Involvement of chitin in exoskeleton morphogenesis in Drosophila melanogaster

Butterfly pupal wing tissue with an eyespot organizer

Butterfly wing eyespots are developmentally determined at the early pupal stage, when prospective eyespot focal cells underneath the pupal cuticle focal spot function as eyespot organizers in the pupal wing tissue. Here, we performed light microscopy and transmission electron microscopy (TEM) to describe cellular structures of pupal wing tissue with an eyespot organizer immediately after pupation using the Blue Pansy butterfly Junonia orithya. The pupal forewing dorsal epidermis was a pseudostratified monolayer of vertically elongated epidermal cells. The apical portion of the cells adhered laterally to one another, but their medial and basal portions were thinner than the apical portion and were tilted to enclose cells at the center, forming a cellular cluster. The cellular cluster at the organizer was relatively large laterally and vertically. The apical portion of the cells and its corresponding cuticle at the organizer were thicker than those in the surroundings. The innermost cuticle layer was being synthesized, indicating high cuticle synthesis and secretion activity of the cells. At the medial and basal portions of the dorsal epidermis, there were many intracellular and extracellular vacuole-like globules, most likely containing extracellular matrix molecules. Some of the basal processes from epidermal cells extended to form protrusions of the basement membrane, which was often attended by hemocytes. These results suggest that the butterfly eyespot organizer is composed of a single or a few cellular clusters that secrete more cuticle than surrounding clusters, supporting the pupal cuticle hypothesis that cuticle formation is critical for eyespot color pattern determination in butterflies.

Lagging Brain Gene Expression Patterns of Drosophila melanogaster Young Adult Males Confound Comparisons Between Sexes

Many species, including fruit flies (Drosophila melanogaster), are sexually dimorphic. Phenotypic variation in morphology, physiology, and behavior can affect development, reproduction, health, and aging. Therefore, designating sex as a variable and sex-blocking should be considered when designing experiments. The brain regulates phenotypes throughout the lifespan by balancing survival and reproduction, and sex-specific development at each life stage is likely. Changes in morphology and physiology are governed by differential gene expression, a quantifiable molecular marker for age- and sex-specific variations. We assessed the fruit fly brain transcriptome at three adult ages for gene expression signatures of sex, age, and sex-by-age: 6698 genes were differentially expressed between sexes, with the most divergence at 3 days. Between ages, 31.1% of 6084 differentially expressed genes (1890 genes) share similar expression patterns from 3 to 7 days in females, and from 7 to 14 days in males. Most of these genes (90.5%, 1712) were upregulated and enriched for chemical stimulus detection and/or cilium regulation. Our data highlight an important delay in male brain gene regulation compared to females. Because significant delays in expression could confound comparisons between sexes, studies of sexual dimorphism at phenotypically comparable life stages rather than chronological age should be more biologically relevant.

The chitinase genes TuCht4 and TuCht10 are indispensable for molting and survival of Tetranychus urticae

Insect chitinases (Chts) play a crucial role in the molting process, enabling continuous growth through sequential developmental stages. Based on their high homology to insect Chts, TuCht1 (group II), TuCht4 (group I) and TuCht10 (group IV) were identified, and their roles during molting process were investigated. TuCht1 was mainly expressed in the deutonymphal stage, while TuCht4 was mainly expressed in the nymphal stage and the highest expression level of TuCht10 was observed in the larvae. Feeding RNAi assays have shown that group I TuCht4 and group Ⅳ TuCht10 are involved in mite molting. Suppression of TuCht4 or TuCht10 resulted in high mortality, molting abnormalities and the absence of distinct electron dense layers of chitinous horizontal laminae in the cuticle, as demonstrated by scanning electron microscopy and transmission electron microscopy. The nanocarrier mediated RNAi had significantly higher RNAi efficiency and caused higher mortality. The results of the present study suggest that chitinase genes TuCht4 and TuCht10 are potential targets for dietary RNAi, and demonstrates a nanocarrier-mediated delivery system to enhance the bioactivity of dsRNA, providing a potential technology for green pest management.

Modulation of host lipid metabolism by virus infection leads to exoskeleton damage in shrimp

The arthropod exoskeleton provides protection and support and is vital for survival and adaption. The integrity and mechanical properties of the exoskeleton are often impaired after pathogenic infection; however, the detailed mechanism by which infection affects the exoskeleton remains largely unknown. Here, we report that the damage to the shrimp exoskeleton is caused by modulation of host lipid profiles after infection with white spot syndrome virus (WSSV). WSSV infection disrupts the mechanical performance of the exoskeleton by inducing the expression of a chitinase (Chi2) in the sub-cuticle epidermis and decreasing the cuticle chitin content. The induction of Chi2 expression is mediated by a nuclear receptor that can be activated by certain enriched long-chain saturated fatty acids after infection. The damage to the exoskeleton, an aftereffect of the induction of host lipogenesis by WSSV, significantly impairs the motor ability of shrimp. Blocking the WSSV-caused lipogenesis restored the mechanical performance of the cuticle and improved the motor ability of infected shrimp. Therefore, this study reveals a mechanism by which WSSV infection modulates shrimp internal metabolism resulting in phenotypic impairment, and provides new insights into the interactions between the arthropod host and virus.

Dynamics of cuticle-associated transcript profiles during moulting of the bed bug Cimexlectularius

The bed bug Cimex lectularius is a worldwide human pest. The sequenced genome allows molecular analyses of all aspects of bed bug biology. The present work was conducted to contribute to bed bug cuticle biology. As in other insect species, the C. lectularius cuticle consists of the three horizontal layers procuticle, epicuticle and envelope. To analyse the genes needed for the establishment of the stratified cuticle, we studied the expression pattern of 42 key cuticle-related genes at the transition of the penultimate nymphal stage to adult animals when a new cuticle is formed. Based on gene expression dynamics, in simplified model, we distinguish two key events during cuticle renewal in C. lectularius. First, upon blood feeding, modulation of ecdysone signalling culminates in the transcriptional activation of the transcription factor Clec-Ftz-F1 that possibly controls the expression of 32 of the 42 genes tested. Second, timed expression of Clec-Ftz-F1 seems to depend also on the insulin signalling pathway as RNA interference against transcripts of the insulin receptor delays Clec-Ftz-F1 expression and stage transition. An important observation of our transcript survey is that genes needed for the construction of the three cuticle layers are largely expressed simultaneously. Based on these data, we hypothesise a considerable synchronous mechanism of layer formation rather than a strictly sequential one. Together, this work provides a basis for functional analyses of cuticle formation in C. lectularius.

Insights Into a Chitin Synthase of Kuruma Shrimp Penaeus japonicus and Its Role in Peritrophic Membrane and Cuticle Formation

Synthesis of chitin is a subject of great interest in the fields of physiology and immunology of crustaceans. Chitinous tissues include not only the carapace, but also an acellular membrane in the intestine called the peritrophic membrane (PM). Here, we describe the first report of chitin synthase (CHS) of a penaeid shrimp, kuruma shrimp Penaeus japonicus. Histological observations showed that fecal matter in the midgut of kuruma shrimp was wrapped with a PM, which physically separated it from the midgut epithelium. Subsequently, the chitin synthase transcript was amplified from the midgut of the shrimp. The chitin synthase gene of kuruma shrimp (MjCHS) encodes 1,523 amino acid residues. Structural prediction analysis showed that the N-terminal region of MjCHS protein included nine transmembrane helices, the middle region included the catalytic region with several conserved motifs which are found in CHSs from other arthropods, and the C-terminal region included seven transmembrane helices. Although insects have distinct exoskeletal and intestinal chitin synthases, the phylogenetic analysis suggested that crustaceans have a single CHS. MjCHS mRNA was constantly detected in the digestive tract, including the midgut and hepatopancreas of both juvenile and adult kuruma shrimp, suggesting a stable synthesis of chitin in those organs. In contrast, MjCHS mRNA was also detected in the hindgut and uropod of juvenile shrimp. After molting, the mRNA levels of MjCHS in the stomach and uropod were higher than other molting cycles. These results suggest that MjCHS contributes to chitin synthesis in both the digestive tract and the epidermis, providing fundamental insights into chitin synthesis of crustaceans.

