Mutation of TweedleD, a member of an unconventional cuticle protein family, alters body shape in Drosophila

A positive loop between relish and cuticle proteins and their roles in regulating AMPs expression during bacterial infection in Eriocheir sinensis

Cuticle proteins (CPs) are the vital components of the cuticle and chitin lining covering the digestive tract of crustaceans. In this study, four new CP genes (designated as EsCP3, EsCP4, EsCP5, and EsCP8) were initially cloned and identified from the Chinese mitten crab Eriocheir sinensis. EsCP3/4/5/8 included 375, 411, 381, and 570 bp open reading frame encoding 124, 136, 126, and 189 amino acid proteins, respectively. Except for EsCP8, EsCP3/4/5 all contained a Chitin_bind_4 domain. EsCP3/4/5/8 were clustered into different groups in the phylogenetic tree. Quantitative real-time PCR results indicated that four EsCP genes have different patterns of tissue distribution. Changes in the expression levels of these four EsCP genes were observed in the intestine of crabs under Vibrio parahaemolyticus challenge. RNA interference assay showed that the knockdown of EsCPs in the intestine could inhibit the expression of antimicrobial peptides (AMPs), including crustins and anti-lipopolysaccharide factors. In addition, the knockdown of EsRelish in the intestine decreased the expression levels of these four EsCP genes. These results indicated that EsCPs were involved in regulating the expression of AMPs, and EsCPs were regulated by EsRelish.

Knockdown of Thitarodes host genes influences dimorphic transition of Ophiocordyceps sinensis in the host hemolymph

The Chinese cordyceps, a unique parasitic complex of Thitarodes/Hepialus ghost moths and Ophiocordyceps sinensis fungus in the Tibetan Plateau, is a highly valuable biological resource for medicine and health foods in Asian countries. Efficient system for artificial cultivation of Chinese cordyceps relies on understanding the gene functions involved in the induction of growing blastospores into hyphae in the larval hemolymph of insect host, during O. sinensis infection. Transcriptome analysis and ribonucleic acid interference (RNA interference) method were employed to identify the key differentially expressed genes and to demonstrate their functions in Thitarodes xiaojinensis. Key larval genes critical for O. sinensis blastospore development or filamentation were identified. Nine of the 20 top upregulated genes encoded cuticles proteins, indicating that these proteins highly activated when the larval hemolymph was full of blastospores. Small interfering RNA (siRNA) knockdown of five larval genes such as Flightin, larval cuticle protein LCP-30, 26-hydroxylase (CYP18A1), cuticle protein 18.6, isoform B, and probable chitinase 3 significantly stimulated the dimorphic transition from blastospores to prehyphae in O. sinensis in the larval hemolymph after 120 h after injection. The expressions of these genes determined by quantitative real-time PCR were suppressed in various levels from 38.64% to 91.54%, compared to the controls. These results demonstrated that injection of the siRNAs of key upregulated genes into the larval hemolymph containing high load of blastospores caused the gene silence in T. xiaojinensis larvae and induced the fungal transition from blastospores to prehyphae, providing novel knowledge on the regulation of O. sinensis fungal dimorphism by Thitarodes host and cues for further study of Thitarodes biology and commercial cultivation of Chinese cordyceps.

The beetle's structural protein CPCFC making elytra tough and rigid

The insect cuticle, which serves as both a protective barrier and an efficient lever system for locomotion, is an extracellular matrix primarily composed of chitin and protein. The cuticle protein CPCFC characterized by a "CFC" motif containing 2 Cys split by the insertion of 5 residues is distributed across most insect species and specifically localized in the hard part of the cuticle. However, their physiological function is not fully understood. Here, we report 2 CPCFC proteins, TcCPCFC1 and TcCPCFC2, derived from the Coleopteran insect Tribolium castaneum. We revealed that TcCPCFC1 and TcCPCFC2 were predominantly expressed during the larval and adult stages of T. castaneum, respectively. The transcription downregulation of TcCPCFC1 significantly decreased the modulus and toughness of the elytral cuticle. We found that TcCPCFC proteins have high binding affinity to chitin. We cloned and produced recombinant TcCPCFC proteins and demonstrated that the addition of TcCPCFC proteins to chitin hydrogel greatly enhanced the hydrogel's modulus and toughness by forming denser chitin fibrous networks. Our findings reveal the functional role of CPCFC proteins in enhancing mechanical properties of insect cuticle, and we validate this process in vitro, and offer a protein candidate for fabrication of advanced chitin-based materials.

Genome-wide annotation and comparative analysis revealed conserved cuticular protein evolution among non-biting midges with varied environmental adaptability

Chironomidae, non-biting midges, a diverse and abundant insect group in global aquatic ecosystems, represent an exceptional model for investigating genetic adaptability mechanisms in aquatic insects due to their extensive species diversity and resilience to various environmental conditions. The cuticle in insects acts as the primary defense against ecological pressures. Cuticular Proteins (CPs) determine cuticle characteristics, facilitating adaptation to diverse challenges. However, systematic annotation of CP genes has only been conducted for one Chironomidae species, Propsilocerus akamusi, by our team. In this study, we expanded this annotation by identifying CP genes in eight additional Chironomidae species, covering all Chironomidae species with available genome data. We identified a total of 889 CP genes, neatly categorized into nine CP families: 215 CPR RR1 genes, 272 CPR RR2 genes, 23 CPR RR3 genes, 21 CPF genes, 16 CPLCA genes, 19 CPLCG genes, 28 CPLCP genes, 77 CPAP genes, and 37 Tweedle genes. Subsequently, we conducted a comprehensive phylogenetic analysis of CPs within the Chironomidae family. This expanded annotation of CP genes across diverse Chironomidae species significantly contributes to our understanding of their remarkable adaptability.

Neurotoxic and behavioral deficit in Drosophila melanogaster exposed to photocatalytic products of Paraquat

The Advanced Oxidative Processes have demonstrated potential for application in the degradation of organic pollutants, such as Paraquat (PQ) from water and wastewater, due to their low price, high efficiency, and non-toxic properties. In this study, we investigated whether the photodegradation of PQ with TiO2 nanotubes reduced its toxicity in Drosophila melanogaster. However, dietary ingestion of degradation products PQ for larvae resulted in a low axial ratio (pupal volume). In the adults, products of photodegradation of PQ exposure markedly diminished climbing ability in a time-dependent manner after 10 days of feeding. In addition, exposure of D. melanogaster to photodegradation of PQ reduced acetylcholinesterase and citrate synthase activities but improved oxidative stress, as evidenced by oxide nitric, protein carbonyl, and lactate production. These results suggest that the photodegradation of PQ with TiO2 nanotubes produced PQ fragments with higher toxicity than PQ, while the precise mechanism of its action needs further investigation.

