Structure and expression of a Manduca sexta larval cuticle gene homologous to Drosophila cuticle genes

Expression profile of cuticular genes of silkworm, Bombyx mori

Background

Insect cuticle plays essential roles in many physiological functions. During molting and metamorphosis tremendous changes occur in silkworm cuticle where multiple proteins exist and genes encoding them constitute about 1.5% of all Bombyx mori genes.

Results

In an effort to determine their expression profiles, a microarray-based investigation was carried out using mRNA collected from larvae to pupae. The results showed that a total of 6676 genes involved in various functions and physiological pathways were activated. The vast majority (93%) of cuticular protein genes were expressed in selected stages with varying expression patterns. There was no correlation between expression patterns and the presence of conserved motifs. Twenty-six RR genes distributed in chromosome 22 were co-expressed at the larval and wandering stages. The 2 kb upstream regions of these genes were further analyzed and three putative elements were identified.

Conclusions

Data from the present study provide, for the first time, a comprehensive expression profile of genes in silkworm epidermal tissues and evidence that putative elements exist to allow massive production of mRNAs from specific cuticular protein genes.

Shotgun strategy-based proteome profiling analysis on the head of silkworm Bombyx mori

Insect head is comprised of important sensory systems to communicate with internal and external environment and endocrine organs such as brain and corpus allatum to regulate insect growth and development. To comprehensively understand how all these components act and interact within the head, it is necessary to investigate their molecular basis at protein level. Here, the spectra of peptides digested from silkworm larval heads were obtained from liquid chromatography tandem mass spectrometry (LC-MS/MS) and were analyzed by bioinformatics methods. Totally, 539 proteins with a low false discovery rate (FDR) were identified by searching against an in-house database with SEQUEST and X!Tandem algorithms followed by trans-proteomic pipeline (TPP) validation. Forty-three proteins had the theoretical isoelectric point (pI) greater than 10 which were too difficult to separate by two-dimensional gel electrophoresis (2-DE). Four chemosensory proteins, one odorant-binding protein, two diapause-related proteins, and a lot of cuticle proteins, interestingly including pupal cuticle proteins were identified. The proteins involved in nervous system development, stress response, apoptosis and so forth were related to the physiological status of head. Pathway analysis revealed that many proteins were highly homologous with the human proteins which involved in human neurodegenerative disease pathways, probably implying a symptom of the forthcoming metamorphosis of silkworm. These data and the analysis methods were expected to be of benefit to the proteomics research of silkworm and other insects.

Structural cuticular proteins from arthropods: annotation, nomenclature, and sequence characteristics in the genomics era

The availability of whole genome sequences of several arthropods has provided new insights into structural cuticular proteins (CPs), in particular the distribution of different families, the recognition that these proteins may comprise almost 2% of the protein coding genes of some species, and the identification of features that should aid in the annotation of new genomes and EST libraries as they become available. Twelve CP families are described: CPR (named after the Rebers and Riddiford Consensus); CPF (named because it has a highly conserved region consisting of about forty-four amino acids); CPFL (like the CPFs in a conserved C-terminal region); the TWDL family, named after a picturesque phenotype of one mutant member; four families in addition to TWDL with a preponderance of low complexity sequence that are not member of the families listed above. These were named after particular diagnostic features as CPLCA, CPLCG, CPLCW, CPLCP. There are also CPG, a lepidopteran family with an abundance of glycines, the apidermin family, named after three proteins in Apis mellifera, and CPAP1 and CPAP3, named because they have features analogous to peritrophins, namely one or three chitin-binding domains. Also described are common motifs and features. Four unusual CPs are discussed in detail. Data that facilitated the analysis of sequence variation of single CP genes in natural populations are analyzed.

Cuticular proteins and seasonal photoperiodism in aphids

For poikilotherm animals such as insects, extreme temperatures can be a severe issue in continental regions. Aphids, which reproduce in spring and summer by viviparity, are prone to death in hard winter conditions. These species exhibit reproductive plasticity adapted to winter by producing oviparous females in autumn, which lay overwintering eggs. This switch is driven by photoperiodism, and long nights are sufficient to trigger the change in reproductive mode. Global transcriptomic analyses applied to the pea aphid Acyrthosiphon pisum for which genomic resources are now available have allowed the identification of several genetic programs regulated by photoperiod shortening. Unexpectedly, one of these genetic programs concerns cuticle proteins and cuticle structure. This opens new tracks for investigations and poses new hypotheses on the link between cuticle modification and neuronal signalisation of photoperiod in aphids in response to seasonal photoperiodism. This review focuses on the description of cuticular protein genes in the pea aphid and their regulation during the change of reproductive mode.

Identification of the chitin-binding proteins from the larval proteins of silkworm, Bombyx mori

The silkworm is a model organism for Lepidoptera. Its cuticle is composed mainly of chitin and proteins, which plays essential roles in multiple physiological functions. The binding of proteins to chitin plays an important role for cuticle formation. In this research, a chitin-binding assay followed by a proteomics analysis was carried out using the proteins extracted from the 5th instar larval cuticles. As results, twenty-two proteins were identified including nine cuticular proteins, two lysozyme precursors, two proteins with chitin-binding-type 2 domains, and other proteins. A cuticular protein with the RR-1 consensus, BmorCPR56, and a silkworm Tweedle protein, BmorCPT1, were detected in the chitin-binding fraction for the first time and their chitin-binding activities were further confirmed in vitro. The results of this research increase our understanding of the structure of the silkworm larval cuticle.

Genes encoding proteins with peritrophin A-type chitin-binding domains in Tribolium castaneum are grouped into three distinct families based on phylogeny, expression and function

This study is focused on the characterization and expression of genes in the red flour beetle, Tribolium castaneum, encoding proteins that possess one or more six-cysteine-containing chitin-binding domains related to the peritrophin A domain (ChtBD2). An exhaustive bioinformatics search of the genome of T. castaneum queried with ChtBD2 sequences yielded 13 previously characterized chitin metabolic enzymes and 29 additional proteins with signal peptides as well as one to 14 ChtBD2s. Using phylogenetic analyses, these additional 29 proteins were classified into three large families. The first family includes 11 proteins closely related to the peritrophins, each containing one to 14 ChtBD2s. These are midgut-specific and are expressed only during feeding stages. We propose the name "Peritrophic Matrix Proteins" (PMP) for this family. The second family contains eight proteins encoded by seven genes (one gene codes for 2 splice variants), which are closely related to gasp/obstructor-like proteins that contain 3 ChtBD2s each. The third family has ten proteins that are of diverse sizes and sequences with only one ChtBD2 each. The genes of the second and third families are expressed in non-midgut tissues throughout all stages of development. We propose the names "Cuticular Proteins Analogous to Peritophins 3" (CPAP3) for the second family that has three ChtBD2s and "Cuticular Proteins Analogous to Peritophins 1 (CPAP1) for the third family that has 1 ChtBD2. Even though proteins of both CPAP1 and CPAP3 families have the "peritrophin A" domain, they are expressed only in cuticle-forming tissues. We determined the exon-intron organization of the genes, encoding these 29 proteins as well as the domain organization of the encoded proteins with ChtBD2s. All 29 proteins have predicted cleavable signal peptides and ChtBD2s, suggesting that they interact with chitin in extracellular locations. Comparison of ChtBD2s-containing proteins in different insect species belonging to different orders suggests that ChtBD2s are ancient protein domains whose affinity for chitin in extracellular matrices has been exploited many times for a range of biological functions. The differences in the expression profiles of PMPs and CPAPs indicate that even though they share the peritrophin A motif for chitin binding, these three families of proteins have quite distinct biological functions.