Comparative transcriptome analysis to unveil genes affecting the host cuticle destruction in Metarhizium rileyi

Insect pathogenic fungi, also known as entomopathogenic fungi, are one of the largest insect pathogenic microorganism communities, represented by Beauveria spp. and Metarhizium spp. Entomopathogenic fungi have been proved to be a great substitute for chemical pesticide in agriculture. In fact, a lot of functional genes were also already characterized in entomopathogenic fungi, but more depth of exploration is still needed to reveal their complicated pathogenic mechanism to insects. Metarhizium rileyi (Nomuraea rileyi) is a great potential biocontrol fungus that can parasitize more than 40 distinct species (mainly Lepidoptera: Noctuidae) to cause large-scale infectious diseases within insect population. In this study, a comparative analysis of transcriptome profile was performed with topical inoculation and hemolymph injection to character the infectious pattern of M. rileyi. Appressorium and multiple hydrolases are indispensable constituents to break the insect host primary cuticle defense in entomopathogenic fungi. Within our transcriptome data, numerous transcripts related to destruction of insect cuticle rather growth regulations were obtained. Most importantly, some unreported ribosomal protein genes and novel unannotated protein (hypothetical protein) genes were proved to participate in the course of pathogenic regulation. Our current data provide a higher efficiency gene library for virulence factors screen in M. rileyi, and this library may be also useful for furnishing valuable information on entomopathogenic fungal pathogenic mechanisms to host.

Live Detection of Intracellular Chitin in Butterfly Wing Epithelial Cells In Vivo Using Fluorescent Brightener 28: Implications for the Development of Scales and Color Patterns

Chitin is the major component of the extracellular cuticle and plays multiple roles in insects. In butterflies, chitin builds wing scales for structural colors. Here, we show that intracellular chitin in live cells can be detected in vivo with fluorescent brightener 28 (FB28), focusing on wing epithelial cells of the small lycaenid butterfly Zizeeria maha immediately after pupation. A relatively small number of cells at the apical surface of the epithelium were strongly FB28-positive in the cytosol and seemed to have extensive ER-Golgi networks, which may be specialized chitin-secreting cells. Some cells had FB28-positive tadpole-tail-like or rod-like structures relative to the nucleus. We detected FB28-positive hexagonal intracellular objects and their associated structures extending toward the apical end of the cell, which may be developing scale bases and shafts. We also observed FB28-positive fibrous intracellular structures extending toward the basal end. Many cells were FB28-negative in the cytosol, which contained FB28-positive dots or discs. The present data are crucial to understanding the differentiation of the butterfly wing epithelium, including scale formation and color pattern determination. The use of FB28 in probing intracellular chitin in live cells may be applicable to other insect systems.

Expressions and functions of RR-1 cuticular protein genes in the integument of Mythimna separata

As the most outer layer between itself and the environment, integuments are necessary for insects with various important functions. Cuticular proteins (CPs) are the main components in integuments, while the functions of CP genes remain unknown in Mythimna separata (Walker), which is a devastating agricultural pest. In this study, 79 CP genes were identified from the transcriptomes of larval integuments, 57 of which were from the family containing conserved Rebers & Riddiford (R&R) consensus (CPR family). Amongst these CPRs, 44 genes belonged to the subfamily with RR-1 motif (RR-1 genes) and clustered into three clades, with the top 15 most abundant RR-1 genes identified based on fragments per kilobase per million mapped fragments (FPKM) values. RT-qPCR analysis showed that most of RR-1 genes such as MsCPR1-4 were highly expressed at larval stages and in their integuments. The expression levels of RR-1 genes were generally decreased at the beginning but increased at the late stage of molting process. RNAi was applied for six RR-1 genes, and MsCPR1-4 were knocked down significantly. Silence of MsCPR2 resulted in abnormal integument formed after molting, while knockdown of MsCPR3 and MsCPR4 led to failure of molting, respectively. No phenotype was obtained for the RNAi of MsCPR1. Therefore, the expression of RR-1 genes and their functions were analyzed in the development of integuments in M. separata, providing new insights of RR-1 genes and potential targets for the development of growth regulators and new insecticides for M. separata.

Protein Delivery to Insect Epithelial Cells In Vivo: Potential Application to Functional Molecular Analysis of Proteins in Butterfly Wing Development

Protein delivery to cells in vivo has great potential for the functional analysis of proteins in nonmodel organisms. In this study, using the butterfly wing system, we investigated a method of protein delivery to insect epithelial cells that allows for easy access, treatment, and observation in real time in vivo. Topical and systemic applications (called the sandwich and injection methods, respectively) were tested. In both methods, green/orange fluorescent proteins (GFP/OFP) were naturally incorporated into intracellular vesicles and occasionally into the cytosol from the apical surface without any delivery reagent. However, the antibodies were not delivered by the sandwich method at all, and were delivered only into vesicles by the injection method. A membrane-lytic peptide, L17E, appeared to slightly improve the delivery of GFP/OFP and antibodies. A novel peptide reagent, ProteoCarry, successfully promoted the delivery of both GFP/OFP and antibodies into the cytosol via both the sandwich and injection methods. These protein delivery results will provide opportunities for the functional molecular analysis of proteins in butterfly wing development, and may offer a new way to deliver proteins into target cells in vivo in nonmodel organisms.

A dynamic interplay between chitin synthase and the proteins Expansion/Rebuf reveals that chitin polymerisation and translocation are uncoupled in Drosophila

Chitin is a highly abundant polymer in nature and a principal component of apical extracellular matrices in insects. In addition, chitin has proved to be an excellent biomaterial with multiple applications. In spite of its importance, the molecular mechanisms of chitin biosynthesis and chitin structural diversity are not fully elucidated yet. To investigate these issues, we use Drosophila as a model. We previously showed that chitin deposition in ectodermal tissues requires the concomitant activities of the chitin synthase enzyme Kkv and the functionally interchangeable proteins Exp and Reb. Exp/Reb are conserved proteins, but their mechanism of activity during chitin deposition has not been elucidated yet. Here, we carry out a cellular and molecular analysis of chitin deposition, and we show that chitin polymerisation and chitin translocation to the extracellular space are uncoupled. We find that Kkv activity in chitin translocation, but not in polymerisation, requires the activity of Exp/Reb, and in particular of its conserved Nα-MH2 domain. The activity of Kkv in chitin polymerisation and translocation correlate with Kkv subcellular localisation, and in absence of Kkv-mediated extracellular chitin deposition, chitin accumulates intracellularly as membrane-less punctae. Unexpectedly, we find that although Kkv and Exp/Reb display largely complementary patterns at the apical domain, Exp/Reb activity nonetheless regulates the topological distribution of Kkv at the apical membrane. We propose a model in which Exp/Reb regulate the organisation of Kkv complexes at the apical membrane, which, in turn, regulates the function of Kkv in extracellular chitin translocation.

The Osiris family genes function as novel regulators of the tube maturation process in the Drosophila trachea

Drosophila trachea is a premier model to study tube morphogenesis. After the formation of continuous tubes, tube maturation follows. Tracheal tube maturation starts with an apical secretion pulse that deposits extracellular matrix components to form a chitin-based apical luminal matrix (aECM). This aECM is then cleared and followed by the maturation of taenidial folds. Finally, air fills the tubes. Meanwhile, the cellular junctions are maintained to ensure tube integrity. Previous research has identified several key components (ER, Golgi, several endosomes) of protein trafficking pathways that regulate the secretion and clearance of aECM, and the maintenance of cellular junctions. The Osiris (Osi) gene family is located at the Triplo-lethal (Tpl) locus on chromosome 3R 83D4-E3 and exhibits dosage sensitivity. Here, we show that three Osi genes (Osi9, Osi15, Osi19), function redundantly to regulate adherens junction (AJ) maintenance, luminal clearance, taenidial fold formation, tube morphology, and air filling during tube maturation. The localization of Osi proteins in endosomes (Rab7-containing late endosomes, Rab11-containing recycling endosomes, Lamp-containing lysosomes) and the reduction of these endosomes in Osi mutants suggest the possible role of Osi genes in tube maturation through endosome-mediated trafficking. We analyzed tube maturation in zygotic rab11 and rab7 mutants, respectively, to determine whether endosome-mediated trafficking is required. Interestingly, similar tube maturation defects were observed in rab11 but not in rab7 mutants, suggesting the involvement of Rab11-mediated trafficking, but not Rab7-mediated trafficking, in this process. To investigate whether Osi genes regulate tube maturation primarily through the maintenance of Rab11-containing endosomes, we overexpressed rab11 in Osi mutant trachea. Surprisingly, no obvious rescue was observed. Thus, increasing endosome numbers is not sufficient to rescue tube maturation defects in Osi mutants. These results suggest that Osi genes regulate other aspects of endosome-mediated trafficking, or regulate an unknown mechanism that converges or acts in parallel with Rab11-mediated trafficking during tube maturation.