Unraveling the Role of Cuticular Protein 3-like (HvCP3L) in the Chitin Pathway through RNAi and Methoxyfenozide Stress Response in Heortia vitessoides Moore

Cuticle proteins (CPs) constitute a multifunctional family; however, the physiological role of Cuticle Protein 3-like (CP3L) in Heortia vitessoides Moore remains largely unclear. In this study, we cloned the HvCP3L gene from the transcriptional library of Heortia vitessoides Moore. RT-qPCR results revealed that HvCP3L exhibited high expression levels during the larval stage of Heortia vitessoides Moore, particularly at the L5D1 stage, observed in both larval and adult heads. Through RNA interference, we successfully silenced the HvCP3L gene, resulting in a significant reduction in the survival rate of Heortia vitessoides Moore, with the survival rate from larvae to adults plummeting to a mere 17.7%, accompanied by phenotypic abnormalities. Additionally, we observed that the knockdown of HvCP3L led to the inhibition of genes in the chitin pathway. Following exposure to methoxyfenozide stress, the HvCP3L gene exhibited significant overexpression, coinciding with phenotypic abnormalities. These findings underscore the pivotal role of HvCP3L in the growth and development of Heortia vitessoides Moore.

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.

The BTB-ZF gene Bm-mamo regulates pigmentation in silkworm caterpillars

The color pattern of insects is one of the most diverse adaptive evolutionary phenotypes. However, the molecular regulation of this color pattern is not fully understood. In this study, we found that the transcription factor Bm-mamo is responsible for black dilute (bd) allele mutations in the silkworm. Bm-mamo belongs to the BTB zinc finger family and is orthologous to mamo in Drosophila melanogaster. This gene has a conserved function in gamete production in Drosophila and silkworms and has evolved a pleiotropic function in the regulation of color patterns in caterpillars. Using RNAi and clustered regularly interspaced short palindromic repeats (CRISPR) technology, we showed that Bm-mamo is a repressor of dark melanin patterns in the larval epidermis. Using in vitro binding assays and gene expression profiling in wild-type and mutant larvae, we also showed that Bm-mamo likely regulates the expression of related pigment synthesis and cuticular protein genes in a coordinated manner to mediate its role in color pattern formation. This mechanism is consistent with the dual role of this transcription factor in regulating both the structure and shape of the cuticle and the pigments that are embedded within it. This study provides new insight into the regulation of color patterns as well as into the construction of more complex epidermal features in some insects.

Genome-wide identification of cuticle protein superfamily in Frankliniella occidentalis provide insight into the control of both insect vectors and plant virus

The structural cuticle proteins (CPs) play important roles in the development and fitness of insects. However, knowledge about CP gene superfamily is limited in virus-transmitting insect vectors, although its importance on transmission of plant virus has been gradually emphasized. In this study, the genome-wide identification of CP superfamily was conducted in western flower thrips Frankliniella occidentalis that is the globally invasive pest and plant virus vector pest. The pest transmits notorious tomato spotted wilt virus (TSWV) around the world, causing large damage to a wide array of plants. One hundred and twenty-eight F. occidentalis CP genes (FoCPs) were annotated in this study and they were classified into 10 distinct families, including 68 CPRs, 16 CPAP1s, 6 CPAP3s, 2 CPCFCs, 10 Tweedles, 4 CPFs, 16 CPLCPs, and 6 CPGs. The comprehensive analysis was performed including phylogenetic relationship, gene location and gene expression profiles during different development stages of F. occidentalis. Transcriptome analysis revealed more than 30% FoCPs were upregulated at least 1.5-fold when F. occidentalis was infected by TSWV, indicating their potential involvement in TSWV interactions. Our study provided an overview of F. occidentalis CP superfamily. The study gave a better understand of CP's role in development and virus transmission, which provided clues for reducing viral damages through silencing CP genes in insect vectors.

Cuticular proteins in codling moth (Cydia pomonella) respond to insecticide and temperature stress

The insect cuticle consists of chitin and cuticular proteins (CPs), which stabilize the body shape and provide an effective physical barrier against the external environment. They are also potential target sites for developing environmentally friendly insect management through the utilization of physiology-based methods. The codling moth, Cydia pomonella, is a pest afflicting fruit orchards worldwide. This study used a comparative genomic approach, whole-genome resequencing, and transcriptome data to understand the role that CPs played in the environmental adaptation of the codling moth. A total of 182 putative CPs were identified in the codling moth genome, which were classified into 12 CP families. 119 CPR genes, including 54 RR-1, 60 RR-2, and 5 RR-3 genes were identified and accounted for 65.4% of the total CPs. Eight and seven gene clusters are formed in RR1 and RR2 subfamily and the ancestor-descendant relationship was explained. Five CPAP genes were highly expressed during the egg stage and exposed to high temperature, which indicated their potential role in aiding codling moth eggs in acclimating to varying external heat conditions. Moreover, six CPs belonging to the CPR and CPLCP families were identified in association with insecticide resistance by population resequencing. Their expression levels increased after exposure to insecticides, suggesting they might be involved in codling moth resistance to the insecticides azinphos-methyl or deltamethrin. Our results provide insight into the evolution of codling moth CPs and their association with high temperature adaptation and insecticide resistance, and provide an additional information required for further analysis of CPs in environmental adaptation.

Insect cuticle and insecticide development

Insecticide resistance poses a significant challenge, diminishing the effectiveness of chemical insecticides. To address this global concern, the development of novel and efficient pest management technologies based on chemical insecticides is an ongoing necessity. The insect cuticle, a highly complex and continuously renewing organ, plays a crucial role in this context. On one hand, as the most vital structure, it serves as a suitable target for insecticides. On the other hand, it acts as the outermost barrier, isolating the insect's inner organs from the environment, and thus offering resistance to contact with insecticides, preventing their entry into insect bodies. Our work focuses on key targets concerning cuticle formation and the interaction between the cuticle and contact insecticides. Deeper studying insect cuticles and understanding their structure-function relationship, formation process, and regulatory mechanisms during cuticle development, as well as investigating insecticide resistance related to the barrier properties of insect cuticles, are promising strategies not only for developing novel insecticides but also for discovering general synergists for contact insecticides. With this comprehensive review, we hope to contribute valuable insights into the development of effective pest management solutions and the mitigation of insecticide resistance.

Tweedle gene family of Drosophila suzukii (Matsumura) larva enhances the basal tolerance to cold and hypoxia

BACKGROUND

Drosophila suzukii (Matsumura) is considered a quarantine pest in the A2 list because it causes serious infection and huge economic losses. Cold and controlled atmosphere treatments have been used to control immature stage pests in fresh fruits. Herein, the basal tolerance response of D. suzukii egg, larva and pupa to cold and hypoxia stress were studied, and underlying transcriptome mechanisms in the larva were pinpointed.