Gene expression associated with changes in cold tolerance levels of the Antarctic springtail, Cryptopygus antarcticus

The ability of the Antarctic microarthropod Cryptopygus antarcticus (Collembola, Isotomidae) to survive low temperatures has been well studied at the physiological level, with recent investigations indicating the importance of the moulting process in conferring this ability. This study investigated gene expression in groups of C. antarcticus that have distinct differences in their ability to survive low temperatures. A microarray containing c. 5400 C. antarcticus expressed sequence tags was used to investigate gene expression differences between groups of animals with different supercooling points (SCP), and to low temperatures close to their SCP. By demonstrating the involvement of moult-related genes in the differential survival of two groups of C. antarcticus with distinct SCP profiles, the results of this investigation add support to the suggestion that moulting plays a role in conferring cold tolerance in C. antarcticus.

Downregulation of a chitin deacetylase-like protein in response to baculovirus infection and its application for improving baculovirus infectivity

Several expressed sequence tags (ESTs) with homology to chitin deacetylase-like protein (CDA) were selected from a group of Helicoverpa armigera genes whose expression changed after infection with H. armigera single nucleopolyhedrovirus (HearNPV). Some of these ESTs coded for a midgut protein containing a chitin deacetylase domain (CDAD). The expressed protein, HaCDA5a, did not show chitin deacetylase activity, but it showed a strong affinity for binding to chitin. Sequence analysis showed the lack of any chitin binding domain, described for all currently known peritrophic membrane (PM) proteins. HaCDA5a has previously been detected in the H. armigera PM. Such localization, together with its downregulation after pathogen infection, led us to hypothesize that this protein might be responsible for the homeostasis of the PM structure and that, by reduction of its expression, the insect may reduce PM permeability, decreasing the entrance of baculovirus. To test this hypothesis, we constructed a recombinant nucleopolyhedrovirus to express HaCDA5a in insect cells and tested its influence on PM permeability as well as the influence of HaCDA5a expression on the performance of the baculovirus. The experiments showed that HaCDA5a increased PM permeability, in a concentration-dependent manner. Bioassays on Spodoptera frugiperda and Spodoptera exigua larvae revealed that NPV expressing HaCDA5a was more infective than its parental virus. However, no difference in virulence was observed when the viruses were injected intrahemocoelically. These findings support the downregulation of a midgut-specific CDA-like protein as a possible mechanism used by H. armigera to reduce susceptibility to baculovirus by decreasing PM permeability.

Molecular evolution of Drosophila cuticular protein genes

Several multigene families have been described that together encode scores of structural cuticular proteins in Drosophila, although the functional significance of this diversity remains to be explored. Here I investigate the evolutionary histories of several multigene families (CPR, Tweedle, CPLCG, and CPF/CPFL) that vary in age, size, and sequence complexity, using sequenced Drosophila genomes and mosquito outgroups. My objective is to describe the rates and mechanisms of ‘cuticle-ome’ divergence, in order to identify conserved and rapidly evolving elements. I also investigate potential examples of interlocus gene conversion and concerted evolution within these families during Drosophila evolution. The absolute rate of change in gene number (per million years) is an order of magnitude lower for cuticular protein families within Drosophila than it is among Drosophila and the two mosquito taxa, implying that major transitions in the cuticle proteome have occurred at higher taxonomic levels. Several hotspots of intergenic conversion and/or gene turnover were identified, e.g. some gene pairs have independently undergone intergenic conversion within different lineages. Some gene conversion hotspots were characterized by conversion tracts initiating near nucleotide repeats within coding regions, and similar repeats were found within concertedly evolving cuticular protein genes in Anopheles gambiae. Rates of amino-acid substitution were generally severalfold higher along the branch connecting the Sophophora and Drosophila species groups, and 13 genes have Ka/Ks significantly greater than one along this branch, indicating adaptive divergence. Insect cuticular proteins appear to be a source of adaptive evolution within genera and, at higher taxonomic levels, subject to periods of gene-family expansion and contraction followed by quiescence. However, this relative stasis is belied by hotspots of molecular evolution, particularly concerted evolution, during the diversification of Drosophila. The prominent association between interlocus gene conversion and repeats within the coding sequence of interacting genes suggests that the latter promote strand exchange.

Annotation and analysis of low-complexity protein families of Anopheles gambiae that are associated with cuticle

We have characterized four new families of homologous genes of the mosquito, Anopheles gambiae, all of which include members shown by previous work to be cuticular in nature. The CPLCG, CPLCW, CPLCP, and CPLCA families (where CPLC is 'cuticular protein of low complexity') encode proteins with a high proportion of low-complexity sequence. We have also annotated the An. gambiae Tweedle genes, a family of cuticular protein genes first described in Drosophila, and additional ungrouped An. gambiae cuticular proteins identified by proteomics. Our annotations reveal multiple gene-family expansions that are specific to Diptera or Culicidae. The CPLCG and CPLCW families occur within a large and dynamic tandem array on chromosome 3R that includes sets of concertedly evolving genes. Most gene families exhibit two or more different expression profiles during development.

Elucidation of the regulation of an adult cuticle gene Acp65A by the transcription factor Broad

Broad (BR), an ecdysone-inducible transcription factor, is a major determinant of the pupal stage. The misexpression of BR-Z1 isoform (BR-Z1) during adult development of Drosophila melanogaster prevents the expression of the adult cuticle protein 65A gene (Acp65A). We found that the proximal 237 bp of the 5' flanking region of Acp65A were sufficient to mediate this suppression. A targeted point mutation of a putative BR-Z1 response element (BRE) within this region showed that it was not involved. Drosophila hormone receptor-like 38 (DHR38) is required for Acp65A expression. We found that BR-Z1 repressed DHR38 expression and that BR's inhibition of Acp65A expression was rescued by exogenous expression of DHR38. Thus, BR-Z1 suppresses Acp65A expression by preventing the normal up-regulation of DHR38 at the time of adult cuticle formation.

Molecular cloning and characterization of a cDNA encoding a novel cuticle protein from the Chinese oak Silkmoth,Antheraea pernyi

In our research to identify gene involved in the cuticle protein, we cloned a novel cuticle protein gene, ApCP13, from the Chinese oak silkmoth, Antheraea pernyi, larvae cDNA library. The ApCP13 gene encodes a 120 amino acid polypeptide with a predicted molecular mass of 13 kDa and a pI of 4.01, and is intron-less gene. The ApCP13 contained a type-specific consensus sequence identifiable in other insect cuticle proteins and the deduced amino acid sequence of the ApCP13 cDNA is most homologous to another wild silkmoth, A. yamamai CP12 (86% protein sequence identity), followed by Bombyx mori LCP18 (35% protein sequence identity). Northern blot analysis revealed that the ApCP13 showed the epidermis-specific expression. This is the first report of cuticle protein gene in the wild silkmoth, A. pernyi.