Polarized transport of membrane and secreted proteins during lumen morphogenesis

A ubiquitous feature of animal development is the formation of fluid-filled cavities or lumina, which transport gases and fluids across tissues and organs. Among different species, lumina vary drastically in size, scale, and complexity. However, all lumen formation processes share key morphogenetic principles that underly their development. Fundamentally, a lumen simply consists of epithelial cells that encapsulate a continuous internal space, and a common way of building a lumen is via opening and enlarging by filling it with fluid and/or macromolecules. Here, we discuss how polarized targeting of membrane and secreted proteins regulates lumen formation, mainly focusing on ion transporters in vertebrate model systems. We also discuss mechanistic differences observed among invertebrates and vertebrates and describe how the unique properties of the Na+/K+-ATPase and junctional proteins can promote polarization of immature epithelia to build lumina de novo in developing organs.

Mutation of a lepidopteran-specific PMP-like protein, BmLSPMP-like, induces a stick body shape in silkworm, Bombyx mori

BACKGROUND

Lepidoptera is one of the largest orders of insects, some of which are major pests of crops and forests. The cuticles of lepidopteran pests play important roles in defense against insecticides and pathogens, and are indispensable for constructing and maintaining extracellular structures and locomotion during their life cycle. Lepidopteran-specific cuticular proteins could be potential targets for lepidopteran pest control. But information on this is limited. Our research aimed to screen the lepidopteran-specific cuticular proteins using the lepidopteran model, the silkworm, to explore the molecular mechanism underlying the involvement of cuticular proteins in body shape construction.

RESULTS

Positional cloning showed that BmLSPMP-like, a gene encoding a lepidopteran-specific peritrophic matrix protein (PMP) like protein which includes a peritrophin A-type chitin-binding domain (CBM_14), is responsible for the stick (sk) mutation. BmLSPMP-like is an evolutionarily conserved gene that exhibits synteny in Lepidoptera and underwent purifying selection during evolution. Expression profiles demonstrated that BmLSPMP-like is expressed in chitin-forming tissues, testis and ovary, and accumulates in the cuticle. BmLSPMP-like knockout, generated with CRISPR/Cas9, resulted in a stick-like larval body shape phenotype. Over-expression of BmLSPMP-like in the sk mutant rescued its abnormal body shape. The results showed that BmLSPMP-like may be involved in assemblage in the larval cuticle.

CONCLUSION

Our results suggested that the dysfunction of BmLSPMP-like may result in a stick body shape phenotype in silkworm, through the regulation of the arrangement of the chitinous laminae and cuticle thickness. Our study provides new evidence of the effects of LSPMP-likes on lepidopteran body shape formation, metamorphosis and mortality, which could be an eco-friendly target for lepidopteran pest management. © 2022 Society of Chemical Industry.

Butterfly Wing Color Pattern Modification Inducers May Act on Chitin in the Apical Extracellular Site: Implications in Morphogenic Signals for Color Pattern Determination

Butterfly wing color patterns are modified by various treatments, such as temperature shock, injection of chemical inducers, and covering materials on pupal wing tissue. Their mechanisms of action have been enigmatic. Here, we investigated the mechanisms of color pattern modifications usingthe blue pansy butterfly Junoniaorithya. We hypothesized that these modification-inducing treatments act on the pupal cuticle or extracellular matrix (ECM). Mechanical load tests revealed that pupae treated with cold shock or chemical inducers were significantly less rigid, suggesting that these treatments made cuticle formation less efficient. A known chitin inhibitor, FB28 (fluorescent brightener 28), was discovered to efficiently induce modifications. Taking advantage of its fluorescent character, fluorescent signals from FB28 were observed in live pupae in vivo from the apical extracellular side and were concentrated at the pupal cuticle focal spots immediately above the eyespot organizing centers. It was shown that chemical modification inducers and covering materials worked additively. Taken together, various modification-inducing treatments likely act extracellularly on chitin or other polysaccharides to inhibit pupal cuticle formation or ECM function, which probably causes retardation of morphogenic signals. It is likely that an interactive ECM is required for morphogenic signals for color pattern determination to travel long distances.

Characterization of cuticular proteins in CPR family in the wolf spider, Pardosa pseudoannulata, and the response of one subfamily genes to environmental stresses

Cuticular protein (CP) plays an essential role in the construction and function of exoskeleton in arthropods. CPR family, CP with Rebers and Riddiford (R&R) Consensus, is the largest CP family in insects, but it lacks systematic research in non-insect arthropods. In this study, we explored CPRs in the wolf spider, Pardosa pseudoannulata, a predator to many insect pests. We totally identified 152 CPRs in P. pseudoannulata genome, which were divided into two subgroups based on R&R Consensus sequences, with 12 CPRs in RR-1 and 140 in RR-2. All RR-2 members presented a novel Consensus with 34 amino acids, G-x(8)-G-x(6)-Y-x-A-x(3)-G-x(7)-N-E-x-G, which was a common characteristic for RR-2 CPRs in chelicerates. Transcriptome data was used to document the expression patterns of CPR genes in different tissues and ecdysis processes. The specific expressions were found for part CPR genes, such as five RR-2 genes that were specifically expressed in male genital bulbs and eleven RR-1 genes that were highly expressed in the integument. Due to the limited number and integument-specific expression of RR-1 genes, we further analyzed their responses to different environmental stresses at the transcriptional level. Except for PapsCPR11, ten RR-1 genes responded to at least one environmental stress, among with the expression of PapsCPR12 was significantly changed by three stresses (dryness, low temperature and imidacloprid treatments). Silencing PapsCPR12 increased the tolerance of P. pseudoannulata to imidacloprid. Overall, the results presented novel Consensus characteristics of CPRs in P. pseudoannulata, which was helpful for the identification and evolution analysis of CPRs in non-insect arthropods.

Characterization of Chitin Synthase A cDNA from Diaphorina citri (Hemiptera: Liviidae) and Its Response to Diflubenzuron

Diaphorina citri Kuwayama is the vector of HLB and one of the most common pests in citrus orchards in southern China. One of the most significant genes in D. citri's growth and development is the chitin synthase gene. In this study, the CHS gene (DcCHSA) of D. citri was cloned and analyzed by bioinformatics. According to RT-qPCR findings, DcCHSA was expressed at many growth processes of D. citri, with the greatest influence in the fifth-instar nymph. The molting failure rate and mortality of D. citri rose as DFB concentration increased in this research, as did the expression level of DcCHSA. Feeding on DcCHSA caused a large drop in target gene expression, affected nymph molting, caused failure or even death in freshly eclosion adults, increased mortality, and reduced the molting success rate over time. These findings showed that DcCHSA was involved in nymph to adult development and may aid in the identification of molecular targets for D. citri regulation. It provided new ideas for further control of D. citri.

Zoledronate Extends Health Span and Survival via the Mevalonate Pathway in a FOXO-dependent Manner

Over recent decades, increased longevity has not been paralleled by extended health span, resulting in more years spent with multiple diseases in older age. As such, interventions to improve health span are urgently required. Zoledronate (Zol) is a nitrogen-containing bisphosphonate, which inhibits the farnesyl pyrophosphate synthase enzyme, central to the mevalonate pathway. It is already used clinically to prevent fractures in osteoporotic patients, who have been reported to derive unexpected and unexplained survival benefits. Using Drosophila as a model we determined the effects of Zol on life span, parameters of health span (climbing ability and intestinal dysplasia), and the ability to confer resistance to oxidative stress using a combination of genetically manipulated Drosophila strains and Western blotting. Our study shows that Zol extended life span, improved climbing activity, and reduced intestinal epithelial dysplasia and permeability with age. Mechanistic studies showed that Zol conferred resistance to oxidative stress and reduced accumulation of X-ray-induced DNA damage via inhibition of farnesyl pyrophosphate synthase. Moreover, Zol was associated with inhibition of phosphorylated AKT in the mammalian traget of rapamycin pathway downstream of the mevalonate pathway and required dFOXO for its action, both molecules associated with increased longevity. Taken together, our work indicates that Zol, a drug already widely used to prevent osteoporosis and dosed only once a year, modulates important mechanisms of aging. Its repurposing holds great promise as a treatment to improve health span.

