Annotation and analysis of a large cuticular protein family with the R&R Consensus in Anopheles gambiae

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.

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.

Identification of insect cuticular protein genes LCP17 and SgAbd5 from Helicoverpa armigera and evaluation their roles in fenvalerate resistance

Insect cuticular protein (ICP) plays an important role in insect growth and development. However, research on the role of ICP in insecticide resistance is very limited. In this study, insect cuticular protein genes LCP17 and SgAbd5 were cloned and characterized in Helicoverpa armigera based on previous transcriptome data. The functions of LCP17 and SgAbd5 genes in fenvalerate resistance were assessed by RNA interference (RNAi), and their response to fenvalerate was further detected. The results showed that LCP17 and SgAbd5 were overexpressed in the fenvalerate-resistant strain comparing with a susceptible strain. The open reading frames of LCP17 and SgAbd5 genes were 423 bp and 369 bp, encoding 141 and 123 amino acids, respectively. LCP17 and SgAbd5 genes were highly expressed in the larval stage, but less expressed in the adult and pupal stages. The expression level of LCP17 and SgAbd5 genes increased significantly after fenvalerate treatment at 24 h. When the cotton bollworms larvae were exposed to fenvalerate at LD50 level, RNAi-mediated silencing of LCP17 and SgAbd5 genes increased the mortality from 50.68% to 68.67% and 63.89%, respectively; the mortality increased to even higher level, which was 73.61%, when these two genes were co-silenced. Moreover, silencing of these two genes caused the cuticle lamellar structure to become loose, which led to increased penetration of fenvalerate into the larvae. The results suggested that LCP17 and SgAbd5 may be involved in the resistance of cotton bollworm to fenvalerate, and LCP17 and SgAbd5 could serve as potential targets for H. armigera control.

Chromosome-level genome of spider Pardosa pseudoannulata and cuticle protein genes in environmental stresses

Spiders are representative arthropods of adaptive radiation. The high-quality genomes have only been reported in several web weaver spider species, leaving the wandering spiders' genomic information scarce. The pond wolf spider, Pardosa pseudoannulata, is a representative species in the retrolateral titial apophysis (RTA) clade. We present a chromosome-level P. pseusoannulata genome assembly of 2.42 Gb in size with a scaffold N50 of 169.99 Mb. Hi-C scaffolding assigns 94.83% of the bases to 15 pseudo-chromosomes. The repeats account for 52.79% of the assembly. The assembly includes 96.2% of the complete arthropod universal single-copy orthologs. Gene annotation predicted 24,530 protein-coding genes with a BUSCO score of 95.8% complete. We identified duplicate clusters of Hox genes and an expanded cuticle protein gene family with 243 genes. The expression patterns of CPR genes change in response to environmental stresses such as coldness and insecticide exposure. The high-quality P. pseudoannulata genome provides valuable information for functional and comparative studies in spiders.

Mosquitoes Possess Specialized Cuticular Proteins That Are Evolutionarily Related to the Elastic Protein Resilin

Resilin is an elastic protein that is vital to insects' vigorous movement. Canonical resilin proteins possess the R&R Consensus, a chitin-binding domain conserved in a family of cuticular proteins, and highly repetitive sequences conferring elastic properties. In the malaria vector mosquito, Anopheles gambiae, however, a cuticular protein has been found that has an R&R Consensus resembling that of resilin but lacks the repetitive sequences (here, we call it resilin-related or resilin-r). The relationship between resilin-r and resilin was unclear. It was also unknown whether resilin-r is conserved in mosquitoes. In this paper, phylogenetic and structural analyses were performed to reveal the relationship of resilin homologous proteins from holometabolous insects. Their chitin-binding abilities were also assessed. A resilin-r was found in each mosquito species, and these proteins constitute a clade with resilin from other insects based on the R&R Consensus sequences, indicating an evolutionary relationship between resilin-r and resilin. The resilin-r showed chitin-binding activity as same as resilin, but had distinct structural features from resilin, suggesting that it plays specialized roles in the mosquito cuticle. Another resilin-like protein was found to exist in each holometabolous insect that possesses resilin-like repetitive sequences but lacks the R&R Consensus. These results suggest that similar evolutionary events occurred to create resilin-r and resilin-like proteins.

Genome-wide analysis of cuticle protein family genes in rice stem borer Chilo suppressalis: Insights into their role in environmental adaptation and insecticidal stress response

Insect cuticle plays a key role in insect survival, adaptation and prosperity by serving as the exoskeleton and the first barrier against environmental stresses. As the major components of insect cuticle, the diverse structural cuticle proteins (CPs) contribute to variation in physical properties and functions of cuticle. However, the roles of CPs in cuticular versatility, especially in the stress response or adaption, remain incompletely understood. In this study, we performed a genome-wide analysis of CP superfamily in the rice-boring pest Chilo suppressalis. A total of 211 CP genes were identified and their encoding proteins were classified into eleven families and three subfamilies (RR1, RR2, and RR3). The comparative genomic analysis of CPs revealed that C. suppressalis had fewer CP genes compared to other lepidopteran species, which largely resulted from a less expansion of his-rich RR2 genes involved in cuticular sclerotization, suggesting long-term boring life of C. suppressalis inside rice hosts might evolutionarily prefer cuticular elasticity rather than cuticular sclerotization. We also investigated the response pattern of all CP genes under insecticidal stresses. >50 % CsCPs were upregulated at least 2-fold under insecticidal stresses. Notably, the majority of the highly upregulated CsCPs formed gene pairs or gene clusters on chromosomes, indicating the rapid response of adjacent CsCPs to insecticidal stress. Most high-response CsCPs encoded AAPA/V/L motifs that are related to cuticular elasticity and >50 % of the sclerotization-related his-rich RR2 genes were also upregulated. These results suggested the potential roles of CsCPs in balancing the elasticity and sclerotization of cuticles, which is essential for the survival and adaptation of plant borers including C. suppressalis. Our study provides valuable information for further developing cuticle-based strategies of both pest management and biomimetic applications.

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.

