Role of the BCL11A/B homologue Chronophage (Cph) in locomotor behaviour of Drosophila melanogaster

Functioning of the nervous system requires proper formation and specification of neurons as well as accurate connectivity and signalling between them. Locomotor behaviour depends upon these events that occur during neural development, and any aberration in them could result in motor disorders. Transcription factors are believed to be master regulators that control these processes, but very few linked to behaviour have been identified so far. The Drosophila homologue of BCL11A (CTIP1) and BCL11B (CTIP2), Chronophage (Cph), was recently shown to be involved in temporal patterning of neural stem cells but its role in post-mitotic neurons is not known. We show that knockdown of Cph in neurons during development results in animals with locomotor defects at both larval and adult stages. The defects are more severe in adults, with inability to stand, uncoordinated behaviour and complete loss of ability to walk, climb, or fly. These defects are similar to the motor difficulties observed in some patients with mutations in BCL11A and BCL11B. Electrophysiological recordings showed reduced evoked activity and irregular neuronal firing. All Cph-expressing neurons in the ventral nerve cord are glutamatergic. Our results imply that Cph modulates primary locomotor activity through configuration of glutamatergic neurons. Thus, this study ascribes a hitherto unknown role to Cph in locomotor behaviour of Drosophila melanogaster.

Genome sequencing and assembly of Indian golden silkmoth, Antheraea assamensis Helfer (Saturniidae, Lepidoptera)

Muga silkworm (Antheraea assamensis), one of the economically important wild silkmoths, is unique among saturniid silkmoths. It is confined to the North-eastern part of India. Muga silk has the highest value among the other silks. Unlike other silkmoths, A. assamensis has a low chromosome number (n = 15), and ZZ/ZO sex chromosome system. Here, we report the first high-quality draft genome of A. assamensis, assembled by employing the Illumina and PacBio sequencing platforms. The assembled genome of A. assamensis is 501.18 Mb long, with 2697 scaffolds and an N50 of 683.23 Kb. The genome encompasses 18,385 protein-coding genes, 86.29% of which were functionally annotated. Phylogenetic analysis of A. assamensis revealed its divergence from other Antheraea species approximately 28.7 million years ago. Moreover, an investigation into detoxification-related gene families, CYP450, GST, and ABC-transporter, revealed a significant expansion in A. assamensis as compared to the Bombyx mori. This expansion is comparable to Spodoptera litura, suggesting adaptive responses linked to the polyphagous behavior observed in these insects. This study provides valuable insights into the molecular basis of evolutionary divergence and adaptations in muga silkmoth. The genome assembly reported in this study will significantly help in the functional genomics studies on A. assamensis and other Antheraea species along with comparative genomics analyses of Bombycoidea insects.

Antibiotic alters host's gut microbiota, fertility, and antimicrobial peptide gene expression vis-à-vis ampicillin treatment on model organism Drosophila melanogaster

Antibiotics are commonly used to treat infectious diseases; however, persistence is often expressed by the pathogenic bacteria and their long-term relative effect on the host have been neglected. The present study investigated the impact of antibiotics in gut microbiota (GM) and metabolism of host. The effect of ampicillin antibiotics on GM of Drosophila melanogaster was analyzed through deep sequencing of 16S rRNA amplicon gene. The dominant phyla consisted of Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, Planctomycetes, Chloroflexi, Euryarchaeota, Acedobacteria, Verrucomicrobia, and Cyanobacteria. It was found that the composition of GM was significantly altered on administration of antibiotics. On antibiotic treatments, there were decline in relative abundance of Proteobacteria and Firmicutes, while there were increase in relative abundance of Chlorophyta and Bacteroidota. High abundance of 14 genera, viz., Wolbachia, Lactobacillus, Bacillus, Pseudomonas, Thiolamprovum, Pseudoalteromonas, Vibrio, Romboutsia, Staphylococcus, Alteromonas, Clostridium, Lysinibacillus, Litoricola, and Cellulophaga were significant (p ≤ 0.05) upon antibiotic treatment. Particularly, the abundance of Acetobacter was significantly (p ≤ 0.05) declined but increased for Wolbachia. Further, a significant (p ≤ 0.05) increase in Wolbachia endosymbiont of D. melanogaster, Wolbachia endosymbiont of Curculio okumai, and Wolbachia pipientis and a decrease in the Acinetobacter sp. were observed. We observed an increase in functional capacity for biosynthesis of certain nucleotides and the enzyme activities. Further, the decrease in antimicrobial peptide production in the treated group and potential effects on the host's defense mechanisms were observed. This study helps shed light on an often-overlooked dimension, namely the persistence of antibiotics' effects on the host.

The association of cysteine to thiomersal attenuates its apoptosis-mediated cytotoxicity in zebrafish

Thiomersal (TM) is an excellent preservative that is used in a wide variety of products, like pharmaceuticals, cosmetics, and vaccines, etc. Its usage has been in decline because of safety concerns. Since vaccine production is on the rise, its use may increase further in low-income and developing countries, as a cost-effective vaccine preservative. Further, Thiomersal is still being used as an essential component in various pharmaceutical preparations. In this light, the present study addresses its mechanism of toxicity in zebrafish and unveils a novel strategy for lessening its negative effects by conjugating cysteine to it, while retaining its antibacterial efficacy. We show that the mitochondrial membrane potential is destabilised by TM, leading to the induction of apoptosis. Interestingly, TM-cysteine conjugate (at a ratio of 1:1) showed no toxicity in zebrafish, whereas TM alone was highly toxic. Importantly, assaying for the bactericidal activity, tested using Escherichia coli (E. coli) and Methicillin-resistant Staphylococcus aureus (MRSA), revealed that the conjugate retains the antibacterial activity, demonstrating that the TM-cysteine conjugate is a safer alternative to TM as a vaccine preservative, and in all the other products that still use TM.

To RNA-binding and beyond: Emerging facets of the role of Rbfox proteins in development and disease

The RNA-binding Fox-1 homologue (Rbfox) proteins represent an ancient family of splicing factors, conserved through evolution. All members share an RNA recognition motif (RRM), and a particular affinity for the GCAUG signature in target RNA molecules. The role of Rbfox, as a splice factor, deciding the tissue-specific inclusion/exclusion of an exon, depending on its binding position on the flanking introns, is well known. Rbfox often acts in concert with other splicing factors, and forms splicing regulatory networks. Apart from this canonical role, recent studies show that Rbfox can also function as a transcription co-factor, and affects mRNA stability and translation. The repertoire of Rbfox targets is vast, including genes involved in the development of tissue lineages, such as neurogenesis, myogenesis, and erythropoeiesis, and molecular processes, including cytoskeletal dynamics, and calcium handling. A second layer of complexity is added by the fact that Rbfox expression itself is regulated by multiple mechanisms, and, in vertebrates, exhibits tissue-specific expression. The optimum dosage of Rbfox is critical, and its misexpression is etiological to various disease conditions. In this review, we discuss the contextual roles played by Rbfox as a tissue-specific regulator for the expression of many important genes with diverse functions, through the lens of the emerging data which highlights its involvement in many human diseases. Furthermore, we explore the mechanistic details provided by studies in model organisms, with emphasis on the work with Drosophila. This article is categorized under: RNA Processing > Splicing Mechanisms RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA Turnover and Surveillance > Regulation of RNA Stability RNA Processing > Splicing Regulation/Alternative Splicing.