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.

A chitin deacetylase and putative insect intestinal lipases are components of the Mamestra configurata (Lepidoptera: Noctuidae) peritrophic matrix

One- and two-dimensional gel electrophoresis coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to identify cDNA encoding a chitin deacetylase (McCDA1) and three insect intestinal lipases (McIIL1, McIIL2 and McIIL3) associated with the Mamestra configurata (bertha armyworm) peritrophic matrix. Recombinant McCDA1 was active and chitin deacetylase activities were detected in the midgut. McCDA1 and the McIIL genes were expressed exclusively in the midgut; however, McCDA1 and McIIL2 were expressed in all larval stages, whereas McIIL1 was expressed mainly in feeding larvae and McIIL3 primarily during the moult.

Catalogue of epidermal genes: genes expressed in the epidermis during larval molt of the silkworm Bombyx mori

BACKGROUND

The insect cuticle is composed of various proteins and formed during the molt under hormonal regulation, although its precise composition and formation mechanism are largely unknown. The exhaustive catalogue of genes expressed in epidermis at the molt constitutes a massive amount of information from which to draw a complete picture of the molt and cuticle formation in insects. Therefore, we have catalogued a library of full-length cDNAs (designated epM) from epidermal cells during the last larval molt of Bombyx mori.

RESULTS

Of the 10,368 sequences in the library, we isolated 6,653 usable expressed sequence tags (ESTs), which were categorized into 1,451 nonredundant gene clusters. Seventy-one clusters were considered to be isoforms or premature forms of other clusters. Therefore, we have identified 1,380 putative genes. Of the 6,653 expressed sequences, 48% were derived from 92 cuticular protein genes (RR-1, 24; RR-2, 17; glycine-rich, 29; other classes, 22). A comparison of epM with another epidermal EST data set, epV3 (feeding stage: fifth instar, day 3), showed marked differences in cuticular protein gene. Various types of cuticular proteins are expressed in epM but virtually only RR-1 proteins were expressed in epV3. Cuticular protein genes expressed specifically in epidermis, with several types of expression patterns during the molt, suggest different types of responses to the ecdysteroid pulse. Compared with other Bombyx EST libraries, 13 genes were preferentially included in epM data set. We isolated 290 genes for proteins other than cuticular proteins, whose amino acid sequences retain putative signal peptides, suggesting that they play some role in cuticle formation or in other molting events. Several gene groups were also included in this data set: hormone metabolism, P450, modifier of cuticular protein structure, small-ligand-binding protein, transcription factor, and pigmentation genes.

CONCLUSION

We have identified 1,380 genes in epM data set and 13 preferentially expressed genes in epidermis at the molt. The comparison of the epM and other EST libraries clarified the totally different gene expression patterns in epidermis between the molting and feeding stages and many novel tissue- and stage-specifically expressed epidermal genes. These data should further our understanding of cuticle formation and the insect molt.

Extensive gene amplification and concerted evolution within the CPR family of cuticular proteins in mosquitoes

Annotation of the Anopheles gambiae genome has revealed a large increase in the number of genes encoding cuticular proteins with the Rebers and Riddiford Consensus (the CPR gene family) relative to Drosophila melanogaster. This increase reflects an expansion of the RR-2 group of CPR genes, particularly the amplification of sets of highly similar paralogs. Patterns of nucleotide variation indicate that extensive concerted evolution is occurring within these clusters. The pattern of concerted evolution is complex, however, as sequence similarity within clusters is uncorrelated with gene order and orientation, and no comparable clusters occur within similarly compact arrays of the RR-1 group in mosquitoes or in either group in D. melanogaster. The dearth of pseudogenes suggests that sequence clusters are maintained by selection for high gene-copy number, perhaps due to selection for high expression rates. This hypothesis is consistent with the apparently parallel evolution of compact gene architectures within sequence clusters relative to single-copy genes. We show that RR-2 proteins from sequence-cluster genes have complex repeats and extreme amino-acid compositions relative to single-copy CPR proteins in An. gambiae, and that the amino-acid composition of the N-terminal and C-terminal sequence flanking the chitin-binding consensus region evolves in a correlated fashion.

Environmental stresses induce the expression of putative glycine-rich insect cuticular protein genes in adult Leptinotarsa decemlineata (Say)

The deposition of cuticular proteins in insects usually occurs during the moulting process. Three putative glycine-rich insect cuticular proteins, Ld-GRP1 to 3, were identified and characterized from the Colorado potato beetle, Leptinotarsa decemlineata. The Ld-GRPs contained conserved GXGX and/or GGXG sequence repeats. Ld-GRP1 also contained a conserved AAPA/V motif commonly found in cuticular proteins. The transcripts of Ld-GRP1 and Ld-GRP2 were detected in the epidermal cell layer by in situ hybridization, making them putative insect cuticular proteins. The putative cuticular protein genes were highly induced by the insecticide azinphosmethyl (organophosphorous) 2-3 weeks after adult moulting. Putative cuticular protein gene expression level was higher in azinphosmethyl-resistant beetles than in susceptible beetles. Furthermore, two of the putative cuticular protein genes were highly induced by dry environmental conditions. These results suggest that the insect might increase cuticular component deposition in the adult stage in response to environmental stresses. This ability may allow the insect to adapt to new or changing environments.

Proteomic analysis of the honey bee worker venom gland focusing on the mechanisms of protection against tissue damage

Honey bee workers use venom for the defence of the colony and themselves when they are exposed to dangers and predators. It is produced by a long thin, convoluted, and bifurcated gland, and consists of several toxic proteins and peptides. The present study was undertaken in order to identify the mechanisms that protect the venom gland secretory cells against these harmful components. Samples of whole venom glands, including the interconnected reservoirs, were separated by two-dimensional gel electrophoresis and the most abundant protein spots were subjected to mass spectrometric identification using MALDI TOF/TOF-MS and LC MS/MS. This proteomic study revealed four antioxidant enzymes: CuZn superoxide dismutase (SOD1), glutathione-S-transferase sigma 1 isoform A (GSTS1), peroxiredoxin 2540 (PXR2540) and thioredoxin peroxidase 1 isoform A (TPX1). Although glutathione-S-transferase (GST) has also been associated with xenobiotic detoxification, the protein we found belongs to the GST Sigma class which is known to protect against oxidative stress only. Moreover, we could demonstrate that the GST and SOD activity of the venom gland was low and moderate, respectively, when compared to other tissues from the adult honey bee. Several proteins involved in other forms of stress were likewise found but it remains uncertain what their function is in the venom gland. In addition to major royal jelly protein 9 (MRJP9), already found in a previous proteomic study, we identified MRJP8 as second member of the MRJP protein family to be associated with the venom gland. Transcripts of both MRJPs were amplified and sequenced. Two endocuticular structural proteins were abundantly present in the 2D-gel and most probably represent a structural component of the epicuticular lining that protects the secretory cells from the toxins they produce.

