Functional redundancy and nonredundancy between two Troponin C isoforms in Drosophila adult muscles

Troponin C is required for copulation and ovulation in Nilaparvata lugens

Troponin C (TnC) is a calcium-binding subunit of the troponin complex that regulates muscle contraction in animals. However, the physiological roles of TnC, especially in insect development and reproduction, remain largely unknown. We identified seven TnC genes encoding four EF-hand motif protein in the rice pest, the brown planthopper Nilaparvata lugens. This species has emerged as an ideal model insect to study gene functions because of the availability of its complete genome sequence and of the susceptibility to RNA interference (RNAi). RT-qPCR combined with in situ hybridization showed that TnCⅠ was highly expressed in the bursa copulatrix of ovaries. RNAi-mediated knockdown of TnCⅠ in 2nd-to 5th-instar nymphs generated significantly lethal deficits, and also led to copulation and ovulation failure in adult females, although males displayed appropriate mating behavior. These new findings provide insights into understanding the physiological functions of TnCⅠ in the survival of, and female reproductive success, in N. lugens. Thus, this gene could be used as a target to explore methods for pest control of this important species.

Proteomic analysis across aged tissues reveals distinct signatures and the crucial involvement of midgut barrier function in the regulation of aging

The process of aging is a natural phenomenon characterized by gradual deterioration in biological functions and systemic homeostasis, which can be modulated by both genetic and environmental factors. Numerous investigations conducted on model organisms, including nematodes, flies, and mice, have elucidated several pivotal aging pathways, such as insulin signaling and AMPK signaling. However, it remains uncertain whether the regulation of the aging process is uniform or diverse across different tissues and whether manipulating the same aging factor can result in consistent outcomes in various tissues. In this study, we utilize the Drosophila organism to investigate tissue-specific proteome signatures during the aging process. Although distinct proteins undergo changes in aged tissues, certain common altered functional networks are constituently identified across different tissues, including the decline of the mitochondrial ribosomal network, autophagic network, and anti-ROS defense networks. Furthermore, downregulation of insulin receptor (InR) in the midguts, muscle, and central nervous system (CNS) of flies leads to a significant extension in fly lifespans. Notably, despite manipulating the same aging gene InR, diverse alterations in proteins are observed across different tissues. Importantly, knockdown of InR in the midguts leads to a distinct proteome compared with other tissues, resulting in enhanced actin nucleation and glutathione metabolism, while attenuating age-related elevation of serine proteases. Consequently, knockdown of InR results in rejuvenation of the integrity of the midgut barrier and augmentation of anti-ROS defense capabilities. Our findings suggest that the barrier function of the midgut plays a pivotal role in defending against aging, underscoring the paramount importance of maintaining optimal gut physiology to effectively delay the aging process. Moreover, when considering age-related changes across various tissues, it is more reasonable to identify functional networks rather than focusing solely on individual proteins.

Effects of different rearing methods on cocoon silk strength in silkworm Bombyx mori (Lepidoptera: Bombycidae)

In recent years, the use of artificial diet to rear silkworm Bombyx mori (L.) (Lepidoptera: Bombycidae) has advanced rapidly in China. However, significant differences are found in the production and performance of silk from silkworms reared on artificial diet and mulberry leaves, thereby affecting the development of artificial diet usage in sericulture. To understand the reasons for these differences, we tested the following 3 rearing methods: all-instar mulberry leaf rearing (Mul), all-instar artificial diet rearing (Diet), and instars 1-3 reared on artificial diet followed by instars 4-5 reared on mulberry leaf (Mix). The results showed that the silk production was significantly lower under Diet than Mix and Mul. Electron microscopy images revealed that the protein synthesis and energy supply were decreased under Dier and Mix compared with Mul. Subsequent strength analysis indicated that the relative strength of silk was highest under Mix, followed by Mul, and weakest under Diet. However, no significant differences in elongation were observed among treatments. The β-sheet content of silk was significantly higher under Mix than Diet and Mul, and a similar trend was observed for the crystallinity. Furthermore, the elevated expression of BmChiNAG and the reduced expression of BmTpn genes may be a significant factor for the notable disparities in cocoon silk fineness and strength among the threes. These findings provide deep insights into the differences in silk produced by silkworms reared on mulberry leaves and artificial diet, as well as providing a reference for improving artificial diet for rearing silkworms.