Is the fundamental pathology in Duchenne's muscular dystrophy caused by a failure of glycogenolysis-glycolysis in costameres?

Duchenne muscular dystrophy (DMD) is the most common form of progressive childhood muscular dystrophy associated with weakness of limbs, loss of ambulation, heart weakness and early death. The mutations causing either loss-of-expression or function of the full-length protein dystrophin (Dp427) from the DMD gene are responsible for the disease pathology. Dp427 forms a part of the large dystroglycan complex, called DAPC, in the sarcolemma, and its absence derails muscle contraction. Muscle biopsies from DMD patients show an overactivation of excitation-contraction-coupling (ECC) activable calcium incursion, sarcolemmal ROS production, NHE1 activation, IL6 secretion, etc. The signalling pathways, like Akt/PBK, STAT3, p38MAPK, and ERK1/2, are also hyperactive in DMD. These pathways are responsible for post-mitotic trophic growth and metabolic adaptation, in response to exercise in healthy muscles, but cause atrophy and cell death in dystrophic muscles. We hypothesize that the metabolic background of repressed glycolysis in DMD, as opposed to excess glycolysis seen in cancers or healthy contracting muscles, changes the outcome of these 'growth pathways'. The reduced glycolysis has been considered a secondary outcome of the cytoskeletal disruptions seen in DMD. Given the cytoskeleton-crosslinking ability of the glycolytic enzymes, we hypothesize that the failure of glycogenolytic and glycolytic enzymes to congregate is the primary pathology, which then affects the subsarcolemmal cytoskeletal organization in costameres and initiates the pathophysiology associated with DMD, giving rise to the tissue-specific differences in disease progression between muscle, heart and brain. The lacunae in the regulation of the key components of the hypothesized metabolome, and the limitations of this theory are deliberated. The considerations for developing future therapies based on known pathological processes are also discussed.

Comparative in-silico analysis of microbial dysbiosis discern potential metabolic link in neurodegenerative diseases

A healthy gut flora contains a diverse and stable commensal group of microorganisms, whereas, in disease conditions, there is a shift toward pathogenic microbes, termed microbial dysbiosis. Many studies associate microbial dysbiosis with neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Multiple sclerosis (MS), and Amyotrophic lateral sclerosis (ALS). Although, an overall comparative analysis of microbes and their metabolic involvement in these diseases is still lacking. In this study, we have performed a comparative analysis of microbial composition changes occurring in these four diseases. Our research showed a high resemblance of microbial dysbiosis signatures between AD, PD, and MS. However, ALS appeared dissimilar. The most common population of microbes to show an increase belonged to the phyla, Bacteroidetes, Actinobacteria, Proteobacteria, and Firmicutes. Although, Bacteroidetes and Firmicutes were the only phyla that showed a decrease in their population. The functional analysis of these dysbiotic microbes showed several potential metabolic links which can be involved in the altered microbiome-gut-brain axis in neurodegenerative diseases. For instance, the microbes with elevated populations lack pathways for synthesizing SCFA acetate and butyrate. Also, these microbes have a high capacity for producing L-glutamate, an excitatory neurotransmitter and precursor of GABA. Contrastingly, Tryptophan and histamine have a lower representation in the annotated genome of elevated microbes. Finally, the neuroprotective compound spermidine was less represented in elevated microbes' genomes. Our study provides a comprehensive catalog of potential dysbiotic microbes and their metabolic involvement in neurodegenerative disorders, including AD, PD, MS, and ALS.

Spatial and temporal requirement of Mlp60A isoforms during muscle development and function in Drosophila melanogaster

Many myofibrillar proteins undergo isoform switching in a spatio-temporal manner during muscle development. The biological significance of the variants of several of these myofibrillar proteins remains elusive. One such myofibrillar protein, the Muscle LIM Protein (MLP), is a vital component of the Z-discs. In this paper, we show that one of the Drosophila MLP encoding genes, Mlp60A, gives rise to two isoforms: a short (279 bp, 10 kDa) and a long (1461 bp, 54 kDa) one. The short isoform is expressed throughout development, but the long isoform is adult-specific, being the dominant of the two isoforms in the indirect flight muscles (IFMs). A concomitant, muscle-specific knockdown of both isoforms leads to partial developmental lethality, with most of the surviving flies being flight defective. A global loss of both isoforms in a Mlp60A-null background also leads to developmental lethality, with muscle defects in the individuals that survive to the third instar larval stage. This lethality could be rescued partially by a muscle-specific overexpression of the short isoform. Genetic perturbation of only the long isoform, through a P-element insertion in the long isoform-specific coding sequence, leads to defective flight, in around 90% of the flies. This phenotype was completely rescued when the P-element insertion was precisely excised from the locus. Hence, our data show that the two Mlp60A isoforms are functionally specialized: the short isoform being essential for normal embryonic muscle development and the long isoform being necessary for normal adult flight muscle function.

Epilepsy Characteristics in Neurodevelopmental Disorders: Research from Patient Cohorts and Animal Models Focusing on Autism Spectrum Disorder

Epilepsy, a heterogeneous group of brain-related diseases, has continued to significantly burden society and families. Epilepsy comorbid with neurodevelopmental disorders (NDDs) is believed to occur due to multifaceted pathophysiological mechanisms involving disruptions in the excitation and inhibition (E/I) balance impeding widespread functional neuronal circuitry. Although the field has received much attention from the scientific community recently, the research has not yet translated into actionable therapeutics to completely cure epilepsy, particularly those comorbid with NDDs. In this review, we sought to elucidate the basic causes underlying epilepsy as well as those contributing to the association of epilepsy with NDDs. Comprehensive emphasis is put on some key neurodevelopmental genes implicated in epilepsy, such as MeCP2, SYNGAP1, FMR1, SHANK1-3 and TSC1, along with a few others, and the main electrophysiological and behavioral deficits are highlighted. For these genes, the progress made in developing appropriate and valid rodent models to accelerate basic research is also detailed. Further, we discuss the recent development in the therapeutic management of epilepsy and provide a briefing on the challenges and caveats in identifying and testing species-specific epilepsy models.

Evaluation of cytogenotoxic potential and embryotoxicity of KRS-Cauvery River water in zebrafish (Danio rerio)

In the Cauvery River (CR), indiscriminate discharge of waste causes unexplained skeletal deformity in some fish species present in the water. To investigate this phenomenon, we analyzed the biological, physical, and chemical parameters present in the water and then evaluated the toxicity effects on the zebrafish (Danio rerio) model. The zebrafish were treated with KRS-CR water samples collected from three stations (fast-flowing water [X], slow-flowing [Y], and stagnant [Z] water), before and after filtration. Firstly, we detected microscopic organisms (MO) such as Cyclops, Daphnia, Spirogyra, Spirochaeta, and total coliform (Escherichia coli), which are bioindicators of water pollution present in the samples. All physicochemical parameters analyzed, including heavy metals before and after filtration of the water with Millipore filter paper (0.45 µm), were within the acceptable limits set by standard organizations, except for decreased dissolved oxygen (DO), and increased biochemical oxygen demand (BOD), and chemical oxygen demand (COD), which are indicators of hypoxic water conditions, as well as the presence of microplastics (polybutene (< 15 µm), polyisobutene (≤ 20 µm), and polymethylpentene (≤3 mm)) and cyclohexyl in CR water samples. Zebrafish embryos treated with the water samples, both before and after filtration exerts the same cytogenotoxic effects by inducing increased reactive oxygen species (ROS) production, which triggers subcellular organelle dysfunctions, DNA damage, apoptosis, pericardial edema, skeletal deformities, and increased mortality. As a result, we observed that both water samples and zebrafish larvae had significantly less oxygen using SEM and EDS. Our findings show that KRS-CR water can induce cytogenotoxic and embryotoxic defects in zebrafish due to hypoxic water conditions triggered by the microplastics influx. The present study would provide valuable insights for health hazards evaluation and future river water treatment strategies.