Developmental expression patterns of cuticular protein genes with the R&R Consensus from Anopheles gambiae

CPR proteins are the largest cuticular protein family in arthropods. The whole genome sequence of Anopheles gambiae revealed 156 genes that code for proteins with the R&R Consensus and named CPRs. This protein family can be divided into RR-1 and RR-2 subgroups, postulated to contribute to different regions of the cuticle. We determined the temporal expression patterns of these genes throughout post-embryonic development by means of real-time qRT-PCR. Based on expression profiles, these genes were grouped into 21 clusters. Most of the genes were expressed with sharp peaks at single or multiple periods associated with molting. Genes coding for RR-1 and RR-2 proteins were found together in several co-expression clusters. Twenty-five genes were expressed exclusively at one metamorphic stage. Five out of six X-linked genes showed equal expression in males and females, supporting the presence of a gene dosage compensation system in A. gambiae. Many RR-2 genes are organized into sequence clusters whose members are extremely similar to each other and generally closely associated on a chromosome. Most genes in each sequence cluster are expressed with the same temporal expression pattern and at the same level, suggesting a shared mechanism to regulate their expression.

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

BACKGROUND

The most abundant family of insect cuticular proteins, the CPR family, is recognized by the R&R Consensus, a domain of about 64 amino acids that binds to chitin and is present throughout arthropods. Several species have now been shown to have more than 100 CPR genes, inviting speculation as to the functional importance of this large number and diversity.

RESULTS

We have identified 156 genes in Anopheles gambiae that code for putative cuticular proteins in this CPR family, over 1% of the total number of predicted genes in this species. Annotation was verified using several criteria including identification of TATA boxes, INRs, and DPEs plus support from proteomic and gene expression analyses. Two previously recognized CPR classes, RR-1 and RR-2, form separate, well-supported clades with the exception of a small set of genes with long branches whose relationships are poorly resolved. Several of these outliers have clear orthologs in other species. Although both clades are under purifying selection, the RR-1 variant of the R&R Consensus is evolving at twice the rate of the RR-2 variant and is structurally more labile. In contrast, the regions flanking the R&R Consensus have diversified in amino-acid composition to a much greater extent in RR-2 genes compared with RR-1 genes. Many genes are found in compact tandem arrays that may include similar or dissimilar genes but always include just one of the two classes. Tandem arrays of RR-2 genes frequently contain subsets of genes coding for highly similar proteins (sequence clusters). Properties of the proteins indicated that each cluster may serve a distinct function in the cuticle.

CONCLUSION

The complete annotation of this large gene family provides insight on the mechanisms of gene family evolution and clues about the need for so many CPR genes. These data also should assist annotation of other Anopheles genes.

Biochemical properties of the major proteins from Rhodnius prolixus eggshell

Two proteins from the eggshell of Rhodnius prolixus were isolated, characterized and named Rp30 and Rp45 according to their molecular masses. Purified proteins were used to obtain specific antiserum which was later used for immunolocalization. The antiserum against Rp30 and Rp45 detected their presence inside the follicle cells, their secretion and their association with oocyte microvilli. Both proteins are expressed during the final stage of vitellogenesis, preserved during embryogenesis and discarded together with the eggshell. The amino terminals were sequenced and both proteins were further cloned using degenerated primers. The amino acid sequences appear to have a tripartite arrangement with a highly conserved central domain which presents a repetitive motif of valine-proline-valine (VPV) at intervals of 15 amino acid residues. Their amino acid sequence showed no similarity to any known eggshell protein. The expression of these proteins was also investigated; the results demonstrated that this occurred strictly in choriogenic follicles. Antifungal activity against Aspergillus niger was found to be associated with Rp45 but not with Rp30. A. niger exposed to Rp45 protein induced growth inhibition and several morphological changes such as large vacuoles, swollen mitochondria, multi-lamellar structures and a disorganized cell wall as demonstrated by electron microscopy analysis.

Gene expression profiling of cuticular proteins across the moult cycle of the crab Portunus pelagicus

Background

Crustaceans represent an attractive model to study biomineralization and cuticle matrix formation, as these events are precisely timed to occur at certain stages of the moult cycle. Moulting, the process by which crustaceans shed their exoskeleton, involves the partial breakdown of the old exoskeleton and the synthesis of a new cuticle. This cuticle is subdivided into layers, some of which become calcified while others remain uncalcified. The cuticle matrix consists of many different proteins that confer the physical properties, such as pliability, of the exoskeleton.

Results

We have used a custom cDNA microarray chip, developed for the blue swimmer crab Portunus pelagicus, to generate expression profiles of genes involved in exoskeletal formation across the moult cycle. A total of 21 distinct moult-cycle related differentially expressed transcripts representing crustacean cuticular proteins were isolated. Of these, 13 contained copies of the cuticle_1 domain previously isolated from calcified regions of the crustacean exoskeleton, four transcripts contained a chitin_bind_4 domain (RR consensus sequence) associated with both the calcified and un-calcified cuticle of crustaceans, and four transcripts contained an unannotated domain (PfamB_109992) previously isolated from C. pagurus. Additionally, cryptocyanin, a hemolymph protein involved in cuticle synthesis and structural integrity, also displays differential expression related to the moult cycle. Moult stage-specific expression analysis of these transcripts revealed that differential gene expression occurs both among transcripts containing the same domain and among transcripts containing different domains.

Conclusion

The large variety of genes associated with cuticle formation, and their differential expression across the crustacean moult cycle, point to the complexity of the processes associated with cuticle formation and hardening. This study provides a molecular entry path into the investigation of the gene networks associated with cuticle formation.

Drosophila cuticular proteins with the R&R Consensus: annotation and classification with a new tool for discriminating RR-1 and RR-2 sequences

The majority of cuticular protein sequences identified to date from a diversity of arthropods have a conserved region known as the Rebers and Riddiford Consensus (R&R Consensus). This consensus region has been used to query the whole genome sequence of Drosophila melanogaster. One hundred one putative cuticular proteins have been annotated. Of these, 29 had been annotated previously, and for several their authenticity as cuticular proteins had been verified by protein sequence data from isolated cuticles or by localization of their transcripts in epidermis when cuticle synthesis was occurring. The original names have been retained, and the 72 newly annotated proteins have been given names beginning with Cpr followed by the chromosomal band in which the gene is located. Proteins with the R&R Consensus can be split into three groups RR-1, RR-2 and RR-3, with some correlation to the type or region of the cuticle in which they occur. Previous classification was manual and subjective. We now have developed a tool using profile hidden Markov models that allows more objective classification. We describe the development and verification of the validity of this tool that is available at the cuticleDB website http://bioinformatics2.biol.uoa.gr/cuticleDB/index.jsp.