Genome-wide in vitro and in vivo RNAi screens reveal Fer3 to be an important regulator of kkv transcription in Drosophila

Krotzkopf verkehrt (kkv) is a key enzyme that catalyzes the synthesis of chitin, an important component of the Drosophila epidermis, trachea, and other tissues. Here, we report the use of comprehensive RNA interference (RNAi) analyses to search for kkv transcriptional regulators. A cell-based RNAi screen identified 537 candidate kkv regulators on a genome-wide scale. Subsequent use of transgenic Drosophila lines expressing RNAi constructs enabled in vivo validation, and we identified six genes as potential kkv transcriptional regulators. Weakening of the kkvDsRed signal, an in vivo reporter indicating kkv promoter activity, was observed when the expression of Akirin, NFAT, 48 related 3 (Fer3), or Autophagy-related 101(Atg101) was knocked down in Drosophila at the 3rd-instar larval stage; whereas we observed disoriented taenidial folds on larval tracheae when Lines (lin) or Autophagy-related 3 (Atg3) was knocked down in the tracheae. Fer3, in particular, has been shown to be an important factor in the activation of kkv transcription via specific binding with the kkv promoter. The genes involved in the chitin synthesis pathway were widely affected by the downregulation of Fer3. Furthermore, Atg101, Atg3, Akirin, Lin, NFAT, Pnr, and Abd-A showed that the potential complex mechanism of kkv transcription is regulated by an interaction network with bithorax complex components. Our study revealed the hitherto unappreciated diversity of modulators impinging on kkv transcription and opens new avenues in the study of kkv regulation and chitin biosynthesis.

Fluorescent Microscopy-Based Detection of Chitin in Intact Drosophila melanogaster

Chitin is the major scaffolding component of the insect cuticle. Ultrastructural analyses revealed that chitin adopts a quasi-crystalline structure building sheets of parallel running microfibrils. These sheets called laminae are stacked either helicoidally or with a preferred orientation of the microfibrils. Precise control of chitin synthesis is mandatory to ensure the correct chitin assembly and in turn proper function of cuticular structures. Thus, evaluation of chitin-metabolism deficient phenotypes is a key to our understanding of the function of the proteins and enzymes involved in cuticle architecture and more generally in cuticle biology in insects. Usually, these phenotypes have been assessed using electron microscopy, which is time-consuming and labor intensive. This stresses the need for rapid and straightforward histological methods to visualize chitin at the whole tissue level. Here, we propose a simple method of chitin staining using the common polysaccharide marker Fluorescent brightener 28 (FB28) in whole-mount Drosophila melanogaster. To overcome the physical barrier of FB28 penetration into the cuticle, staining is performed at 65°C without affecting intactness. We quantify FB28 fluorescence in three functionally different cuticular structures namely wings, dorsal abdomens and forelegs by fluorescence microscopy. We find that, as expected, cuticle pigmentation may interfere with FB28 staining. Down-regulation of critical genes involved in chitin metabolism, including those coding for chitin synthase or chitinases, show that FB28 fluorescence reflects chitin content in these organs. We think that this simple method could be easily applied to a large variety of intact insects.

Chitin synthase 1 and five cuticle protein genes are involved in serosal cuticle formation during early embryogenesis to enhance eggshells in Nilaparvata lugens

Many holo- and hemimetabolous insects enhance their eggshells during embryogenesis by forming a serosal cuticle (SC). To date, scholarly understanding of the SC composition and SC-related gene functions has been limited, especially for hemimetabolous insects. In this study, we initially performed transmission electron microscopic (TEM) observation and chitin staining of the SC in Nilaparvata lugens, a hemimetabolous rice pest known as the brown planthopper (BPH). We confirmed that the SC was a chitin-rich lamellar structure deposited gradually during the early embryogenesis. Parental RNA interference (RNAi) against Nilaparvata lugens chitin synthase 1 (NlCHS1) in newly emerged and matured females resulted in decreases of egg hatchability by 100% and 76%, respectively. Ultrastructural analyses revealed loss of the lamellar structure of the SC in dsNlCHS1-treated eggs. According to temporal expression profiles, five cuticle protein coding genes, NlugCpr1/2/3/8/90, were specifically or highly expressed during the SC formation period, and NlugCpr1/2/3/90 were further detected in 72 h eggshells extract by ultra-performance liquid chromatography-tandem mass spectrometry/mass spectrometry. NlugCpr2/3/90 were likely three SC-specific cuticle proteins. TEM observations of the SC following parental RNAi against NlugCpr1/2/3/8/90 demonstrated that NlugCpr3/8/90 were essential for SC formation. The study provided an understanding of the SC formation process and SC-related cuticle proteins in BPHs, which offer potential targets for pest control in the egg stage as well.

Characterization of Gfat1 (zeppelin) and Gfat2, Essential Paralogous Genes Which Encode the Enzymes That Catalyze the Rate-Limiting Step in the Hexosamine Biosynthetic Pathway in Drosophila melanogaster

The zeppelin (zep) locus is known for its essential role in the development of the embryonic cuticle of Drosophila melanogaster. We show here that zep encodes Gfat1 (Glutamine: Fructose-6-Phosphate Aminotransferase 1; CG12449), the enzyme that catalyzes the rate-limiting step in the hexosamine biosynthesis pathway (HBP). This conserved pathway diverts 2%-5% of cellular glucose from glycolysis and is a nexus of sugar (fructose-6-phosphate), amino acid (glutamine), fatty acid [acetyl-coenzymeA (CoA)], and nucleotide/energy (UDP) metabolism. We also describe the isolation and characterization of lethal mutants in the euchromatic paralog, Gfat2 (CG1345), and demonstrate that ubiquitous expression of Gfat1+ or Gfat2+ transgenes can rescue lethal mutations in either gene. Gfat1 and Gfat2 show differences in mRNA and protein expression during embryogenesis and in essential tissue-specific requirements for Gfat1 and Gfat2, suggesting a degree of functional evolutionary divergence. An evolutionary, cytogenetic analysis of the two genes in six Drosophila species revealed Gfat2 to be located within euchromatin in all six species. Gfat1 localizes to heterochromatin in three melanogaster-group species, and to euchromatin in the more distantly related species. We have also found that the pattern of flanking-gene microsynteny is highly conserved for Gfat1 and somewhat less conserved for Gfat2.

Chitin deacetylase 2 is essential for molting and survival of Tetranychus urticae

Chitin metabolism has long been considered promising targets for development of biorational pesticides. Considering the increasing challenges of controlling the twospotted spider mite, Tetranychus urticae Koch, the roles of chitin deacetylases (CDAs) during molting process and mite development are explored. TuCDA1 and TuCDA2 differ in expression patterns during the development process. Feeding of double-strand RNA (dsRNA) against TuCDA1 or TuCDA2 has lethal effects on the mites. Especially TuCDA2 displays a much stronger phenotype than TuCDA1 (p = 0.0003). The treated mites fail to shed the old cuticle and are trapped within exuviate until they die. The aberrant cuticle structure observed by scanning electronmicroscopy (SEM) and transmission electron microscopy (TEM) may be responsible for the lethal phenotype of TuCDA1 and TuCDA2 knocked down mites. However, treatment with both dsRNA-CDA1 and dsRNA-CDA2 cannot significantly enhance the lethal effects of dsRNA-CDA2, which indicates partially redundant function of TuCDA1 and TuCDA2. TuCDA2 may play a key role during the molting and development process. Chitin-modifying enzyme such as TuCDA2 is potential target of RNA interference through feeding.

Knockdown of specific cuticular proteins analogous to peritrophin 3 genes disrupt larval and ovarian development in Bactrocera dorsalis (Diptera: Tephritidae)

Cuticular proteins (CPs) are critical components of the insect cuticle and play important roles in maintaining normal insect development and defense against various environmental stresses. The oriental fruit fly (Bactrocera dorsalis) is one of the most destructive pests worldwide, and its eight CPs analogous to peritrophin 3 (BdCPAP3) family genes have been identified in our previous study. In the present study, we further explored the possible roles of CPAP3 genes in B. dorsalis development. Each sequence of BdCPAP3 genes contained three conserved ChtBD2 (chitin-binding) domains. Spatial and temporal expression patterns revealed that the four BdCPAP3 genes (BdCPAP3-A1, B, E, and E2) might play important roles in larval pupariation of B. dorsalis. Moreover, treatment with a juvenile hormone analog (methoprene) significantly restricted expression of these four CPAP3 genes, whereas treatment with 20-hydroxy-ecdysone induced expression. The RNA interference (RNAi) results revealed that down-regulated CPAP3 genes led to significant delay of pupariation, and injection of dsBdCPAP3-E into 5-d-old B. dorsalis larvae caused approximately 40% mortality. Interestingly, we also confirmed that BdCPAP3-D2 was involved in B. dorsalis ovarian development. This study showed that some specific CPAP3 genes had crucial roles in B. dorsalis development, and these CP genes could be used as potential targets to control this pest via RNAi.

