdown of tmtc3 in flies resulted in increased susceptibility to induced seizures. Importantly, this phenotype was rescued by neuron-specific expression of human TMTC3, suggesting a role for TMTC3 in seizure biology. In addition, we observed co-localization of TMTC3 in the rat brain with vesicular GABA transporter (VGAT), a presynaptic marker for inhibitory synapses. TMTC3 is localized at VGAT positive pre-synaptic terminals and boutons in the rat hypothalamus and piriform cortex, suggesting a role for TMTC3 in the regulation of GABAergic inhibitory synapses. TMTC3 did not co-localize with Vglut2, a presynaptic marker for excitatory neurons. Our data identified TMTC3 as a synaptic protein that is involved in PVNH with ID and epilepsy, in addition to its previously described association with cobblestone lissencephaly.

Epigenetic mechanisms modulate differences in Drosophila foraging behavior.

Little is known about how genetic variation and epigenetic marks interact to shape differences in behavior. The foraging (for) gene regulates behavioral differences between the rover and sitter Drosophila melanogaster strains, but the molecular mechanisms through which it does so have remained elusive. We show that the epigenetic regulator G9a interacts with for to regulate strain-specific adult foraging behavior through allele-specific histone methylation of a for promoter (pr4). Rovers have higher pr4 H3K9me dimethylation, lower pr4 RNA expression, and higher foraging scores than sitters. The rover-sitter differences disappear in the presence of G9a null mutant alleles, showing that G9a is necessary for these differences. Furthermore, rover foraging scores can be phenocopied by transgenically reducing pr4 expression in sitters. This compelling evidence shows that genetic variation can interact with an epigenetic modifier to produce differences in gene expression, establishing a behavioral polymorphism in Drosophila.

Functional convergence of histone methyltransferases EHMT1 and KMT2C involved in intellectual disability and autism spectrum disorder.

Kleefstra syndrome, caused by haploinsufficiency of euchromatin histone methyltransferase 1 (EHMT1), is characterized by intellectual disability (ID), autism spectrum disorder (ASD), characteristic facial dysmorphisms, and other variable clinical features. In addition to EHMT1 mutations, de novo variants were reported in four additional genes (MBD5, SMARCB1, NR1I3, and KMT2C), in single individuals with clinical characteristics overlapping Kleefstra syndrome. Here, we present a novel cohort of five patients with de novo loss of function mutations affecting the histone methyltransferase KMT2C. Our clinical data delineates the KMT2C phenotypic spectrum and reinforces the phenotypic overlap with Kleefstra syndrome and other related ID disorders. To elucidate the common molecular basis of the neuropathology associated with mutations in KMT2C and EHMT1, we characterized the role of the Drosophila KMT2C ortholog, trithorax related (trr), in the nervous system. Similar to the Drosophila EHMT1 ortholog, G9a, trr is required in the mushroom body for short term memory. Trr ChIP-seq identified 3371 binding sites, mainly in the promoter of genes involved in neuronal processes. Transcriptional profiling of pan-neuronal trr knockdown and G9a null mutant fly heads identified 613 and 1123 misregulated genes, respectively. These gene sets show a significant overlap and are associated with nearly identical gene ontology enrichments. The majority of the observed biological convergence is derived from predicted indirect target genes. However, trr and G9a also have common direct targets, including the Drosophila ortholog of Arc (Arc1), a key regulator of synaptic plasticity. Our data highlight the clinical and molecular convergence between the KMT2 and EHMT protein families, which may contribute to a molecular network underlying a larger group of ID/ASD-related disorders.

Drosophila Courtship Conditioning As a Measure of Learning and Memory.

Many insights into the molecular mechanisms underlying learning and memory have been elucidated through the use of simple behavioral assays in model organisms such as the fruit fly, Drosophila melanogaster. Drosophila is useful for understanding the basic neurobiology underlying cognitive deficits resulting from mutations in genes associated with human cognitive disorders, such as intellectual disability (ID) and autism. This work describes a methodology for testing learning and memory using a classic paradigm in Drosophila known as courtship conditioning. Male flies court females using a distinct pattern of easily recognizable behaviors. Premated females are not receptive to mating and will reject the male's copulation attempts. In response to this rejection, male flies reduce their courtship behavior. This learned reduction in courtship behavior is measured over time, serving as an indicator of learning and memory. The basic numerical output of this assay is the courtship index (CI), which is defined as the percentage of time that a male spends courting during a 10 min interval. The learning index (LI) is the relative reduction of CI in flies that have been exposed to a premated female compared to naïve flies with no previous social encounters. For the statistical comparison of LIs between genotypes, a randomization test with bootstrapping is used. To illustrate how the assay can be used to address the role of a gene relating to learning and memory, the pan-neuronal knockdown of Dihydroxyacetone phosphate acyltransferase (Dhap-at) was characterized here. The human ortholog of Dhap-at, glyceronephosphate O-acyltransferase (GNPT), is involved in rhizomelic chondrodysplasia punctata type 2, an autosomal-recessive syndrome characterized by severe ID. Using the courtship conditioning assay, it was determined that Dhap-at is required for long-term memory, but not for short-term memory. This result serves as a basis for further investigation of the underlying molecular mechanisms.

Systematic Phenomics Analysis Deconvolutes Genes Mutated in Intellectual Disability into Biologically Coherent Modules.