RESULTS

The third instar was more tolerant than 12-h-old egg and 8-day-old pupa when treated at 3 °C + 1% O2 for 7 days, with 34.00% ± 5.22% larval survival. Hypoxia influenced the effect of cold treatment on D. suzukii. Larval survival decreased at 3 °C + 1% O2 , but increased at 0 °C + 1% O2 . Survival increased with temperature between 0 and 5 °C + 1% O2 , but decreased significantly at 25 °C + 1% O2 . RNA-sequencing results showed that the Tweedle (Twdl) family was upregulated and uniquely enriched in larvae treated at 3 °C + 1% O2 . In addition, RNA interference-mediated silencing of a key Twdl gene reduced the survival rate after cold and hypoxia treatment.

CONCLUSION

Hypoxia was able to influence the effect of cold treatment on the survival of D. suzukii positively or negatively. Structural constituents of the chitin-based cuticle, in particular Twdl genes, body morphogenesis, and ATP synthesis-coupled proton transport were involved in the tolerance to cold and hypoxia. In future, the Twdl gene could be used as a nanocarrier delivering RNA pesticides to control D. suzukii in the field and so prevent its worldwide spread. © 2023 Society of Chemical Industry.

Identification of cuticular protein genes and analysis of their roles in phosphine resistance of the rusty grain beetle Cryptolestes ferrugineus

The rusty grain beetle, Cryptolestes ferrugineus (Stephens) is one of the most economically important stored grain pests, and it has evolved the high resistance to phosphine. Cuticular proteins (CPs) are the major structural components of insect cuticle, and previous studies have confirmed that CPs were involved in insecticide resistance. However, the CPs of C. ferrugineus are still poorly characterized, and thus we conducted transcriptome-wide identification of CP genes and analyze their possible relationships with phosphine resistance in this pest. In this study, a total of 122 putative CPs were annotated in the C. ferrugineus transcriptome data by blasting with the known CPs of Tribolium castaneum. The analysis of conserved motifs revealed these CPs of C. ferrugineus belonging to 9 different families, including 87 CPR, 13 CPAP1, 7 CPAP3, 3 Tweedle, 1 CPLCA, 1 CPLCG, 5 CPLCP, 2 CPCFC, and 3 CPFL proteins. The further phylogenetic analysis showed the different evolutionary patterns of CPs. Namely, we found some CPs (CPR family) formed species-specific protein clusters, indicating these CPs might occur independently among insect taxa, and while some other CPs (CPAP1 and CPAP3 family) shared a closer correlation based on the architecture of protein domains. Subsequently, the previous RNA-seq data were applied to establish the expression profiles of CPs in a phosphine susceptible and resistant populations of C. ferrugineus, and a large amount of CP genes were found to be over-expressed in resistant insects. Lastly, an up-regulated CP gene (CPR family) was selected for the further functional analysis, and after this gene was silenced via RNA interference (RNAi), the sensitivity to phosphine was significantly enhanced in C. ferrugineus. In conclusion, the present results provided us an overview of C. ferrugineus CPs, and which suggested that the CPs might play the critical roles in phosphine resistance.

Genome-Wide Identification and Transcriptome-Based Expression Profile of Cuticular Protein Genes in Antheraea pernyi

Antheraea pernyi is one of the most famous edible and silk-producing wild silkworms of Saturniidae. Structural cuticular proteins (CPs) are the primary component of insect cuticle. In this paper, the CPs in the genome of A. pernyi were identified and compared with those of the lepidopteran model species Bombyx mori, and expression patterns were analyzed based on the transcriptomic data from the larval epidermis/integument (epidermis in the following) and some non-epidermis tissues/organs of two silkworm species. A total of 217 CPs was identified in the A. pernyi genome, a comparable number to B. mori (236 CPs), with CPLCP and CPG families being the main contribution to the number difference between two silkworm species. We found more RR-2 genes expressed in the larval epidermis of fifth instar of A. pernyi than B. mori, but less RR-2 genes expressed in the prothoracic gland of A. pernyi than B. mori, which suggests that the hardness difference in the larval epidermis and prothoracic gland between the two species may be caused by the number of RR-2 genes expressed. We also revealed that, in B. mori, the number of CP genes expressed in the corpus allatum and prothoracic gland of fifth instar was higher than that in the larval epidermis. Our work provided an overall framework for functional research into the CP genes of Saturniidae.

Over-expression of CP9 and CP83 increases whitefly cell cuticle thickness leading to imidacloprid resistance

Cuticular proteins (CPs) play an important role in protecting insects from adverse environmental conditions, like neonicotinoid insecticides, which are heavily used for numerous pests and caused environmental problems and public health concerns worldwide. However, the relationship between CPs and insecticides resistance in Bemisia tabaci, a serious and developed high insecticide resistance, is lacking. In this study, 125 CPs genes were identified in B. tabaci. Further phylogenetic tree showed the RR-2-type genes formed large gene groups in B. tabaci. Transcriptional expression levels of CPs genes at different developmental stages revealed that some CPs genes may play a specific role in insect development. The TEM results indicated that the cuticle thickness of susceptible strain was thinner than imidacloprid-resistance strain. Furthermore, 16 CPs genes (5 in RR-1 subfamily, 7 in RR-2 subfamily, 3 in CPAP3 subfamily and 1 in CPCFC subfamily) were activated in response to imidacloprid. And RNAi results indicated that CP9 and CP83 involved in imidacloprid resistance. In conclusion, this study was the first time to establish a basic information framework and evolutionary relationship between CPs and imidacloprid resistance in B. tabaci, which provides a basis for proposing integrated pest management strategies.

Piranhea trifoliata extracts ameliorate muscular decline in Drosophila melanogaster exposed to Paraquat

In this study, we have demonstrated, for the first time, the muscular protective effects of Piranhea trifoliata bark extract against Paraquat (PQ)-induced oxidative stress in Drosophila melanogaster. Exposure of D. melanogaster (Canton Special) to PQ caused oxidative stress, as evidenced by protein carbonyl and elevated acetylcholinesterase (AChE) activity levels. However, a diet supplemented with the P. trifoliata extracts (0.1 mg/ml) for 10 days ameliorates protein carbonyl levels and enzymatic activities of AChE and citrate synthase to prevent PQ damage. Also, P. trifoliata bark extracts showed in phytochemical assays the presence of phenols, at 46.06 mg EAG/g extract of total phenolic compounds, and a 40% 2,2-diphenyl-1-picryl-hydrazyl scavenging effect. The study showed the muscular protective function of the P. trifoliata extracts in D. melanogaster exposed to PQ. On the basis of the results, we contemplate that the bark of P. trifoliata might prevent and ameliorate human diseases caused by oxidative stress. The muscular action of the P. trifoliata extract can be attributed to the antioxidant constituents, while the precise mechanism of its action needs further investigation.