Rbfox1 is required for myofibril development and maintaining fiber type-specific isoform expression in Drosophila muscles

Protein isoform transitions confer muscle fibers with distinct properties and are regulated by differential transcription and alternative splicing. RNA-binding Fox protein 1 (Rbfox1) can affect both transcript levels and splicing, and is known to contribute to normal muscle development and physiology in vertebrates, although the detailed mechanisms remain obscure. In this study, we report that Rbfox1 contributes to the generation of adult muscle diversity in Drosophila Rbfox1 is differentially expressed among muscle fiber types, and RNAi knockdown causes a hypercontraction phenotype that leads to behavioral and eclosion defects. Misregulation of fiber type-specific gene and splice isoform expression, notably loss of an indirect flight muscle-specific isoform of Troponin-I that is critical for regulating myosin activity, leads to structural defects. We further show that Rbfox1 directly binds the 3'-UTR of target transcripts, regulates the expression level of myogenic transcription factors myocyte enhancer factor 2 and Salm, and both modulates expression of and genetically interacts with the CELF family RNA-binding protein Bruno1 (Bru1). Rbfox1 and Bru1 co-regulate fiber type-specific alternative splicing of structural genes, indicating that regulatory interactions between FOX and CELF family RNA-binding proteins are conserved in fly muscle. Rbfox1 thus affects muscle development by regulating fiber type-specific splicing and expression dynamics of identity genes and structural proteins.

Indirect flight muscles in Drosophila melanogaster as a tractable model to study muscle development and disease

Myogenesis is a complex multifactorial process leading to the formation of the adult muscle. An amalgamation of autonomous processes including myoblast fusion and myofibrillogenesis, as well as non-autonomous processes, such as innervations from neurons and precise connections with attachment sites, are responsible for successful development and function of muscles. In this review, we describe the development of the indirect flight muscles (IFMs) in Drosophila melanogaster, and highlight the use of the IFMs as a model for studying muscle development and disease, based on recent studies on the development and function of IFMs.

Matrilineal analysis of mutations in the DMD gene in a multigenerational South Indian cohort using DMD gene panel sequencing

BACKGROUND

Duchenne muscular dystrophy (DMD) is an X-linked recessive neuromuscular disorder characterised by progressive irreversible muscle weakness, primarily of the skeletal and the cardiac muscles. DMD is characterised by mutations in the dystrophin gene, resulting in the absence or sparse quantities of dystrophin protein. A precise and timely molecular detection of DMD mutations encourages interventions such as carrier genetic counselling and in undertaking therapeutic measures for the DMD patients.

RESULTS

In this study, we developed a 2.1 Mb custom DMD gene panel that spans the entire DMD gene, including the exons and introns. The panel also includes the probes against 80 additional genes known to be mutated in other muscular dystrophies. This custom DMD gene panel was used to identify single nucleotide variants (SNVs) and large deletions with precise breakpoints in 77 samples that included 24 DMD patients and their matrilineage across four generations. We used this panel to evaluate the inheritance pattern of DMD mutations in maternal subjects representing 24 DMD patients.

CONCLUSION

Here we report our observations on the inheritance pattern of DMD gene mutations in matrilineage samples across four generations. Additionally, our data suggest that the DMD gene panel designed by us can be routinely used as a single genetic test to identify all DMD gene variants in DMD patients and the carrier mothers.

Exome sequencing and functional studies in zebrafish identify WDR8 as the causative gene for isolated Microspherophakia in Indian families

Isolated Microspherophakia (MSP) is an autosomal recessive disorder characterized by a smaller than normal spherical lens. Till date, LTBP2 is the only gene shown to cause MSP. We used homozygosity mapping and whole-exome sequencing and identified a homozygous mutation, c.1148C > T (p.Pro383Leu), in the WDR8 (or WRAP73) gene in two Indian MSP families. In vitro experiments showed that the missense mutation renders the protein unstable. WDR8 is a centriolar protein that has important roles in centrosomal assembly, spindle pole formation and ciliogenesis. Co-immunoprecipitation experiments from HeLa cells indicated that the mutation interferes with the interaction of WDR8 with its binding partners. In zebrafish, both morpholino-mediated knockdown and CRISPR/Cas knockout of wdr8 resulted in decreased eye and lens size. The lack of wdr8 affected cell cycle progression in the retinal cells, causing a reduction in cell numbers in the retina and lens. The reduction in eye size and the cell cycle defects were rescued by exogenous expression of the human wild-type WDR8. However, the human mutant WDR8 (p.Pro383Leu) was unable to rescue the eye defects, indicating that the missense mutation abrogates WDR8 protein function. Thus, our zebrafish results suggested that WDR8 is the causative gene for MSP in these Indian families.

A Dominant C150Y Mutation in FHL1 Induces Structural Alterations in LIM2 Domain Causing Protein Aggregation In Human and Drosophila Indirect Flight Muscles

FHL1-related myopathies are rare X-linked dominant myopathies. Though clinically classified into several subgroups, spinal and scapuloperoneal muscle involvement are common to all. In this study, we identified c.449G > A, p.C150Y mutation by clinical exome sequencing in two patients from same family (son and mother) of Indian origin who presented with multiple contractures. Muscle biopsy showed numerous intracytoplasmic aggregates intensely stained on HE and MGT. The strong reactions to M-NBT revealed aggregates to be reducing bodies and positively labeled to anti-FHL1 antibody. Ultrastructurally, Z-band streaming and granular and granulofilamentous material were seen. Further, the translational evidence of mutant peptide was confirmed using mass spectrometric analysis. To establish p.C150Y as the cause for protein aggregation, in vivo studies were carried out using transgenic Drosophila model which highlighted Z-band abnormalities and protein aggregates in indirect flight muscles with compromised physiological function. Thus, recapitulating the X-linked human disease phenotype. Additionally, the molecular dynamics simulation analysis unraveled the drastic change in α-helix of LIM2, the region immediately next to site of C150Y mutation that could be the plausible cause for protein aggregation. To the best of our knowledge, this is the first study of p.C150Y mutation in FHL1 identified in Indian patients with in vivo and in silico analysis to establish the cause for protein aggregation in muscle.

