Distribution of cuticular protein mRNAs in silk moth integument and imaginal discs

Bio-inspired Incrustation Interfacial Polymerization of Dopamine and Cross-linking with Gelatin toward Robust, Biodegradable Three-Dimensional Hydrogels

In nature, laccase enzymatically catalyzes the reaction of phenolic compounds with oxygen to produce hardened surfaces known as cuticles on insects and plants. Inspired by this natural process, the present work investigated a robust, biodegradable hydrogel synthesized from dopamine and gelatin. This gel is obtained by the oxidation of dopamine dissolved in water, after which the resulting quinone compound automatically undergoes self-polymerization. The oxidized dopamine subsequently undergoes Schiff base and Michael addition reactions with gelatin, such that the exposed gelatin surface cross-links to generate a continuous hardened hydrogel film. Because gelatin transitions between sol and gel states with changes in temperature, two- and three-dimensional structures could be obtained from the gel state. This bio-inspired interfacial cross-linking reaction provides a simple means of forming complex morphologies and represents a promising technique for bio-applications.

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.

Genome-wide annotation and comparative analysis of cuticular protein genes in the noctuid pest Spodoptera litura

Insect cuticle is considered an adaptable and versatile building material with roles in the construction and function of exoskeleton. Its physical properties are varied, as the biological requirements differ among diverse structures and change during the life cycle of the insect. Although the bulk of cuticle consists basically of cuticular proteins (CPs) associated with chitin, the degree of cuticular sclerotization is an important factor in determining its physical properties. Spodoptera litura, the tobacco cutworm, is an important agricultural pest in Asia. Compared to the domestic silkworm, Bombyx mori, another lepidopteran whose CP genes have been well annotated, S. litura has a shorter life cycle, hides in soil during daytime beginning in the 5th instar and is exposed to soil in the pupal stage without the protection of a cocoon. In order to understand how the CP genes may have been adapted to support the characteristic life style of S. litura, we searched its genome and found 287 putative cuticular proteins that can be classified into 9 CP families (CPR with three groups (RR-1, RR-2, RR-3), CPAP1, CPAP3, CPF, CPFL, CPT, CPG, CPCFC and CPLCA), and a collection of unclassified CPs named CPH. There were also 112 cuticular proteins enriched in Histidine residues with content varying from 6% to 30%, comprising many more His-rich cuticular proteins than B. mori. A phylogenetic analysis between S. litura, M. sexta and B. mori uncovered large expansions of RR-1 and RR-2 CPs, forming large gene clusters in different regions of S. litura chromosome 9. We used RNA-seq analysis to document the expression profiles of CPs in different developmental stages and tissues of S. litura. The comparative genomic analysis of CPs between S. litura and B. mori integrated with the unique behavior and life cycle of the two species offers new insights into their contrasting ecological adaptations.

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.

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.

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.

Genome-wide identification of cuticular protein genes in the silkworm, Bombyx mori

Many kinds of cuticular proteins are found in a single insect species and their numbers and features are diversified among insects. Because there are so many cuticular proteins and so much sequence variation among them, an overview of cuticular protein gene is needed. Recently, a complete silkworm genome sequence was obtained through the integration of data from two whole genome sequence projects performed independently in 2004. To identify cuticular protein genes in the silkworm Bombyx mori exhaustively, we searched both the Bombyx whole genome sequence as well as various EST libraries, and found 220 putative cuticular protein genes. We also revised the annotation of the gene model, and named each identified cuticular protein based on its motif. The phylogenetic tree of cuticular protein genes among B. mori, Drosophila melanogaster, and Apis mellifera revealed that duplicate cuticular protein clusters have evolved independently among insects. Comparison of EST libraries and northern blot analyses showed that the tissue- and stage-specific expression of each gene was intricately regulated, even between adjacent genes in the same gene cluster. This study reveals many novel cuticular protein genes as well as insights into cuticular protein gene regulation.