RNAi for chitin synthase 1 rather than 2 causes growth delay and molting defect in Henosepilachna vigintioctopunctata

Chitin synthase (CHS) plays a critical role in chitin synthesis and excretion. In most insects, CHSs have been segregated into 1 and 2 classes. CHS1 is responsible for chitin production in the ectodermally-derived epidermal cells. CHS2 is dedicated to chitin biosynthesis in the midgut peritrophic matrix (PM). Henosepilachna vigintioctopunctata is a serious pest of Solanaceae and Cucurbitaceae plants. In this study, we identified HvCHS1 and HvCHS2. We found that HvCHS1 was abundantly transcribed in the larval tracheae and epidermis, whereas HvCHS2 was mainly expressed in the guts. Escherichia coli HT115 expressed double stranded RNAs targeting HvCHS1 and HvCHS2 (dsCHS1 and dsCHS2) were used to immerse potato foliage and the treated leaves were provided to the newly-molted fourth- and third-instar larvae. Ingestion of dsCHS1 by the fourth-instar larvae significantly diminished the target mRNA level and had slight influence on the expression of HvCHS2. In contrast, consumption of dsCHS2 significantly lowered the target mRNA level but triggered the transcription of HvCHS1. Knockdown of HvCHS1, rather than HvCHS2, arrested larval development and impaired larva-pupa-adult transition. A large proportion of HvCHS1 hypomorphs became stunting prepupae, deformed pupae or misshapen adults. Moreover, knockdown of HvCHS1 damaged gut integrity, decreased cuticle thickness, and delayed the formation of newly-generated cuticle layer during ecdysis. Furthermore, depletion of HvCHS1 inhibited the development of trachea system and thinned tracheal taenidia. Ingestion of dsCHS1 at the third-instar stage caused similar but severe negative effects. Our results demonstrated that HvCHS1 is responsible for chitin biosynthesis during ecdysis. Moreover, HvCHS1 is a potential amenable target gene and young larvae are more susceptible to dsRNA.

Identification and expression analysis of cuticular protein genes in the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

Structural cuticular proteins (CPs) are major components of the insect cuticle, and they play critical roles in insect development and insecticide resistance. Here, a total of 196 CP genes were successfully annotated in the Plutella xylostella genome. On the basis of motif analysis, these CPs were classified into 10 different families, including 122 CPR, 12 CPAP1, 8 CPAP3, 9 CPLCP, 2 Tweedle, 1 CPF, 1 CPFL, 1 CPCFC, 17 CPG and 2 18 aa proteins, and the remaining 21 unclassified CPs were classed as cuticular proteins hypothetical (CPH). A phylogenetic analysis of CPs from different insects revealed species-specific clades of RR-1 and RR-2 genes, suggesting that CP gene duplication might occur independently among insect taxa, while we also found that some other CPs (such as CPAP1 and CPAP3) had a closer relationship based on their conserved domain architecture. Using available RNAseq libraries, the expression profiles of the CPs were analyzed over the four developmental stages of the insect (i.e., egg, larva, pupa, and adult), revealing stage-specific expression patterns for the CPs. In a chlorpyrifos resistant strain, 18 CP genes were found to be more than two-fold upregulated compared to the susceptible control strain, and qRT-PCR analysis showed that these CP genes were overexpressed after exposure to chlorpyrifos, suggesting a potential role in the molecular mechanism of insecticide resistance in P. xylostella. This study provides the tools and molecular basis to study the role of CPs in the post-embryonal development and the mechanisms of insecticide resistance of P. xylostella.

Transcriptional identification of differentially expressed genes during the prepupal-pupal transition in the oriental armyworm, Mythimna separata (Walker) (Lepidoptera: Noctuidae)

The oriental armyworm, Mythimna separata (Walker) is a serious pest of agriculture that does particular damage to Gramineae crops in Asia, Europe, and Oceania. Metamorphosis is a key developmental stage in insects, although the genes underlying the metamorphic transition in M. separata remain largely unknown. Here, we sequenced the transcriptomes of five stages; mature larvae (ML), wandering (W), and pupation (1, 5, and 10 days after pupation, designated P1, P5, and P10) to identify transition-associated genes. Four libraries were generated, with 22,884, 23,534, 26,643, and 33,238 differentially expressed genes (DEGs) for the ML-vs-W, W-vs-P1, P1-vs-P5, and P5-vs-P10, respectively. Gene ontology enrichment analysis of DEGs showed that genes regulating the biosynthesis of the membrane and integral components of the membrane, which includes the cuticular protein (CP), 20-hydroxyecdysone (20E), and juvenile hormone (JH) biosynthesis, were enriched. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that DEGs were enriched in the metabolic pathways. Of these DEGs, thirty CP, seventeen 20E, and seven JH genes were differentially expressed across the developmental stages. For transcriptome validation, ten CP, 20E, and JH-related genes were selected and verified by real-time PCR quantitative. Collectively, our results provided a basis for further studies of the molecular mechanism of metamorphosis in M. separata.

RNA-seq analysis of gene expression changes in cuticles during the larval-pupal metamorphosis of Plutella xylostella

The diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae) is a holometabolous insect that its cuticles must undergo the significant changes during the larval-pupal metamorphosis development. To elucidate these changes at molecular levels, RNA-seq analysis of cuticles from LLS (later fourth instar larval stage), PPS (prepupal stage) and PS (pupal stage) were performed in P. xylostella. In this paper, a total of 17,710 transcripts were obtained in the larval-pupal transition of P. xylostella, and out of which 2293 (881 up-regulated and 1412 down-regulated) and 2989 transcripts (2062 up-regulated and 927 down-regulated) were identified to be differentially expressed between LLS and PPS, as well as PPS and PS, respectively. The further GO and KEGG analysis of differentially expressed genes (DEGs) revealed that the 'structural constituent of cuticle', 'chitin metabolic process', 'chitin binding', 'tyrosine metabolism' and 'insect hormone biosynthesis' pathways were significantly enriched, indicating these pathways might be involved in the process of larval pupation in P. xylostella. Then, we found some genes that encoded cuticular proteins, chitinolytic enzymes, chitin synthesis enzymes, and cuticle tanning proteins changed their expression levels remarkably, indicating these genes might play important roles in the restruction (degradation and biosynthesis) of insect cuticles during the larval metamorphosis. Additionally, the significant changes in the mRNA levels of 20-hydroxyecdysone (20E) and juvenile hormone (JH) related genes suggested their crucial roles in regulating cuticle remodeling during the larval metamorphosis of P. xylostella. In conclusion, the present study provide us the comprehensive gene expression profiles to explore the molecular mechanisms of cuticle metamorphosis in P. xylostella, which laid a molecular basis to study roles of specific pathways and genes in insect development.

Glycosyltransferases: the multifaceted enzymatic regulator in insects

Glycosyltransferases (GTs) catalyse the reaction of glyco-conjugation of various biomolecules by transferring the saccharide moieties from an activated nucleotide sugar to nucleophilic glycosyl acceptor. In insects, GTs show diverse temporal and site-specific expression patterns and thus play significant roles in forming the complex biomolecular structures that are necessary for insect survival, growth and development. Several insects exhibit GT-mediated detoxification as a key defence strategy against plant allelochemicals and xenobiotic compounds, as well as a mechanism for pesticide cross-resistance. Also, these enzymes act as crucial effectors and modulators in various developmental processes of insects such as eye development, UV shielding, cuticle formation, epithelial development and other specialized functions. Furthermore, many of the known insect GTs have been shown to play a fundamental role in other physiological processes like body pigmentation, cuticular tanning, chemosensation and stress response. This review provides a detailed overview of the multifaceted functionality of insect GTs and summarizes numerous case studies associated with it.

