Optimization of wrMTrck to monitor Drosophila larval locomotor activity

Identifying potential dietary treatments for inherited metabolic disorders using Drosophila nutrigenomics

Inherited metabolic disorders are a group of genetic conditions that can cause severe neurological impairment and child mortality. Uniquely, these disorders respond to dietary treatment; however, this option remains largely unexplored because of low disorder prevalence and the lack of a suitable paradigm for testing diets. Here, we screened 35 Drosophila amino acid disorder models for disease-diet interactions and found 26 with diet-altered development and/or survival. Using a targeted multi-nutrient array, we examine the interaction in a model of isolated sulfite oxidase deficiency, an infant-lethal disorder. We show that dietary cysteine depletion normalizes their metabolic profile and rescues development, neurophysiology, behavior, and lifelong fly survival, thus providing a basis for further study into the pathogenic mechanisms involved in this disorder. Our work highlights the diet-sensitive nature of metabolic disorders and establishes Drosophila as a valuable tool for nutrigenomic studies for informing potential dietary therapies.

FAME4-associating YEATS2 knockdown impairs dopaminergic synaptic integrity and leads to seizure-like behaviours in Drosophila melanogaster

Familial adult myoclonus epilepsy (FAME) is a neurological disorder caused by a TTTTA/TTTCA intronic repeat expansion. FAME4 is one of the six types of FAME that results from the repeat expansion in the first intron of the gene YEATS2. Although the RNA toxicity is believed to be the primary mechanism underlying FAME, the role of genes where repeat expansions reside is still unclear, particularly in the case of YEATS2 in neurons. This study used Drosophila to explore the effects of reducing YEATS2 expression. Two pan-neuronally driven dsDNA were used for knockdown of Drosophila YEATS2 (dYEATS2), and the resulting molecular and behavioural outcomes were evaluated. Drosophila with reduced dYEATS2 expression exhibited decreased tolerance to acute stress, disturbed locomotion, abnormal social behaviour, and decreased motivated activity. Additionally, reducing dYEATS2 expression negatively affected tyrosine hydroxylase (TH) gene expression, resulting in decreased dopamine biosynthesis. Remarkably, seizure-like behaviours induced by knocking down dYEATS2 were rescued by the administration of L-DOPA. This study reveals a novel role of YEATS2 in neurons in regulating acute stress responses, locomotion, and complex behaviours, and suggests that haploinsufficiency of YEATS2 may play a role in FAME4.

A Simple Method for Quantifying Larval Locomotion in Drosophila melanogaster

The fruit fly Drosophila melanogaster is a powerful genetic model that has been used for many decades to study nervous system function, development, and behavior. There are a large number of developmental and behavioral traits that can be measured to provide a broad readout of neurological function. These include patterned motor behaviors, such as larval locomotion, which can be used to assess whether genetic or environmental factors affect nervous system function to provide an entry point for deeper mechanistic studies. Here, we describe a protocol for quantifying larval locomotion using a simple camera setup and a freely available image analysis software. This protocol can be readily applied to human disease models or in toxicology studies, for example, to broadly assess the impact of treatments on neurological function.

Drosophila melanogaster Neuromuscular Junction as a Model to Study Synaptopathies and Neuronal Autophagy

Neuronal synapse dysfunction is a key characteristic of several neurodegenerative disorders, such as Alzheimer's disease, spinocerebellar ataxias, and Huntington's disease. Modeling these disorders to study synaptic dysfunction requires a robust and reproducible method for assaying the subtle changes associated with synaptopathies in terms of structure and function of the synapses. Drosophila melanogaster neuromuscular junctions (NMJs) serve as good models to study such alterations. Further, modifications in the microenvironment of synapses can sometimes reflect in the behavior of the animal, which can also be assayed in a high-throughput manner. The methods outlined in this chapter highlight assays to study the behavioral changes associated with synaptic dysfunction in a spinocerebellar ataxia type 3 (SCA3) model. Further, molecular assessment of alterations in NMJ structure and function is also summarized, followed by effects of autophagy pathway upregulation in providing neuroprotection. These methods can be further extended and modified to study the therapeutic effects of drugs or small molecules in providing neuroprotection for any synaptopathy models.

Locomotor Assays in Drosophila Larvae and Adult Flies

Brain defects often lead to motor dysfunctions in humans. Drosophila melanogaster has been one of the most useful organisms in the study of neuronal biology due to its similarities with humans and has contributed to a more detailed understanding of the effects of genetic dysfunctions in the brain on behavior. We herein present modified protocols for the crawling assay with larvae and the climbing assay with adult flies that are simple to perform as well as a series of commands for ImageJ to automatically analyze data for the crawling assay.

Knockdown of Chronophage in the nervous system mimics features of neurodevelopmental disorders caused by BCL11A/B variants

Neurodevelopmental disorders (NDD) are a group of disorders that include intellectual disability. Although several genes have been implicated in NDD, the molecular mechanisms underlying its pathogenesis remain unclear. Therefore, it is important to develop novel models to analyze the functions of NDD-causing genes in vivo. Recently, rare pathogenic variants of the B-cell lymphoma/leukemia11A/B (BCL11A/B) gene have been identified in several patients with NDD. Drosophila carries the Chronophage (Cph) gene, which has been predicted to be a homolog of BCL11A/B based on the conservation of the amino acid sequence. In the present study, we investigated whether nervous system-specific knockdown of Cph mimics NDD phenotypes in Drosophila. Nervous system-specific knockdown of Cph induced learning and locomotor defects in larvae and epilepsy-like behaviors in adults. The number of synaptic branches was also elevated in the larval neuromuscular junction without a corresponding increase in the number of boutons. Furthermore, the expression levels of putative target genes that are Drosophila homologs of the mammalian BCL11 target genes were decreased in Cph knockdown flies. These results suggest that Cph knockdown flies are a promising model for investigating the pathology of NDD-induced BCL11A/B dysfunction.

A Novel Drosophila-based Drug Repurposing Platform Identified Fingolimod As a Potential Therapeutic for TDP-43 Proteinopathy

Pathogenic changes to TAR DNA-binding protein 43 (TDP-43) leading to alteration of its homeostasis are a common feature shared by several progressive neurodegenerative diseases for which there is no effective therapy. Here, we developed Drosophila lines expressing either wild type TDP-43 (WT) or that carrying an Amyotrophic Lateral Sclerosis /Frontotemporal Lobar Degeneration-associating G384C mutation that recapitulate several aspects of the TDP-43 pathology. To identify potential therapeutics for TDP-43-related diseases, we implemented a drug repurposing strategy that involved three consecutive steps. Firstly, we evaluated the improvement of eclosion rate, followed by the assessment of locomotive functions at early and late developmental stages. Through this approach, we successfully identified fingolimod, as a promising candidate for modulating TDP-43 toxicity. Fingolimod exhibited several beneficial effects in both WT and mutant models of TDP-43 pathology, including post-transcriptional reduction of TDP-43 levels, rescue of pupal lethality, and improvement of locomotor dysfunctions. These findings provide compelling evidence for the therapeutic potential of fingolimod in addressing TDP-43 pathology, thereby strengthening the rationale for further investigation and consideration of clinical trials. Furthermore, our study demonstrates the utility of our Drosophila-based screening pipeline in identifying novel therapeutics for TDP-43-related diseases. These findings encourage further scale-up screening endeavors using this platform to discover additional compounds with therapeutic potential for TDP-43 pathology.