Enhanced expression of the myogenic factor Myocyte enhancer factor-2 in imaginal disc myoblasts activates a partial, but incomplete, muscle development program

The Myocyte enhancer factor-2 (MEF2) transcription factor plays a vital role in orchestrating muscle differentiation. While MEF2 cannot effectively induce myogenesis in naïve cells, it can potently accelerate myogenesis in mesodermal cells. This includes in Drosophila melanogaster imaginal disc myoblasts, where triggering premature muscle gene expression in these adult muscle progenitors has become a paradigm for understanding the regulation of the myogenic program. Here, we investigated the global consequences of MEF2 overexpression in the imaginal wing disc myoblasts, by combining RNA-sequencing with RT-qPCR and immunofluorescence. We observed the formation of sarcomere-like structures that contained both muscle and cytoplasmic myosin, and significant upregulation of muscle gene expression, especially genes essential for myofibril formation and function. These transcripts were functional since numerous myofibrillar proteins were detected in discs using immunofluorescence. Interestingly, muscle genes whose expression is restricted to the adult stages were not activated in these adult myoblasts. These studies confirm a broad activation of the myogenic program in response to MEF2 expression and suggest that additional regulatory factors are required for promoting the adult muscle-specific program. Our findings contribute to understanding the regulatory mechanisms governing muscle development and highlight the multifaceted role of MEF2 in orchestrating this intricate process.

Energy consumption during insect flight and bioinspiration for MAV design: A review

The excellent biological characteristics of insects provide an important source of inspiration for designing micro air vehicles (MAVs). Insect flight is an incredibly complex and energy-intensive process. Unique insect flight muscles and contraction mechanisms enable flapping at high frequencies. Moreover, the metabolic rate during flight can reach hundreds of times the resting state. Understanding energy consumption during flight is crucial for designing efficient biomimetic aircraft. This paper summarizes the structures and contraction mechanisms of insect flight muscles, explores the underlying metabolic processes, and identifies methods for energy substrate identification and detection, and discusses inspiration for biomimetic MAV design. This paper reviews energy consumption during insect flight, promotes the understanding of insect bioenergetics, and applies this information to the design of MAVs.

Quantitative model of aging-related muscle degeneration: a Drosophila study

Changes in the composition and functionality of somatic muscles is a universal hallmark of aging that is displayed by a wide range of species. In humans, complications arising from muscle decline due to sarcopenia aggravate morbidity and mortality rates. The genetics of aging-related deterioration of muscle tissue is not well understood, which prompted us to characterize aging-related muscle degeneration in Drosophila melanogaster (fruit fly), a leading model organism in experimental genetics. Adult flies demonstrate spontaneous degeneration of muscle fibers in all types of somatic muscles, which correlates with functional, chronological, and populational aging. Morphological data imply that individual muscle fibers die by necrosis. Using quantitative analysis, we demonstrate that muscle degeneration in aging flies has a genetic component. Chronic neuronal overstimulation of muscles promotes fiber degeneration rates, suggesting a role for the nervous system in muscle aging. From the other hand, muscles decoupled from neuronal stimulation retain a basal level of spontaneous degeneration, suggesting the presence of intrinsic factors. Based on our characterization, Drosophila can be adopted for systematic screening and validation of genetic factors linked to aging-related muscle loss.

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.