A Tale of Two Transcriptomic Responses in Agricultural Pests via Host Defenses and Viral Replication

Autographa californica Multiple Nucleopolyhedrovirus (AcMNPV) is a baculovirus that causes systemic infections in many arthropod pests. The specific molecular processes underlying the biocidal activity of AcMNPV on its insect hosts are largely unknown. We describe the transcriptional responses in two major pests, Spodoptera frugiperda (fall armyworm) and Trichoplusia ni (cabbage looper), to determine the host-pathogen responses during systemic infection, concurrently with the viral response to the host. We assembled species-specific transcriptomes of the hemolymph to identify host transcriptional responses during systemic infection and assessed the viral transcript abundance in infected hemolymph from both species. We found transcriptional suppression of chitin metabolism and tracheal development in infected hosts. Synergistic transcriptional support was observed to suggest suppression of immune responses and induction of oxidative stress indicating disease progression in the host. The entire AcMNPV core genome was expressed in the infected host hemolymph with a proportional high abundance detected for viral transcripts associated with replication, structure, and movement. Interestingly, several of the host genes that were targeted by AcMNPV as revealed by our study are also targets of chemical insecticides currently used commercially to control arthropod pests. Our results reveal an extensive overlap between biological processes represented by transcriptional responses in both hosts, as well as convergence on highly abundant viral genes expressed in the two hosts, providing an overview of the host-pathogen transcriptomic landscape during systemic infection.

Isolation of Chitin from Black Soldier Fly (Hermetia illucens) and Its Usage to Metal Sorption

Chitin has become a desirable raw material used in various areas of life. The black soldier fly (Hermetia illucens) can be a source of this substance. In the literature, there are many methods of obtaining chitin but there is no one universal method of isolating it. In this publication, we present various procedures for the isolation of chitin from H. illucens pupal exuviae. The obtained chitin variants were characterized using different techniques (optical and confocal microscopy, FTIR, XRD, EDX, thermogravimetric analysis). The tested chitin isolated with an efficiency of 5.69-7.95% was the α form with a crystallinity degree of 60% and maximum degradation temperature of 392 °C. Furthermore, we characterized the nickel ion biosorption process on chitin and proposed the mechanism of this process to be ion exchange and complexation. There have been no such studies thus far on the isolation of chitin from H. illucens exuviae or on the biosorption of nickel ions on this type of biosorbent. The conducted research can be used to develop the application of chitin as a metal biosorbent that can be obtained with relatively high efficiency and good sorption properties.

Drosophila, Chitin and Insect Pest Management

Insects are a great menace in agriculture and vectors of human diseases. Hence, controlling insect populations is an important issue worldwide. A common strategy to control insects is the application of insecticides. However, insecticides entail three major problems. First, insecticides are chemicals that stress ecosystems and may even be harmful to humans. Second, insecticides are often unspecific and also eradicate beneficial insect species like the honeybee. Third, insects are able to develop resistance to insecticides. Therefore, the efficient generation of new potent insecticides and their intelligent delivery are the major tasks in agriculture. In addition, acceptance or refusal in society is a major issue that has to be considered in the application of a pest management strategy. In this paper, we unify two issues: 1) we illustrate that our molecular knowledge of the chitin synthesis and organization pathways may offer new opportunities to design novel insecticides that are environmentally harmless at the same time being specific to a pest species; and 2) we advocate that the fruit fly Drosophila melanogaster may serve as an excellent model of insect to study the effects of insecticides at the genetic, molecular and histology level in order to better understand their mode of action and to optimize their impact. Especially, chitin synthesis and organization proteins and enzymes are excellently dissected in the fruit fly, providing a rich source for new insecticide targets. Thus, D. melanogaster offers a cheap, efficient and fast assay system to address agricultural questions, as has been demonstrated to be the case in bio-medical research areas.

The Developmental Transcriptome of Bagworm, Metisa plana (Lepidoptera: Psychidae) and Insights into Chitin Biosynthesis Genes

Bagworm, Metisa plana (Lepidoptera: Psychidae) is a ubiquitous insect pest in the oil palm plantations. M. plana infestation could reduce the oil palm productivity by 40% if it remains untreated over two consecutive years. Despite the urgency to tackle this issue, the genome and transcriptome of M. plana have not yet been fully elucidated. Here, we report a comprehensive transcriptome dataset from four different developmental stages of M. plana, comprising of egg, third instar larva, pupa and female adult. The de novo transcriptome assembly of the raw data had produced a total of 193,686 transcripts, which were then annotated against UniProt, NCBI non-redundant (NR) database, Gene Ontology, Cluster of Orthologous Group, and Kyoto Encyclopedia of Genes and Genomes databases. From this, 46,534 transcripts were annotated and mapped to 146 known metabolic or signalling KEGG pathways. The paper further identified 41 differentially expressed transcripts encoding seven genes in the chitin biosynthesis pathways, and their expressions across each developmental stage were further analysed. The genetic diversity of M. plana was profiled whereby there were 21,516 microsatellite sequences and 379,895 SNPs loci found in the transcriptome of M. plana. These datasets add valuable transcriptomic resources for further study of developmental gene expression, transcriptional regulations and functional gene activities involved in the development of M. plana. Identification of regulatory genes in the chitin biosynthesis pathway may also help in developing an RNAi-mediated pest control management by targeting certain pathways, and functional studies of the genes in M. plana.

The Evolution of Phenotypic Plasticity in Response to Temperature Stress

Phenotypic plasticity is the ability of a single genotype to produce different phenotypes in response to environmental variation. The importance of phenotypic plasticity in natural populations and its contribution to phenotypic evolution during rapid environmental change is widely debated. Here, we show that thermal plasticity of gene expression in natural populations is a key component of its adaptation: evolution to novel thermal environments increases ancestral plasticity rather than mean genetic expression. We determined the evolution of plasticity in gene expression by conducting laboratory natural selection on a Drosophila simulans population in hot and cold environments. After more than 60 generations in the hot environment, 325 genes evolved a change in plasticity relative to the natural ancestral population. Plasticity increased in 75% of these genes, which were strongly enriched for several well-defined functional categories (e.g., chitin metabolism, glycolysis, and oxidative phosphorylation). Furthermore, we show that plasticity in gene expression of populations exposed to different temperatures is rather similar across species. We conclude that most of the ancestral plasticity can evolve further in more extreme environments.

Novaluron prevents oogenesis and oviposition by inducing ultrastructural changes in ovarian tissue of young adult Lygus lineolaris

BACKGROUND

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), has emerged as a major pest of cotton, Gossypium hirsutum L, in the mid-southern USA. In the early 1990s L. lineolaris populations developed resistance to several classes of conventional insecticides, increasing the need for insecticides with alternative modes of action such as insect growth regulators (IGRs) for integrated pest management (IPM). The benzoylphenyl urea (BPU) class of IGRs acts by disrupting the growth and development of immature stages of insects, but little is known about its impact on adult stages.

RESULTS

The effect of novaluron (Diamond™ 0.83EC), a BPU with known chitin synthesis inhibitor activity, was investigated on adult females of L. lineolaris. Treatment of 1-day-old adults with 600 ppm of novaluron in the diet prevented oviposition, while treatment of older females had no impact on oviposition. Oral novaluron exposure of adults of all ages reduced the viability of eggs laid. Novaluron treatment caused ultrastructural changes in the ovaries of 1-day-old adults (48 h post exposure), distorting the follicular epithelial cell architecture of developing oocytes. Additionally, novaluron treatment decreased the chitin content in ovarian tissue.

CONCLUSION

Our results suggest that chitin or chitin-like components in the developing ovaries of adult L. lineolaris are a target of IGRs such as novaluron, but its activity is specific to a critical time during development. This enhances our understanding of the effects of BPUs on adult insects and could lead to incorporation of IGRs in IPM for controlling adult insect pest populations in the field. © 2020 Society of Chemical Industry.

Chitinase 10 controls chitin amounts and organization in the wing cuticle of Drosophila

Wings are essential for insect fitness. A number of proteins and enzymes have been identified to be involved in wing terminal differentiation, which is characterized by the formation of the wing cuticle. Here, we addressed the question whether chitinase 10 (Cht10) may play an important role in chitin organization in the wings of the fruit fly Drosophila melanogaster. Initially, we first found that Cht10 expression coincides with the expression of the chitin synthase coding gene kkv. This suggests that the respective proteins may cooperate during wing differentiation. In tissue-specific RNA interference experiments, we demonstrate that suppression of Cht10 causes an excess in chitin amounts in the wing cuticle. Chitin organization is severely disrupted in these wings. Based on these data, we hypothesize that Cht10 restricts chitin amounts produced by Kkv in order to ensure normal chitin organization and wing cuticle formation. In addition, we found by scanning electron microscopy that Cht10 suppression also affects the cuticle surface. In turn, cuticle inward permeability is enhanced in Cht10-less wings. Moreover, flies with reduced Cht10 function are unable to fly. In conclusion, Cht10 is essential for wing terminal differentiation and function.