Genome-wide annotation of cuticular protein genes in non-biting midge Propsilocerus akamusi and transcriptome analysis of their response to heavy metal pollution

The insect cuticle is a sophisticated chitin-protein extracellular structure for mutable functions. The cuticles varied their structures and properties in different species, and the same species but in different regions or at different stages, to fill the requirements of different functions. The alteration of cuticle structures may also be induced due to challenges by some environmental crises, such as pollution exposures. The physical properties of the cuticle were determined by the cuticle proteins (CPs) they contain. The cuticle proteins are large protein groups in all insects, which are commonly divided into different families according to their conserved protein sequence motifs. Although Chironomidae is an abundant and universal insect in global aquatic ecosystems and a popular model for aquatic toxicology, no systematic annotation of CPs was done for any species in Chironomidae before. In this work, we annotated the CP genes of Propsilocerus akamusi, the most abundant Chironomidae species in Asia. A total of 160 CP genes were identified, and 97 of them could be well classified into eight CP families: 76 CPR genes can be subdivided into three groups (further divided into three subgroups: 36 RR1 genes, 37 RR2 genes, and 3 RR3 genes), 2 CPF genes, 3 CPLCA genes, 1 CPLCG gene, 8 CPAP genes, and 3 Tweedle genes. Additionally, we analyzed the response of P. akamusi CP genes at expression level to Cu exposure, which is related to the high heavy metal tolerance and the earlier onset of pupariation in heavy metal polluted water.

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.

Independent pathways control muscle tissue size and sarcomere remodeling

Cell growth and proliferation must be balanced during development to attain a final adult size with the appropriate proportions of internal organs to maximize fitness and reproduction. While multiple signaling pathways coordinate Drosophila development, it is unclear how multi-organ communication within and between tissues converge to regulate systemic growth. One such growth pathway, mediated by insulin-like peptides that bind to and activate the insulin receptor in multiple target tissues, is a primary mediator of organismal size. Here we uncover a signaling role for the NUAK serine/threonine kinase in muscle tissue that impinges upon insulin pathway activity to limit overall body size, including a reduction in the growth of individual organs. In skeletal muscle tissue, manipulation of NUAK or insulin pathway components influences sarcomere number concomitant with modulation of thin and thick filament lengths, possibly by modulating the localization of Lasp, a nebulin repeat protein known to set thin filament length. This mode of sarcomere remodeling does not occur in other mutants that also exhibit smaller muscles, suggesting that a sensing mechanism exists in muscle tissue to regulate sarcomere growth that is independent of tissue size control.

Cuticular protein genes involve heat acclimation of insect larvae under global warming

Cuticular proteins (CPs) play important roles in insect growth and development. However, it is unknown whether CPs are related to heat tolerance. Cnaphalocrocis medinalis, a serious pest of rice, occurs in summer and exhibits strong adaptability to high temperature, but the underlying mechanism is unclear. Here, the role of CP genes in heat acclimation was studied. Heat tolerance of the heat-acclimated larvae was significantly stronger than the unacclimated larvae. The cuticular protein content in the heat-acclimated larvae was higher than that of the unacclimated larvae. 191 presumed CP genes of C. medinalis (CmCPs) were identified. Expression patterns of 14 CmCPs were different between the heat acclimated (S39) and unacclimated (S27) larvae under heat stress. CmCPs were specifically expressed in epidermis and the head except CmCPR20 mainly expressed in Malpighian tubules. CmCPR20 was upregulated in S39 while downregulated in S27, but CmTweedle1 and CmCPG1 were upregulated in S27 and downregulated in S39. RNAi CmTweedle1 or CmCPG1 remarkably decreased heat tolerance and cuticular protein content of the heat-acclimated larvae but not the unacclimated larvae. RNAi CmCPR20 decreased heat tolerance and cuticular protein content of the unacclimated larvae but not the heat-acclimated larvae. CmTweedle1 and CmCPG1 genes involve heat acclimation of C. medinalis.

Chitin and cuticle proteins form the cuticular layer in the spinning duct of silkworm

Chitin is found in the exoskeleton and peritrophic matrix of arthropods, but recent studies have also identified chitin in the spinning duct of silk-spinning arthropods. Here, we report the presence and function of chitin and cuticle proteins ASSCP1 and ASSCP2 in the spinning duct of silkworm. We show that chitin and these proteins are co-located in the cuticular layer of the spinning duct. Ultrastructural analysis indicates that the cuticular layer has a multilayer structure by layered stacking of the chitin laminae. After knocking down ASSCP1 and ASSCP2, the fine structure of this layer was disrupted, which had negative impacts on the mechanical properties of silk. This work clarifies the function of chitin in the spinning duct of silkworm. Chitin and cuticle proteins are the main components of the cuticular layer, providing the shearing stress during silk fibrillogenesis and regulating the final mechanical properties of silk. STATEMENT OF SIGNIFICANCE: Recent studies have identified chitin in the spinning duct of silk-spinning arthropods. However, the role of chitin in this specific organ remains unclear. This study reports that chitin and cuticle proteins form the cuticular layer, a unique structure of the spinning duct of silkworm. This layer with a precise laminate structure gives the spinning duct flexible properties, provides shearing forces for silk fibrillogenesis, and contributes to silk final mechanical properties. Our work clarifies the component, ultrastructure, and biological significance of the silkworm cuticular layer, describes the specific process of silk fiber formation, and proposes new molecular targets (chitin and cuticle proteins) for the improvement of animal silks.

Integrated Analysis of Transcriptome and Proteome to Reveal Pupal Color Switch in Papilio xuthus Butterflies

Pupal color polyphenism in Papilio butterflies, including green, intermediate, or brown, is an excellent study system for understanding phenotypic plasticity. Previous studies suggested that development of brown pupae may be controlled by a hormone called pupal-cuticle-melanizing-hormone (PCMH) which is synthesized and secreted from brain-suboesophageal ganglion and prothoracic ganglion complexes (Br-SG-TG1) during the pre-pupa stage. However, detailed molecular mechanisms of neuroendocrine regulation in pupal color development remain unknown. In this study, we integrated the expression profiles of transcriptome and proteome at pre-pupa stages [2 h after gut purge (T1) and 3 h after forming the garter around the body (T2)] and pigmentation stages [10 h after ecdysis (T3) and 24 h after ecdysis (T4)] to identify important genes and pathways underlying the development of green and brown pupa in the swallowtail butterfly Papilio xuthus. Combined comparisons of each developmental stage and each tissue under green and brown conditions, a total of 1042 differentially expressed genes (DEGs) and 430 different abundance proteins (DAPs) were identified. Weighted gene co-expression network analysis (WGCNA) and enrichment analysis indicate that these DEGs were mainly related to oxidation-reduction, structural constituent of cuticle, and pigment binding. Soft clustering by Mfuzz and enrichment analysis indicate that these DAPs are mainly involved in tyrosine metabolism, insect hormone biosynthesis, and melanogenesis. By homologous alignment, we further identified those genes encoding neuropeptides (51), GPCRs (116), G-proteins (8), cuticular proteins (226), chitinases (16), and chitin deacetylases (8) in the whole genome of P. xuthus and analyzed their expression profiles. Although we identified no gene satisfying with hypothesized expression profile of PCMH, we found some genes in the neuropeptide cascade showed differentially expressed under two pupal color conditions. We also found that Toll signaling pathway genes, juvenile hormone (JH) related genes, and multiple cuticular proteins play important roles in the formation of selective pupal colors during the prepupal-pupal transition. Our data also suggest that both green and brown pupa include complex pigment system that is regulated by genes involved in black, blue, and yellow pigments. Our results provide important insights into the evolution of pupal protective colors among swallowtail butterflies.