Marf-mediated mitochondrial fusion is imperative for the development and functioning of indirect flight muscles (IFMs) in drosophila

Dynamic changes in mitochondrial shape and size are vital for mitochondrial health and for tissue development and function. Adult Drosophila indirect flight muscles contain densely packed mitochondria. We show here that mitochondrial fusion is critical during early muscle development (in pupa) and that silencing of the outer mitochondrial membrane fusion gene, Marf, in muscles results in smaller mitochondria that are functionally defective. This leads to abnormal muscle development resulting in muscle dysfunction in adult flies. However, post-developmental silencing of Marf has no obvious effects on mitochondrial and muscle phenotype in adult flies, indicating the importance of mitochondrial fusion during early muscle development.

Evaluation of developmental toxicity and genotoxicity of aqueous seed extract of Croton tiglium L. using zebrafish

Croton tiglium L. has been used in Ayurvedic and Chinese herbal medicinal formulations from ancient times. Although its seeds are widely prescribed as traditional medicine, there is a dearth of information, regarding its toxic effects, and the mechanisms underlying its toxicity. This study aims to investigate the developmental toxicity and genotoxicity of the aqueous seed extract of C. tiglium L. (AECT) in zebrafish. We have examined the effects of AECT on the early embryonic development of zebrafish. Zebrafish embryos, treated with different concentrations of the AECT, suffered embryonic lethality and displayed various developmental defects. The 96 h-LC₅₀ of AECT was found to be 162.78 µg/ml. Interestingly, the developmental abnormalities observed, such as pericardial edema (PE), yolk sac edema (YSE), spinal curvature (SC), and delayed hatching, varied in severity, in a dose-dependent manner. Zebrafish embryos, treated with different concentrations of AECT, exhibited exaggerated cell death in the anatomical regions of brain, heart, and trunk. Our data suggest that the phenomenon of apoptosis is probably responsible for both embryonic lethality and developmental toxicity in zebrafish embryos. Furthermore, the genotoxic potential of the AECT, in vivo, was evaluated using micronucleus assay and comet assay, on the peripheral blood of zebrafish. The results suggest that AECT has the potential to cause genotoxicity in the peripheral blood of zebrafish.

Beadex, a homologue of the vertebrate LIM domain only protein, is a novel regulator of crystal cell development in Drosophila melanogaster

Haematopoiesis is a complex process in which the regulatory mechanisms of several implicated transcription factors remain uncertain. Drosophila melanogaster is an excellent model to resolve the unanswered questions about the blood cell development. This study describes the role of Beadex, a Drosophila homologue of LIM domain only 2 (LMO2), in haematopoiesis. Mutants of Beadex were analysed for blood cell abnormalities. Crystal cells, a subset of haemocytes, were significantly more in Beadex hypermorphic flies. Similarly, Beadex misexpression in prohemocytes altered the crystal cell numbers. Stage-specific misexpression analyses demonstrated that Beadex functions after the prohemocytes enter the crystal cell lineage. We also discovered that Pannier-U-shaped complex is a negative regulator of the crystal cell differentiation and is possibly negatively regulated by Beadex through its interaction with Pannier. We, therefore, suggest the mechanism of two novel regulators of crystal cell specification-Beadex and Pannier-during Drosophila haematopoiesis.

Targeted sequencing of the DMD locus: A comprehensive diagnostic tool for all mutations

Background & objectives:

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder and is caused mainly by deletion, duplication and point mutations in the DMD gene. Diagnosis of DMD has been a challenge as the mutations in the DMD gene are heterogeneous and require more than one diagnostic strategy for the validation of the mutation. This study was planned to evaluate the targeted next-generation sequencing (NGS) as a single platform to detect all types of mutations in the DMD gene, thereby reducing the time and costs compared to conventional sequential testing and also provide precise genetic information for emerging gene therapies.

Methods:

The study included 20 unrelated families and 22 patients from an Indian population who were screened for DMD based on phenotypes such as scoliosis, toe walking and loss of ambulation. Peripheral blood DNA was isolated and subjected to multiplex ligation-dependent probe amplification (MLPA) and targeted NGS of the DMD gene to identify the nature of the mutation.

Results:

In the study patients, 77 per cent of large deletion mutations and 23 per cent single-nucleotide variations (SNVs) were identified. Novel mutations were also identified along with reported deletions, point mutations and partial deletions within the exon of the DMD gene.

Interpretation & conclusions:

Our findings showed the importance of NGS in the routine diagnostic practice in the identification of DMD mutations over sequential testing. It may be used as a single-point diagnostic strategy irrespective of the mutation type, thereby reducing the turnaround time and cost for multiple diagnostic tests such as MLPA and Sanger sequencing. Though MLPA is a sensitive technique and is the first line of a diagnostic test, the targeted NGS of the DMD gene may have an advantage of having a single diagnostic test. A study on a larger number of patients is needed to highlight NGS as a single, comprehensive platform for the diagnosis of DMD.

Beadex, a Drosophila LIM domain only protein, function in follicle cells is essential for egg development and fertility

LIM domain, constituted by two tandem C2H2 zinc finger motif, proteins regulate several biological processes. They are usually found associated with various functional domains like Homeodomain, kinase domain and other protein binding domains. LIM proteins that are devoid of other domains are called LIM only proteins (LMO). LMO proteins were first identified in humans and are implicated in development and oncogenesis. They regulate various cell specifications by regulating the activity of respective transcriptional complexes. The Drosophila LMO protein (dLMO), Beadex (Bx), regulates various developmental processes like wing margin development and bristle development. It also regulates Drosophila behavior in response to cocaine and ethanol. We have previously generated Bx null flies and shown its essential function in neurons for multiple aspects of female reproduction. However, it was not known whether Bx affects reproduction through its independent function in ovaries. In this paper we show that female flies null for Bx lay eggs with multiple defects. Further, through knock down studies we demonstrate that function of Bx in follicle cells is required for normal egg development. We also show that function of Bx is particularly required in border cells for Drosophila fertility.

Transcriptome analysis of IFM-specific actin and myosin nulls in Drosophila melanogaster unravels lesion-specific expression blueprints across muscle mutations

Muscle contraction is a highly fine-tuned process that requires the precise and timely construction of large protein sub-assemblies to form sarcomeres. Mutations in many genes encoding constituent proteins of this macromolecular machine result in defective functioning of the muscle tissue. However, the pathways underlying muscle degeneration, and manifestation of myopathy phenotypes are not well understood. In this study, we explored transcriptional alterations that ensue from the absence of the two major muscle proteins - myosin and actin - using the Drosophila indirect flight muscles. Our aim was to understand how the muscle tissue responds as a whole to the absence of either of the major scaffold proteins, whether the responses are generic to the tissue; or unique to the thick versus thin filament systems. Our results indicated that muscles respond by altering gene transcriptional levels in multiple systems active in muscle remodelling, protein degradation and heat shock responses. However, there were some responses that were filament-specific signatures of muscle degeneration, like immune responses, metabolic alterations and alterations in expression of muscle structural genes and mitochondrial ribosomal genes. These general and filament-specific changes in gene expression may be of relevance to human myopathies.