CPF and CPFL, two related gene families encoding cuticular proteins of Anopheles gambiae and other insects

Cuticular proteins (CPs) are structural proteins of insects as well as other arthropods. Several CP families have been described, among them a small family defined by a 51 amino acid motif [Andersen, S.O., Rafn, K., Roepstorff, P., 1997. Sequence studies of proteins from larval and pupal cuticle of the yellow meal worm, Tenebrio molitor. Insect Biochem. Mol. Biol. 27, 121-131]. We identified four proteins of this family in Anopheles gambiae that we have named CPF. We have also identified CPFs from other insects by searching databases. Alignment of these CPF proteins showed that the conserved region is only 44 aa long and revealed another conserved motif at the C-terminus. A dendrogram divided the CPF proteins into four groups, one basal and three specialized. We also identified several proteins of another CP family, CPFL, which has similarities to CPFs. CPFs and CPFLs share some protein motifs. Expression studies with real-time qRT-PCR of the A. gambiae CPFs and CPFLs showed that the four CPFs and one CPFL gene are expressed just before pupal or adult ecdysis, suggesting that they are components of the outer layer of pupal and adult cuticles. The other CPFLs appear to contribute to larval cuticle. Recombinant CPF proteins did not bind to chitin in the assay we used.

In vitro association between the helper component–proteinase of zucchini yellow mosaic virus and cuticle proteins of Myzus persicae

Potyviruses, as typical non-persistently transmitted viruses, are carried within the stylets of aphids. Cuticle proteins (CuPs), which are a major component of the insect cuticle, were examined forin vitrobinding to the potyviral helper component–proteinase (HC–Pro). Proteins in 8 M urea extracts fromMyzus persicaewere separated by SDS-PAGE, electroblotted onto membranes and identified as CuPs by using specific antibodies toM. persicaeCuP. BlottedM. persicaeprotein extracts were overlaid with two HC–Pros, differing by the presence of K or E in the KLSC domain. The HC–Pro with KLSC, known to assist transmission, was found to bindM. persicaeproteins, whereas the HC–Pro with ELSC, being deficient in assisting transmission, did not. To identify CuPs that react with HC–Pro, protein extracts were separated by two-dimensional gel electrophoresis. Nine proteins reacting with HC–Pro were sequenced by mass spectrometry. Sequences of peptides in four proteins, of molecular masses between 22 and 31 kDa, were identified as CuPs according to comparison with sequences in GenBank. The putative CuPs fromM. persicaethat bind HC–Pro are potentially of interest in locating receptors for virions bound to HC–Pro in aphids’ stylets.

Significance of the N- and C-terminal regions of CAP-1, a cuticle calcification-associated peptide from the exoskeleton of the crayfish, for calcification

Calcification-associated peptide (CAP)-1 is considered to play an important role in calcification of the exoskeleton of the crayfish, Procambarus clarkii. In this study, in order to clarify the molecular mechanism of calcification, we constructed expression systems of recombinant molecules of CAP-1 and its related peptides in Escherichia coli, and verified the structure-activity relationship of these peptides. The inhibitory assay on calcium carbonate precipitation and the calcium-binding assay showed that the C-terminal acidic region was most important for both activities. The CD spectra of these peptides varied depending on calcium concentration and showed that the N-terminal region is associated with the peptide conformation. These results indicate that the C-terminal part of CAP-1 may concentrate calcium ions for nucleation and/or interact with calcium carbonate precipitate to control the growth and that the N-terminal part contribute to maintaining the peptide conformation.

Differential expression of eight transcripts and their roles in the cuticle of the blue crab, Callinectes sapidus

Eight cuticle protein transcripts from Callinectes sapidus were sequenced and their expression determined across the molt cycle in both calcifying and arthrodial cuticle hypodermis using quantitative PCR, Northern blots, and in situ hybridization. Four transcripts, designated CsAMP, are found only in non-calcifying arthrodial membrane hypodermis. They all code for a Rebers-Riddiford-1 motif, known to bind chitin. CsAMP9.3 is most likely an exocuticle constituent since it is expressed only during pre-molt. The other three arthrodial transcripts are present both before and after ecdysis. One of these, CsAMP16.3, codes for a RGD cell-attachment motif that could be involved in anchoring chitin-protein fibers to pore canals, cellular extensions of the hypodermis in the cuticle. The other four transcripts, designated CsCP, were found only in calcifying hypodermis. CsCP14.1 contains an RR-1 motif, which is more commonly found in non-calcifying cuticle proteins. CsCP6.1 is expressed post-molt and contains a partial RR motif, suggesting that it could bind to chitin in the endocuticle. The other two transcripts from calcifying hypodermis do not code for RR proteins, but both contain three copies of a different insect cuticle motif. One of these, CsCP19.0, is expressed only post-molt while the other, CsCP15.0, is present both before and after ecdysis.

Characterization of RR-1 and RR-2 cuticular proteins from Myzus persicae

A cDNA library for Myzus persicae has served to identify sequences coding for cuticular proteins (CPs) with RR-1 and RR-2 consensus. Two putative CPs showed a common RR-2 chitin binding domain (CBD) but differed in their C and N terminals. Two other predicted CPs showed a typical RR-1 CBD but differed in size and sequence of the C and N terminals. An additional sequence encoding for a protein that showed terminal amino acid repeats similar to those of putative CPs from M. persicae, but lacked the R & R consensus, was also described. A comparison of the sequences obtained from the cDNA library with those attained from the genomic DNA, confirmed their identity as cuticular proteins genes. Presence of introns was revealed in the Mpcp4 and Mpcp5 genes coding for CPs with an RR-1 consensus. The Mpcp4 has a single large intron, while the Mpcp5 has two shorter ones. Introns were not found in the Mpcp2 and Mpcp3 genes encoding for CPs with RR-2 consensus. Differences were also noticed for 3' UTR and 5' UTR of both the RR-1 and RR-2 CPs. CPs genes were expressed in bacteria, and the resulting protein was identified as a CP by amino acid sequencing.

Locating the barnacle settlement pheromone: spatial and ontogenetic expression of the settlement-inducing protein complex of Balanus amphitrite

Barnacles are prominent members of hard substratum benthic communities and their study has been important to advances in experimental ecology and contemporary ecological theory. Having recently characterized the cue to gregarious settlement of Balanus amphitrite, the settlement-inducing protein complex (SIPC), we use two polyclonal antibodies to examine the tissue distribution and ontogenetic expression of this glycoprotein. These antibodies were raised against two separate peptides located near the N- and C-termini of the SIPC and were used to detect the glycoprotein by western blotting and immunohistochemistry. By in situ hybridization we also show that the SIPC mRNA co-occurs with the expressed glycoprotein in the cuticles of both nauplius and cypris larval stages and the adult. In the larvae, the SIPC is expressed most strongly in the mouthparts and the hindgut of the stage 2 nauplius and in the thoracopods, antennules and bivalved carapace of the cyprid. In adult B. amphitrite, the expressed SIPC is present in protein extracts of the shell and in all organs that are lined by cuticular tissues. We suggest that the SIPC is produced by the epidermal cells that secrete the cuticle and discuss these observations with regard to earlier studies and the role of the SIPC as a contact pheromone.

Fast sequence evolution of Hox and Hox-derived genes in the genus Drosophila

Background

It is expected that genes that are expressed early in development and have a complex expression pattern are under strong purifying selection and thus evolve slowly. Hox genes fulfill these criteria and thus, should have a low evolutionary rate. However, some observations point to a completely different scenario. Hox genes are usually highly conserved inside the homeobox, but very variable outside it.