CRISPR-Cas Genome Editing for Insect Pest Stress Management in Crop Plants

Global crop yield and food security are being threatened by phytophagous insects. Innovative methods are required to increase agricultural output while reducing reliance on hazardous synthetic insecticides. Using the revolutionary CRISPR-Cas technology to develop insect-resistant plants appears to be highly efficient at lowering production costs and increasing farm profitability. The genomes of both a model insect, Drosophila melanogaster, and major phytophagous insect genera, viz. Spodoptera, Helicoverpa, Nilaparvata, Locusta, Tribolium, Agrotis, etc., were successfully edited by the CRISPR-Cas toolkits. This new method, however, has the ability to alter an insect’s DNA in order to either induce a gene drive or overcome an insect’s tolerance to certain insecticides. The rapid progress in the methodologies of CRISPR technology and their diverse applications show a high promise in the development of insect-resistant plant varieties or other strategies for the sustainable management of insect pests to ensure food security. This paper reviewed and critically discussed the use of CRISPR-Cas genome-editing technology in long-term insect pest management. The emphasis of this review was on the prospective uses of the CRISPR-Cas system for insect stress management in crop production through the creation of genome-edited crop plants or insects. The potential and the difficulties of using CRISPR-Cas technology to reduce pest stress in crop plants were critically examined and discussed.

CRISPR/Cas9 for Insect Pests Management: A Comprehensive Review of Advances and Applications

Insect pests impose a serious threat to agricultural productivity. Initially, for pest management, several breeding approaches were applied which have now been gradually replaced by genome editing (GE) strategies as they are more efficient and less laborious. CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeat/CRISPR-associated system) was discovered as an adaptive immune system of bacteria and with the scientific advancements, it has been improvised into a revolutionary genome editing technique. Due to its specificity and easy handling, CRISPR/Cas9-based genome editing has been applied to a wide range of organisms for various research purposes. For pest control, diverse approaches have been applied utilizing CRISPR/Cas9-like systems, thereby making the pests susceptible to various insecticides, compromising the reproductive fitness of the pest, hindering the metamorphosis of the pest, and there have been many other benefits. This article reviews the efficiency of CRISPR/Cas9 and proposes potential research ideas for CRISPR/Cas9-based integrated pest management. CRISPR/Cas9 technology has been successfully applied to several insect pest species. However, there is no review available which thoroughly summarizes the application of the technique in insect genome editing for pest control. Further, authors have highlighted the advancements in CRISPR/Cas9 research and have discussed its future possibilities in pest management.

Fly Cell Atlas: A single-nucleus transcriptomic atlas of the adult fruit fly

For more than 100 years, the fruit fly Drosophila melanogaster has been one of the most studied model organisms. Here, we present a single-cell atlas of the adult fly, Tabula Drosophilae, that includes 580,000 nuclei from 15 individually dissected sexed tissues as well as the entire head and body, annotated to >250 distinct cell types. We provide an in-depth analysis of cell type-related gene signatures and transcription factor markers, as well as sexual dimorphism, across the whole animal. Analysis of common cell types between tissues, such as blood and muscle cells, reveals rare cell types and tissue-specific subtypes. This atlas provides a valuable resource for the Drosophila community and serves as a reference to study genetic perturbations and disease models at single-cell resolution.

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.

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.

A Candidate RNAi Screen Reveals Diverse RNA-Binding Protein Phenotypes in Drosophila Flight Muscle

The proper regulation of RNA processing is critical for muscle development and the fine-tuning of contractile ability among muscle fiber-types. RNA binding proteins (RBPs) regulate the diverse steps in RNA processing, including alternative splicing, which generates fiber-type specific isoforms of structural proteins that confer contractile sarcomeres with distinct biomechanical properties. Alternative splicing is disrupted in muscle diseases such as myotonic dystrophy and dilated cardiomyopathy and is altered after intense exercise as well as with aging. It is therefore important to understand splicing and RBP function, but currently, only a small fraction of the hundreds of annotated RBPs expressed in muscle have been characterized. Here, we demonstrate the utility of Drosophila as a genetic model system to investigate basic developmental mechanisms of RBP function in myogenesis. We find that RBPs exhibit dynamic temporal and fiber-type specific expression patterns in mRNA-Seq data and display muscle-specific phenotypes. We performed knockdown with 105 RNAi hairpins targeting 35 RBPs and report associated lethality, flight, myofiber and sarcomere defects, including flight muscle phenotypes for Doa, Rm62, mub, mbl, sbr, and clu. Knockdown phenotypes of spliceosome components, as highlighted by phenotypes for A-complex components SF1 and Hrb87F (hnRNPA1), revealed level- and temporal-dependent myofibril defects. We further show that splicing mediated by SF1 and Hrb87F is necessary for Z-disc stability and proper myofibril development, and strong knockdown of either gene results in impaired localization of kettin to the Z-disc. Our results expand the number of RBPs with a described phenotype in muscle and underscore the diversity in myofibril and transcriptomic phenotypes associated with splicing defects. Drosophila is thus a powerful model to gain disease-relevant insight into cellular and molecular phenotypes observed when expression levels of splicing factors, spliceosome components and splicing dynamics are altered.