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.

A corset function of exoskeletal ECM promotes body elongation in Drosophila

Body elongation is a general feature of development. Postembryonically, the body needs to be framed and protected by extracellular materials, such as the skeleton, the skin and the shell, which have greater strength than cells. Thus, body elongation after embryogenesis must be reconciled with those rigid extracellular materials. Here we show that the exoskeleton (cuticle) coating the Drosophila larval body has a mechanical property to expand less efficiently along the body circumference than along the anteroposterior axis. This “corset” property of the cuticle directs a change in body shape during body growth from a relatively round shape to an elongated one. Furthermore, the corset property depends on the functions of Cuticular protein 11 A and Tubby, protein components of a sub-surface layer of the larval cuticle. Thus, constructing a stretchable cuticle and supplying it with components that confer circumferential stiffness is the fly’s strategy for executing postembryonic body elongation.

Tajiri et al. describe how the cuticle coating the Drosophila larval body expands less efficiently along the body circumference than along the anteroposterior axis to drive body elongation. This “corset” property depends on cuticular proteins Cpr11A and Tubby, which may work together to change larval body shape.

Tweedle proteins form extracellular two-dimensional structures defining body and cell shape in Drosophila melanogaster

Tissue function and shape rely on the organization of the extracellular matrix (ECM) produced by the respective cells. Our understanding of the underlying molecular mechanisms is limited. Here, we show that extracellular Tweedle (Twdl) proteins in the fruit fly Drosophila melanogaster form two adjacent two-dimensional sheets underneath the cuticle surface and above a distinct layer of dityrosinylated and probably elastic proteins enwrapping the whole body. Dominant mutations in twdl genes cause ectopic spherical aggregation of Twdl proteins that recruit dityrosinylated proteins at their periphery within lower cuticle regions. These aggregates perturb parallel ridges at the surface of epidermal cells that have been demonstrated to be crucial for body shaping. In one scenario, hence, this disorientation of epidermal ridges may explain the squatty phenotype of Twdl mutant larvae. In an alternative scenario, this phenotype may be due to the depletion of the dityrosinylated and elastic layer, and the consequent weakening of cuticle resistance against the internal hydrostatic pressure. According to Barlow's formula describing the distribution of internal pressure forces in pipes in dependence of pipe wall material properties, it follows that this reduction in turn causes lateral expansion at the expense of the antero-posterior elongation of the body.

Identification and temporal expression profiles of cuticular proteins in the endoparasitoid wasp, Microplitis mediator

Recently, parasitoid wasp species Microplitis mediator has evoked increasing research attention due to its possible use in the control of Lepidoptera insects. Because insect development involves changes in cuticle composition, identification and expression analysis of M. mediator cuticular proteins may clarify the mechanisms involved in parasite development processes. We found 70 cuticular proteins from the M. mediator transcriptome and divided them into seven distinct families. Expression profiling indicated that most of these cuticular protein genes have expression peaks specific for one particular developmental stage of M. mediator. Eggs and pupae have the highest number of transcriptionally active cuticular protein genes (47 and 52 respectively). Only 12 of these genes maintained high expression activity during late larval development. Functional analysis of two larval proteins, MmCPR3 and MmCPR14, suggested their important role in the proper organization of the cuticle layers of larvae. During M. mediator larval development, normal cuticle formation can be supported by a limited number of cuticular proteins.

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.

Prepupae and pupae transcriptomic characterization of Trichogramma chilonis

The egg parasitoid, Trichogramma chilonis, has significant control effects on agriculture and forestry pests and is widely employed in southern China for the biological control of lepidopteran pests. In this study, transcriptomic analysis was used to gain a clear understanding of the molecular changes in prepupae and pupae of T. chilonis. A total of 16.88 Gb of clean data were obtained and finally assembled into 43,136 unigenes, 18,880 of which were annotated. After FPKM standardization, 117 and 838 specific expression genes were found in prepupae and pupae, respectively. There were 3129 differentially expressed genes between prepupae and pupae. Compared to pupae, 806 genes were up-regulated and 2323 were down-regulated in prepupae. Background on the T. chilonis transcriptome, the enriched GO function and KEGG pathway analysis of DEGs were considered. As indicated by GO classification, up-regulated genes were mainly involved in chitin metabolism, cell adhesion and endocytic, while most down-regulated genes were involved in synthesis of cell components, ion transport and biological regulation. KEGG enrichment analysis showed that 458 DEGs were enriched in 94 metabolic pathways. DEGs involved in nucleotide replication and transcription, substance metabolism, insect hormone biosynthesis, cell growth and death, reproductive metabolism, circadian rhythms and signal transduction pathways were up-regulated or down-regulated to different degrees, indicating that these genes played important roles during the process of metamorphosis in T. chilonis. This study provides a rich data source for the future study of T. chilonis molecular and biological mechanisms. A large number of genes related to metamorphosis were found based on comparison analysis between prepupae and pupae transcriptomes. This study lays a good foundation for in-depth study of gene transcription and regulation mechanisms during T. chilonis metamorphosis.

Transcriptomic and Functional Analyses of Phenotypic Plasticity in a Higher Termite, Macrotermes barneyi Light

Eusocial termites have a complex caste system, which leads to the division of labor. Previous studies offered some insight into the caste differentiation in lower termites; however, few studies were focusing on the molecular mechanisms of higher termites with sophisticated societies. Comparative transcriptomic analyses of five immature castes of a higher termite, Macrotermes barneyi Light, suggest that phenotypic plasticity is modulated by an array of transcriptional changes, including differentially expressed genes (e.g., caste-biased genes Vtg and TnC), co-expression networks (e.g., genes associated with nymph reproduction), and alternative splicing (e.g., events related to muscle development in presoldiers). Transcriptional (RT-PCR and RT-qPCR) and functional (in vivo RNAi) validation studies reveal multiple molecular mechanisms contributing to the phenotypic plasticity in eusocial termites. Molecular mechanisms governing the phenotypic plasticity in M. barneyi could be a rule rather than an exception in the evolution of sociality.