Identification of stage-specific larval camouflage associated genes in the swallowtail butterfly, Papilio xuthus

The swallowtail butterfly Papilio xuthus changes its larval body pattern dramatically during the fourth ecdysis. The penultimate (fourth) instar larvae mimic bird droppings that have many tubercle structures on their surface, whereas the final (fifth) instar larvae have a green camouflage color. To identify the genes involved in stage-specific larval mimicry markings, we compared the epidermal messenger ribonucleic acid expression between the third and fourth molts of P. xuthus using a complementary deoxyribonucleic acid subtraction method. After analyzing 2,072 clones from two subtractive libraries, we obtained 31 and 64 candidate genes for final (Fsg) or penultimate instar-specific genes (Psg), respectively. The expression pattern of each gene was examined by reverse transcriptase polymerase chain reaction and in situ hybridization. Among Fsgs, Fsg02 and Fsg20 were expressed in the presumptive green region only during the fourth molt, suggesting that these two genes were correlated with green coloration in the final instar. Among Psgs, 11 cuticular protein genes were expressed specifically in the tubercle structures during the third molt. These genes are likely to be involved in the formation of the unique tubercle structures observed in the juvenile instar. We found that genes with similar expression patterns do not necessarily share the same protein motifs and vice versa. This study provides novel molecular markers and insights into the molecular mechanisms of the larval color pattern and body shape.

Expressed sequence tags from the midgut of Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae)

The midgut is a key tissue in insect science. Physiological roles include digestion and peritrophic membrane function, as well as being an important target for insecticides. We used an expressed sequence tag (EST) approach to identify candidate genes and gene families involved in these processes in the light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae). Two cDNA libraries were constructed from dissected midgut of third to fifth instar larvae. Clustering analysis of 6416 expressed sequence tags produced 1178 tentative unique genes comprising 725 tentative contigs and 453 singletons. The sequences show similar codon usage to sequences from other lepidopterans, a Kozak consensus sequence similar to Drosophila and single nucleotide polymorphisms (SNPs) were detected at a frequency of 1.35/kb. The identity of the most common Interpro families correlates well with major known functions of the midgut. Phylogenetic analysis was conducted on representative sequences from selected multigene families. Gene families include a broad range of digestive proteases, lipases and carbohydrases that appear to have degradative capacity against the major food components found in leaves, the diet of these larvae; and carboxylesterases, glutathione-S-transferases and cytochrome P450 monooxygenases, potentially involved in xenobiotic degradation. Two of the larger multigene families, serine proteases and lipases, expressed a high proportion of genes that are likely to be catalytically inactive.

The morphostatic actions of juvenile hormone

The maintenance of "status quo" in larvae by juvenile hormone (JH) involves both the programming of ecdysteroid-dependent synthesis during the molt and the suppression of morphogenetic growth during the intermolt. The latter morphostatic action does not require ecdysteroids, and has been studied in the formation of imaginal discs in Manduca sexta. Preultimate larval instars have both invaginated discs and imaginal primordia, both of which grow isomorphically with the larva. In the last instar, the young discs/primordia initiate the morphogenesis and patterning that results in a mature disc. JH suppresses both the initiation and progression of the signaling that transforms immature discs or primordia into a fully patterned imaginal disc. This transformation normally occurs in the context of the rapid growth of the last larval stage, and nutrient-dependent factors appear to be able to override the JH suppression. The morphostatic action of JH may have been important for the evolution of the larval stage. Studies on embryos of basal, hemimetabolous insects show that their premature exposure to JH can truncate patterning programs and cause precocious tissue maturation, factors essential for organizing a novel larval form. This suppression of embryonic patterning then results in embryonic fields that remain dormant as long as JH is present. These are the primordia that can transform into imaginal discs once JH disappears in preparation for metamorphosis.

Identification of molting fluid carboxypeptidase A (MF-CPA) in Bombyx mori

Using microarray analyses, we identified carboxypeptidase A (MF-CPA), which was induced during pupal ecdysis in the wing discs of Bombyx mori. Here, we report the functional characterization of MF-CPA. MF-CPA has amino acid sequence similarities with the proteins in the carboxypeptidase A/B subfamily, from human to nematode. The MF-CPA gene is expressed during the molting periods in the epithelial tissues. MF-CPA is detected in the molting fluid, which fills the space between the old and new cuticle during molting. By Western blot analysis, we show that MF-CPA is secreted as a zymogen and processed in the molting fluid. Recombinant MF-CPA expressed in the insect cells has carboxypeptidase A activity. We propose that MF-CPA degrades the proteins from the old cuticle during the molting periods and contributes to recycling of the amino acids.