Lipin knockdown in pan-neuron of Drosophila induces reduction of lifespan, deficient locomotive behavior, and abnormal morphology of motor neuron

The Lipin family is evolutionarily conserved among insects and mammals, and its crucial roles in lipid synthesis and homeostatic control of energy balance have been well documented. This study investigated the function of Lipin in neuronal function and neurodegeneration. The GAL4/UAS system was used to knock down Lipin in the nervous system of Drosophila and investigate its behavioral and cellular phenotypes. The neuromuscular junction (NMJ) morphology was detected by immunostaining. Moreover, triacylglycerol and ATP levels were analyzed by using assay Kit. This study found that Lipin is localized almost in the cytoplasm of neurons in the brain lobe and ventral nerve cord, which are part of the central nervous system (CNS) of Drosophila melanogaster. Lipin knockdown larvae exhibit decreased locomotor activity, aberrant morphology of motor nerve terminals at NMJs, and reduced number and size of lipid droplets in the CNS. Furthermore, neuron-specific knockdown of Lipin leads to locomotor defects and a shortened lifespan, accompanied by a reduction in ATP levels in the adult stage. These results indicate that Lipin plays a crucial role in the CNS of Drosophila.

High-resolution analysis of individual Drosophila melanogaster larvae uncovers individual variability in locomotion and its neurogenetic modulation

Neuronally orchestrated muscular movement and locomotion are defining faculties of multicellular animals. Due to its simple brain and genetic accessibility, the larva of the fruit fly Drosophila melanogaster allows one to study these processes at tractable levels of complexity. However, although the faculty of locomotion clearly pertains to the individual, most studies of locomotion in larvae use measurements aggregated across animals, or animals tested one by one, an extravagance for larger-scale analyses. This prevents grasping the inter- and intra-individual variability in locomotion and its neurogenetic determinants. Here, we present the IMBA (individual maggot behaviour analyser) for analysing the behaviour of individual larvae within groups, reliably resolving individual identity across collisions. We use the IMBA to systematically describe the inter- and intra-individual variability in locomotion of wild-type animals, and how the variability is reduced by associative learning. We then report a novel locomotion phenotype of an adhesion GPCR mutant. We further investigated the modulation of locomotion across repeated activations of dopamine neurons in individual animals, and the transient backward locomotion induced by brief optogenetic activation of the brain-descending 'mooncrawler' neurons. In summary, the IMBA is an easy-to-use toolbox allowing an unprecedentedly rich view of the behaviour and its variability of individual larvae, with utility in multiple biomedical research contexts.

Innexin-Mediated Adhesion between Glia Is Required for Axon Ensheathment in the Peripheral Nervous System

Glia are essential to protecting and enabling nervous system function and a key glial function is the formation of the glial sheath around peripheral axons. Each peripheral nerve in the Drosophila larva is ensheathed by three glial layers, which structurally support and insulate the peripheral axons. How peripheral glia communicate with each other and between layers is not well established and we investigated the role of Innexins in mediating glial function in the Drosophila periphery. Of the eight Drosophila Innexins, we found two (Inx1 and Inx2) are important for peripheral glia development. In particular loss of Inx1 and Inx2 resulted in defects in the wrapping glia leading to disruption of the glia wrap. Of interest loss of Inx2 in the subperineurial glia also resulted in defects in the neighboring wrapping glia. Inx plaques were observed between the subperineurial glia and the wrapping glia suggesting that gap junctions link these two glial cell types. We found Inx2 is key to Ca2+ pulses in the peripheral subperineurial glia but not in the wrapping glia, and we found no evidence of gap junction communication between subperineurial and wrapping glia. Rather we have clear evidence that Inx2 plays an adhesive and channel-independent role between the subperineurial and wrapping glia to ensure the integrity of the glial wrap.SIGNIFICANCE STATEMENT Gap junctions are critical for glia communication and formation of myelin in myelinating glia. However, the role of gap junctions in non-myelinating glia is not well studied, yet non-myelinating glia are critical for peripheral nerve function. We found the Innexin gap junction proteins are present between different classes of peripheral glia in Drosophila. Here Innexins form junctions to facilitate adhesion between the different glia but do so in a channel-independent manner. Loss of adhesion leads to disruption of the glial wrap around axons and leads to fragmentation of the wrapping glia membranes. Our work points to an important role for gap junction proteins in mediating insulation by non-myelinating glia.

Parkin Knockdown Modulates Dopamine Release in the Central Complex, but Not the Mushroom Body Heel, of Aging Drosophila

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic neurons leading to reduced locomotion. Mutations of parkin gene in Drosophila produce the same phenotypes as vertebrate models, but the effect of parkin knockdown on dopamine release is not known. Here, we report age-dependent, spatial variation of dopamine release in the brain of parkin-RNAi adult Drosophila. Dopamine was repetitively stimulated by local application of acetylcholine and quantified by fast-scan cyclic voltammetry in the central complex or mushroom body heel. In the central complex, the main area controlling locomotor function, dopamine release is maintained for repeated stimulations in aged control flies, but lower concentrations of dopamine are released in the central complex of aged parkin-RNAi flies. In the mushroom body heel, the dopamine release decrease in older parkin-RNAi flies is similar to controls. There is not significant dopaminergic neuronal loss even in older parkin knockdown flies, which indicates that the changes in stimulated dopamine release are due to alterations of neuronal function. In young parkin-RNAi flies, locomotion is inhibited by 30%, while in older parkin-RNAi flies it is inhibited by 85%. Overall, stimulated dopamine release is modulated by parkin in an age and brain region dependent manner. Correlating the functional state of the dopaminergic system with behavioral phenotypes provides unique insights into the PD mechanism. Drosophila can be used to study dopamine functionality in PD, elucidate how genetics influence dopamine, and test potential therapies to maintain dopamine release.

A Drosophila model of the neurological symptoms in Mpv17-related diseases

Mutations in the Mpv17 gene are responsible for MPV17-related hepatocerebral mitochondrial DNA depletion syndrome and Charcot-Marie-Tooth (CMT) disease. Although several models including mouse, zebrafish, and cultured human cells, have been developed, the models do not show any neurological defects, which are often observed in patients. Therefore, we knocked down CG11077 (Drosophila Mpv17; dMpv17), an ortholog of human MPV17, in the nervous system in Drosophila melanogaster and investigated the behavioral and cellular phenotypes. The resulting dMpv17 knockdown larvae showed impaired locomotor activity and learning ability consistent with mitochondrial defects suggested by the reductions in mitochondrial DNA and ATP production and the increases in the levels of lactate and reactive oxygen species. Furthermore, an abnormal morphology of the neuromuscular junction, at the presynaptic terminal, was observed in dMpv17 knockdown larvae. These results reproduce well the symptoms of human diseases and partially reproduce the phenotypes of Mpv17-deficient model organisms. Therefore, we suggest that neuron-specific dMpv17 knockdown in Drosophila is a useful model for investigation of MPV17-related hepatocerebral mitochondrial DNA depletion syndrome and CMT caused by Mpv17 dysfunction.