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.

The putative C-type lectin Schlaff ensures epidermal barrier compactness in Drosophila

The stability of extracellular matrices is in general ensured by cross-linking of its components. Previously, we had shown that the integrity of the layered Drosophila cuticle relies on the presence of a covalent cuticular dityrosine network. Production and composition of this structure remained unstudied. In this work, we present our analyses of the schlaff (slf) gene coding for a putative C-type lectin that is needed for the adhesion between the horizontal cuticle layers. The Slf protein mainly localizes between the two layers called epicuticle and procuticle that separate from each other when the function of Slf is reduced or eliminated paralleling the phenotype of a cuticle with reduced extracellular dityrosine. Localisation of the dityrosinylated protein Resilin to the epicuticle-procuticle interface suggests that the dityrosine network mediates the adhesion of the epicuticle to the procuticle. Ultimately, compromised Slf function is associated with massive water loss. In summary, we propose that Slf is implied in the stabilisation of a dityrosine layer especially between the epicuticle and the procuticle that in turn constitutes an outward barrier against uncontrolled water flow.

Identification of Cuticular Protein Genes in the Colorado Potato Beetle Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Structural cuticular proteins (CPs) are the primary components of insect cuticle, linings of salivary gland, foregut, hindgut and tracheae, and midgut peritrophic membrane. Variation of CPs in insect cuticle can cause penetration resistance to insecticides. Moreover, depletion of specific CP by RNA interference may be a suitable way for the development of potential pest control traits. Leptinotarsa decemlineata (Say) CPs are poorly characterized at present, and therefore, we mined the genome and transcriptome data to better annotate and classify L. decemlineata CPs in this study, by comparison with the annotated CPs of Tribolium castaneum Browse (Coleoptera: Tenebrionidae). We identified 175 CP genes. Except one miscellaneous CP with an 18-amino acid motif, these CPs were classified into 7 families based on motifs and phylogenetic analyses (CPs with a Rebers and Riddiford motif, CPR; CPs analogous to peritrophins, CPAP3 and CPAP1; CPs with a tweedle motif, TWDL; CPs with a 44-amino acid motif, CPF; CPs that are CPF-like, CPFL; and CPs with two to three copies of C-X5-C motif, CPCFC). Leptinotarsa decemlineata CPRs could be categorized into three subfamilies: RR-1 (50), RR-2 (85), and RR-3 (2). The RR-1 proteins had an additional motif with a conserved YTADENGF sequence. The RR-2 members possessed a conserved RDGDVVKG region and three copes of G-x(3)-VV. Few genes were found in TWDL (9), CPAP1 (9), CPAP3 (8), CPF (5), CPFL (4), and CPCFC (2) families. The findings provide valuable information to explore molecular modes of penetration resistance to insecticides and to develop dsRNA-based control method in L. decemlineata.

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.

Chitinous Structures as Potential Targets for Insect Pest Control

Chitinous structures are physiologically fundamental in insects. They form the insect exoskeleton, play important roles in physiological systems and provide physical, chemical and biological protections in insects. As critically important structures in insects, chitinous structures are attractive target sites for the development of new insect-pest-control strategies. Chitinous structures in insects are complex and their formation and maintenance are dynamically regulated with the growth and development of insects. In the past few decades, studies on insect chitinous structures have shed lights on the physiological functions, compositions, structural formation, and regulation of the chitinous structures. Current understanding of the chitinous structures has indicated opportunities for exploring new target sites for insect control. Mechanisms to disrupt chitinous structures in insects have been studied and strategies for the potential development of new means of insect control by targeting chitinous structures have been proposed and are practically to be explored.

Chitin in Arthropods: Biosynthesis, Modification, and Metabolism

Chitin is a structural constituent of extracellular matrices including the cuticle of the exoskeleton and the peritrophic matrix (PM) of the midgut in arthropods. Chitin chains are synthesized through multiple biochemical reactions, organized in several hierarchical levels and associated with various proteins that give their unique physicochemical characteristics of the cuticle and PM. Because, arthropod growth and morphogenesis are dependent on the capability of remodeling chitin-containing structures, chitin biosynthesis and degradation are highly regulated, allowing ecdysis and regeneration of the cuticle and PM. Over the past 20 years, much progress has been made in understanding the physiological functions of chitinous matrices. In this chapter, we mainly discussed the biochemical processes of chitin biosynthesis, modification and degradation, and various enzymes involved in these processes. We also discussed cuticular proteins and PM proteins, which largely determine the physicochemical properties of the cuticle and PM. Although rapid advances in genomics, proteomics, RNA interference, and other technologies have considerably facilitated our research in chitin biosynthesis, modification, and metabolism in recent years, many aspects of these processes are still partially understood. Further research is needed in understanding how the structural organization of chitin synthase in plasma membrane accommodate chitin biosynthesis, transport of chitin chain across the plasma membrane, and release of the chitin chain from the enzyme. Other research is also needed in elucidating the roles of chitin deacetylases in chitin organization and the mechanism controlling the formation of different types of chitin in arthropods.

The genome of the water strider Gerris buenoi reveals expansions of gene repertoires associated with adaptations to life on the water

BACKGROUND

Having conquered water surfaces worldwide, the semi-aquatic bugs occupy ponds, streams, lakes, mangroves, and even open oceans. The diversity of this group has inspired a range of scientific studies from ecology and evolution to developmental genetics and hydrodynamics of fluid locomotion. However, the lack of a representative water strider genome hinders our ability to more thoroughly investigate the molecular mechanisms underlying the processes of adaptation and diversification within this group.

RESULTS

Here we report the sequencing and manual annotation of the Gerris buenoi (G. buenoi) genome; the first water strider genome to be sequenced thus far. The size of the G. buenoi genome is approximately 1,000 Mb, and this sequencing effort has recovered 20,949 predicted protein-coding genes. Manual annotation uncovered a number of local (tandem and proximal) gene duplications and expansions of gene families known for their importance in a variety of processes associated with morphological and physiological adaptations to a water surface lifestyle. These expansions may affect key processes associated with growth, vision, desiccation resistance, detoxification, olfaction and epigenetic regulation. Strikingly, the G. buenoi genome contains three insulin receptors, suggesting key changes in the rewiring and function of the insulin pathway. Other genomic changes affecting with opsin genes may be associated with wavelength sensitivity shifts in opsins, which is likely to be key in facilitating specific adaptations in vision for diverse water habitats.