Intellectual disability (ID) disorders are genetically and phenotypically extremely heterogeneous. Can this complexity be depicted in a comprehensive way as a means of facilitating the understanding of ID disorders and their underlying biology? We provide a curated database of 746 currently known genes, mutations in which cause ID (ID-associated genes [ID-AGs]), classified according to ID manifestation and associated clinical features. Using this integrated resource, we show that ID-AGs are substantially enriched with co-expression, protein-protein interactions, and specific biological functions. Systematic identification of highly enriched functional themes and phenotypes revealed typical phenotype combinations characterizing process-defined groups of ID disorders, such as chromatin-related disorders and deficiencies in DNA repair. Strikingly, phenotype classification efficiently breaks down ID-AGs into subsets with significantly elevated biological coherence and predictive power. Custom-made functional Drosophila datasets revealed further characteristic phenotypes among ID-AGs and specific clinical classes. Our study and resource provide systematic insights into the molecular and clinical landscape of ID disorders, represent a significant step toward overcoming current limitations in ID research, and prove the utility of systematic human and cross-species phenomics analyses in highly heterogeneous genetic disorders.

Regulation of cell differentiation and function by the euchromatin histone methyltranserfases G9a and GLP.

The euchromatin histone methyltransferases (EHMTs) are an evolutionarily conserved protein family that are known for their ability to dimethylate histone 3 at lysine 9 in euchromatic regions of the genome. In mammals there are two EHMT proteins, G9a, encoded by EHMT2, and GLP, encoded by EHMT1. EHMTs have diverse roles in the differentiation of different tissues and cell types and are involved in adult-specific processes like memory, drug addiction, and immune response. This review discusses recent findings from rodent and Drosophila models that are beginning to reveal the broad biological role and complex mechanistic functioning of EHMT proteins.

Conditional depletion of intellectual disability and Parkinsonism candidate gene ATP6AP2 in fly and mouse induces cognitive impairment and neurodegeneration.

ATP6AP2, an essential accessory component of the vacuolar H+ ATPase (V-ATPase), has been associated with intellectual disability (ID) and Parkinsonism. ATP6AP2 has been implicated in several signalling pathways; however, little is known regarding its role in the nervous system. To decipher its function in behaviour and cognition, we generated and characterized conditional knockdowns of ATP6AP2 in the nervous system of Drosophila and mouse models. In Drosophila, ATP6AP2 knockdown induced defective phototaxis and vacuolated photoreceptor neurons and pigment cells when depleted in eyes and altered short- and long-term memory when depleted in the mushroom body. In mouse, conditional Atp6ap2 deletion in glutamatergic neurons (Atp6ap2(Camk2aCre/0) mice) caused increased spontaneous locomotor activity and altered fear memory. Both Drosophila ATP6AP2 knockdown and Atp6ap2(Camk2aCre/0) mice presented with presynaptic transmission defects, and with an abnormal number and morphology of synapses. In addition, Atp6ap2(Camk2aCre/0) mice showed autophagy defects that led to axonal and neuronal degeneration in the cortex and hippocampus. Surprisingly, axon myelination was affected in our mutant mice, and axonal transport alterations were observed in Drosophila. In accordance with the identified phenotypes across species, genome-wide transcriptome profiling of Atp6ap2(Camk2aCre/0) mouse hippocampi revealed dysregulation of genes involved in myelination, action potential, membrane-bound vesicles and motor behaviour. In summary, ATP6AP2 disruption in mouse and fly leads to cognitive impairment and neurodegeneration, mimicking aspects of the neuropathology associated with ATP6AP2 mutations in humans. Our results identify ATP6AP2 as an essential gene for the nervous system.

The epigenetic regulator G9a mediates tolerance to RNA virus infection in Drosophila.

Little is known about the tolerance mechanisms that reduce the negative effects of microbial infection on host fitness. Here, we demonstrate that the histone H3 lysine 9 methyltransferase G9a regulates tolerance to virus infection by shaping the response of the evolutionary conserved Jak-Stat pathway in Drosophila. G9a-deficient mutants are more sensitive to RNA virus infection and succumb faster to infection than wild-type controls, which was associated with strongly increased Jak-Stat dependent responses, but not with major differences in viral load. Genetic experiments indicate that hyperactivated Jak-Stat responses are associated with early lethality in virus-infected flies. Our results identify an essential epigenetic mechanism underlying tolerance to virus infection.

Altered GPM6A/M6 dosage impairs cognition and causes phenotypes responsive to cholesterol in human and Drosophila.

Glycoprotein M6A (GPM6A) is a neuronal transmembrane protein of the PLP/DM20 (proteolipid protein) family that associates with cholesterol-rich lipid rafts and promotes filopodia formation. We identified a de novo duplication of the GPM6A gene in a patient with learning disability and behavioral anomalies. Expression analysis in blood lymphocytes showed increased GPM6A levels. An increase of patient-derived lymphoblastoid cells carrying membrane protrusions supports a functional effect of this duplication. To study the consequences of GPM6A dosage alterations in an intact nervous system, we employed Drosophila melanogaster as a model organism. We found that knockdown of Drosophila M6, the sole member of the PLP family in flies, in the wing, and whole organism causes malformation and lethality, respectively. These phenotypes as well as the protrusions of patient-derived lymphoblastoid cells with increased GPM6A levels can be alleviated by cholesterol supplementation. Notably, overexpression as well as loss of M6 in neurons specifically compromises long-term memory in the courtship conditioning paradigm. Our findings thus indicate a critical role of correct GPM6A/M6 levels for cognitive function and support a role of the GPM6A duplication for the patient's phenotype. Together with other recent findings, this study highlights compromised cholesterol homeostasis as a recurrent feature in cognitive phenotypes.