WiFi Related Radiofrequency Electromagnetic Fields Promote Transposable Element Dysregulation and Genomic Instability in Drosophila melanogaster

Exposure to artificial radio frequency electromagnetic fields (RF-EMFs) has greatly increased in recent years, thus promoting a growing scientific and social interest in deepening the biological impact of EMFs on living organisms. The current legislation governing the exposure to RF-EMFs is based exclusively on their thermal effects, without considering the possible non-thermal adverse health effects from long term exposure to EMFs. In this study we investigated the biological non-thermal effects of low-level indoor exposure to RF-EMFs produced by WiFi wireless technologies, using Drosophila melanogaster as the model system. Flies were exposed to 2.4 GHz radiofrequency in a Transverse Electromagnetic (TEM) cell device to ensure homogenous controlled fields. Signals were continuously monitored during the experiments and regulated at non thermal levels. The results of this study demonstrate that WiFi electromagnetic radiation causes extensive heterochromatin decondensation and thus a general loss of transposable elements epigenetic silencing in both germinal and neural tissues. Moreover, our findings provide evidence that WiFi related radiofrequency electromagnetic fields can induce reactive oxygen species (ROS) accumulation, genomic instability, and behavioural abnormalities. Finally, we demonstrate that WiFi radiation can synergize with Ras^V12 to drive tumor progression and invasion. All together, these data indicate that radiofrequency radiation emitted from WiFi devices could exert genotoxic effects in Drosophila and set the stage to further explore the biological effects of WiFi electromagnetic radiation on living organisms.

Effects of mutant lamins on nucleo-cytoskeletal coupling in Drosophila models of LMNA muscular dystrophy

The nuclei of multinucleated skeletal muscles experience substantial external force during development and muscle contraction. Protection from such forces is partly provided by lamins, intermediate filaments that form a scaffold lining the inner nuclear membrane. Lamins play a myriad of roles, including maintenance of nuclear shape and stability, mediation of nuclear mechanoresponses, and nucleo-cytoskeletal coupling. Herein, we investigate how disease-causing mutant lamins alter myonuclear properties in response to mechanical force. This was accomplished via a novel application of a micropipette harpooning assay applied to larval body wall muscles of Drosophila models of lamin-associated muscular dystrophy. The assay enables the measurement of both nuclear deformability and intracellular force transmission between the cytoskeleton and nuclear interior in intact muscle fibers. Our studies revealed that specific mutant lamins increase nuclear deformability while other mutant lamins cause nucleo-cytoskeletal coupling defects, which were associated with loss of microtubular nuclear caging. We found that microtubule caging of the nucleus depended on Msp300, a KASH domain protein that is a component of the linker of nucleoskeleton and cytoskeleton (LINC) complex. Taken together, these findings identified residues in lamins required for connecting the nucleus to the cytoskeleton and suggest that not all muscle disease-causing mutant lamins produce similar defects in subcellular mechanics.

A pathogenic mechanism associated with myopathies and structural birth defects involves TPM2-directed myogenesis

Nemaline myopathy (NM) is the most common congenital myopathy, characterized by extreme weakness of the respiratory, limb, and facial muscles. Pathogenic variants in Tropomyosin 2 (TPM2), which encodes a skeletal muscle-specific actin binding protein essential for sarcomere function, cause a spectrum of musculoskeletal disorders that include NM as well as cap myopathy, congenital fiber type disproportion, and distal arthrogryposis (DA). The in vivo pathomechanisms underlying TPM2-related disorders are unknown, so we expressed a series of dominant, pathogenic TPM2 variants in Drosophila embryos and found 4 variants significantly affected muscle development and muscle function. Transient overexpression of the 4 variants also disrupted the morphogenesis of mouse myotubes in vitro and negatively affected zebrafish muscle development in vivo. We used transient overexpression assays in zebrafish to characterize 2 potentially novel TPM2 variants and 1 recurring variant that we identified in patients with DA (V129A, E139K, A155T, respectively) and found these variants caused musculoskeletal defects similar to those of known pathogenic variants. The consistency of musculoskeletal phenotypes in our assays correlated with the severity of clinical phenotypes observed in our patients with DA, suggesting disrupted myogenesis is a potentially novel pathomechanism of TPM2 disorders and that our myogenic assays can predict the clinical severity of TPM2 variants.

Analyses of locomotion, wing morphology, and microbiome in Drosophila nigrosparsa after recovery from antibiotics

Antibiotics, such as tetracycline, have been frequently used to cure arthropods of Wolbachia endosymbionts. After the symbionts have been removed, the hosts must recover for some generations from the side effects of the antibiotics. However, most studies do not assess the direct and indirect longer‐term effects of antibiotics used to remove Wolbachia, which may question the exact contribution of this endosymbiont to the effects observed. Here, we used the fly Drosophila nigrosparsa treated or not with tetracycline for three generations followed by two generations of recovery to investigate the effects of this antibiotic on the fly locomotion, wing morphology, and the gut microbiome. We found that antibiotic treatment did not affect fly locomotion two generations after being treated with the antibiotic. In addition, gut‐microbiome restoration was tested as a more efficient solution to reduce the potential side effects of tetracycline on the microbiome. There was no significant difference in alpha diversity between gut restoration and other treatments, but the abundance of some bacterial taxa differed significantly between the gut‐restoration treatment and the control. We conclude that in D. nigrosparsa the recovery period of two generations after being treated with the antibiotic is sufficient for locomotion, and suggest a general assessment of direct and indirect effects of antibiotics after a particular recovery time.

Taking flight: an educational primer for use with "A novel mechanism for activation of myosin regulatory light chain by protein kinase C-delta in Drosophila"

Muscles are required for animal movement, feeding, heartbeat, and reproduction. Disruption of muscle function can lead to mobility impairments and diseases like muscular dystrophy and cardiac myopathy; therefore, research in this area has significant implications for public health. Recent work by Vaziri and colleagues has taken genetic, cell biological, and biochemical approaches to identify Protein kinase C-d (Pkcδ) as a novel regulator of the essential myosin light chain 2 (MLC2) by phosphorylation. The authors determine which residues of MLC2 are modified by Pkcδ and show that phosphorylation by Pkcδ is required for proper sarcomere assembly and function. This study underscores the importance of Drosophila melanogaster as a model system for muscle function and highlights how protein phosphorylation is a vital part of post-translational gene regulation.