4-Hydroxyisophthalic acid from Decalepis hamiltonii rescues the neurobehavioral deficit in transgenic Drosophila model of taupathies

Oxidative stress is one of the major etiological factors implicated in pathogenesis of neurodegenerative diseases. Since neurons are more sensitive to oxidative damage there is an increasing interest in developing novel antioxidant therapies, especially herbal preparations due to their safety profile and high efficiency. In this regard, the neuroprotective potential of a novel antioxidant compound, 4-hydroxyisophthalic acid (4-HIPA) isolated from aqueous extract of Decalepis hamiltonii roots was examined using transgenic Drosophila model of taupathy expressing wild-type and mutant forms of 2N4R isoform of human microtubule associated protein tau (MAPT). Taupathy model flies showed cognitive deficits in olfactory memory and deteriorated circadian rhythm of locomotory activities. Administration of 0.1 mg/ml 4-HIPA, markedly enhanced their olfactory memory performance and restored circadian rhythmicity of the transgenic flies locomotory behavior to the normal range. The mechanism of action that underlies 4-HIPA neuroprotection involves enhancement in efficiency of cellular antioxidant defense system by means of elevation in antioxidant enzyme activities and attenuation of oxidative stress. The molecule could positively affect the activity of neurotransmitter enzymes, which in turn enhances neuronal function and ameliorates the Tau-induced neurobehavioral deficits. Our findings showed that 4-HIPA can be considered as a suitable therapeutic candidate for drug development towards treatment of neurodegenerative disorders.

A newly evolved Drosophila Cytorace-9 shows trade-off between longevity and immune response

Species with an efficient immune system would be at an advantage to evade pathogenic challenges and adapt to an ever changing ecological niche. The upkeep of immunity is a costly affair, thus trade-offs between immunity and other life history traits are expected. However, studies on the relation between immunity and life span have yielded paradoxical results. Drosophila Cytoraces, being at different stages of evolutionary divergence, provide an excellent experimental model system to study how evolving populations gain novel traits in the absence of selection. We found that in the absence of pathogenic infections, the Cytorace-9 flies lived longer than those of Cytorace-3. However, when these Cytoraces were challenged with different pathogenic microbes, the trend was opposite. After infection with pathogens, the long-lived Cytorace-9 survived worse than the short lived Cytorace-3, which can be attributed to a reduction in its immune response. This study provides evidence to support the existence of a trade-off between life span and immunity.

Muscles provide protection during microbial infection by activating innate immune response pathways in Drosophila and zebrafish

Muscle contraction brings about movement and locomotion in animals. However, muscles have also been implicated in several atypical physiological processes including immune response. The role of muscles in immunity and the mechanism involved has not yet been deciphered. In this paper, using Drosophila indirect flight muscles (IFMs) as a model, we show that muscles are immune-responsive tissues. Flies with defective IFMs are incapable of mounting a potent humoral immune response. Upon immune challenge, the IFMs produce anti-microbial peptides (AMPs) through the activation of canonical signaling pathways, and these IFM-synthesized AMPs are essential for survival upon infection. The trunk muscles of zebrafish, a vertebrate model system, also possess the capacity to mount an immune response against bacterial infections, thus establishing that immune responsiveness of muscles is evolutionarily conserved. Our results suggest that physiologically fit muscles might boost the innate immune response of an individual.

Summary: Using fruit fly and zebrafish models, we show that skeletal muscles are immune responsive tissues; they mount innate immune responses during bacterial infection – an evolutionarily conserved defense mechanism.

Curtailed light sheet microscopy for rapid imaging of macroscopic biological specimens

We study the feasibility of volume imaging from a few angular views/scans in a light sheet fluorescence microscopy. Two-dimensional (2D) images (angular views) were acquired at an angular separation of 10° and volume images were constructed with merely 18, 9, and 6 views. We study the structural changes in a 5-day old Zebrafish embryo labeled with Phalloidin TRITC that binds to F-Actin of embryo cell. To collect the data, the specimen is rotated (for varying sampling angles Δθ) with respect to a fixed vertical axis passing through the volume-of-interest (yolk sac). In the proposed realization of selective plane illumination microscopy (SPIM) technique, the translation is completely avoided. Analysis shows rich structural information with marginal reduction in contrast. Comparison with the state-of-the-art SPIM shows appreciable volume reconstruction (from an order less 2D scans) that may be good enough for rapid monitoring of macroscopic specimens. Microsc. Res. Tech. 79:455-458, 2016. © 2016 Wiley Periodicals, Inc.

Transgenic Drosophila model to study apolipoprotein E4-induced neurodegeneration

The ε4 isoform of apolipoprotein E (ApoE4) that is involved in neuron-glial lipid metabolism has been demonstrated as the main genetic risk factor in late-onset of Alzheimer's disease. However, the mechanism underlying ApoE4-mediated neurodegeneration remains unclear. We created a transgenic model of neurodegenerative disorder by expressing ε3 and ε4 isoforms of human ApoE in the Drosophila melanogaster. The genetic models exhibited progressive neurodegeneration, shortened lifespan and memory impairment. Genetic interaction studies between amyloid precursor protein and ApoE in axon pathology of the disease revealed that over expression of hApoE in Appl-expressing neurons of Drosophila brain causes neurodegeneration. Moreover, acute oxidative damage in the hApoE transgenic flies triggered a neuroprotective response of hApoE3 while chronic induction of oxidative damage accelerated the rate of neurodegeneration. This Drosophila model may facilitate analysis of the molecular and cellular events implicated in hApoE4 neurotoxicity.

Docking, molecular dynamics and QM/MM studies to delineate the mode of binding of CucurbitacinE to F-actin

CucurbitacinE (CurE) has been known to bind covalently to F-actin and inhibit depolymerization. However, the mode of binding of CurE to F-actin and the consequent changes in the F-actin dynamics have not been studied. Through quantum mechanical/molecular mechanical (QM/MM) and density function theory (DFT) simulations after the molecular dynamics (MD) simulations of the docked complex of F-actin and CurE, a detailed transition state (TS) model for the Michael reaction is proposed. The TS model shows nucleophilic attack of the sulphur of Cys257 at the β-carbon of Michael Acceptor of CurE producing an enol intermediate that forms a covalent bond with CurE. The MD results show a clear difference between the structure of the F-actin in free form and F-actin complexed with CurE. CurE affects the conformation of the nucleotide binding pocket increasing the binding affinity between F-actin and ADP, which in turn could affect the nucleotide exchange. CurE binding also limits the correlated displacement of the relatively flexible domain 1 of F-actin causing the protein to retain a flat structure and to transform into a stable "tense" state. This structural transition could inhibit depolymerization of F-actin. In conclusion, CurE allosterically modulates ADP and stabilizes F-actin structure, thereby affecting nucleotide exchange and depolymerization of F-actin.

Quantitative characterization of adhesion and stiffness of corneal lens of Drosophila melanogaster using atomic force microscopy

Atomic force Microscopy (AFM) has become a versatile tool in biology due to its advantage of high-resolution imaging of biological samples close to their native condition. Apart from imaging, AFM can also measure the local mechanical properties of the surfaces. In this study, we explore the possibility of using AFM to quantify the rough eye phenotype of Drosophila melanogaster through mechanical properties. We have measured adhesion force, stiffness and elastic modulus of the corneal lens using AFM. Various parameters affecting these measurements like cantilever stiffness and tip geometry are systematically studied and the measurement procedures are standardized. Results show that the mean adhesion force of the ommatidial surface varies from 36 nN to 16 nN based on the location. The mean stiffness is 483 ± 5 N/m, and the elastic modulus is 3.4 ± 0.05 GPa (95% confidence level) at the center of ommatidia. These properties are found to be different in corneal lens of eye expressing human mutant tau gene (mutant). The adhesion force, stiffness and elastic modulus are decreased in the mutant. We conclude that the measurement of surface and mechanical properties of D. melanogaster using AFM can be used for quantitative evaluation of 'rough eye' surface.