Results

We have measured the rates of nucleotide divergence and indel fixation of three Hox genes, labial (lab), proboscipedia (pb) and abdominal-A (abd-A), and compared them with those of three genes derived by duplication from Hox3, bicoid (bcd), zerknüllt (zen) and zerknüllt-related (zen2), and 15 non-Hox genes in sets of orthologous sequences of three species of the genus Drosophila. These rates were compared to test the hypothesis that Hox genes evolve slowly. Our results show that the evolutionary rate of Hox genes is higher than that of non-Hox genes when both amino acid differences and indels are taken into account: 43.39% of the amino acid sequence is altered in Hox genes, versus 30.97% in non-Hox genes and 64.73% in Hox-derived genes. Microsatellites scattered along the coding sequence of Hox genes explain partially, but not fully, their fast sequence evolution.

Conclusion

These results show that Hox genes have a higher evolutionary dynamics than other developmental genes, and emphasize the need to take into account indels in addition to nucleotide substitutions in order to accurately estimate evolutionary rates.

Glycine-rich protein genes, which encode a major component of the cuticle, have different developmental profiles from other cuticle protein genes in Bombyx mori

Three types of GRP (glycine-rich proteins) cDNAs were identified in the EST database of Bombyx mori. These came from 21 ESTs in the W3-stage wing disc EST library. We named them BmGRP1, BmGRP2 and BmGRP3. BmGRP1 and BmGRP2 had 57% identity in deduced amino acid sequences. Expression of all BmGRPs was observed in the epidermis at the fourth molting stage, and in the wing at pupation and mid-pupal stage. It is suggested that BmGRPs contribute to larval, pupal and adult cuticles together with other cuticle proteins. Transcripts of BmGRP2 increased after 7 days of pupal stage. BmGRP2 is suggested to construct adult trachea in the wing. Hormonal response of BmGRPs was compared with that of another group of cuticular protein genes, BMWCPs. BmGRPs were induced by a pulse of 20E. Induction of BmGRP3 was observed in W1 wing discs in the presence of JHA which was added with 20E, whereas that of BMWCP2 was inhibited in the presence of JHA. Induction of BmGRPs was observed in the wing discs of V3 and W1 stages, while that of BMWCP2 was not observed in the V3 wing discs. These differences between BMWCPs and BmGRPs in response to hormones at different developmental stages are discussed.

Caste-based differences in gene expression in the polyembryonic wasp Copidosoma floridanum

The polyembryonic parasitoid Copidosoma floridanum produces two larval castes, soldiers and reproductives, during development within its host. Soldier larvae defend the brood against competitors while reproductive larvae develop into adult wasps. As with other caste-forming insects, the distinct morphological and behavioral features of soldier and reproductive larvae likely involve differential gene expression. In this study we used a bi-directional suppression subtractive hybridization (SSH) approach to isolate differentially expressed genes from C. floridanum soldier and reproductive larvae. We isolated 230 novel expressed sequence tags (ESTs) from the two subtractions (114 soldier/116 reproductive ESTs). Among these ESTs were sequences with significant similarity to genes coding for serine proteinases, proteinase inhibitors, odorant-binding and chemosensory proteins, and cuticular proteins. Also, three novel genes were isolated that resemble one another in conceptual translation and share the cysteine spacing pattern of short scorpion toxins and insect defensins. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of 20 ESTs from the two libraries indicated that 85% were differentially expressed in one caste or the other. We conclude that our SSH strategy was effective in identifying a number of genes differentially expressed in soldier and reproductive larvae and that several of these genes will be useful in characterizing caste-specific gene networks in C. floridanum.

The extensible alloscutal cuticle of the tick, Ixodes ricinus

The proteins in the distensible alloscutal cuticle of the blood-feeding tick, Ixodes ricinus, have been characterized by electrophoresis and chromatography, two of the proteins were purified and their total amino acid sequence determined. They show sequence similarity to cuticular proteins from the spider, Araneus diadematus, and the horseshoe crab, Limulus polyphemus, and to a lesser extent to insect cuticular proteins. They contain a conserved sequence region, which is closely related to the chitin-binding Rebers-Riddiford consensus sequence present in many insect cuticular proteins. Only a fraction of the alloscutal proteins can be readily dissolved, and the dissolved proteins are difficult to separate by electrophoresis and column chromatography. The insoluble fraction can only be dissolved after degradation to smaller peptides. The mixture of extractable proteins as well as hydrolysates of the insoluble fraction are fluorescent when exposed to ultraviolet light, and the fluorescence corresponds in excitation and emission maxima to the fluorescence of the rubber-like arthropodan protein, resilin, and to the amino acid dityrosine. Small amounts of dityrosine were obtained from ticks in the early phase of a blood meal when the cuticle weighs less than 4 mg; increasing amounts were obtained from animals in the initial period of feeding, during which the cuticular weight increases from 4 to 11 mg, whereas little increase in dityrosine content was observed during the final period of engorgement. Cuticle from fully distended ticks contains about 60-80 nmole dityrosine per tick, corresponding to 2-3 microg/mg cuticle. It is suggested that the major part of the cuticular proteins is made inextractable by cross-linking by dityrosine residues, and that dityrosine plays a role in stabilizing the cuticular structure during the extensive distension occurring during a blood meal. Small amounts of 3-monochlorotyrosine and 3,5-dichlorotyrosine were obtained from the distended tick cuticle, corresponding to chlorination of between 0.5% and 1.5% of the tyrosine residues. It is suggested that the chlorotyrosines are a side-product of oxidative processes in the cuticle.

Comprehensive sequence analysis of horseshoe crab cuticular proteins and their involvement in transglutaminase-dependent cross-linking

Arthropod cuticles play an important role as the first barrier against invading pathogens. We extensively determined the sequences of horseshoe crab cuticular proteins. Proteins extracted from a part of the ventral side of the cuticle were purified by chitin-affinity chromatography, and separated by two-dimensional SDS/PAGE. Proteins appearing on the gel were designated high molecular mass chitin-binding proteins, and these proteins were then grouped into classes based on their approximate isoelectric points and predominant amino acid compositions. Members of groups designated basic G, basic Y, and acidic S groups contained a so-called Rebers and Riddiford consensus found in arthropod cuticular proteins. Proteins designated acidic DE25 and DE29 each contained a Cys-rich domain with sequences similar to those of insect peritrophic matrix proteins and chitinases. In contrast, basic QH4 and QH10 contained no consensus sequences found in known chitin-binding proteins. Alternatively, a low molecular mass chitin-binding fraction was prepared by size exclusion chromatography, and 15 low molecular mass chitin-binding proteins, named P1 through P15, were isolated. With the exception of P9 and P15, all were found to be identical to known antimicrobial peptides. P9 consisted of a Kunitz-type chymotrypsin inhibitor sequence, and P15 contained a Cys-rich motif found in insulin-like growth factor-binding proteins. Interestingly, we observed transglutaminase-dependent polymerization of nearly all high molecular mass chitin-binding proteins, a finding suggests that transglutaminase-dependent cross-linking plays an important role in host defense in the arthropod cuticle, analogous to that observed in the epidermal cornified cell envelope in mammals.