Polyglutamine-Specific Gold Nanoparticle Complex Alleviates Mutant Huntingtin-Induced Toxicity

Huntington's disease (HD) belongs to protein misfolding disorders associated with polyglutamine (polyQ)-rich mutant huntingtin (mHtt) protein inclusions. Currently, it is indicated that the aggregation of polyQ-rich mHtt participates in neuronal toxicity and dysfunction. Here, we designed and synthesized a polyglutamine-specific gold nanoparticle (AuNP) complex, which specifically targeted mHtt and alleviated its toxicity. The polyglutamine-specific AuNPs were prepared by decorating the surface of AuNPs with an amphiphilic peptide (JLD1) consisting of both polyglutamine-binding sequences and negatively charged sequences. By applying the polyQ aggregation model system, we demonstrated that AuNPs-JLD1 dissociated the fibrillary aggregates from the polyQ peptide and reduced its β-sheet content in a concentration-dependent manner. By further integrating polyethyleneimine (PEI) onto AuNPs-JLD1, we generated a complex (AuNPs-JLD1-PEI). We showed that this complex could penetrate cells, bind to cytosolic mHtt proteins, dissociate mHtt inclusions, reduce mHtt oligomers, and ameliorate mHtt-induced toxicity. AuNPs-JLD1-PEI was also able to be transported to the brain and improved the functional deterioration in the HD Drosophila larva model. Our results revealed the feasibility of combining AuNPs, JLD1s, and cell-penetrating polymers against mHtt protein aggregation and oligomerization, which hinted on the early therapeutic strategies against HD.

Three-Dimensional Tracking of Multiple Small Insects by a Single Camera

Many systems to monitor insect behavior have been developed recently. Yet most of these can only detect two-dimensional behavior for convenient analysis and exclude other activities, such as jumping or flying. Therefore, the development of a three-dimensional (3D) monitoring system is necessary to investigate the 3D behavior of insects. In such a system, multiple-camera setups are often used to accomplish this purpose. Here, a system with a single camera for tracking small insects in a 3D space is proposed, eliminating the synchronization problems that typically occur when multiple cameras are instead used. With this setup, two other images are obtained via mirrors fixed at other viewing angles. Using the proposed algorithms, the tracking accuracy of five individual drain flies, Clogmia albipunctata (Williston) (Diptera: Psychodidae), flitting about in a spherical arena (78 mm in diameter) is as high as 98.7%, whereas the accuracy of 10 individuals is 96.3%. With this proposed method, the 3D trajectory monitoring experiments of insects can be performed more efficiently.

Assembly of higher-order SMN oligomers is essential for metazoan viability and requires an exposed structural motif present in the YG zipper dimer

Protein oligomerization is one mechanism by which homogenous solutions can separate into distinct liquid phases, enabling assembly of membraneless organelles. Survival Motor Neuron (SMN) is the eponymous component of a large macromolecular complex that chaperones biogenesis of eukaryotic ribonucleoproteins and localizes to distinct membraneless organelles in both the nucleus and cytoplasm. SMN forms the oligomeric core of this complex, and missense mutations within its YG box domain are known to cause Spinal Muscular Atrophy (SMA). The SMN YG box utilizes a unique variant of the glycine zipper motif to form dimers, but the mechanism of higher-order oligomerization remains unknown. Here, we use a combination of molecular genetic, phylogenetic, biophysical, biochemical and computational approaches to show that formation of higher-order SMN oligomers depends on a set of YG box residues that are not involved in dimerization. Mutation of key residues within this new structural motif restricts assembly of SMN to dimers and causes locomotor dysfunction and viability defects in animal models.

The Serine Protease Homolog, Scarface, Is Sensitive to Nutrient Availability and Modulates the Development of the Drosophila Blood-Brain Barrier

The adaptable transcriptional response to changes in food availability not only ensures animal survival but also lets embryonic development progress. Interestingly, the CNS is preferentially protected from periods of malnutrition, a phenomenon known as “brain sparing.” However, the mechanisms that mediate this response remain poorly understood. To get a better understanding of this, we used Drosophila melanogaster as a model, analyzing the transcriptional response of neural stem cells (neuroblasts) and glia of the blood–brain barrier (BBB) from larvae of both sexes during nutrient restriction using targeted DamID. We found differentially expressed genes in both neuroblasts and glia of the BBB, although the effect of nutrient deficiency was primarily observed in the BBB. We characterized the function of a nutritional sensitive gene expressed in the BBB, the serine protease homolog, scarface (scaf). Scaf is expressed in subperineurial glia in the BBB in response to nutrition. Tissue-specific knockdown of scaf increases subperineurial glia endoreplication and proliferation of perineurial glia in the blood–brain barrier. Furthermore, neuroblast proliferation is diminished on scaf knockdown in subperineurial glia. Interestingly, reexpression of Scaf in subperineurial glia is able to enhance neuroblast proliferation and brain growth of animals in starvation. Finally, we show that loss of scaf in the blood–brain barrier increases sensitivity to drugs in adulthood, suggesting a physiological impairment. We propose that Scaf integrates the nutrient status to modulate the balance between neurogenesis and growth of the BBB, preserving the proper equilibrium between the size of the barrier and the brain.

SIGNIFICANCE STATEMENT The Drosophila BBB separates the CNS from the open circulatory system. The BBB glia are not only acting as a physical segregation of tissues but participate in the regulation of the metabolism and neurogenesis during development. Here we analyze the transcriptional response of the BBB glia to nutrient deprivation during larval development, a condition in which protective mechanisms are switched on in the brain. Our findings show that the gene scarface reduces growth in the BBB while promoting the proliferation of neural stem, assuring the balanced growth of the larval brain. Thus, Scarface would link animal nutrition with brain development, coordinating neurogenesis with the growth of the BBB.

Ilex kudingcha C.J. Tseng Mitigates Phenotypic Characteristics of Human Autism Spectrum Disorders in a Drosophila Melanogaster Rugose Mutant

Autism spectrum disorders (ASD) have heterogeneous etiologies involving dysfunction of central nervous systems, for which no effective pan-specific treatments are available. Ilex kudingcha (IK) C.J. Tseng is a nootropic botanical used in Asia for neuroprotection and improvement of cognition. This study establishes that a chemically characterized extract from IK (IKE) mitigates behavioral traits in the Drosophila melanogaster rugose mutant, whose traits resemble human ASD, and examines possible mechanisms. IKE treatment significantly ameliorated deficits in social interaction, short-term memory, and locomotor activity in Drosophila rugose, and significantly increased synaptic bouton number of size more than 2 μm² in the neuromuscular junctions (NMJs) of Drosophila rugose. To clarify mechanism(s) of IKE action, methylphenidate (MPH), a dopamine transporter inhibitor, was included as a reference drug in the behavioral assays: MPH significantly improved social interaction and short-term memory deficit in Drosophila rugose; administration of the dopamine D1 receptor antagonist SCH23390 and dopamine D2 receptor antagonist sulpiride reversed the ameliorative effects of both MPH and IKE on the social interaction deficits of Drosophila rugose. To extend analysis of IKE treatment to the vertebrate central nervous system, ASD-associated gene expression in mouse hippocampus was studied by RNA-seq: IKE treatment altered the expression of genes coding phosphoinositide 3-kinases/protein kinase B (PI3K-Akt), proteins in glutamatergic, dopaminergic, serotonergic, and GABAergic synapses, cAMP response element-binding protein (CREB), and RNA transporter proteins. These results provide a foundation for further analysis of IKE as a candidate for treatment of some forms of ASD.