A Novel Cuticular Protein-like Cpr21L Is Essential for Nymph Survival and Male Fecundity in the Brown Planthopper

Cuticular proteins (CPs) are a large family and perform a variety of functions. However, the physiological roles of cuticle protein 21-like (Cpr21L) in the brown planthopper (Nilaparvata lugens, BPH), one of the most destructive insect pests of rice, are largely unclear. In this study, Cpr21L was revealed to be expressed in both BPH nymphs and adults, and the mRNA expression level was much higher in male adults than female adults. Spatially, the expression of Cpr21L in the testis was higher than in the ovary. The RNA interference (RNAi) of Cpr21L seriously decreased nymph survival, and no individual survived 8 days post-dsCpr21L injection. The RNAi of Cpr21L in adults also decreased the fertility of males, especially in the dsCpr21L♂ × dsGFP♀ group. The average number of eggs laid by one female in this group significantly decreased by 50.1%, and the eggs' hatchability decreased from 76.5% to 23.8% compared with the control (dsGFP♂ × dsGFP♀). Furthermore, observations under a stereomicroscope showed that the RNAi of Cpr21L severely impaired the development of the testes. Therefore, Cpr21L is essential for the nymphal survival and male fecundity of BPH, thus providing a possible target for pest control.

Global Gene Expression Analysis Reveals Complex Cuticle Organization of the Tribolium Compound Eye

The red flour beetle Tribolium castaneum is a resource-rich model for genomic and developmental studies. To extend previous studies on Tribolium eye development, we produced transcriptomes for normal-eyed and eye-depleted heads of pupae and adults to identify differentially transcript-enriched (DE) genes in the visual system. Unexpectedly, cuticle-related genes were the largest functional class in the pupal compound eye DE gene population, indicating differential enrichment in three distinct cuticle components: clear lens facet cuticle, highly melanized cuticle of the ocular diaphragm, which surrounds the Tribolium compound eye for internal fortification, and newly identified facet margins of the tanned cuticle, possibly enhancing external fortification. Phylogenetic, linkage, and high-throughput gene knockdown data suggest that most cuticle proteins (CPs) expressed in the Tribolium compound eye stem from the deployment of ancient CP genes. Consistent with this, TcasCPR15, which we identified as the major lens CP gene in Tribolium, is a beetle-specific but pleiotropic paralog of the ancient CPR RR-2 CP gene family. The less abundant yet most likely even more lens-specific TcasCP63 is a member of a sprawling family of noncanonical CP genes, documenting a role of local gene family expansions in the emergence of the Tribolium compound eye CP repertoire. Comparisons with Drosophila and the mosquito Anopheles gambiae reveal a steady turnover of lens-enriched CP genes during insect evolution.

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.

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.

Cuticle Protein LmACP19 Is Required for the Stability of Epidermal Cells in Wing Development and Morphogenesis of Locusta migratoria

Insect wing consists of a double layer of epidermal cells that produce and secrete the dorsal and ventral cuticular components. It is important for the stability of epidermal cells during wing development and morphogenesis, but its specific gene expression and physiological function during this process remain unclear. In our previous work, a wing cuticle protein gene LmACP19 was identified in Locusta migratoria based on transcriptomic data. Here, we report on its roles in wing development and morphogenesis. LmACP19 encodes a chitin-binding protein belonging to RR-2 subfamily of CPR family, which is highly homologous to CP19-like proteins in other insect species. RT-qPCR analysis revealed that LmACP19 is highly expressed in wing pads of fifth-instar nymphs, and its encoded protein is located in two layers of epidermal cells but not in the cuticle. Suppression of LmACP19 by RNA interference led to abnormal wing pad and wing morphogenesis with curved, unclosed, and wrinkled phenotypes during nymph-to-nymph and nymph-to-adult transition, respectively. Furthermore, deficiency of LmACP19 affected arrangement of epidermal cells, resulting in apoptosis. Our results indicate that LmACP19 is indispensable for wing development and normal morphological structure by maintaining the stability of epidermal cells during L. migratoria molting.

Unveiling characteristic proteins for the structural development of beetle elytra

Beetles possess a set of highly modified and tanned forewings, elytra, which are lightweight yet rigid and tough. Immediately after eclosion, the elytra are initially thin, pale and soft. However, they rapidly expand and subsequently become hardened and often dark, resulting from both pigmentation and sclerotization. Here, we identified changes in protein composition during the developmental processes of the elytra in the Japanese rhinoceros beetle, Trypoxylus dichotomus. Using mass spectrometry, a total of 414 proteins were identified from both untanned and tanned elytra, including 31 cuticular proteins (CPs), which constitute one of the major components of insect cuticles. Moreover, CPs containing Rebers and Riddiford motifs (CPR), the most abundant CP family, were separated into two groups based on their expression and amino acid sequences, such as a Gly-rich sequence region and Ala-Ala-Pro repeats. These protein groups may play crucial roles in elytra formation at different time points, likely including self-assembly of chitin nanofibers that control elytral macro and microstructures and dictate changes in other properties (i.e., mechanical property). Clarification of the protein functions will enhance the understanding of elytra formation and potentially benefit the development of lightweight materials for industrial and biomedical applications. STATEMENT OF SIGNIFICANCE: The beetle elytron is a light-weight natural bio-composite which displays high stiffness and toughness. This structure is composed of chitin fibrils and proteins, some of which are responsible for architectural development and hardening. This work, which involves insights from molecular biology and materials science, investigated changes in proteomic, architectural, and localized mechanical characteristics of elytra from the Japanese rhinoceros beetle to understand molecular mechanisms driving elytra development. In the present study, we identified a set of new protein groups which are likely related to the structural development of elytra and has potential for new pathways for processing green materials.