A mycobacterial phosphoribosyltransferase promotes bacillary survival by inhibiting oxidative stress and autophagy pathways in macrophages and zebrafish

Mycobacterium tuberculosis employs various strategies to modulate host immune responses to facilitate its persistence in macrophages. The M. tuberculosis cell wall contains numerous glycoproteins with unknown roles in pathogenesis. Here, by using Concanavalin A and LC-MS analysis, we identified a novel mannosylated glycoprotein phosphoribosyltransferase, encoded by Rv3242c from M. tuberculosis cell walls. Homology modeling, bioinformatic analyses, and an assay of phosphoribosyltransferase activity in Mycobacterium smegmatis expressing recombinant Rv3242c (MsmRv3242c) confirmed the mass spectrometry data. Using Mycobacterium marinum-zebrafish and the surrogate MsmRv3242c infection models, we proved that phosphoribosyltransferase is involved in mycobacterial virulence. Histological and infection assays showed that the M. marinum mimG mutant, an Rv3242c orthologue in a pathogenic M. marinum strain, was strongly attenuated in adult zebrafish and also survived less in macrophages. In contrast, infection with wild type and the complemented ΔmimG:Rv3242c M. marinum strains showed prominent pathological features, such as severe emaciation, skin lesions, hemorrhaging, and more zebrafish death. Similarly, recombinant MsmRv3242c bacteria showed increased invasion in non-phagocytic epithelial cells and longer intracellular survival in macrophages as compared with wild type and vector control M. smegmatis strains. Further mechanistic studies revealed that the Rv3242c- and mimG-mediated enhancement of intramacrophagic survival was due to inhibition of autophagy, reactive oxygen species, and reduced activities of superoxide dismutase and catalase enzymes. Infection with MsmRv3242c also activated the MAPK pathway, NF-κB, and inflammatory cytokines. In summary, we show that a novel mycobacterial mannosylated phosphoribosyltransferase acts as a virulence and immunomodulatory factor, suggesting that it may constitute a novel target for antimycobacterial drugs.

Raman spectroscopic studies on screening of myopathies

Myopathies are among the major causes of mortality in the world. There is no complete cure for this heterogeneous group of diseases, but a sensitive, specific, and fast diagnostic tool may improve therapy effectiveness. In this study, Raman spectroscopy is applied to discriminate between muscle mutants in Drosophila on the basis of associated changes at the molecular level. Raman spectra were collected from indirect flight muscles of mutants, upheld(1) (up(1)), heldup(2) (hdp(2)), myosin heavy chain(7) (Mhc(7)), actin88F(KM88) (Act88F(KM88)), upheld(101) (up(101)), and Canton-S (CS) control group, for both 2 and 12 days old flies. Difference spectra (mutant minus control) of all the mutants showed an increase in nucleic acid and β-sheet and/or random coil protein content along with a decrease in α-helix protein. Interestingly, the 12th day samples of up(1) and Act88F(KM88) showed significantly higher levels of glycogen and carotenoids than CS. A principal components based linear discriminant analysis classification model was developed based on multidimensional Raman spectra, which classified the mutants according to their pathophysiology and yielded an overall accuracy of 97% and 93% for 2 and 12 days old flies, respectively. The up(1) and Act88F(KM88) (nemaline-myopathy) mutants form a group that is clearly separated in a linear discriminant plane from up(101) and hdp(2) (cardiomyopathy) mutants. Notably, Raman spectra from a human sample with nemaline-myopathy formed a cluster with the corresponding Drosophila mutant (up(1)). In conclusion, this is the first demonstration in which myopathies, despite their heterogeneity, were screened on the basis of biochemical differences using Raman spectroscopy.

Pomegranate Juice Enhances Healthy Lifespan in Drosophila melanogaster: An Exploratory Study

Exploring innovative ways to ensure healthy aging of populations is a pre-requisite to contain rising healthcare costs. Scientific research into the principles and practices of traditional medicines can provide new insights and simple solutions to lead a healthy life. Rasayana is a dedicated branch of Ayurveda (an Indian medicine) that deals with methods to increase vitality and delay aging through the use of diet, herbal supplements, and other lifestyle practices. The life-span and health-span enhancing actions of the fruits of pomegranate (Punica granatum L.), a well-known Rasayana, were tested on Drosophila melanogaster (fruitfly) model. Supplementation of standard corn meal with 10% (v/v) pomegranate juice (PJ) extended the life-span of male and female flies by 18 and 8%, respectively. When male and female flies were mixed and reared together, there was 19% increase in the longevity of PJ fed flies, as assessed by MSD, the median survival day (24.8). MSD for control and resveratrol (RV) groups was at 20.8 and 23.1 days, respectively. A two-fold enhancement in fecundity, improved resistance to oxidative stress (H₂O₂ and paraquat induced) and to Candida albicans infection were observed in PJ fed flies. Further, the flies in the PJ fed group were physically active over an extended period of time, as assessed by the climbing assay. PJ thus outperformed both control and RV groups in the life-span and health-span parameters tested. This study provides the scope to explore the potential of PJ as a nutraceutical to improve health span and lifespan in human beings.

Beadex function in the motor neurons is essential for female reproduction in Drosophila melanogaster

Drosophila melanogaster has served as an excellent model system for understanding the neuronal circuits and molecular mechanisms regulating complex behaviors. The Drosophila female reproductive circuits, in particular, are well studied and can be used as a tool to understand the role of novel genes in neuronal function in general and female reproduction in particular. In the present study, the role of Beadex, a transcription co-activator, in Drosophila female reproduction was assessed by generation of mutant and knock down studies. Null allele of Beadex was generated by transposase induced excision of P-element present within an intron of Beadex gene. The mutant showed highly compromised reproductive abilities as evaluated by reduced fecundity and fertility, abnormal oviposition and more importantly, the failure of sperm release from storage organs. However, no defect was found in the overall ovariole development. Tissue specific, targeted knock down of Beadex indicated that its function in neurons is important for efficient female reproduction, since its neuronal knock down led to compromised female reproductive abilities, similar to Beadex null females. Further, different neuronal class specific knock down studies revealed that Beadex function is required in motor neurons for normal fecundity and fertility of females. Thus, the present study attributes a novel and essential role for Beadex in female reproduction through neurons.