Identification of Rpd3 as a novel epigenetic regulator of Drosophila FIG 4, a Charcot-Marie-Tooth disease-causing gene

Mutations in the factor-induced-gene 4 (FIG 4) gene are associated with multiple disorders, including Charcot-Marie-Tooth disease (CMT), epilepsy with polymicrogyria, Yunis-Varón syndrome and amyotrophic lateral sclerosis. The wide spectrum of disorders associated with FIG 4 may be related to the dysregulated epigenetics. Using Gene Expression Omnibus, we found that HDAC1 binds to the FIG 4 gene locus in the genome of human CD4+ T cells. Rpd3 is a well-known Drosophila homolog of human HDAC1. We previously established Drosophila models targeting Drosophila FIG 4 (dFIG 4) that exhibited defective locomotive ability, abnormal synapse morphology at neuromuscular junctions, enlarged vacuoles in the fat body and aberrant compound eye morphology. Genetic crossing experiments followed by physiological and immunocytochemical analyses revealed that Rpd3 mutations suppressed these defects induced by dFIG 4 knockdown. This demonstrated Rpd3 to be an important epigenetic regulator of dFIG 4, suggesting that the inhibition of HDAC1 represses the pathogenesis of FIG 4-associated disorders, including CMT. Defects in epigenetic regulators, such as HDAC1, may also explain the diverse symptoms of FIG 4-associated disorders.

Ionotropic Receptor-dependent cool cells control the transition of temperature preference in Drosophila larvae

Temperature sensation guides animals to avoid temperature extremes and to seek their optimal temperatures. The larval stage of Drosophila development has a dramatic effect on temperature preference. While early-stage Drosophila larvae pursue a warm temperature, late-stage larvae seek a significantly lower temperature. Previous studies suggest that this transition depends on multiple rhodopsins at the late larval stage. Here, we show that early-stage larvae, in which dorsal organ cool cells (DOCCs) are functionally blocked, exhibit similar cool preference to that of wild type late-stage larvae. The molecular thermoreceptors in DOCCs are formed by three members of the Ionotropic Receptor (IR) family, IR21a, IR93a, and IR25a. Early-stage larvae of each Ir mutant pursue a cool temperature, similar to that of wild type late-stage larvae. At the late larval stage, DOCCs express decreased IR proteins and exhibit reduced cool responses. Importantly, late-stage larvae that overexpress IR21a, IR93a, and IR25a in DOCCs exhibit similar warm preference to that of wild type early-stage larvae. These data suggest that IR21a, IR93a, and IR25a in DOCCs navigate early-stage larvae to avoid cool temperatures and the reduction of these IR proteins in DOCCs results in animals remaining in cool regions during the late larval stage. Together with previous studies, we conclude that multiple temperature-sensing systems are regulated for the transition of temperature preference in fruit fly larvae.

Animals depend on their temperature-sensing systems to avoid noxious temperature extremes and to seek optimal temperatures to survive, mate, and reproduce. Some animals pursue different optimal temperatures during development. We use fruit flies as a model to investigate how temperature-sensing systems are modulated to guide animals to distinct optimal temperatures during development. While early-stage fruit fly larvae pursue a warm temperature, late-stage larvae seek a lower temperature. Previous studies find that this transition depends on multiple rhodopsin molecules. In this study, we find an additional mechanism that also contributes to this transition. At the early larval stage, a set of cool-sensing cells express a high level of cool responsive molecules, respond strongly to low temperatures, and drive animals to avoid cool regions. At the late larval stage, these cool-sensing cells become less sensitive to low temperatures due to the decreased expression of cool responsive molecules and, thus, animals remain in cool regions. Together with previous studies, we conclude that multiple temperature-sensing systems are regulated for the transition of temperature preference in fruit fly larvae.

Analyzing muscle structure and function throughout the larval instars in live Drosophila

Drosophila larval musculature is a genetically and optically accessible system to study muscle development. Each larval muscle is a single fiber with conserved cytoarchitecture, including its sarcomere structure and composition. Here, we present a workflow for systematically analyzing muscle structure and function at discrete larval stages, as well as throughout the larval instars, using both newly developed and adapted methods.

For complete details on the use and execution of this protocol, please refer to Balakrishnan et al. (2020).

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Detailed methods for preparation and analysis of Drosophila larval muscle structure

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Methods for muscle structure and function analysis in the same larva over time

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Steps for analyzing sarcomere size and organization

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Pitfalls and troubleshooting approaches described

Costameric integrin and sarcoglycan protein levels are altered in a Drosophila model for Limb-girdle muscular dystrophy type 2H

Mutations in two different domains of the ubiquitously expressed TRIM32 protein give rise to two clinically separate diseases, one of which is Limb-girdle muscular dystrophy type 2H (LGMD2H). Uncovering the muscle-specific role of TRIM32 in LGMD2H pathogenesis has proven difficult, as neurogenic phenotypes, independent of LGMD2H pathology, are present in TRIM32 KO mice. We previously established a platform to study LGMD2H pathogenesis using Drosophila melanogaster as a model. Here we show that LGMD2H disease-causing mutations in the NHL domain are molecularly and structurally conserved between fly and human TRIM32. Furthermore, transgenic expression of a subset of myopathic alleles (R394H, D487N, and 520fs) induce myofibril abnormalities, altered nuclear morphology, and reduced TRIM32 protein levels, mimicking phenotypes in patients afflicted with LGMD2H. Intriguingly, we also report for the first time that the protein levels of βPS integrin and sarcoglycan δ, both core components of costameres, are elevated in TRIM32 disease-causing alleles. Similarly, murine myoblasts overexpressing a catalytically inactive TRIM32 mutant aberrantly accumulate α- and β-dystroglycan and α-sarcoglycan. We speculate that the stoichiometric loss of costamere components disrupts costamere complexes to promote muscle degeneration.

Assessing the influence of curcumin in sex-specific oxidative stress, survival and behavior in Drosophila melanogaster

Oxidative stress, which occurs from an imbalance of reactive oxygen and nitrogen species (RONS) and both endogenous and exogenous antioxidants, promotes aging and underlies sex-specific differences in longevity and susceptibility to age-related neurodegeneration. Recent evidence suggests that curcumin, a yellow pigment derived from turmeric and shown to exhibit antioxidant properties as a RONS scavenger, influences the regulation of genetic elements in endogenous antioxidant pathways. To investigate the role of curcumin in sex-specific in vivo responses to oxidative stress, Drosophila were reared on media supplemented with 0.25, 2.5 or 25 mmol l-1 curcuminoids (consisting of curcumin, demethoxycurcumin and bisdemethoxycurcumin) and resistance to oxidative stress and neural parameters were assessed. High levels of curcuminoids exhibited two sex-specific effects: protection from hydrogen peroxide as an oxidative stressor and alterations in turning rate in an open field. Taken together, these results suggest that the influence of curcuminoids as antioxidants probably relies on changes in gene expression and that sexual dimorphism exists in the in vivo response to curcuminoids.

Modeling Mucopolysaccharidosis Type II in the Fruit Fly by Using the RNA Interference Approach

Mucopolysaccharidosis type II (MPS II) is a lysosomal storage disorder that occurs due to the deficit of the lysosomal enzyme iduronate 2-sulfatase (IDS) that leads to the storage of the glycosaminoglycan heparan- and dermatan-sulfate in all organs and tissues. It is characterized by important clinical features and the severe form presents with a heavy neurological involvement. However, almost nothing is known about the neuropathogenesis of MPS II. To address this issue, we developed a ubiquitous, neuronal, and glial-specific knockdown model in Drosophila melanogaster by using the RNA interference (RNAi) approach. Knockdown of the Ids/CG12014 gene resulted in a significant reduction of the Ids gene expression and enzymatic activity. However, glycosaminoglycan storage, survival, molecular markers (Atg8a, Lamp1, Rab11), and locomotion behavior were not affected. Even strongly reduced, IDS-activity was enough to prevent a pathological phenotype in a MPS II RNAi fruit fly. Thus, a Drosophila MPS II model requires complete abolishment of the enzymatic activity.