CPR63 promotes pyrethroid resistance by increasing cuticle thickness in Culex pipiens pallens

The cuticle protein (CP) encoded by CPR63 plays a role in deltamethrin resistance in Culex pipiens pallens. Herein, we investigated the distribution of CPR63 transcripts in this organism and observed high expression levels in legs and wings. Furthermore, expression of CPR63 in the legs of deltamethrin-resistant (DR) strains was 2.17-fold higher than in deltamethrin-susceptible (DS) strains. Cuticle analysis of small interfering RNA (siRNA) groups by scanning electron microscopy (SEM) revealed a significantly thinner cuticle of the tarsi in the siCPR63 group than in the siNC (negative control siRNA) group. Transmission electron microscopy (TEM) revealed that the exocuticle and endocuticle thickness of the tarsi were significantly thinner, which contributes the thinner procuticle of tarsi in the siCPR63 group than in the siNC group. Our results suggested that CPR63 might contribute to the resistance phenotype by thickening the cuticle and thereby possibly increasing the tolerance of mosquitoes to deltamethrin.

Antifungal roles of adult-specific cuticular protein genes of the red flour beetle, Tribolium castaneum

The insect cuticle is a composite structure that can further be divided into a few sub-structural layers. Its large moiety comprises a lattice of chitin fibrils and structural proteins, both of which are stabilized by covalent bonding among them. The cuticle covers the whole surface of insect body, and thus has long been suggested for the involvement in defense against entomopathogens, especially entomopathogenic fungi that infect percutaneously. We have been addressing this issue in the past few years and have so far demonstrated experimentally that chitin synthase 1, laccase2 as well as benzoquinone synthesis-related genes of Tribolium castaneum have indispensable roles in the antifungal host defense. In the present study we focused on another major component of the insect cuticular integument, structural cuticular proteins. We chose three genes coding for adult-specific cuticular proteins, namely CPR4, CPR18 and CPR27, and examined their roles in forming immunologically sound adult cuticular integuments. Analyses of developmental expression revealed that the three genes showed high level expression in the pupal stage. These results are consistent with their proposed roles in constructing cuticle of adult beetles. The RNA interference-mediated gene knockdown was employed to silence these genes, and the administration of double strand RNAs in pupae resulted in the adults with malformed elytra. The single knockdown of the three genes attenuated somewhat the defense of the resulting adult beetles against Beauveria bassiana and Metarhizium anisopliae, but statistical analyses indicated no significant differences from controls. In contrast, the double or triple knockdown mutant beetles displayed a drastic disruption of the host defense against the two entomopathogenic fungal species irrespective of the combination of targeted cuticular protein genes, demonstrating the important roles of the three cuticular protein genes in conferring robust antifungal properties on the adult cuticle. Scanning electron microscopic observation revealed that the germination of conidia attached on the adult body surface was still suppressed after the gene knockdown as in the case of wild-type beetles, suggesting that the weakened antifungal phenotypes resulted from the combined knockdown of the adult-specific cuticular protein genes could not be accounted for by the disfunction of secretion/retention of fungistatic benzoquinone derivatives.

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.

Resilin matrix distribution, variability and function in Drosophila

Background

Elasticity prevents fatigue of tissues that are extensively and repeatedly deformed. Resilin is a resilient and elastic extracellular protein matrix in joints and hinges of insects. For its mechanical properties, Resilin is extensively analysed and applied in biomaterial and biomedical sciences. However, there is only indirect evidence for Resilin distribution and function in an insect. Commonly, the presence of dityrosines that covalently link Resilin protein monomers (Pro-Resilin), which are responsible for its mechanical properties and fluoresce upon UV excitation, has been considered to reflect Resilin incidence.

Results

Using a GFP-tagged Resilin version, we directly identify Resilin in pliable regions of the Drosophila body, some of which were not described before. Interestingly, the amounts of dityrosines are not proportional to the amounts of Resilin in different areas of the fly body, arguing that the mechanical properties of Resilin matrices vary according to their need. For a functional analysis of Resilin matrices, applying the RNA interference and Crispr/Cas9 techniques, we generated flies with reduced or eliminated Resilin function, respectively. We find that these flies are flightless but capable of locomotion and viable suggesting that other proteins may partially compensate for Resilin function. Indeed, localizations of the potentially elastic protein Cpr56F and Resilin occasionally coincide.

Conclusions

Thus, Resilin-matrices are composite in the way that varying amounts of different elastic proteins and dityrosinylation define material properties. Understanding the biology of Resilin will have an impact on Resilin-based biomaterial and biomedical sciences.

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.

Cuticular Structure Proteomics in the Pea Aphid Acyrthosiphon pisum Reveals New Plant Virus Receptor Candidates at the Tip of Maxillary Stylets

Aphids are phloem-feeding insects known as major pests in agriculture that are able to transmit hundreds of plant viruses. The majority of these viruses, classified as noncirculative, are retained and transported on the inner surface of the cuticle of the needle-like mouthparts while the aphids move from plant to plant. Identification of receptors of viruses within insect vectors is a key challenge because they are promising targets for alternative control strategies. The acrostyle, an organ discovered earlier within the common food/salivary canal at the tip of aphid maxillary stylets, displays proteins at the cuticle-fluid interface, some of which are receptors of noncirculative viruses. To assess the presence of stylet- and acrostyle-specific proteins and identify putative receptors, we have developed a comprehensive comparative analysis of the proteomes of four cuticular anatomical structures of the pea aphid, stylets, antennae, legs, and wings. In addition, we performed systematic immunolabeling detection of the cuticular proteins identified by mass spectrometry in dissected stylets. We thereby establish the first proteome of stylets of an insect and determine the minimal repertoire of the cuticular proteins composing the acrostyle. Most importantly, we propose a short list of plant virus receptor candidates, among which RR-1 proteins are remarkably predominant. The data are available via ProteomeXchange (PXD016517).