Four differentially expressed cDNAs in Callinectes sapidus containing the Rebers–Riddiford consensus sequence

Decapod crustaceans such as Callinectes sapidus, the blue crab, provide unique opportunities to study proteins involved in biomineralization. Subsequent to each molt, the previously deposited soft cuticle is calcified while the postecdysial layers are simultaneously deposited and mineralized. Though the majority of the exoskeleton hardens, morphologically similar cuticle at the joints, called arthrodial membrane, remains flexible. It seems reasonable that hypodermal cells producing these cuticle types should be synthesizing proteins that regulate mineralization. Data presented here are consistent with this hypothesis, showing that transcripts coding for proteins containing the chitin-binding Rebers-Riddiford (RR) consensus sequence (Gx(8)Gx(7)YxAxExGYx(7)Px(2)P) are differentially expressed. Two RR-containing transcripts, CsAMP8.1 and CsAMP6.0, are found only in arthrodial membrane and are expressed uniformly both before and after ecdysis. They have high sequence homology with RR-containing proteins from uncalcified portions of the cuticle of Cancer pagurus, Penaeus japonicus, and Homarus americanus. The other two transcripts, CsCP8.5 and CsCP8.2, are expressed solely in premolt and in hypodermis depositing calcifying cuticle rather than arthrodial membrane. They have high sequence homology with calcification-associated peptides containing the RR sequence obtained from the calcified cuticle of Procambarus clarkii. This suggests possible involvement in the postmolt mineralization of the pre-ecdysial cuticle.

Unique features of the structural model of 'hard' cuticle proteins: implications for chitin-protein interactions and cross-linking in cuticle

Cuticular proteins are one of the determinants of the physical properties of cuticle. A common consensus region (extended R&R Consensus) in these proteins binds to chitin, the other major component of cuticle. We previously predicted the preponderance of beta-pleated sheet in the consensus region and proposed its responsibility for the formation of helicoidal cuticle (Iconomidou et al., Insect Biochem. Mol. Biol. 29 (1999) 285). Subsequently, we verified experimentally the abundance of antiparallel beta-pleated sheet in the structure of cuticle proteins (Iconomidou et al., Insect Biochem. Mol. Biol. 31 (2001) 877). Homology modelling of soft (RR-1) cuticular proteins using bovine plasma retinol binding protein (RBP) as a template revealed an antiparallel beta-sheet half-barrel structure as the basic folding motif (Hamodrakas et al., Insect Biochem. Molec. Biol. 32 (2002) 1577). The RR-2 proteins characteristic of hard cuticle, have a far more conserved consensus and frequently more histidine residues. Extension of modelling to this class of consensus, in this work, reveals in detail several unique features of the proposed structural model to serve as a chitin binding structural motif, thus providing the basis for elucidating cuticle's overall architecture and chitin-protein interactions in cuticle.

A crustacean Ca2+-binding protein with a glutamate-rich sequence promotes CaCO3 crystallization

The DD4 mRNA of the penaeid prawn Penaeus japonicus was shown previously to be expressed in the epidermis adjacent to the exoskeleton specifically during the post-moult period, when calcification of the exoskeleton took place. The encoded protein possessed a Ca2+-binding site, suggesting its involvement in the calcification of the exoskeleton. In the present study, an additional ORF (open reading frame) of 289 amino acids was identified at the 5' end of the previous ORF. The newly identified part of the encoded protein included a region of approx. 120 amino acids that was highly rich in glutamate residues, and contained one or more Ca2+-binding sites. In an immunohistochemical study, signals were detected within calcified regions in the endocuticular layer of the exoskeleton. Bacterially expressed partial segments of the protein induced CaCO3 crystallization in vitro. Finally, a reverse transcription-PCR study showed that the expression was limited to an early part of the post-moult period, preceding significant calcification of the exoskeleton. These observations argue for the possibility that the encoded protein, renamed crustocalcin (CCN), promotes formation of CaCO3 crystals in the exoskeleton by inducing nucleation.

Screening of genes expressed in developing mandibles during soldier differentiation in the termite Hodotermopsis sjostedti

We investigated the morphological changes accompanying soldier differentiation in the damp-wood termite Hodotermopsis sjostedti. Genes expressed in the developing mandibles, which undergo the most remarkable morphological changes during soldier differentiation, were screened using fluorescent differential display. Database searches for sequence similarities were conducted and the relative expression levels were then quantified by real-time polymerase chain reaction. Among the identified candidate genes, 12 genes were upregulated during soldier differentiation. These included genes for cuticle proteins, nucleic acid binding proteins, ribosomal proteins and actin-binding protein, which were inferred to be involved in caste-specific morphogenesis in termites.

A functional analysis of ACP-20, an adult-specific cuticular protein gene from the beetle Tenebrio: role of an intronic sequence in transcriptional activation during the late metamorphic period

A gene encoding the adult cuticular protein ACP-20 was isolated in Tenebrio. It consists of three exons interspersed by two introns, intron 1 interrupting the signal peptide. To understand the regulatory mechanisms of ACP-20 expression, ACP-20 promoter-luciferase reporter gene constructs were transfected into cultured pharate adult wing epidermis. Transfection assays needed the presence of 20-hydroxyecdysone, confirming that ACP-20 is up-regulated by ecdysteroids. Analysis of 5' deletion constructs revealed that three regions are necessary for high levels of transcription. Interaction experiments between intronic fragments and epidermal nuclear proteins confirmed the importance of intron 1 in ACP-20 transcriptional control, which results from the combined activity of regulatory cis-acting elements of the promoter and those of intron 1.

Analysis of the chitin recognition mechanism of cuticle proteins from the soft cuticle of the silkworm, Bombyx mori

Insect cuticle is composed mainly of chitin, a polymer of N-acetylglucosamine, and chitin-binding cuticle proteins. Four major cuticle proteins, BMCP30, 22, 18, and 17, have been previously identified and purified from the larval cuticle of silkworm, B. mori. We analyzed the chitin-binding activity of BMCP30 by use of chitin-affinity chromatography. The pH optimum for the binding of BMCP30 to chitin is 6.4, which corresponds to hemolymph pH. Competition experiments using chitooligosaccharides suggested that BMCP30 recognizes 4-6 mer of N-acetylglucosamine in chitin fiber as a unit for binding. The comparison of the binding properties of BMCP30 with those of BMCP18 showed that their binding activities to chitin are similar in a standard buffer but that BMCP30 binds to chitin more stably than BMCP18 in the presence of urea. BMCPs possess the RR-1 form of the R&R consensus, about 70 amino acids region conserved widely among cuticle proteins mainly from the soft cuticle of many insect and arthropod species. Analysis of the binding activity using deletion mutants of BMCPs revealed that this type of conserved region also functions as the chitin-binding domain, similarly to the RR-2 region previously shown to confer chitin binding. Thus, the extended R&R consensus is the general chitin-binding domain of cuticle proteins in Arthropoda.

cuticleDB: a relational database of Arthropod cuticular proteins

Background

The insect exoskeleton or cuticle is a bi-partite composite of proteins and chitin that provides protective, skeletal and structural functions. Little information is available about the molecular structure of this important complex that exhibits a helicoidal architecture. Scores of sequences of cuticular proteins have been obtained from direct protein sequencing, from cDNAs, and from genomic analyses.