A double chitin catalytic domain-containing chitinase targeted by c-Jun is involved in immune responses in shrimp

Chitinases are a group of chitin-degrading enzymes widely distributed in organisms. Chitinases containing two chitin catalytic domains have been widely found in arthropods but their functions remain unclear. In this study, a member of these chitinases from Litopenaeus vannamei (dChi) was identified and functionally studied in the context of immunity. The promoter of dChi contained activator protein 1 (AP-1) binding sites and could be regulated by c-Jun. The recombinant dChi protein showed no bacteriostatic activity in vitro but knockdown of dChi in vivo increased the mortality of shrimp and the bacterial load in tissues after Vibrio parahaemolyticus infection, suggesting that dChi could play a positive role in antibacterial responses. However, silencing of dChi expression significantly decreased the mortality of WSSV-infected shrimp and down-regulated the viral load in tissues, indicating that dChi could facilitate WSSV infection. We further demonstrated that dChi was involved in regulation of the bacterial phagocytosis of hemocytes and expression of a series of immune related transcription factors and antimicrobial peptides. These indicated that the roles of dChi in antibacterial responses and anti-WSSV responses in vivo could result from its regulatory effects on the immune system. Taken together, the current study suggests that double chitin catalytic domain-containing chitinases could be important players in immune regulation in crustaceans.

Susceptibility of Chrysoperla externa (Hagen, 1861) (Neuroptera: Crysopidae) to insecticides used in coffee crops

The coffee crop hosts pests such as mites, mealybugs, and aphids which serve as food for the predator Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae). The preservation of this chrysopid in coffee agroecosystem is very important to achieve sustainability of this agricultural sector, and can be obtained by applying low toxicity insecticides. The present study aimed to evaluate the susceptibility of C. externa to azadiracthin, chlorpyrifos, ethiprole and teflubenzuron. Predator eggs, third instar larvae, pupae and adults were exposed to insecticides by Potter tower spraying. When evaluating exposure of C. externa eggs we observed that chlorpyrifos, ethiprole and teflubenzuron reduced larvae hatching, while azadiracthin prolonged first instar duration. Meanwhile, the exposure of third instar larvae to chlorpyrifos and ethiprole caused mortality of all insects after 72 h, while azadiracthin prolonged the larval development time; we also observed that no compound allowed the formation of adults. After pupae were exposed to chlorpyrifos and teflubenzuron, it was observed a reduction on the emergence of adults, while the longevity of adults from these pupae and the evaluated reproductive parameters were reduced by all insecticides. For the bioassay with adults, chlorpyrifos, ethiprole and teflubenzuron reduced the longevity of insects, while the reproductive parameters evaluated were negatively affected after exposure to azadiracthin and teflubenzuron. It was concluded that all insecticides negatively affected at least one biological characteristic of the predator in at least one of the insect's developmental stages, requiring further research in semi-field and field conditions to prove its toxicity.

Involvement of mind the gap in the organization of the tracheal apical extracellular matrix in Drosophila and Nilaparvata lugens

The tracheal apical extracellular matrix (aECM) is vital for expansion of the tracheal lumen and supports the normal structure of the lumen to guarantee air entry and circulation in insects. Although it has been found that some cuticular proteins are involved in the organization of the aECM, unidentified factors still exist. Here, we found that mind the gap (Mtg), a predicted chitin-binding protein, is required for the normal formation of the apical chitin matrix of airway tubes in the model holometabolous insect Drosophila melanogaster. Similar to chitin, the Mtg protein was linearly arranged in the tracheal dorsal trunk of the tracheae in Drosophila. Decreased mtg expression in the tracheae seriously affected the viability of larvae and caused tracheal chitin spiral defects in some larvae. Analysis of mtg mutant showed that mtg was required for normal development of tracheae in embryos. Irregular taenidial folds of some mtg mutant embryos were found on either lateral view of tracheal dorsal trunk or internal view of transmission electron microscopy analysis. These abnormal tracheae were not fully filled with gas and accompanied by a reduction in tracheal width, which are characteristic phenotypes of tracheal aECM defects. Furthermore, in the hemimetabolous brown planthopper (BPH) Nilaparvata lugens, downregulation of NlCPAP1-N (a homolog of mtg) also led to the formation of abnormal tracheal chitin spirals and death. These results suggest that mtg and its homolog are involved in the proper organization of the tracheal aECMs in flies and BPH, and that this function may be conserved in insects.

Temporal Coordination of Collective Migration and Lumen Formation by Antagonism between Two Nuclear Receptors

During development, cells undergo multiple, distinct morphogenetic processes to form a tissue or organ, but how their temporal order and time interval are determined remain poorly understood. Here we show that the nuclear receptors E75 and DHR3 regulate the temporal order and time interval between the collective migration and lumen formation of a coherent group of cells named border cells during Drosophila oogenesis. We show that E75, in response to ecdysone signaling, antagonizes the activity of DHR3 during border cell migration, and DHR3 is necessary and sufficient for the subsequent lumen formation that is critical for micropyle morphogenesis. DHR3's lumen-inducing function is mainly mediated through βFtz-f1, another nuclear receptor and transcription factor. Furthermore, both DHR3 and βFtz-f1 are required for chitin secretion into the lumen, whereas DHR3 is sufficient for chitin secretion. Lastly, DHR3 and βFtz-f1 suppress JNK signaling in the border cells to downregulate cell adhesion during lumen formation.

•

E75 antagonizes DHR3's function in inducing lumen formation of border cells (BCs)

•

E75 and DHR3 temporally coordinate collective migration and lumen formation of BCs

•

DHR3 is required and sufficient for chitin secretion into the lumen

•

DHR3 and βFtz-f1 downregulate JNK signaling and cell adhesion in the BCs

Insect Cuticular Chitin Contributes to Form and Function

Chitin contributes to the rigidity of the insect cuticle and serves as an attachment matrix for other cuticular proteins. Deficiency of chitin results in abnormal embryos, cuticular structural defects and growth arrest. When chitin is not turned over during molting, the developing insect is trapped inside the old cuticle. Partial deacetylation of cuticular chitin is also required for proper laminar organization of the cuticle and vertical pore canals, molting, and locomotion. Thus, chitin and its modifications strongly influence the structure of the exoskeleton as well as the physiological functions of the insect. Internal tendons and specialized epithelial cells called "tendon cells" that arise from the outer layer of epidermal cells provide attachment sites at both ends of adult limb muscles. Membrane processes emanating from both tendon and muscle cells interdigitate extensively to strengthen the attachment of muscles to the extracellular matrix (ECM). Protein ligands that bind to membrane-bound integrin complexes further enhance the adhesion between muscles and tendons. Tendon cells contain F-actin fiber arrays that contribute to their rigidity. In the cytoplasm of muscle cells, proteins such as talin and other proteins provide attachment sites for cytoskeletal actin, thereby increasing integrin binding and activation to mechanically couple the ECM with actin in muscle cells. Mutations in integrins and their ligands, as well as depletion of chitin deacetylases, result in defective locomotion and muscle detachment from the ECM. Thus, chitin in the cuticle and chitin deacetylases strongly influence the shape and functions of the exoskeleton as well as locomotion of insects.

Excess melanin precursors rescue defective cuticular traits in stony mutant silkworms probably by upregulating four genes encoding RR1-type larval cuticular proteins

Melanin and cuticular proteins are vital cuticle components in insects. Cuticular defects caused by mutations in cuticular protein-encoding genes can obstruct melanin deposition. The effects of changes in melanin on the expression of cuticular protein-encoding genes, the cuticular and morphological traits, and the origins of these effects are unknown. We found that the cuticular physical characteristics and the expression patterns of larval cuticular protein-encoding genes markedly differed between the melanic and non-melanic integument regions. By using four p multiple-allele color pattern mutants with increasing degrees of melanism (+^p, p^M, p^S, and p^B), we found that the degree of melanism and the expression of four RR1-type larval cuticular protein-encoding genes (BmCPR2, BmLcp18, BmLcp22, and BmLcp30) were positively correlated. By modulating the content of melanin precursors and the expression of cuticular protein-encoding genes in cells in tissues and in vivo, we showed that this positive correlation was due to the induction of melanin precursors. More importantly, the melanism trait introduced into the BmCPR2 deletion strain Dazao-stony induced up-regulation of three other similar chitin-binding characteristic larval cuticular protein-encoding genes, thus rescuing the cuticular, morphological and adaptability defects of the Dazao-stony strain. This rescue ability increased with increasing melanism levels. This is the first study reporting the induction of cuticular protein-encoding genes by melanin and the biological importance of this induction in affecting the physiological characteristics of the cuticle.