Downregulation of imidacloprid resistant genes alters the biological parameters in Colorado potato beetle, Leptinotarsa decemlineata Say (chrysomelidae: Coleoptera)

Colorado potato beetle, Leptinotarsa decemlineata Say (coleoptera: chrysomelidae), is the important pest of potato all over the world. This insect pest is resistant to more than 50 active compounds belonging to various chemical groups. Potential of RNA interference (RNAi) was explored to knock down transcript levels of imidacloprid resistant genes in Colorado potato beetle (CPB) under laboratory conditions. Three important genes belonging to cuticular protein (CP), cytochrome P450 monoxygenases (P450) and glutathione synthetase (GSS) families encoding imidacloprid resistance were targeted. Feeding bio-assays were conducted on various stages of imidacloprid resistant CPB lab population by applying HT115 expressing dsRNA on potato leaflets. Survival rate of insects exposed to CP-dsRNA decreased to 4.23%, 15.32% and 47.35% in 2nd, 3rd and 4th instar larvae respectively. Larval weight and pre-adult duration were also affected due to dsRNAs feeding. Synergism of RNAi with imidacloprid conducted on the 2nd instar larvae, exhibited 100% mortality of larvae when subjected to reduced doses of GSS and CP dsRNAs along with imidacloprid. Utilization of three different dsRNAs against imidacloprid resistant CPB population reveal that dsRNAs targeting CP, P450 and GSS enzymes could be useful tool in management of imidacloprid resistant CPB populations.

Genome-wide identification and analysis of genes encoding cuticular proteins in the endoparasitoid wasp Pteromalus puparum (Hymenoptera: Pteromalidae)

The multifunctional insect cuticle serves as the exoskeleton, determines body shape, restricts water loss, provides attachment sites for muscles and internal organs and is a formidable barrier to invaders. It is morphologically divided into three layers, including envelope, epicuticle, and procuticle and is composed of chitin and cuticular proteins (CPs). Annotation of CPs and their cognate genes may help understand the structure and functions of insect cuticles. In this paper, we interrogated the genome of Pteromalus puparum, an endoparasitoid wasp that parasitizes Pieris rapae and Papilio xuthus pupae, and identified 82 genes encoding CPs belonging to six CP families, including 62 in the CPR family, 8 in CPAP3, 5 in CPF/CPFL, 2 low complexity proteins, 2 in TWDL, and 3 in Apidermin. We used six RNA-seq libraries to determine CP gene expression profiles through development and compared the cuticle hydrophobicity between the P. puparum and the ectoparasitoid Nasonia vitripennis based on GRAVY values of CPR sequences. In the Nasonia-Pteromalus comparison, we found in both N. vitripennis and P. puparum, the peak of their CPR hydrophobicity displayed at their pupal stage, whereas their adult stage showed the lowest level. Except at the adult stage, the CPR hydrophobicity in N. vitripennis is always higher than P. puparum. Finally, we identified three novel Apidermin genes, a family found solely in Hymenoptera and revealed a new sequence feature of this family. This new information contributes to a broader understanding of insect CPs generally.

Dynamic transcriptome profiling exploring cold tolerance in forensically important blow fly, Aldrichina grahami (Diptera: Calliphoridae)

Background

Aldrichina grahami (Diptera: Calliphoridae) is a forensically important fly, which has been widely applied to practical legal investigations. Unlike other necrophagous flies, A. grahami exhibits cold tolerance which helps to maintain its activity during low-temperature months, when other species are usually not active. Hence, A. grahami is considered an important forensic insect especially in cold seasons. In this study, we aim to explore the molecular mechanisms of cold tolerance of A. grahami through transcriptome.

Results

We collected eggs and larvae (first-instar, second-instar and third-instar) at three different temperatures (4 °C, 12 °C and 20 °C) and performed RNA-seq analyses. The differentially expressed genes (DEGs) associated with the cold-tolerance were screened out. The Venn analysis of DEGs from egg to third-instar larvae at three different temperatures showed there were 9 common genes. Candidate biological processes and genes were identified which refer to growth, and development of different temperatures, especially the chitin and cuticle metabolic process. The series-clusters showed crucial and unique trends when the temperature changed. Moreover, by comparing the results of growth and developmental transcriptomes from different temperatures, we found that DEGs belonging to the family of larval cuticle proteins (LCP), pupal cuticle protein (CUP), and heat shock proteins (HSP) have certain differences.

Conclusions

This study identified functional genes and showed differences in the expression pattern of diverse temperatures. The DEGs series-clusters with increasing or decreasing trends were analyzed which may play an important role in cold-tolerance. Moreover, the findings in LCP, CUP and HSP showed more possible modulations in a cold environment. This work will provide valuable information for the future investigation of the molecular mechanism of cold tolerance in A. grahami.

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.

Proteomics reveals localization of cuticular proteins in Anopheles gambiae

Anopheles gambiae devotes over 2% of its protein coding genes to its 298 structural cuticular proteins (CPs). This paper provides new LC-MS/MS data on two adult structures, proboscises and palps, as well as three larval samples - 4th instar larvae, just their terminal segment, and a preparation enriched in their tracheae. These data were combined with our previously published results of proteins from five other adult structures, whole adults, and two preparations chosen for their relatively clean cuticle, the larval head capsules left behind after ecdysis and the pupal cuticles left behind after adult eclosion. Peptides from 28 CPs were recovered in all adult structures; 24 CPs were identified for the first time, 6 of these were members of the TWDL family. Most newly identified proteins came from the larval sources. Based solely on peptide recovery, from our data and from other investigators, most available on VectorBase, there were only 4 CPs that were restricted to a single adult structure. More were restricted to a single metamorphic stage, 14 in larvae, 0 in pupae and 32 in adults. Expression data from our earlier RT-qPCR studies reduces these numbers. Charting restriction of CPs to stage or structure is a step forward in establishing their specific roles.

Chitin: Structure, Chemistry and Biology

Chitin is a linear polysaccharide of the amino sugar N-acetyl glucosamine. It is present in the extracellular matrix of a variety of invertebrates including sponges, molluscs, nematodes and arthropods and fungi. Generally, it is an important component of protective or supportive extracellular matrices that cover the tissue that produces it or the whole body of the organism. Chitin fibres associate with each other adopting one of three possible crystalline organisations, i.e. α-, β- or γ-chitin. Usually, chitin fibre bundles interact with chitin-binding proteins forming higher order structures. Chitin laminae, which are two-dimensional sheets of α-chitin crystals with antiparallel running chitin fibres in association with β-folded proteins, are primary constituents of the arthropod cuticle and the fibrous extracellular matrix in sponges. A tri-dimensional composite material of proteins coacervates and β-chitin constitute hard biomaterials such as the squid beak. The molecular composition of γ-chitin-based structures that contribute to the physical barrier found in insect cocoons is less well studied. In principle, chitin is a versatile extracellular polysaccharide that in association with proteins defines the mechanical properties of tissues and organisms.