Most of these cuticular protein sequences contain motifs found only in arthropod proteins.

Description

cuticleDB is a relational database containing all structural proteins of Arthropod cuticle identified to date. Many come from direct sequencing of proteins isolated from cuticle and from sequences from cDNAs that share common features with these authentic cuticular proteins. It also includes proteins from the Drosophila melanogaster and the Anopheles gambiae genomes, that have been predicted to be cuticular proteins, based on a Pfam motif (PF00379) responsible for chitin binding in Arthropod cuticle. The total number of the database entries is 445: 370 derive from insects, 60 from Crustacea and 15 from Chelicerata. The database can be accessed from our web server at .

Conclusions

CuticleDB was primarily designed to contain correct and full annotation of cuticular protein data. The database will be of help to future genome annotators. Users will be able to test hypotheses for the existence of known and also of yet unknown motifs in cuticular proteins. An analysis of motifs may contribute to understanding how proteins contribute to the physical properties of cuticle as well as to the precise nature of their interaction with chitin.

A novel calcium-binding peptide from the cuticle of the crayfish, Procambarus clarkii

A novel peptide named calcification-associated peptide (CAP)-2 was isolated from the exoskeleton of the crayfish, Procambarus clarkii. CAP-2 consists of 65 amino acid residues and has a 44% sequence identity with CAP-1 characterized previously. It has a chitin-binding domain observed in many arthropod cuticle proteins. CAP-2 showed inhibitory activity on calcium carbonate precipitation and chitin-binding ability. A CAP-2 cDNA was cloned using RT-PCR and RACE and the open reading frame encoded a precursor peptide consisting of a signal peptide and CAP-2. RT-PCR revealed that CAP-2 mRNA was exclusively expressed in the epidermal tissue during the postmolt stage, the site and stage being associated with calcification. Calcium-binding assay using recombinant CAP-2 revealed that this peptide had affinity for calcium ions with a Kd value of about 1 mM. All these results suggest that CAP-2 serves as a nucleator or a regulator in the calcification of the exoskeleton.

Partial N-terminal sequences of larval cuticular proteins from the dipteran Ceratitis capitata

The partial amino acid sequences ranging in length over 17-30 residues from the N-terminus, have been obtained for nine cuticular proteins of Ceratitis capitata. Sequence similarities indicate that the proteins belong to a family which is related to cuticular proteins isolated from flexible cuticles of Drosophila melanogaster, Manduca sexta, Sarcophaga bullata and Hyalophora cecropia.

Molecular cloning of three cDNAs encoding putative larval cuticle protein expressed differentially after larval ecdysis from the mulberry longicorn beetle, Apriona germari

Three cDNAs encoding putative larval cuticle protein (LCP) were cloned from the mulberry longicorn beetle, Apriona germari. The three cDNA sequences were 309 bp, 396 bp and 408 bp in length, encoding 103, 132 and 136 amino acid residues, respectively. The predicted molecular masses for these LCPs were approximately 9.2 kDa (AgLCP9.2), 12.3 kDa (AgLCP12.3) and 12.6 kDa (AgLCP12.6). Pairwise identity among AgLCP9.2, AgLCP12.3 and AgLCP12.6 were relatively low. Each AgLCP contained a type-specific consensus sequence identifiable in other insect cuticle proteins. The deduced amino acid sequence of AgLCP9.2 is most similar to Bombyx mori LCP18 and those of AgLCP12.3 and AgLCP12.6 are both most similar to B. mori LCP17. Northern blot analysis revealed that the three AgLCPs showed epidermis-specific expression. The expression profile of AgLCPs after larval ecdysis revealed by Northern blot analysis that the high-level mRNA expression of AgLCPs was detected on the first day of larval ecdysis for AgLCP9.2, on the fifth day for AgLCP12.3 and from the first day of larval ecdysis to the fifth day after larval ecdysis for AgLCP12.6, demonstrating that AgLCP mRNAs are differentially expressed in epidermis after larval ecdysis.

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

The distributions of mRNAs for two cuticular proteins of Hyalophora cecropia were examined with RT-PCR and in situ hybridization. For major regions of larval and pupal cuticle, there was a strong correspondence between the type of cuticle and the predominant cuticular protein message found. Epidermal cells underlying soft cuticle had mRNA for HCCP12, with a RR-1 consensus attributed to soft cuticle, while the epidermal cells associated with hard cuticle had predominantly mRNA for HCCP66, a protein with the RR-2 consensus attributed to hard cuticle. Both messages were found in all areas of the pupal fore- and hind-wings, with modest area-specific difference in concentration being much less than differences in the relative abundance of these cuticular proteins.mRNA for HCCP12 was present in imaginal discs of feeding larvae of H cecropia. Data from Bombyx mori available at SilkBase (http://www.ab.a.u-tokyo.ac.jp/silkbase/) revealed that imaginal discs from feeding larvae had abundant mRNA for RR-1 cuticular proteins, representing six distinct gene products. Only discs from spinning larvae had mRNAs that coded for RR-2 proteins arising from 10 distinct genes. Thus, lepidopteran wing imaginal discs can no longer be regarded as inactive in larval cuticle production.

Comparison of newly isolated cuticular protein genes from six aphid species

This paper reports on the first aphids' cuticular proteins. One gene (Mpcp1) was obtained by screening a cDNA library of Myzus persicae with antibodies to a lepidopteran cuticle protein. MpCP1 presents a putative signal peptide, a central extended R&R domain, flanked by N- and C-terminal repeats of alanine, tyrosine and proline. The mRNA of Mpcp1 could be detected in a larval and in adult stages. Primers based on Mpcp1 allowed isolating and comparing cuticle protein genes from five aphid species, but not from whitefly or thrips. Comparison revealed a high degree of similarity. Data from this paper suggest that this cuticle protein family is typical and predominant to aphids. The conformation of these cuticle proteins and the significance on particular properties of aphid cuticle is discussed.

Isolation and comparison of different ecdysone-responsive cuticle protein genes in wing discs of Bombyx mori

Microarray analysis was used to isolate an ecdysone up-regulated cuticle protein gene from wing discs of Bombyx mori. Transcripts of isolated cDNAs were identified by Northern blot analysis. Expression of the BMWCP10 gene was observed during the W0-W3 stages with the strongest signal being at the W2 stage. In contrast, expression of the BMWCP2 gene was observed at the W3and P0 stages. Expression of BMWCP10 was identified after exposure to 20E in vitro, while that of BMWCP2 was identified after exposure to 20E followed by its removal. Induction of BMWCP10 by 20E was observed in 30 min and was not inhibited by cycloheximide. Expression of BMWCP2 was observed in wing discs cultured for more than 18 h in a hormone-free medium after 20E removal. At least 4 h exposure to 20E was required before removal for induction of BMWCP2. Induction of BMWCP2 required protein synthesis. Thus, different ecdysone-responsive cuticle protein genes in wing discs of Bombyx mori were isolated.