Role of Chitin Deacetylase 1 in the Molting and Metamorphosis of the Cigarette Beetle Lasioderma serricorne

Chitin deacetylases (CDAs) are chitin-modifying enzymes known to play vital roles in insect metamorphosis and development. In this study, we identified and characterized a chitin deacetylase1 gene (LsCDA1) from the cigarette beetle Lasioderma serricorne. LsCDA1 contains a 1614 bp open reading frame encoding a protein of 537 amino acids that includes domain structures typical of CDAs. LsCDA1 was mainly expressed in the late larval and late pupal stages. In larval tissues, the highest level of LsCDA1 was detected in the integument. The expression of LsCDA1 was induced by 20-hydroxyecdysone (20E) in vivo, and it was significantly suppressed by knocking down the expression of ecdysteroidogenesis genes and 20E signaling genes. RNA interference (RNAi)-aided silencing of LsCDA1 in fifth-instar larvae prevented the larval–pupal molt and caused 75% larval mortality. In the late pupal stage, depletion of LsCDA1 resulted in the inhibition of pupal growth and wing abnormalities, and the expression levels of four wing development-related genes (LsDY, LsWG, LsVG, and LsAP) were dramatically decreased. Meanwhile, the chitin contents of LsCDA1 RNAi beetles were significantly reduced, and expressions of three chitin synthesis pathway genes (LsTRE1, LsUAP1, and LsCHS1) were greatly decreased. The results suggest that LsCDA1 is indispensable for larval–pupal and pupal–adult molts, and that it is a potential target for the RNAi-based control of L. serricorne.

Knockdown of β-N-acetylglucosaminidase 2 Impairs Molting and Wing Development in Lasioderma serricorne (Fabricius)

β-N-acetylglucosaminidases (NAGs) are carbohydrate enzymes that degrade chitin oligosaccharides into N-acetylglucosamine monomers. This process is important for chitin degradation during insect development and metamorphosis. We identified and evaluated a β-N-acetylglucosaminidase 2 gene (LsNAG2) from the cigarette beetle, Lasioderma serricorne (Fabricius). The full-length open reading frame of LsNAG2 was 1776 bp and encoded a 591 amino acid protein. The glycoside hydrolase family 20 (GH20) catalytic domain and an additional GH20b domain of the LsNAG2 protein were highly conserved. Phylogenetic analysis revealed that LsNAG2 clustered with the group II NAGs. Quantitative real-time PCR analyses showed that LsNAG2 was expressed in all developmental stages and was most highly expressed in the late larval and late pupal stages. In the larval stage, LsNAG2 was predominantly expressed in the integument. Knockdown of LsNAG2 in fifth instar larvae disrupted larval-pupal molting and reduced the expression of four chitin synthesis genes (trehalase 1 (LsTRE1), UDP-N-acetylglucosamine pyrophosphorylase 1 and 2 (LsUAP1 and LsUAP2), and chitin synthase 1 (LsCHS1)). In late pupae, LsNAG2 depletion resulted in abnormal adult eclosion and wing deformities. The expression of five wing development-related genes (teashirt (LsTSH), vestigial (LsVG), wingless (LsWG), ventral veins lacking (LsVVL), and distal-less (LsDLL)) significantly declined in the LsNAG2-depleted beetles. These findings suggest that LsNAG2 is important for successful molting and wing development of L. serricorne.

The putative chitin deacetylases Serpentine and Vermiform have non-redundant functions during Drosophila wing development

The chitin modifying deacetylases (CDA) CDA1 and CDA2 have been reported to play partially redundant roles during insect cuticle formation and molting and tracheal morphogenesis in various insect species. In order to distinguish possible functional differences between these two enzymes, we analyzed their function during wing development in the fruit fly Drosophila melanogaster. In tissue-specific RNA interference experiments, we demonstrate that DmCDA1 (Serpentine, Serp) and DmCDA2 (Vermiform, Verm) have distinct functions during Drosophila adult wing cuticle differentiation. Chitosan staining revealed that Serp is the major enzyme responsible for chitin deacetylation during wing cuticle formation, while Verm does not seem to be needed for this process. Indeed, it is questionable whether Verm is a chitin deacetylase at all. Atomic force microscopy suggested that Serp and Verm have distinct roles in establishing the shape of nanoscale bumps at the wing surface. Moreover, our data indicate that Verm but not Serp is required for the laminar arrangement of chitin. Both enzymes participate in the establishment of the cuticular inward barrier against penetration of xenobiotics. Taken together, correct differentiation of the wing cuticle involves both Serp and Verm in parallel in largely non-overlapping functions.

Inhibition of fatty acid desaturation impairs cuticle differentiation in Drosophila melanogaster

Previously, we showed that inhibition of the activity of fatty acid desaturases (Desat) perturbs signalling of the developmental timing hormone ecdysone in the fruit fly Drosophila melanogaster. To understand the impact of this effect on cuticle differentiation, a process regulated by ecdysone, we analysed the cuticle of D. melanogaster larvae fed with the Desat inhibitor CA10556. In these larvae, the expression of most of the key cuticle genes is normal or slightly elevated at day one of CA10556 feeding. As an exception, expression of twdlM coding for a yet uncharacterised cuticle protein is completely suppressed. The cuticle of these larvae appears to be normal at the morphological level. However, these animals are sensitive to desiccation, a trait that according to our data, among others, may be associated with reduced TwdlM amounts. At day two of CA10556 feeding, expression of most of the cuticle genes tested including twdlM is suppressed. Expression of cpr47Eb coding for a chitin-binding protein is, by contrast, highly elevated suggesting that Cpr47Eb participates at a specific compensation program. Overall, the cuticle of these larvae is thinner than the cuticle of control larvae. Taken together, lipid desaturation is necessary for a coordinated deployment of a normal cuticle differentiation program.

Exploring integument transcriptomes, cuticle ultrastructure, and cuticular hydrocarbons profiles in eusocial and solitary bee species displaying heterochronic adult cuticle maturation

Differences in the timing of exoskeleton melanization and sclerotization are evident when comparing eusocial and solitary bees. This cuticular maturation heterochrony may be associated with life style, considering that eusocial bees remain protected inside the nest for many days after emergence, while the solitary bees immediately start outside activities. To address this issue, we characterized gene expression using large-scale RNA sequencing (RNA-seq), and quantified cuticular hydrocarbon (CHC) through gas chromatography-mass spectrometry in comparative studies of the integument (cuticle plus its underlying epidermis) of two eusocial and a solitary bee species. In addition, we used transmission electron microscopy (TEM) for studying the developing cuticle of these and other three bee species also differing in life style. We found 13,200, 55,209 and 30,161 transcript types in the integument of the eusocial Apis mellifera and Frieseomelitta varia, and the solitary Centris analis, respectively. In general, structural cuticle proteins and chitin-related genes were upregulated in pharate-adults and newly-emerged bees whereas transcripts for odorant binding proteins, cytochrome P450 and antioxidant proteins were overrepresented in foragers. Consistent with our hypothesis, a distance correlation analysis based on the differentially expressed genes suggested delayed cuticle maturation in A. mellifera in comparison to the solitary bee. However, this was not confirmed in the comparison with F. varia. The expression profiles of 27 of 119 genes displaying functional attributes related to cuticle formation/differentiation were positively correlated between A. mellifera and F. varia, and negatively or non-correlated with C. analis, suggesting roles in cuticular maturation heterochrony. However, we also found transcript profiles positively correlated between each one of the eusocial species and C. analis. Gene co-expression networks greatly differed between the bee species, but we identified common gene interactions exclusively between the eusocial species. Except for F. varia, the TEM analysis is consistent with cuticle development timing adapted to the social or solitary life style. In support to our hypothesis, the absolute quantities of n-alkanes and unsaturated CHCs were significantly higher in foragers than in the earlier developmental phases of the eusocial bees, but did not discriminate newly-emerged from foragers in C. analis. By highlighting differences in integument gene expression, cuticle ultrastructure, and CHC profiles between eusocial and solitary bees, our data provided insights into the process of heterochronic cuticle maturation associated to the way of life.