Drosophila Erect wing (Ewg) controls mitochondrial fusion during muscle growth and maintenance by regulation of the Opa1-like gene

Mitochondrial biogenesis and morphological changes are associated with tissue-specific functional demand, but the factors and pathways that regulate these processes have not been completely identified. A lack of mitochondrial fusion has been implicated in various developmental and pathological defects. The spatiotemporal regulation of mitochondrial fusion in a tissue such as muscle is not well understood. Here, we show in Drosophila indirect flight muscles (IFMs) that the nuclear-encoded mitochondrial inner membrane fusion gene, Opa1-like, is regulated in a spatiotemporal fashion by the transcription factor/co-activator Erect wing (Ewg). In IFMs null for Ewg, mitochondria undergo mitophagy and/or autophagy accompanied by reduced mitochondrial functioning and muscle degeneration. By following the dynamics of mitochondrial growth and shape in IFMs, we found that mitochondria grow extensively and fuse during late pupal development to form the large tubular mitochondria. Our evidence shows that Ewg expression during early IFM development is sufficient to upregulate Opa1-like, which itself is a requisite for both late pupal mitochondrial fusion and muscle maintenance. Concomitantly, by knocking down Opa1-like during early muscle development, we show that it is important for mitochondrial fusion, muscle differentiation and muscle organization. However, knocking down Opa1-like, after the expression window of Ewg did not cause mitochondrial or muscle defects. This study identifies a mechanism by which mitochondrial fusion is regulated spatiotemporally by Ewg through Opa1-like during IFM differentiation and growth.

Mutations in Drosophila myosin rod cause defects in myofibril assembly

The roles of myosin during muscle contraction are well studied, but how different domains of this protein are involved in myofibril assembly in vivo is far less understood. The indirect flight muscles (IFMs) of Drosophila melanogaster provide a good model for understanding muscle development and function in vivo. We show that two missense mutations in the rod region of the myosin heavy-chain gene, Mhc, give rise to IFM defects and abnormal myofibrils. These defects likely result from thick filament abnormalities that manifest during early sarcomere development or later by hypercontraction. The thick filament defects are accompanied by marked reduction in accumulation of flightin, a myosin binding protein, and its phosphorylated forms, which are required to stabilise thick filaments. We investigated with purified rod fragments whether the mutations affect the coiled-coil structure, rod aggregate size or rod stability. No significant changes in these parameters were detected, except for rod thermodynamic stability in one mutation. Molecular dynamics simulations suggest that these mutations may produce localised rod instabilities. We conclude that the aberrant myofibrils are a result of thick filament defects, but that these in vivo effects cannot be detected in vitro using the biophysical techniques employed. The in vivo investigation of these mutant phenotypes in IFM development and function provides a useful platform for studying myosin rod and thick filament formation generically, with application to the aetiology of human myosin rod myopathies.

Cardiac remodeling in Drosophila arises from changes in actin gene expression and from a contribution of lymph gland-like cells to the heart musculature

Understanding the basis of normal heart remodeling can provide insight into the plasticity of the cardiac state, and into the potential for treating diseased tissue. In Drosophila, the adult heart arises during metamorphosis from a series of events, that include the remodeling of an existing cardiac tube, the elaboration of new inflow tracts, and the addition of a layer of longitudinal muscle fibers. We have identified genes active in all these three processes, and studied their expression in order to characterize in greater detail normal cardiac remodeling. Using a Transglutaminase-lacZ transgenic line, that is expressed in the inflow tracts of the larval and adult heart, we confirm the existence of five inflow tracts in the adult structure. In addition, expression of the Actin87E actin gene is initiated in the remodeling cardiac tube, but not in the longitudinal fibers, and we have identified an Act87E promoter fragment that recapitulates this switch in expression. We also establish that the longitudinal fibers are multinucleated, characterizing these cells as specialized skeletal muscles. Furthermore, we have defined the origin of the longitudinal fibers, as a subset of lymph gland cells associated with the larval dorsal vessel. These studies underline the myriad contributors to the formation of the adult Drosophila heart, and provide new molecular insights into the development of this complex organ.

Aberrant splicing of an alternative exon in the Drosophila troponin-T gene affects flight muscle development

During myofibrillogenesis, many muscle structural proteins assemble to form the highly ordered contractile sarcomere. Mutations in these proteins can lead to dysfunctional muscle and various myopathies. We have analyzed the Drosophila melanogaster troponin T (TnT) up1 mutant that specifically affects the indirect flight muscles (IFM) to explore troponin function during myofibrillogenesis. The up1 muscles lack normal sarcomeres and contain "zebra bodies," a phenotypic feature of human nemaline myopathies. We show that the up(1) mutation causes defective splicing of a newly identified alternative TnT exon (10a) that encodes part of the TnT C terminus. This exon is used to generate a TnT isoform specific to the IFM and jump muscles, which during IFM development replaces the exon 10b isoform. Functional differences between the 10a and 10b TnT isoforms may be due to different potential phosphorylation sites, none of which correspond to known phosphorylation sites in human cardiac TnT. The absence of TnT mRNA in up1 IFM reduces mRNA levels of an IFM-specific troponin I (TnI) isoform, but not actin, tropomyosin, or troponin C, suggesting a mechanism controlling expression of TnT and TnI genes may exist that must be examined in the context of human myopathies caused by mutations of these thin filament proteins.

Neuromuscular organization and aminergic modulation of contractions in the Drosophila ovary

Background

The processes by which eggs develop in the insect ovary are well characterized. Despite a large number of Drosophila mutants that cannot lay eggs, the way that the egg is moved along the reproductive tract from ovary to uterus is less well understood. We remedy this with an integrative study on the reproductive tract muscles (anatomy, innervation, contractions, aminergic modulation) in female flies.

Results

Each ovary, consisting of 15–20 ovarioles, is surrounded by a contractile meshwork, the peritoneal sheath. Individual ovarioles are contained within a contractile epithelial sheath. Both sheaths contain striated muscle fibres. The oviduct and uterine walls contain a circular striated muscle layer. No longitudinal muscle fibres are seen.

Neurons that innervate the peritoneal sheath and lateral oviduct have many varicosities and terminate in swellings just outside the muscles of the peritoneal sheath. They all express tyrosine decarboxylase (required for tyramine and octopamine synthesis) and Drosophila vesicular monoamine transporter (DVMAT). No fibres innervate the ovarioles. The common oviduct and uterus are innervated by two classes of neurons, one with similar morphology to those of the peritoneal sheath and another with repeated branches and axon endings similar to type I neuromuscular junctions.

In isolated genital tracts from 3- and 7-day old flies, each ovariole contracts irregularly (12.5 ± 6.4 contractions/minute; mean ± 95% confidence interval). Peritoneal sheath contractions (5.7 ± 1.6 contractions/minute) move over the ovary, from tip to base or vice versa, propagating down the oviduct. Rhythmical spermathecal rotations (1.5 ± 0.29 contractions/minute) also occur. Each genital tract organ exhibits its own endogenous myogenic rhythm.

The amplitude of contractions of the peritoneal sheath increase in octopamine (100 nM, 81% P < 0.02) but 1 μM tyramine has no effect. Neither affects the frequency of peritoneal sheath contractions.

Conclusion

The muscle fibres of the reproductive tract are circular and have complex bursting myogenic rhythms under octopaminergic neuromodulation. We propose a new model of tissue-specific actions of octopamine, in which strengthening of peritoneal sheath contractions, coupled with relaxation of the oviduct, eases ovulation. This model accounts for reduced ovulation in flies with mutations in the octopaminergic system.