Identification and characterization of troponin genes in Locusta migratoria

Troponin complex comprises three subunits, namely troponin C (TpnC), troponin I (TpnI) and troponin T (TpnT), and regulates the contraction of striated muscle. We found that the locust Locusta migratoria genome has one TpnT gene (LmTpnT), one TpnI gene (LmTpnI) and three TpnC genes (LmTpnC1, LmTpnC2 and LmTpnC3). Through alternative splicing, LmTpnT and LmTpnI potentially encode two and eight isoforms, respectively. The flight muscle and the jump muscle of L. migratoria express an identical LmTpnT isoform, but different LmTpnC isoforms and LmTpnI isoforms. LmTpnC2 and LmTpnC3 both contain highly conserved residues essential for calcium binding in the EF-hand II and IV, thus belonging two-site isoform. LmTpnC1 contains non-conserved substitutions in the EF-hand II and all highly conserved residues for calcium binding in the EF-hand IV. Mutagenesis and tyrosine fluorescence spectroscopic analysis show that both the EF-hand II and IV of LmTpnC1 can serve as calcium-binding site. Therefore, all three LmTpnC isoforms belong to two-site isoform. This is in contrast to the situation in the insect with asynchronous flight muscle, which expresses both one-site isoform and two-site isoform of TpnC. Those results suggest that the origination of insect asynchronous flight muscle is associated with the emergence of one-site isoform of TpnC.

Contributions of alternative splicing to muscle type development and function

Animals possess a wide variety of muscle types that support different kinds of movements. Different muscles have distinct locations, morphologies and contractile properties, raising the question of how muscle diversity is generated during development. Normal aging processes and muscle disorders differentially affect particular muscle types, thus understanding how muscles normally develop and are maintained provides insight into alterations in disease and senescence. As muscle structure and basic developmental mechanisms are highly conserved, many important insights into disease mechanisms in humans as well as into basic principles of muscle development have come from model organisms such as Drosophila, zebrafish and mouse. While transcriptional regulation has been characterized to play an important role in myogenesis, there is a growing recognition of the contributions of alternative splicing to myogenesis and the refinement of muscle function. Here we review our current understanding of muscle type specific alternative splicing, using examples of isoforms with distinct functions from both vertebrates and Drosophila. Future exploration of the vast potential of alternative splicing to fine-tune muscle development and function will likely uncover novel mechanisms of isoform-specific regulation and a more holistic understanding of muscle development, disease and aging.

Regulation of fiber-specific actin expression by the Drosophila SRF ortholog Blistered

Serum response factor (SRF) has an established role in controlling actin homeostasis in mammalian cells, yet its role in non-vertebrate muscle development has remained enigmatic. Here, we demonstrate that the single Drosophila SRF ortholog, termed Blistered (Bs), is expressed in all adult muscles, but Bs is required for muscle organization only in the adult indirect flight muscles. Bs is a direct activator of the flight muscle actin gene Act88F, via a conserved promoter-proximal binding site. However, Bs only activates Act88F expression in the context of the flight muscle regulatory program provided by the Pbx and Meis orthologs Extradenticle and Homothorax, and appears to function in a similar manner to mammalian SRF in muscle maturation. These studies place Bs in a regulatory framework where it functions to sustain the flight muscle phenotype in Drosophila Our studies uncover an evolutionarily ancient role for SRF in regulating muscle actin expression, and provide a model for how SRF might function to sustain muscle fate downstream of pioneer factors.