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.

High level efficacy of lufenuron against sea lice (Lepeophtheirus salmonis) linked to rapid impact on moulting processes

Drug resistance in the salmon louse Lepeophtheirus salmonis is a global issue for Atlantic salmon aquaculture. Multiple resistance has been described across most available compound classes with the exception of the benzoylureas. To target this gap in effective management of L. salmonis and other species of sea lice (e.g. Caligus spp.), Elanco Animal Health is developing an in-feed treatment containing lufenuron (a benzoylurea) to be administered prior to seawater transfer of salmon smolts and to provide long-term protection of salmon against sea lice infestations. Benzoylureas disrupt chitin synthesis, formation, and deposition during all moulting events. However, the mechanism(s) of action are not yet fully understood and most research completed to date has focused on insects. We exposed the first parasitic stage of L. salmonis to 700 ppb lufenuron for three hours and observed over 90% reduction in survival to the chalimus II life stage on the host, as compared to vehicle controls. This agrees with a follow up in vivo administration study on the host, which showed >95% reduction by the chalimus I stage. Transcriptomic responses of salmon lice exposed to lufenuron included genes related to moulting, epithelial differentiation, solute transport, and general developmental processes. Global metabolite profiles also suggest that membrane stability and fluidity is impacted in treated lice. These molecular signals are likely the underpinnings of an abnormal moulting process and cuticle formation observed ultrastructurally using transmission electron microscopy. Treated nauplii-staged lice exhibited multiple abnormalities in the integument, suggesting that the coordinated assembly of the epi- and procuticle is impaired. In all cases, treatment with lufenuron had rapid impacts on L. salmonis development. We describe multiple experiments to characterize the efficacy of lufenuron on eggs, larvae, and parasitic stages of L. salmonis, and provide the most comprehensive assessment of the physiological responses of a marine arthropod to a benzoylurea chemical.

Insect cuticle: a critical determinant of insecticide resistance

Intense use of insecticides has resulted in the selection of extreme levels of resistance in insect populations. Therefore understanding the molecular basis of insecticide resistance mechanisms becomes critical. Penetration resistance refers to modifications in the cuticle that will eventually slow down the penetration of insecticide molecules within insects' body. So far, two mechanisms of penetration resistance have been described, the cuticle thickening and the altering of cuticle composition. Cuticular modifications are attributed to the over-expression of diversified genes or proteins, which belong to structural components (cuticular proteins mainly), enzymes that catalyze enzymatic reactions (CYP4G16 and laccase 2) or ABC transporters that promote cuticular translocation. In the present review we summarize recent studies and discuss future perspectives.

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.

The Evolution and Metamorphosis of Arthropod Proteomics and Genomics

This article presents an overview of the development of techniques for analyzing cuticular proteins (CPs), their transcripts, and their genes over the past 50 years based primarily on experience in the laboratory of J.H. Willis. It emphasizes changes in the kind of data that can be gathered and how such data provided insights into the molecular underpinnings of insect metamorphosis and cuticle structure. It describes the techniques that allowed visualization of the location of CPs at both the anatomical and intracuticular levels and measurement of the appearance and deployment of transcripts from CP genes as well as what was learned from genomic and transcriptomic data. Most of the early work was done with the cecropia silkmoth, Hyalophora cecropia, and later work was with Anopheles gambiae.

Microscopic cuticle structure comparison of pupal melanic and wild strain of Spodoptera exigua and their gene expression profiles in three time points

The beet armyworm, Spodoptera exigua (Hubner), is one of the major crop pests and is a target for current pest control approaches using insecticides. S. exigua melanic mutants (SEM) spontaneously occurred in the S. exigua wild type (SEW) strain and have been maintained under laboratory conditions on an artificial diet. Scanning electron microscopy showed that the inner cuticle of the SEM had a denser and less orderly structure. We investigated the cuticle protein genes using RNA-seq at three different developmental stages of both SEM and SEW. Comparison of cDNA libraries showed that 7257 CPs were significantly up-regulated and 664 genes were significantly downregulated in SEM at the developmental stage of 46-h in the fifth instar. In addition, 460 genes were significantly up-regulated and 439 genes were significantly down-regulated in the SEM at the development stage of 4-h before pupation. Moreover, 162 genes were significantly up-regulated and 293 genes were significantly downregulated in the SEM, just after pupation. Two genes CPR63 and CPR97 were identified from RNA sequences to verify the differentially expressed gene (DEG) results through quantitative real-time PCR (qRT-PCR). The results show that expression of both CPR63 and CPR97 structural cuticular proteins were significantly different between SEM and SEW. This functional analysis may help in understanding the role that these genes play in the cuticle pattern of the SEM.

Proteomic composition of the acrostyle: Novel approaches to identify cuticular proteins involved in virus-insect interactions

The acrostyle is a distinct anatomical region present on the cuticle at the inner face of the common food/salivary canal at the tip of aphid maxillary stylets. This conserved structure is of particular interest as it harbors the protein receptors of at least 1 plant virus, Cauliflower mosaic virus, and presumably has other roles in plant-insect interactions. Previously we reported immunolabeling of a highly conserved motif of cuticular proteins from the CPR family (named for the presence of a Rebers and Riddiford consensus) within the acrostyle. Here we report the development of novel tools to further study the proteomic composition of this region and to identify proteins involved in insect-virus interactions. Using a series of antibodies against cuticular proteins from the RR-2 subfamily, we identified additional peptides present within the acrostyle. Our results demonstrated that the acrostyle is a complex structure containing multiple domains of cuticular proteins accessible for interaction. In addition, an array of overlapping peptides, which covers the diversity of the majority of the RR-2 subfamily, was developed as a generic tool to characterize cuticular protein/pathogen interactions. Upon probing this array with Cucumber mosaic virus particles, consensus peptide sequences from hybridizing peptides were identified. Use of these novel tools has extended our knowledge of the proteomic composition of insect maxillary stylets and identified sequences that could be involved in virus binding, thus contributing to further elucidation of the various properties and functions of the acrostyle.