A novel Drosophila model for neurodevelopmental disorders associated with Shwachman-Diamond syndrome

Genetic defects in ribosome biogenesis result in a group of diseases called ribosomopathies. Patients with ribosomopathies manifest multiorgan phenotypes, including neurological impairments. A well-characterized ribosomopathy, Shwachman-Diamond syndrome (SDS), is mainly associated with loss-of-function mutations in the causal gene SBDS. Children with SDS have neurodevelopmental disorders; however, the neurological consequences of SBDS dysfunction remain poorly defined. In the present study, we investigated the phenotype of Drosophila melanogaster following knockdown of CG8549, the Drosophila ortholog of human SBDS, to provide evidence for the neurological consequences of reduction in physiological SBDS functions. The pan-neuron-specific knockdown of CG8549 was associated with locomotive disabilities, mechanically induced seizures, hyperactivity, learning impairments, and anatomical defects in presynaptic terminals. These results provide the first evidence of a direct link between a reduction in physiological SBDS function and neurological impairments.

Honeybee products and edible insect powders improve locomotive and learning abilities of Ubiquilin-knockdown Drosophila

BACKGROUND

Mutations in the human Ubiquilin 2 gene are associated with neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) with or without frontotemporal dementia (FTD), the fatal neurodegenerative disease that progressively affected neuronal cells in both brain and spinal cord. There is currently no effective therapy for these diseases. Over the last decade, researchers have focused on the potential use of natural products especially in neurodegenerative studies. Insect products have been used as traditional medicines, however, scientific information is still lacking. Fruit fly is recently used as a model organism to investigate degenerative diseases related to the nervous system because it has a short life span and produces a large number of offspring.

METHODS

The present study investigated the effects of honeybee products and edible insect powders on the locomotive and learning abilities, neuromuscular junctions (NMJs) structure, and reactive oxygen species (ROS) in larval brains of Ubiquilin- knockdown Drosophila.

RESULTS

dUbqn knockdown flies showed defects in locomotive and learning abilities accompanied with structural defects in NMJs. The results obtained revealed that the recovery of locomotive defects was significantly greater in dUbqn knockdown flies fed with coffee honey from Apis cerana (1% v/v) or Apis dorsata melittin (0.5 μg/ml) or wasp powder (2 mg/ml) than that of in untreated dUbqn knockdown flies. Furthermore, dUbqn knockdown flies fed with coffee honey showed the partial rescue of structural defects in NMJs, improved learning ability, and reduced the accumulation of ROS caused by dUbqn depletion in the brain over the untreated group.

CONCLUSION

These results suggest that coffee honey from Apis cerana contains a neuroprotective agent that will contribute to the development of a novel treatment for ALS/FTD.

Loss of the Drosophila branched-chain α-ketoacid dehydrogenase complex results in neuronal dysfunction

Maple syrup urine disease (MSUD) is an inherited error in the metabolism of branched-chain amino acids (BCAAs) caused by a severe deficiency of the branched-chain α-ketoacid dehydrogenase (BCKDH) complex, which ultimately leads to neurological disorders. The limited therapies, including protein-restricted diets and liver transplants, are not as effective as they could be for the treatment of MSUD due to the current lack of molecular insights into the disease pathogenesis. To address this issue, we developed a Drosophila model of MSUD by knocking out the dDBT gene, an ortholog of the human gene encoding the dihydrolipoamide branched chain transacylase (DBT) subunit of BCKDH. The homozygous dDBT mutant larvae recapitulate an array of MSUD phenotypes, including aberrant BCAA accumulation, developmental defects, poor mobile behavior and disrupted L-glutamate homeostasis. Moreover, the dDBT mutation causes neuronal apoptosis during the developmental progression of larval brains. The genetic and functional evidence generated by in vivo depletion of dDBT expression in the eye indicates severe impairment of retinal rhabdomeres. Further, the dDBT mutant shows elevated oxidative stress and higher lipid peroxidation accumulation in the larval brain. Therefore, we conclude from in vivo evidence that the loss of dDBT results in oxidative brain damage that may lead to neuronal cell death and contribute to aspects of MSUD pathology. Importantly, when the dDBT mutants were administrated with Metformin, the aberrances in BCAA levels and motor behavior were ameliorated. This intriguing outcome strongly merits the use of the dDBT mutant as a platform for developing MSUD therapies.This article has an associated First Person interview with the joint first authors of the paper.

Novel Drosophila model for parkinsonism by targeting phosphoglycerate kinase

Patients with Parkinson's disease (PD) show a common progressive neurodegenerative movement disorder characterized by rigidity, tremors, postural instability, and bradykinesia due to the loss of dopaminergic neurons in the substantia nigra, and is often accompanied by several non-motor symptoms, called parkinsonism. Several lines of recent evidence support the hypothesis that mutations in the gene encoding phosphoglycerate kinase (PGK) play an important role in the PD mechanism. PGK is a key enzyme in the glycolytic pathway that catalyzes the reaction from 1,3-diphosphoglycerate to 3-phosphoglycerate. We herein established a parkinsonism model targeting Drosophila Pgk. Dopaminergic (DA) neuron-specific Pgk knockdown lead to locomotive defects in both young and aged adult flies and was accompanied by progressive DA neuron loss with aging. Pgk knockdown in DA neurons decreased dopamine levels in the central nervous system (CNS) of both young and aged adult flies. These phenotypes are similar to the defects observed in human PD patients, suggesting that the Pgk knockdown flies established herein are a promising model for parkinsonism. Furthermore, pan-neuron-specific Pgk knockdown induced low ATP levels and the accumulation of reactive oxygen species (ROS) in the CNS of third instar larvae. Collectively, these results indicate that a failure in the energy production system of Pgk knockdown flies causes locomotive defects accompanied by neuronal dysfunction and degeneration in DA neurons.

Temperature-sensitive spinal muscular atrophy-causing point mutations lead to SMN instability, locomotor defects and premature lethality in Drosophila

Spinal muscular atrophy (SMA) is the leading genetic cause of death in young children, arising from homozygous deletion or mutation of the survival motor neuron 1 (SMN1) gene. SMN protein expressed from a paralogous gene, SMN2, is the primary genetic modifier of SMA; small changes in overall SMN levels cause dramatic changes in disease severity. Thus, deeper insight into mechanisms that regulate SMN protein stability should lead to better therapeutic outcomes. Here, we show that SMA patient-derived missense mutations in the Drosophila SMN Tudor domain exhibit a pronounced temperature sensitivity that affects organismal viability, larval locomotor function and adult longevity. These disease-related phenotypes are domain specific and result from decreased SMN stability at elevated temperature. This system was utilized to manipulate SMN levels during various stages of Drosophila development. Owing to a large maternal contribution of mRNA and protein, Smn is not expressed zygotically during embryogenesis. Interestingly, we find that only baseline levels of SMN are required during larval stages, whereas high levels of the protein are required during pupation. This previously uncharacterized period of elevated SMN expression, during which the majority of adult tissues are formed and differentiated, could be an important and translationally relevant developmental stage in which to study SMN function. Taken together, these findings illustrate a novel in vivo role for the SMN Tudor domain in maintaining SMN homeostasis and highlight the necessity for high SMN levels at crucial developmental time points that are conserved from Drosophila to humans.