CONCLUSIONS

Our findings suggest that local gene duplications might have played an important role during the evolution of water striders. Along with these findings, the sequencing of the G. buenoi genome now provides us the opportunity to pursue exciting research opportunities to further understand the genomic underpinnings of traits associated with the extreme body plan and life history of water striders.

Proteomic Analysis of Larval Integument in a Dominant Obese Translucent (Obs) Silkworm Mutant

The dominant obese translucent (Obs) mutant of the silkworm (Bombyx mori) results in a short and stout larval body, translucent phenotype, and abnormal pigmentation in the integument. The Obs mutant also displays deficiency in ecdysis and metamorphosis. In the present study, to gain an understanding of multiple Obs phenotypes, we investigated the phenotypes of Obs and performed a comparative analysis of the larval integument proteomes of Obs and normal silkworms. The phenotypic analysis revealed that the Obs larvae were indeed short and fat, and that chitin and uric acid content were lower but melanin content was higher in the Obs mutant. Proteomic analysis revealed that 244 proteins were significantly differentially expressed between Obs and normal silkworms, some of which were involved in uric acid metabolism and melanin pigmentation. Twenty-six proteins were annotated as cuticular proteins, including RR motif-rich cuticular proteins (CPR), glycine-rich cuticular protein (CPG), hypothetical cuticular protein (CPH), cuticular protein analogous to peritrophins (CPAPs), and the chitin_bind_3 motif proteins, and accounted for over 84% of the abundance of the total significantly differentially expressed proteins. Moreover, 22 of the 26 cuticular proteins were downregulated in the Obs mutant. Comparative proteomic analysis suggested that the multiple phenotypes of the Obs mutant might be related to changes in the expression of proteins that participate in cuticular formation, uric acid metabolism, and melanin pigmentation. These results could lay a basis for further identification of the gene responsible for the Obs mutant. The data have been deposited to ProteomeXchange with identifier PXD010998.

Comparative Analysis of the Integument Transcriptomes between Stick Mutant and Wild-Type Silkworms

In insects, the integument provides mechanical support for the whole body and protects them from infections, physical and chemical injuries, and dehydration. Diversity in integument properties is often related to body shape, behavior, and survival rate. The stick (sk) silkworm is a spontaneous mutant with a stick-like larval body that is firm to the touch and, thus, less flexible. Analysis of the mechanical properties of the cuticles at day 3 of the fifth instar (L5D3) of sk larvae revealed higher storage modulus and lower loss tangent. Transcriptome sequencing identified a total of 19,969 transcripts that were expressed between wild-type Dazao and the sk mutant at L5D2, of which 11,596 transcripts were novel and detected in the integument. Differential expression analyses identified 710 upregulated genes and 1009 downregulated genes in the sk mutant. Gene Ontology (GO) enrichment analysis indicated that four chitin-binding peritrophin A domain genes and a chitinase gene were upregulated, whereas another four chitin-binding peritrophin A domain genes, a trehalase, and nine antimicrobial peptides were downregulated. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that two functional pathways, namely, fructose and mannose metabolism and tyrosine metabolism, were significantly enriched with differentially-expressed transcripts. This study provides a foundation for understanding the molecular mechanisms underlying the development of the stiff exoskeleton in the sk mutant.

Genome-wide identification, characterization and evolution of cuticular protein genes in the malaria vector Anopheles sinensis (Diptera: Culicidae)

Thirteen cuticular protein (CP) families have been recognized in arthropods. In this study, 250 Anopheles sinensis CP genes were identified and named based on genome and transcriptome sequences. They were classified into 10 families based on motifs and phylogenetic analyses. In 11 other insect species, nine had CP numbers > 150 while Apis mellifera and Tribolium castaneum had CP numbers less than 52. The CPs of eight species occupied > 1.4% of the total genomic gene number, whereas in three species the CPs occupied < 1%. The phylogenies for each CP family in An. sinensis were constructed and discussed. The 250 CPs each had 1-8 exons with 144 CPs (57.6%) having two exons. The intron length ranged from 66-3888 bp with 174 introns (54.0%) being 66-100 bp long. Except for two CPs on two contigs, 248 CPs were mapped onto 28 scaffolds with 136 genes (54.4%) restricted to five scaffolds. A total of 107 CPs were clustered and located at 27 loci. The CPR family had the conserved motif GSYSLVEPDGTVRTV. The RR-1 subfamily had an additional 21 amino acid (aa) motifs with the YVADENGF sequence that is common in insects. The RR-2 subfamily had an additional 50 aa motifs with two additional regions RDGDVVKG and G-x(3)-VV. A comparison with 115 orthologous counterparts of An. gambiae CPs suggested purifying selection for all of these genes. This study provides basic information useful for further studies on biological functions of An. sinensis CPs as well as for comparative genomics of insect CPs.

An ungrouped cuticular protein is essential for normal endocuticle formation in the brown planthopper

Using transcriptome analysis of tissues of the brown planthopper (BPH), Nilaparvata lugens, we identified a gene tentatively designated NlCP21.92 that was expressed at high levels in the integument. Spatiotemporal expression profiling with quantitative PCR and Western blotting verified its integument-specific expression and showed periodic expression during molting. The open reading frame was GC-rich and encoded a hydrophobic polypeptide. The polypeptide contained AAPA/V repeat motifs and other sequence features similar to several reported cuticular proteins but lacked an R&R consensus and other chitin-binding domains. Double-stranded RNA-mediated RNA interference of the NlCP21.92 resulted in abnormal and lethal morphological phenotypes, and transmission electron microscopy revealed the corresponding ultrastructural defects. Immunohistochemical staining demonstrated that the NlCP21.92 protein was primarily located in the procuticle. Our results suggest that NlCP21.92 is a novel ungrouped cuticular protein essential for normal endocuticle formation.

Cuticular protein defective Bamboo mutant of Bombyx mori is sensitive to environmental stresses

Insect cuticle acts as a primary protective barrier against environment stresses that may directly impact the insect body. Here, we report the mechanical defense function of a structural cuticular protein, BmorCPH24, to environmental stresses using a silkworm Bamboo (Bo) mutant with this gene mutation. Ultraviolet (UV) irradiation and topical application of an acetone insecticide were used as environmental stresses to determine the differences in susceptibility between Bo and wild-type larvae. UV irradiation resulted in a sunburn phenotype in the Bo strains earlier than the wild-type indicating the sensitivity of Bo. Higher malondialdehyde (MDA) content and a lower survival ratio were also observed in the Bo strains. Treatment with deltamethrin revealed that Bo larvae were more sensitive to insecticides than the wild-type. Furthermore, cuticle analysis by microsection revealed thinner cuticle and a significant decrease in the endocuticle layer (∼64.0%) in Bo. These results suggest that BmorCPH24 mutation can lead to deficiency in resources required to construct the cuticle in Bo resulting in thin cuticle and reduced resistance to UV and insecticides. These results provide us new insight into the role of structural cuticular proteins in insect cuticle against environment stresses.