Isolation and functional identification of three cuticle protein genes during metamorphosis of the beet armyworm, Spodoptera exigua

The beet armyworm, Spodoptera exigua (Hubner), is one of the major crop pests and is a target for current pest control approaches using insecticides. In this study three cuticular protein genes CPG316, CPG860 and CPG4855 have been cloned from 0 h pupal integument of S. exigua through race PCR Strategy. The deduced amino acid sequences were found to contain the RR-2 consensus region of other insect cuticular proteins and construct phylogenetic trees for each protein. Using quantitative RT-PCR, the developmental expression of the three genes through several larval and the early pupal stages was studied. All three genes contribute to the endocuticle although CPG316 may have a different role from the other two genes. All three newly isolated genes were analyzed and their functions were determined by using direct injection of the dsRNA into early 5^th instar larvae. All genes are expressed in the larvae and early pupae but in different patterns. Furthermore, phenotypic results show that these genes have differing effects on the development of cuticle, its flexibility and a big role in metamorphosis in both larval and pupal stages.

The cuticular nature of corneal lenses in Drosophila melanogaster

The dioptric visual system relies on precisely focusing lenses that project light onto a neural retina. While the proteins that constitute the lenses of many vertebrates are relatively well characterized, less is known about the proteins that constitute invertebrate lenses, especially the lens facets in insect compound eyes. To address this question, we used mass spectrophotometry to define the major proteins that comprise the corneal lenses from the adult Drosophila melanogaster compound eye. This led to the identification of four cuticular proteins: two previously identified lens proteins, drosocrystallin and retinin, and two newly identified proteins, Cpr66D and Cpr72Ec. To determine which ommatidial cells contribute each of these proteins to the lens, we conducted in situ hybridization at 50% pupal development, a key age for lens secretion. Our results confirm previous reports that drosocrystallin and retinin are expressed in the two primary corneagenous cells-cone cells and primary pigment cells. Cpr72Ec and Cpr66D, on the other hand, are more highly expressed in higher order interommatidial pigment cells. These data suggest that the complementary expression of cuticular proteins give rise to the center vs periphery of the corneal lens facet, possibly facilitating a refractive gradient that is known to reduce spherical aberration. Moreover, these studies provide a framework for future studies aimed at understanding the cuticular basis of corneal lens function in holometabolous insect eyes.

Identification and expression of cuticular protein genes based on Locusta migratoria transcriptome

Many types of cuticular proteins are found in a single insect species, and their number and features are very diversified among insects. The cuticle matrix consists of many different proteins that confer the physical properties of the exoskeleton. However, the number and properties of cuticle proteins in Locusta migratoria remain unclear. In the present study, Illumina sequencing and de novo assembly were combined to characterize the transcriptome of L. migratoria. Eighty-one cuticular protein genes were identified and divided into five groups: the CPR family (51), Tweedle (2), CPF/CPFLs (9), CPAP family (9), and other genes (10). Based on the expression patterns in different tissues and stages, most of the genes as a test were distributed in the integument, pronotum and wings, and expressed in selected stages with different patterns. The results showed no obvious correlation between the expression patterns and the conservative motifs. Additionally, each cluster displayed a different expression pattern that may possess a different function in the cuticle. Furthermore, the complexity of the large variety of genes displayed differential expression during the molting cycle may be associated with cuticle formation and may provide insights into the gene networks related to cuticle formation.

Identification, expression pattern, and feature analysis of cuticular protein genes in the pine moth Dendrolimus punctatus (Lepidoptera: Lasiocampidae)

Cuticular proteins (CPs) are vital components of the insects' cuticle that support movement and protect insect from adverse environmental conditions. The CPs exist in a large number and diversiform structures, thus, the accurate annotation is the first step to interpreting their roles in insect growth. The rapid development of sequencing technology has simplified the access to the information on protein sequences, especially for non-model species. Dendrolimus punctatus is a Lepidopteran defoliator, and its periodic outbreaks cause severe damage to the coniferous forests. The transcriptome of D. punctatus integrating the whole developmental periods are available for the potential investigation of CPs. In this study, we identified 216 CPs from D. punctatus, including 147 from CPR family, 4 from TWDL family, 3 from CPF/CPFL families, 22 from CPAP families, 8 low complexity proteins, 1 CPCPC and 31 from other CP families. The putative CPs were compared with homologs in other species such as Bombyx mori, Manduca sexta and Drosophila melanogaster. We further identified five co-orthologous groups have highly similar sequences of CRPs in nine lepidopteran species, which exclusively presented in RR-2 subfamily rather than RR-1. We inferred that in Lepidoptera the difference in RR-2 numbers was maintained by homologs in co-orthologous groups, coincided with observation in Drosophila and Anopheles that gene cluster was the model and source for the expansion of RR-2 genes. In combination with the variation of members in each CP family among different species, these results indicated the evolution of CPs was highly correlated to the adaptation of insect to environment. Furthermore, we compared the amino acid composition of the different types CPRs, and examined the expression patterns of CP genes in various developmental stages. The comprehensive overview of CPs from our study provides an insight into their evolution and the association between them and insect development.

Mechanical Control of Whole Body Shape by a Single Cuticular Protein Obstructor-E in Drosophila melanogaster

Body shapes are much more variable than body plans. One way to alter body shapes independently of body plans would be to mechanically deform bodies. To what extent body shapes are regulated physically, or molecules involved in physical control of morphogenesis, remain elusive. During fly metamorphosis, the cuticle (exoskeleton) covering the larval body contracts longitudinally and expands laterally to become the ellipsoidal pupal case (puparium). Here we show that Drosophila melanogaster Obstructor-E (Obst-E) is a protein constituent of the larval cuticle that confers the oriented contractility/expandability. In the absence of obst-E function, the larval cuticle fails to undergo metamorphic shape change and finally becomes a twiggy puparium. We present results indicating that Obst-E regulates the arrangement of chitin, a long-chain polysaccharide and a central component of the insect cuticle, and directs the formation of supracellular ridges on the larval cuticle. We further show that Obst-E is locally required for the oriented shape change of the cuticle during metamorphosis, which is associated with changes in the morphology of those ridges. Thus, Obst-E dramatically affects the body shape in a direct, physical manner by controlling the mechanical property of the exoskeleton.