Wolbachia affect behavior and possibly reproductive compatibility but not thermoresistance, fecundity, and morphology in a novel transinfected host, Drosophila nigrosparsa

Wolbachia, intracellular endosymbionts, are estimated to infect about half of all arthropod species. These bacteria manipulate their hosts in various ways for their maximum benefits. The rising global temperature may accelerate species migration, and thus, horizontal transfer of Wolbachia may occur across species previously not in contact. We transinfected and then cured the alpine fly Drosophila nigrosparsa with Wolbachia strain wMel to study its effects on this species. We found low Wolbachia titer, possibly cytoplasmic incompatibility, and an increase in locomotion of both infected larvae and adults compared with cured ones. However, no change in fecundity, no impact on heat and cold tolerance, and no change in wing morphology were observed. Although Wolbachia increased locomotor activities in this species, we conclude that D. nigrosparsa may not benefit from the infection. Still, D. nigrosparsa can serve as a host for Wolbachia because vertical transmission is possible but may not be as high as in the native host of wMel, Drosophila melanogaster.

Cellular secretion and cytotoxicity of transthyretin mutant proteins underlie late-onset amyloidosis and neurodegeneration

Transthyretin amyloidosis (ATTR) is a progressive life-threatening disease characterized by the deposition of transthyretin (TTR) amyloid fibrils. Several pathogenic variants have been shown to destabilize TTR tetramers, leading to aggregation of misfolded TTR fibrils. However, factors that underlie the differential age of disease onset amongst amyloidogenic TTR variants remain elusive. Here, we examined the biological properties of various TTR mutations and found that the cellular secretory pattern of the wild-type (WT) TTR was similar to those of the late-onset mutant (Ala97Ser, p. Ala117Ser), stable mutant (Thr119Met, p. Thr139Met), early-onset mutant (Val30Met, p. Val50Met), but not in the unstable mutant (Asp18Gly, p. Asp38Gly). Cytotoxicity assays revealed their toxicities in the order of Val30Met > Ala97Ser > WT > Thr119Met in neuroblastoma cells. Surprisingly, while early-onset amyloidogenic TTR monomers (M-TTRs) are retained by the endoplasmic reticulum quality control (ERQC), late-onset amyloidogenic M-TTRs can be secreted extracellularly. Treatment of thapsigargin (Tg) to activate the unfolded protein response (UPR) alleviates Ala97Ser M-TTR secretion. Interestingly, Ala97Ser TTR overexpression in Drosophila causes late-onset fast neurodegeneration and a relatively short lifespan, recapitulating human disease progression. Our study demonstrates that the escape of TTR monomers from the ERQC may underlie late-onset amyloidogenesis in patients and suggests that targeting ERQC could mitigate late-onset ATTR.

Drosophila NUAK functions with Starvin/BAG3 in autophagic protein turnover

The inability to remove protein aggregates in post-mitotic cells such as muscles or neurons is a cellular hallmark of aging cells and is a key factor in the initiation and progression of protein misfolding diseases. While protein aggregate disorders share common features, the molecular level events that culminate in abnormal protein accumulation cannot be explained by a single mechanism. Here we show that loss of the serine/threonine kinase NUAK causes cellular degeneration resulting from the incomplete clearance of protein aggregates in Drosophila larval muscles. In NUAK mutant muscles, regions that lack the myofibrillar proteins F-actin and Myosin heavy chain (MHC) instead contain damaged organelles and the accumulation of select proteins, including Filamin (Fil) and CryAB. NUAK biochemically and genetically interacts with Drosophila Starvin (Stv), the ortholog of mammalian Bcl-2-associated athanogene 3 (BAG3). Consistent with a known role for the co-chaperone BAG3 and the Heat shock cognate 71 kDa (HSC70)/HSPA8 ATPase in the autophagic clearance of proteins, RNA interference (RNAi) of Drosophila Stv, Hsc70-4, or autophagy-related 8a (Atg8a) all exhibit muscle degeneration and muscle contraction defects that phenocopy NUAK mutants. We further demonstrate that Fil is a target of NUAK kinase activity and abnormally accumulates upon loss of the BAG3-Hsc70-4 complex. In addition, Ubiquitin (Ub), ref(2)p/p62, and Atg8a are increased in regions of protein aggregation, consistent with a block in autophagy upon loss of NUAK. Collectively, our results establish a novel role for NUAK with the Stv-Hsc70-4 complex in the autophagic clearance of proteins that may eventually lead to treatment options for protein aggregate diseases.

Drosophila TRIM32 cooperates with glycolytic enzymes to promote cell growth

Cell growth and/or proliferation may require the reprogramming of metabolic pathways, whereby a switch from oxidative to glycolytic metabolism diverts glycolytic intermediates towards anabolic pathways. Herein, we identify a novel role for TRIM32 in the maintenance of glycolytic flux mediated by biochemical interactions with the glycolytic enzymes Aldolase and Phosphoglycerate mutase. Loss of Drosophila TRIM32, encoded by thin (tn), shows reduced levels of glycolytic intermediates and amino acids. This altered metabolic profile correlates with a reduction in the size of glycolytic larval muscle and brain tissue. Consistent with a role for metabolic intermediates in glycolysis-driven biomass production, dietary amino acid supplementation in tn mutants improves muscle mass. Remarkably, TRIM32 is also required for ectopic growth - loss of TRIM32 in a wing disc-associated tumor model reduces glycolytic metabolism and restricts growth. Overall, our results reveal a novel role for TRIM32 for controlling glycolysis in the context of both normal development and tumor growth.

Unc-4 acts to promote neuronal identity and development of the take-off circuit in the Drosophila CNS

The Drosophila ventral nerve cord (VNC) is composed of thousands of neurons born from a set of individually identifiable stem cells. The VNC harbors neuronal circuits required to execute key behaviors, such as flying and walking. Leveraging the lineage-based functional organization of the VNC, we investigated the developmental and molecular basis of behavior by focusing on lineage-specific functions of the homeodomain transcription factor, Unc-4. We found that Unc-4 functions in lineage 11A to promote cholinergic neurotransmitter identity and suppress the GABA fate. In lineage 7B, Unc-4 promotes proper neuronal projections to the leg neuropil and a specific flight-related take-off behavior. We also uncovered that Unc-4 acts peripherally to promote proprioceptive sensory organ development and the execution of specific leg-related behaviors. Through time-dependent conditional knock-out of Unc-4, we found that its function is required during development, but not in the adult, to regulate the above events.