A serine protease homologue Bombyx mori scarface induces a short and fat body shape in silkworm

Body shape is one of the most prominent and basic characteristics of any organism. In insects, abundant variations in body shape can be observed both within and amongst species. However, the molecular mechanism underlying body shape fine-tuning is very complex and has been largely unknown until now. In the silkworm Bombyx mori, the tubby (tub) mutant has an abnormal short fat body shape and the abdomen of tub larvae expands to form a fusiform body shape. Morphological investigation revealed that the body length was shorter and the body width was wider than that of the Dazao strain. Thus, this mutant is a good model for studying the molecular mechanisms of body shape fine-tuning. Using positional cloning, we identified a gene encoding the serine protease homologue, B. mori scarface (Bmscarface), which is associated with the tub phenotype. Sequence analysis revealed a specific 312-bp deletion from an exon of Bmscarface in the tub strain. In addition, recombination was not observed between the tub and Bmscarface loci. Moreover, RNA interference of Bmscarface resulted in the tub-like phenotype. These results indicate that Bmscarface is responsible for the tub mutant phenotype. This is the first study to report that mutation of a serine protease homologue can induce an abnormal body shape in insects.

Isolation of a natural DNA virus of Drosophila melanogaster, and characterisation of host resistance and immune responses

Drosophila melanogaster has played a key role in our understanding of invertebrate immunity. However, both functional and evolutionary studies of host-virus interaction in Drosophila have been limited by a dearth of native virus isolates. In particular, despite a long history of virus research, DNA viruses of D. melanogaster have only recently been described, and none have been available for experimental study. Here we report the isolation and comprehensive characterisation of Kallithea virus, a large double-stranded DNA virus, and the first DNA virus to have been reported from wild populations of D. melanogaster. We find that Kallithea virus infection is costly for adult flies, reaching high titres in both sexes and disproportionately reducing survival in males, and movement and late fecundity in females. Using the Drosophila Genetic Reference Panel, we quantify host genetic variance for virus-induced mortality and viral titre and identify candidate host genes that may underlie this variation, including Cdc42-interacting protein 4. Using full transcriptome sequencing of infected males and females, we examine the transcriptional response of flies to Kallithea virus infection and describe differential regulation of virus-responsive genes. This work establishes Kallithea virus as a new tractable model to study the natural interaction between D. melanogaster and DNA viruses, and we hope it will serve as a basis for future studies of immune responses to DNA viruses in insects.

Genome-wide annotation of cuticular proteins in the oriental fruit fly (Bactrocera dorsalis), changes during pupariation and expression analysis of CPAP3 protein genes in response to environmental stresses

Cuticular proteins (CPs) are essential components of the insect cuticle as they create a structural and protective shield and may have a role in insect development. In this paper, we studied the CPs in the oriental fruit fly (Bactrocera dorsalis), one of the most economically important pests in the Tephritidae family around the world. The availability of a complete genome sequence (NCBI Assembly: ASM78921v2) allowed the identification of 164 CP genes in B. dorsalis. Comparative analysis of the CPs in B. dorsalis with those in the model insect Drosophila melanogaster and the closely related Ceratitis capitata, and CPs from mosquitoes, Lepidoptera, Hymenoptera and Coleoptera identified Diptera-specific genes and cuticle development patterns. Analysis of their evolutionary relationship revealed that some CP families had evolved according to the phylogeny of the different insect species, while others shared a closer relationship based on domain architecture. Subsequently, transcriptome analysis showed that while most of the CPs (60-100% of the family members) are expressed in the epidermis, some were also present in internal organs such as the fat body and the reproductive organs. Furthermore, the study of the expression profiles throughout development revealed a profound change in the expression of CPs during the formation of the puparium (pupariation). Further analysis of the expression profiles of the CPAP3 genes under various environmental stresses revealed them to be involved in the response to pesticides and arid and extreme temperatures conditions. In conclusion, the data provide a particular overview of CPs and their evolutionary and transcriptional dynamics, and in turn they lay a molecular foundation to explore their roles in the unique developmental process of insect metamorphosis and stress responses.

3,4-Dihydroxyphenylacetaldehyde synthase and cuticle formation in insects

Cuticle is the most important structure that protects mosquitoes and other insect species from adverse environmental conditions and infections of microorganism. The physiology and biochemistry of insect cuticle formation have been studied for many years and our understanding of cuticle formation and hardening has increased considerably. This is especially true for flexible cuticle. The recent discovery of a novel enzyme that catalyzes the production of 3,4-dihydroxyphenylacetaldehyde (DOPAL) in insects provides intriguing insights concerning the flexible cuticle formation in insects. For convenience, the enzyme that catalyzes the production DOPAL from l-dopa is named DOPAL synthase. In this mini-review, we summarize the biochemical pathways of cuticle formation and hardening in general and discuss DOPAL synthase-mediated protein crosslinking in insect flexible cuticle in particular.

Trynity models a tube valve in the Drosophila larval airway system

Terminal differentiation of an organ is the last step in development that enables the organism to survive in the outside world after birth. Terminal differentiation of the insect tracheae that ends with filling the tubular network with gas is not fully understood at the tissue level. Here, we demonstrate that yet unidentified valves at the end of the tracheal system of the fruit fly Drosophila melanogaster embryo are important elements allowing terminal differentiation of this organ. Formation of these valves depends on the function of the zona pellucida protein Trynity (Tyn). The tracheae of tyn mutant embryos that lack these structures do not fill with gas. Additionally, external material penetrates into the tracheal tubes indicating that the tyn spiracles are permanently open. We conclude that the tracheal endings have to be closed to ensure gas-filling. We speculate that according to physical models closing of the tubular tracheal network provokes initial increase of the internal hydrostatic pressure necessary for gas generation through cavitation when the pressure is subsequently decreased.

An ancient family of lytic polysaccharide monooxygenases with roles in arthropod development and biomass digestion

Thermobia domestica belongs to an ancient group of insects and has a remarkable ability to digest crystalline cellulose without microbial assistance. By investigating the digestive proteome of Thermobia, we have identified over 20 members of an uncharacterized family of lytic polysaccharide monooxygenases (LPMOs). We show that this LPMO family spans across several clades of the Tree of Life, is of ancient origin, and was recruited by early arthropods with possible roles in remodeling endogenous chitin scaffolds during development and metamorphosis. Based on our in-depth characterization of Thermobia's LPMOs, we propose that diversification of these enzymes toward cellulose digestion might have endowed ancestral insects with an effective biochemical apparatus for biomass degradation, allowing the early colonization of land during the Paleozoic Era. The vital role of LPMOs in modern agricultural pests and disease vectors offers new opportunities to help tackle global challenges in food security and the control of infectious diseases.