Shapes of objects, living or not, should depend on their material properties and forces acting on them. Mechanical processes that create whole body shapes of multicellular organisms, or genes that regulate such processes, are largely unknown. Insect bodies are coated by cuticle, a matrix composed of proteins and the polysaccharide chitin. We show that, during metamorphosis of the fruit fly Drosophila melanogaster, the cuticle covering the long and thin larva (maggot) undergoes longitudinal contraction and lateral expansion to become the short and stout puparium covering the pupa. Furthermore, we identify a single protein component of the larval cuticle that confers the oriented contractility/expandability, thereby determining the pupal body shape in a mechanical manner.

Localization of RR-1 and RR-2 cuticular proteins within the cuticle of Anopheles gambiae

The largest arthropod cuticular protein family, CPR, has the Rebers and Riddiford (R&R) Consensus that in an extended form confers chitin-binding properties. Two forms of the Consensus, RR-1 and RR-2, have been recognized and initial data suggested that the RR-1 and RR-2 proteins were present in different regions within the cuticle itself. Thus, RR-2 proteins would contribute to exocuticle that becomes sclerotized, while RR-1s would be found in endocuticle that remains soft. An alternative, and more common, suggestion is that RR-1 proteins are used for soft, flexible cuticles such as intersegmental membranes, while RR-2s are associated with hard cuticle such as sclerites and head capsules. We used TEM immunogold detection to localize the position of several RR-1 and RR-2 proteins in the cuticle of Anopheles gambiae. RR-1s were localized in the procuticle of the soft intersegmental membrane except for one protein found in the endocuticle of hard cuticle. RR-2s were consistently found in hard cuticle and not in flexible cuticle. All RR-2 antibodies localized to the exocuticle and four out of six were also found in the endocuticle. Hence the location of RR-1s and RR-2s depends more on properties of individual proteins than on either hypothesis.

Immunolocalization of cuticular proteins in Johnston's organ and the corneal lens of Anopheles gambiae

Previous work with EM immunolocalization examined the intracuticular placement of several antibodies directed against cuticular proteins (CPs) in various structures of Anopheles gambiae. Those structures had long stretches of fairly uniform cuticle. We have now used 19 antibodies directed against members of five CP families on two adult structures with considerable complexity, Johnston's organ and the corneal lens of the compound eye. We also localized chitin with colloidal-gold labeled wheat germ agglutinin. Twelve of these antibodies recognized structures in Johnston's organ. Only 6 were detected in the outer pedicel wall, but the internal structures were more complex with distinct distributions of members of the five CP families in six different structures. The corneal lens had four distinct regions of laminar cuticle. Thirteen of the 15 members of the CPR family were detected, none from the other CP families. Specific antibodies were localized to different regions and in different laminae within a region. The specificity of deployment of cuticular proteins revealed in this study is helping to explain why An. gambiae allocates about 2% of its protein coding genes to structural CPs.

Cuticle formation and pigmentation in beetles

Adult beetles (Coleoptera) are covered primarily by a hard exoskeleton or cuticle. For example, the beetle elytron is a cuticle-rich highly modified forewing structure that shields the underlying hindwing and dorsal body surface from a variety of harmful environmental factors by acting as an armor plate. The elytron comes in a variety of colors and shapes depending on the coleopteran species. As in many other insect species, the cuticular tanning pathway begins with tyrosine and is responsible for production of a variety of melanin-like and other types of pigments. Tanning metabolism involves quinones and quinone methides, which also act as protein cross-linking agents for cuticle sclerotization. Electron microscopic analyses of rigid cuticles of the red flour beetle, Tribolium castaneum, have revealed not only numerous horizontal chitin-protein laminae but also vertically oriented columnar structures called pore canal fibers. This structural architecture together with tyrosine metabolism for cuticle tanning is likely to contribute to the rigidity and coloration of the beetle exoskeleton.

The whole genome sequence of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), reveals insights into the biology and adaptive evolution of a highly invasive pest species

Background

The Mediterranean fruit fly (medfly), Ceratitis capitata, is a major destructive insect pest due to its broad host range, which includes hundreds of fruits and vegetables. It exhibits a unique ability to invade and adapt to ecological niches throughout tropical and subtropical regions of the world, though medfly infestations have been prevented and controlled by the sterile insect technique (SIT) as part of integrated pest management programs (IPMs). The genetic analysis and manipulation of medfly has been subject to intensive study in an effort to improve SIT efficacy and other aspects of IPM control.

Results

The 479 Mb medfly genome is sequenced from adult flies from lines inbred for 20 generations. A high-quality assembly is achieved having a contig N50 of 45.7 kb and scaffold N50 of 4.06 Mb. In-depth curation of more than 1800 messenger RNAs shows specific gene expansions that can be related to invasiveness and host adaptation, including gene families for chemoreception, toxin and insecticide metabolism, cuticle proteins, opsins, and aquaporins. We identify genes relevant to IPM control, including those required to improve SIT.

Conclusions

The medfly genome sequence provides critical insights into the biology of one of the most serious and widespread agricultural pests. This knowledge should significantly advance the means of controlling the size and invasive potential of medfly populations. Its close relationship to Drosophila, and other insect species important to agriculture and human health, will further comparative functional and structural studies of insect genomes that should broaden our understanding of gene family evolution.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-016-1049-2) contains supplementary material, which is available to authorized users.