Distance and force production during jumping in wild-type and mutant Drosophila melanogaster

In many insects renowned for their jumping ability, elastic storage is used so that high forces can be developed prior to jumping. We have combined physiological, behavioural and genetic approaches to test whether elastic energy storage makes a major contribution to jumping in Drosophila. We describe a sensitive strain gauge setup, which measures the forces produced by tethered flies through their mesothoracic legs. The peak force produced by the main jumping muscle of female flies from a wild-type (Canton-S) strain is 101+/-4.4 microN [and this is indistinguishable from a second wild-type (Texas) strain]. The force takes 8.2 ms to reach its peak. The peak force is not affected significantly by altering the leg angle (femur-tibia joint angle) in the range of 75-120 degrees, but the peak force declines as the leg is extended further. Measurements of jumping ability (distance jumped) showed that female Drosophila (with their wings removed) of two wild-type strains, Canton-S and Texas, produced jumps of 28.6+/-0.7 and 30.2+/-1.0 mm (mean +/- s.e.m.). For a female wild-type Drosophila, a jump of 30 mm corresponds to a kinetic energy of 200 nJ on take-off (allowing 20% of the energy to overcome air resistance). We develop equations of motion for a linear force-time model of take-off and calculate that the time to take-off is 5.0 ms and the peak force should be 274 microN (137 microN leg(-1)). We predicted, from the role of octopamine in enhancing muscle tension in several locust muscles, that if stored elastic energy plays no part in force development, then genetic manipulation of the octopaminergic system would directly affect force production and jumping in Drosophila. Using two mutants deficient in the octopaminergic system, TbhnM18 (M18) and TyrRhono (hono), we found significantly reduced jumping distances (20.7+/-0.7 and 20.7+/-0.4 mm, respectively) and force production (52% and 55%, respectively) compared with wild type. From the reduced distance and force production in M18, a mutant deficient in octopamine synthesis, and in hono, a tyramine/octopamine receptor mutant, we conclude that in Drosophila, as in locusts, octopamine modulates escape jumping. We conclude that the fly does not need to store large quantities of elastic energy in order to make its jump because (1) the measured and calculated forces agree to within 40% and (2) the reduction in distances jumped by the mutants correlates well with their reduction in measured peak force.

Troponin I is required for myofibrillogenesis and sarcomere formation inDrosophilaflight muscle

Myofibrillar proteins assemble to form the highly ordered repetitive contractile structural unit known as a sarcomere. Studies of myogenesis in vertebrate cell culture and embryonic developmental systems have identified some of the processes involved during sarcomere formation. However, isoform changes during vertebrate muscle development and a lack of mutants have made it difficult to determine how these proteins assemble to form sarcomeres. The indirect flight muscles (IFMs) of Drosophila provide a unique genetic system with which to study myofibrillogenesis in vivo. We show in this paper that neither sarcomeric myosin nor actin are required for myoblast fusion or the subsequent morphogenesis of muscle fibres, i.e. fibre morphogenesis does not depend on myofibrillogenesis. However, fibre formation and myofibrillogenesis are very sensitive to the interactions between the sarcomeric proteins. A troponin I (TnI) mutation, hdp3, leads to an absence of TnI in the IFMs and tergal depressor of trochanter (TDT) muscles due to a transcript-splicing defect. Sarcomeres do not form and the muscles degenerate. TnI is part of the thin filament troponin complex which regulates muscle contraction. The effects of the hdp3 mutation are probably caused by unregulated acto-myosin interactions between the thin and thick filaments as they assemble. We have tested this proposal by using a transgenic myosin construct to remove the force-producing myosin heads. The defects in sarcomeric organisation and fibre degeneration in hdp3 IFMs are suppressed, although not completely, indicating the need for inhibition of muscle contraction during muscle development. We show that mRNA and translated protein products of all the major thin filament proteins are reduced in hdp3 muscles and discuss how this and previous studies of thin filament protein mutants indicate a common co-ordinated control mechanism that may be the primary cause of the muscle defects.

Suppression of muscle hypercontraction by mutations in the myosin heavy chain gene of Drosophila melanogaster

The indirect flight muscles (IFM) of Drosophila melanogaster provide a good genetic system with which to investigate muscle function. Flight muscle contraction is regulated by both stretch and Ca(2+)-induced thin filament (actin + tropomyosin + troponin complex) activation. Some mutants in troponin-I (TnI) and troponin-T (TnT) genes cause a "hypercontraction" muscle phenotype, suggesting that this condition arises from defects in Ca(2+) regulation and actomyosin-generated tension. We have tested the hypothesis that missense mutations of the myosin heavy chain gene, Mhc, which suppress the hypercontraction of the TnI mutant held-up(2) (hdp(2)), do so by reducing actomyosin force production. Here we show that a "headless" Mhc transgenic fly construct that reduces the myosin head concentration in the muscle thick filaments acts as a dose-dependent suppressor of hypercontracting alleles of TnI, TnT, Mhc, and flightin genes. The data suggest that most, if not all, mutants causing hypercontraction require actomyosin-produced forces to do so. Whether all Mhc suppressors act simply by reducing the force production of the thick filament is discussed with respect to current models of myosin function and thin filament activation by the binding of calcium to the troponin complex.

Expression and function of the Drosophila ACT88F actin isoform is not restricted to the indirect flight muscles

Most higher eukaryotic genomes contain multiple actin genes, yet the sequence differences between isoforms are few. In Drosophila melanogaster it was previously established that one of the six actin genes, Act88F, is expressed only in the indirect flight muscles (IFMs). These muscles are highly specialised for oscillatory contractions to power flight. The implication was that this isoform had tissue-specific properties. In this paper we show using two reporter constructs expressing either beta-galactosidase, Act88F-lacZ, or the green fluorescent protein, Act88F-GFP, that the Act88F promoter is active in a small number of other muscles, including leg (femoral) and uterine muscles. However, the levels of Act88F driven non-IFM expression are much less than in the IFMs. We have confirmed endogenous Act88F gene expression in these other muscles by in situ hybridisation studies. Using null and antimorphic mutants to show decreased walking ability and delayed/reduced oviposition we demonstrated that Act88F expression is functionally important in multiple muscle groups. Since the mutant effects are mild, this supports the expectation that other actin genes are also expressed in these muscles. The Act88F-GFP promoter-reporter also detects Act88F-driven expression in the bristle-forming cells in the pupal wings. The implications of these results for the functions and developmental expression of the Drosophila ACT88F isoform are discussed.

A tropomyosin-2 mutation suppresses a troponin I myopathy in Drosophila

A suppressor mutation, D53, of the held-up(2) allele of the Drosophila melanogaster Troponin I (wupA) gene is described. D53, a missense mutation, S185F, of the tropomyosin-2, Tm2, gene fully suppresses all the phenotypic effects of held-up(2), including the destructive hypercontraction of the indirect flight muscles (IFMs), a lack of jumping, the progressive myopathy of the walking muscles, and reductions in larval crawling and feeding behavior. The suppressor restores normal function of the IFMs, but flight ability decreases with age and correlates with an unusual, progressive structural collapse of the myofibrillar lattice starting at the center. The S185F substitution in Tm2 is close to a troponin T binding site on tropomyosin. Models to explain suppression by D53, derived from current knowledge of the vertebrate troponin-tropomyosin complex structure and functions, are discussed. The effects of S185F are compared with those of two mutations in residues 175 and 180 of human alpha-tropomyosin 1 which cause familial hypertrophic cardiomyopathy (HCM).