Comprehensive Modeling of Spinal Muscular Atrophy in Drosophila melanogaster

Spinal muscular atrophy (SMA) is a neurodegenerative disorder that affects motor neurons, primarily in young children. SMA is caused by mutations in the Survival Motor Neuron 1 (SMN1) gene. SMN functions in the assembly of spliceosomal RNPs and is well conserved in many model systems including mouse, zebrafish, fruit fly, nematode, and fission yeast. Work in Drosophila has focused on the loss of SMN function during larval stages, primarily using null alleles or strong hypomorphs. A systematic analysis of SMA-related phenotypes in the context of moderate alleles that more closely mimic the genetics of SMA has not been performed in the fly, leading to debate over the validity and translational value of this model. We, therefore, examined 14 Drosophila lines expressing SMA patient-derived missense mutations in Smn, with a focus on neuromuscular phenotypes in the adult stage. Animals were evaluated on the basis of organismal viability and longevity, locomotor function, neuromuscular junction structure, and muscle health. In all cases, we observed phenotypes similar to those of SMA patients, including progressive loss of adult motor function. The severity of these defects is variable and forms a broad spectrum across the 14 lines examined, recapitulating the full range of phenotypic severity observed in human SMA. This includes late-onset models of SMA, which have been difficult to produce in other model systems. The results provide direct evidence that SMA-related locomotor decline can be reproduced in the fly and support the use of patient-derived SMN missense mutations as a comprehensive system for modeling SMA.

A tissue communication network coordinating innate immune response during muscle stress

Complex tissue communication networks function throughout an organism's lifespan to maintain tissue homeostasis. Using the genetic model Drosophila melanogaster, we have defined a network of immune responses that are activated following the induction of muscle stresses, including hypercontraction, detachment and oxidative stress. Of these stressors, loss of the genes that cause muscle detachment produced the strongest levels of JAK-STAT activation. In one of these mutants, fondue (fon), we also observe hemocyte recruitment and the accumulation of melanin at muscle attachment sites (MASs), indicating a broad involvement of innate immune responses upon muscle detachment. Loss of fon results in pathogen-independent Toll signaling in the fat body and increased expression of the Toll-dependent antimicrobial peptide Drosomycin. Interestingly, genetic interactions between fon and various Toll pathway components enhance muscle detachment. Finally, we show that JAK-STAT and Toll signaling are capable of reciprocal activation in larval tissues. We propose a model of tissue communication for the integration of immune responses at the local and systemic level in response to altered muscle physiology.

Thin is required for cell death in the Drosophila abdominal muscles by targeting DIAP1

In holometabolous insects, developmentally controlled programmed cell death (PCD) is a conserved process that destroys a subset of larval tissues for the eventual creation of new adult structures. This process of histolysis is relatively well studied in salivary gland and midgut tissues, while knowledge concerning larval muscle destruction is limited. Here, we have examined the histolysis of a group of Drosophila larval abdominal muscles called the dorsal external oblique muscles (DEOMs). Previous studies have defined apoptosis as the primary mediator of DEOM breakdown, whose timing is controlled by ecdysone signaling. However, very little is known about other factors that contribute to DEOM destruction. In this paper, we examine the role of thin (tn), which encodes for the Drosophila homolog of mammalian TRIM32, in the regulation of DEOM histolysis. We find that loss of Tn blocks DEOM degradation independent of ecdysone signaling. Instead, tn genetically functions in a pathway with the death-associated inhibitor of apoptosis (DIAP1), Dronc, and death-associated APAF1-related killer (Dark) to regulate apoptosis. Importantly, blocking Tn results in the absence of active Caspase-3 immunostaining, upregulation of DIAP1 protein levels, and inhibition of Dronc activation. DIAP1 and Dronc mRNA levels are not altered in tn mutants, showing that Tn acts post-transcriptionally on DIAP1 to regulate apoptosis. Herein, we also find that the RING domain of Tn is required for DEOM histolysis as loss of this domain results in higher DIAP1 levels. Together, our results suggest that the direct control of DIAP1 levels, likely through the E3 ubiquitin ligase activity of Tn, provides a mechanism to regulate caspase activity and to facilitate muscle cell death.

Comparison of the behavioural effects of pharmaceuticals and pesticides on Diamesa zernyi larvae (Chironomidae)

Several studies have indicated the presence of contaminants in Alpine aquatic ecosystems. Even if measured concentrations are far below those that cause acute effects, continuous exposure to sub-lethal concentrations may have detrimental effects on the aquatic species present in these remote environments. This may lead to a cascade of indirect effects at higher levels of the ecological hierarchy (i.e., the community). To improve the determination of ecologically relevant risk endpoints, behavioural alterations in organisms due to pollutants are increasingly studied in ecotoxicology. In fact, behaviour links physiological function with ecological processes, and can be very sensitive to environmental stimuli and chemical exposure. This is the first study on behavioural alteration in a wild population of an Alpine species. In the present study, a video tracking system was standardized and subsequently used to identify contaminant-induced behavioural alterations in Diamesa zernyi larvae (Diptera, Chironomidae). Diamesa zernyi larvae, collected in an Italian Alpine stream (Rio Presena, Trentino Region), were acclimated for 24 h and successively exposed to several aquatic contaminants (pesticides: chlorpyrifos, metolachlor, boscalid, captan; pharmaceuticals: ibuprofen, furosemide, trimethoprim) at concentrations corresponding to their Lowest Observed Effect Concentration (LOEC). After 24, 48, 72, and 96 h of exposure, changes in the distance moved, the average speed, and the frequency of body bends were taken to reflect contaminant- and time-dependent effects on larval behaviour. In general, metolachlor, captan, and trimethoprim tended to reduce all the endpoints under consideration, whereas chlorpyrifos, boscalid, ibuprofen, and furosemide seemed to increase the distances moved by the larvae. This could be related to the different mechanisms of action of the investigated chemicals. Independently of the contaminant, after 72 h a general slowing down of all the behavioural activities occurred. Finally, we propose a behavioural stress indicator to compare the overall behavioural effects induced by the various contaminants.

A new Drosophila model of Ubiquilin knockdown shows the effect of impaired proteostasis on locomotive and learning abilities

Ubiquilin (UBQLN) plays a crucial role in cellular proteostasis through its involvement in the ubiquitin proteasome system and autophagy. Mutations in the UBQLN2 gene have been implicated in amyotrophic lateral sclerosis (ALS) and ALS with frontotemporal lobar dementia (ALS/FTLD). Previous studies reported a key role for UBQLN in Alzheimer's disease (AD); however, the mechanistic involvement of UBQLN in other neurodegenerative diseases remains unclear. The genome of Drosophila contains a single UBQLN homolog (dUbqn) that shows high similarity to UBQLN1 and UBQLN2; therefore, the fly is a useful model for characterizing the role of UBQLN in vivo in neurological disorders affecting locomotion and learning abilities. We herein performed a phenotypic and molecular characterization of diverse dUbqn RNAi lines. We found that the depletion of dUbqn induced the accumulation of polyubiquitinated proteins and caused morphological defects in various tissues. Our results showed that structural defects in larval neuromuscular junctions, abdominal neuromeres, and mushroom bodies correlated with limited abilities in locomotion, learning, and memory. These results contribute to our understanding of the impact of impaired proteostasis in neurodegenerative diseases and provide a useful Drosophila model for the development of promising therapies for ALS and FTLD.