Myogenesis in Drosophila melanogaster: Dissection of Distinct Muscle Types for Molecular Analysis

Drosophila is a useful model organism for studying the molecular signatures that define specific muscle types during myogenesis. It possesses significant genetic conservation with humans for muscle disease causing genes and a lack of redundancy that simplifies functional analysis. Traditional molecular methods can be utilized to understand muscle developmental processes such as Western blots, in situ hybridizations, RT-PCR and RNAseq, to name a few. However, one challenge for these molecular methods is the ability to dissect different muscle types. In this protocol we describe some useful techniques for extracting muscles from the pupal and adult stages of development using flight and jump muscles as an example.

Tropomyosin isoforms differentially affect muscle contractility in the head and body regions of the nematode Caenorhabditis elegans

Tropomyosin, one of the major actin filament-binding proteins, regulates actin-myosin interaction and actin-filament stability. Multicellular organisms express a number of tropomyosin isoforms, but understanding of isoform-specific tropomyosin functions is incomplete. The nematode Caenorhabditis elegans has a single tropomyosin gene, lev-11, which has been reported to express four isoforms by using two separate promoters and alternative splicing. Here, we report a fifth tropomyosin isoform, LEV-11O, which is produced by alternative splicing that includes a newly identified seventh exon, exon 7a. By visualizing specific splicing events in vivo, we find that exon 7a is predominantly selected in a subset of the body wall muscles in the head, while exon 7b, which is the alternative to exon 7a, is utilized in the rest of the body. Point mutations in exon 7a and exon 7b cause resistance to levamisole--induced muscle contraction specifically in the head and the main body, respectively. Overexpression of LEV-11O, but not LEV-11A, in the main body results in weak levamisole resistance. These results demonstrate that specific tropomyosin isoforms are expressed in the head and body regions of the muscles and contribute differentially to the regulation of muscle contractility.

Progress and Prospects of CRISPR/Cas Systems in Insects and Other Arthropods

Clustered regularly interspaced short palindromic repeats (CRISPR) and the CRISPR-associated gene Cas9 represent an invaluable system for the precise editing of genes in diverse species. The CRISPR/Cas9 system is an adaptive mechanism that enables bacteria and archaeal species to resist invading viruses and phages or plasmids. Compared with zinc finger nucleases and transcription activator-like effector nucleases, the CRISPR/Cas9 system has the advantage of requiring less time and effort. This efficient technology has been used in many species, including diverse arthropods that are relevant to agriculture, forestry, fisheries, and public health; however, there is no review that systematically summarizes its successful application in the editing of both insect and non-insect arthropod genomes. Thus, this paper seeks to provide a comprehensive and impartial overview of the progress of the CRISPR/Cas9 system in different arthropods, reviewing not only fundamental studies related to gene function exploration and experimental optimization but also applied studies in areas such as insect modification and pest control. In addition, we also describe the latest research advances regarding two novel CRISPR/Cas systems (CRISPR/Cpf1 and CRISPR/C2c2) and discuss their future prospects for becoming crucial technologies in arthropods.

Stretch activation properties of Drosophila and Lethocerus indirect flight muscle suggest similar calcium-dependent mechanisms

Muscle stretch activation (SA) is critical for optimal cardiac and insect indirect flight muscle (IFM) power generation. The SA mechanism has been investigated for decades with many theories proposed, but none proven. One reason for the slow progress could be that multiple SA mechanisms may have evolved in multiple species or muscle types. Laboratories studying IFM SA in the same or different species have reported differing SA functional properties which would, if true, suggest divergent mechanisms. However, these conflicting results might be due to different experimental methodologies. Thus, we directly compared SA characteristics of IFMs from two SA model systems, Drosophila and Lethocerus, using two different fiber bathing solutions. Compared with Drosophila IFM, Lethocerus IFM isometric tension is 10- or 17-fold higher and SA tension was 5- or 10-fold higher, depending on the bathing solution. However, the rate of SA tension generation was 9-fold faster for Drosophila IFM. The inverse differences between rate and tension in the two species causes maximum power output to be similar, where Drosophila power is optimized in the bathing solution that favors faster muscle kinetics and Lethocerus in the solution that favors greater tension generation. We found that isometric tension and SA tension increased with calcium concentration for both species in both solutions, reaching a maximum plateau around pCa 5.0. Our results favor a similar mechanism for both species, perhaps involving a troponin complex that does not fully calcium activate the thin filament thus leaving room for further tension generation by SA.