Distribution of cuticular proteins in different structures of adult Anopheles gambiae

Anopheles gambiae devotes over 2% (295) of its protein coding genes to structural cuticular proteins (CPs) that have been classified into 13 different families plus ten low complexity proteins not assigned to families. Small groups of genes code for identical proteins reducing the total number of unique cuticular proteins to 282. Is the large number because different structures utilize different CPs, or are all of the genes widely expressed? We used LC-MS/MS to learn how many products of these genes were found in five adult structures: Johnston's organs, the remainder of the male antennae, eye lenses, legs, and wings. Data were analyzed against both the entire proteome and a smaller database of just CPs. We recovered unique peptides for 97 CPs and shared peptides for another 35. Members of 11 of the 13 families were recovered as well as some unclassified. Only 11 CPs were present exclusively in only one structure while 43 CPs were recovered from all five structures. A quantitative analysis, using normalized spectral counts, revealed that only a few CPs were abundant in each structure. When the MS/MS data were run against the entire proteome, the majority of the top hits were to CPs, but peptides were recovered from an additional 467 proteins. CP peptides were frequently recovered from chitin-binding domains, confirming that protein-chitin interactions are not mediated by covalent bonds. Comparison with three other MS/MS analyses of cuticles or cuticle-rich structures augmented the current analysis. Our findings provide new insights into the composition of different mosquito structures and reveal the complexity of selection and utilization of genes coding for structural cuticular proteins.

Comparative Analysis of Transcriptomes among Bombyx mori Strains and Sexes Reveals the Genes Regulating Melanic Morph and the Related Phenotypes

As a source of insect polymorphism, melanism plays an important role in ecological adaption and usually endows advantageous phenotypic-effects on insects. However, due to the mechanistic diversity, there are knowledge gaps in the molecular mechanisms underlying melanism and the related phenotypes. In silk moths, a recessive melanic mutant (sex-controlled melanism, sml) strain exhibits extended adult longevity. We took a transcriptome approach to perform a comparative analysis between this sml strain and a wild-type strain (Dazao). Our analysis resulted in the identification of 59 unique differentially expressed genes in the melanic mutant. Two key genes (laccase2 and yellow) involved in melanin formation were significantly up-regulated in melanic individuals. The laccase2 B-type isoform (BGIBMGA006746) was found to likely participate in the silkworm cuticular melanism process at late pupal stage. Moreover, we discovered 22 cuticular protein encoding genes with the possible function in melanin transport and/or maintenance. Based on our findings, we presume that the longer survival of the melanic sml male moths might be associated with the enhanced antioxidant defense systems and a reduction in the insulin/IGF-1 signaling pathway (IIS). These findings will facilitate the understanding of the molecular basis underlying melanism and the derived phenotypic-effects.

Unique features of a global human ectoparasite identified through sequencing of the bed bug genome

The bed bug, Cimex lectularius, has re-established itself as a ubiquitous human ectoparasite throughout much of the world during the past two decades. This global resurgence is likely linked to increased international travel and commerce in addition to widespread insecticide resistance. Analyses of the C. lectularius sequenced genome (650 Mb) and 14,220 predicted protein-coding genes provide a comprehensive representation of genes that are linked to traumatic insemination, a reduced chemosensory repertoire of genes related to obligate hematophagy, host–symbiont interactions, and several mechanisms of insecticide resistance. In addition, we document the presence of multiple putative lateral gene transfer events. Genome sequencing and annotation establish a solid foundation for future research on mechanisms of insecticide resistance, human–bed bug and symbiont–bed bug associations, and unique features of bed bug biology that contribute to the unprecedented success of C. lectularius as a human ectoparasite.

The bed bug, Cimex lectularius, is a ubiquitous human ectoparasite with global distribution. Here, the authors sequence the genome of the bed bug and identify reductions in chemosensory genes, expansion of genes associated with blood digestion and genes linked to pesticide resistance.

SEM characterization of anatomical variation in chitin organization in insect and arthropod cuticles

The cuticles of insects and arthropods have some of the most diverse material properties observed in nature, so much so that it is difficult to imagine that all cutciles are primarily composed of the same two materials: a fibrous chitin network and a matrix composed of cuticle proteins. Various factors contribute to the mechanical and optical properties of an insect or arthropod cuticle including the thickness and composition. In this paper, we also identified another factor that may contribute to the optical, surface, and mechanical properties of a cuticle, i.e. the organization of chitin nanofibers and chitin fiber bundles. Self-assembled chitin nanofibers serve as the foundation for all higher order chitin structures in the cuticles of insects and other arthropods via interactions with structural cuticle proteins. Using a technique that enables the characterization of chitin organization in the cuticle of intact insects and arthropod exoskeletons, we demonstrate a structure/function correlation of chitin organization with larger scale anatomical structures. The chitin scaffolds in cuticles display an extraordinarily diverse set of morphologies that may reflect specific mechanical or physical properties. After removal of the proteinaceous and mineral matrix of a cuticle, we observe using SEM diverse nanoscale and micro scale organization of in-situ chitin in the wing, head, eye, leg, and dorsal and ventral thoracic regions of the periodical cicada Magicicada septendecim and in other insects and arthropods. The organization of chitin also appears to have a significant role in the organization of nanoscale surface structures. While microscale bristles and hairs have long been known to be chitin based materials formed as cellular extensions, we have found a nanostructured layer of chitin in the cuticle of the wing of the dog day annual cicada Tibicen tibicens, which may be the scaffold for the nanocone arrays found on the wing. We also use this process to examine the chitin organizations in the fruit fly, Drosophila melanogaster, and the Atlantic brown shrimp, Farfantepenaeus aztecus. Interestingly many of the homologous anatomical structures from diverse arthropods exhibit similar patterns of chitin organization suggesting that a common set of parameters, govern chitin organization.

Ordering of protein and water molecules at their interfaces with chitin nano-crystals

Synchrotron X-ray diffraction was applied to study the structure of biogenic α-chitin crystals composing the tendon of the spider Cupiennius salei. Measurements were carried out on pristine chitin crystals stabilized by proteins and water, as well as after their deproteinization and dehydration. We found substantial shifts (up to Δq/q=9% in the wave vector in q-space) in the (020) diffraction peak position between intact and purified chitin samples. However, chitin lattice parameters extracted from the set of reflections (hkl), which did not contain the (020)-reflection, showed no systematic variation between the pristine and the processed samples. The observed shifts in the (020) peak position are discussed in terms of the ordering-induced modulation of the protein and water electron density near the surface of the ultra-thin chitin fibrils due to strong protein/chitin and water/chitin interactions. The extracted modulation periods can be used as a quantitative parameter characterizing the interaction length.