Structure and expression of mRNA for a pupal cuticle protein of the silkworm, Bombyx mori

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.

Comparative Transcriptome Analysis Reveals Molecular Insights in Overwintering Monochamus alternatus (Coleoptera: Cerambycidae)

Monochamus alternatus, the dominant vector of Bursaphelenchus xylophilus (Aphelenchida: Aphelenchoididae), has caused immense damage to forest resources. In China, this vector was native to the southern regions but has spread northward recently. To adapt to more challenging environments in the northern winter, M. alternatus has evolved an intricate strategy for overwintering, which remains largely unknown. Herein, we compared the transcriptome data of the overwintering and non-overwintering larvae of M. alternatus larvae to investigate the molecular mechanisms in overwintering. A total of 53.10 GB clean bases and 28, 245 unigenes were obtained by RNA-seq. Analysis of 2597 upregulated and 2429 downregulated unigenes, as well as the enrichment of DEGs showed that many genes and pathways were jointly involved in the overwintering period. Besides, the accuracy of the RNA-seq data was tested by using qPCR experiment involving 13 selected genes. The results revealed that the overwintering process relied largely on the energy allocation trade-off. Specifically, overwintering M. alternatus inhibited energy-intensive activities, such as growth and molting, detoxification, and trehalose transport, and the reserved energy was skewed towards the synthesis of antifreeze compounds and immune response to cope with the deleterious effects of winter.

Genomic insights into the sessile life and biofouling of barnacles (Crustacea: Cirripedia)

Members of the infraclass Cirripedia, commonly called barnacles, are unique among the subphylum Crustacea in that they exhibit a biphasic life cycle with a planktonic larval stage and a sessile adult stage. Understanding their unique sessile life and mechanisms of attachment are hampered by the lack of genomic resources. Here, we present a 746 Mb genome assembly of Lepas anserifera – the first sequenced stalked barnacle genome. We estimate that Cirripedia first arose ~495 million years ago (MYA) and further diversified since Mesozoic. A demographic analysis revealed remarkable population changes of the barnacle in relation to sea-level fluctuations in the last 2 MYA. Comparative genomic analyses revealed the expansion of a number of developmental related genes families in barnacle genomes, such as Br–C, PCP20 and Lola, which are potentially important for the evolution of metamorphosis, cuticle development and central nervous system. Phylogenetic analysis and tissue expression profiling showed the possible roles of gene duplication, functional diversification and co-option in shaping the genomic evolution of barnacles. Overall, our study provides not only a valuable draft genome for comparative genomic analysis of crustacean evolution, but also facilitates studies of biofouling control.

CPAP3 proteins in the mineralized cuticle of a decapod crustacean

The pancrustacean theory groups crustaceans and hexapods (once thought to comprise separate clades within the Arthropoda) into a single clade. A key feature common to all pancrustaceans is their chitinous exoskeleton, with a major contribution by cuticular proteins. Among these, are the CPAP3’s, a family of cuticular proteins, first identified in the hexapod Drosophila melanogaster and characterized by an N-terminal signaling peptide and three chitin-binding domains. In this study, CPAP3 proteins were mined from a transcriptomic library of a decapod crustacean, the crayfish Cherax quadricarinatus. Phylogenetic analysis of other CPAP3 proteins from hexapods and other crustaceans showed a high degree of conservation. Characterization of the crayfish proteins, designated CqCPAP3’s, suggested a major role for CPAP3’sin cuticle formation. Loss-of-function experiments using RNAi supported such a notion by demonstrating crucial roles for several CqCPAP3 proteins during molting. A putative mode of action for the CqCPAP3 proteins –theoretically binding three chitin strands– was suggested by the structural data obtained from a representative recombinant CqCPAP3. The similarities between the CqCPAP3 proteins and their hexapod homologues further demonstrated common genetic and proteinaceous features of cuticle formation in pancrustaceans, thereby reinforcing the linkage between these two highly important phylogenetic groups.

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.

Annotation and expression analysis of cuticular proteins from the tobacco hornworm, Manduca sexta

The insect cuticle is a unique material that covers the exterior of the animal as well as lining the foregut, hindgut, and tracheae. It offers protection from predators and desiccation, defines body shape, and serves as an attachment site for internal organs and muscle. It has demonstrated remarkable variations in hardness, flexibility and elasticity, all the while being light weight, which allows for ease of movement and flight. It is composed primarily of chitin, proteins, catecholamines, and lipids. Proteomic analyses of cuticle from different life stages and species of insects has allowed for a more detailed examination of the protein content and how it relates to cuticle mechanical properties. It is now recognized that several groups of cuticular proteins exist and that they can be classified according to conserved amino acid sequence motifs. We have annotated the genome of the tobacco hornworm, Manduca sexta, for genes that encode putative cuticular proteins that belong to seven different groups: proteins with a Rebers and Riddiford motif (CPR), proteins analogous to peritrophins (CPAP), proteins with a tweedle motif (CPT), proteins with a 44 amino acid motif (CPF), proteins that are CPF-like (CPFL), proteins with an 18 amino acid motif (18 aa), and proteins with two to three copies of a C-X5-C motif (CPCFC). In total we annotated 248 genes, of which 207 belong to the CPR family, the most for any insect genome annotated to date. Additionally, we discovered new members of the CPAP family and determined that orthologous genes are present in other insects. We established orthology between the M. sexta and Bombyx mori genes and identified duplication events that occurred after separation of the two species. Finally, we utilized 52 RNAseq libraries to ascertain gene expression profiles that revealed commonalities and differences between different tissues and developmental stages.

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.

A genetic linkage map for the domesticated silkworm, Bombyx mori, based on restriction fragment length polymorphisms

We present data for the initial construction of a molecular linkage map for the domesticated silkworm, Bombyx mori, based on 52 progeny from an F2 cross from a pair mating of inbred strains p50 and C108, using restriction fragment length polymorphisms (RFLPs). The map contains 15 characterized single copy sequences, 36 anonymous sequences derived from a follicular cDNA library, and 10 loci corresponding to a low copy number retrotransposon, mag. The 15 linkage groups and 8 ungrouped loci account for 23 of the 28 chromosomes and span a total recombination length of 413 cM; 10 linkage groups were correlated with established classic genetic maps. Scoring data from Southern blots were analysed using two Pascal programs written specifically to analyse linkage data in Lepidoptera, where females are the heterogametic sex and have achiasmatic meiosis (no crossing-over). These first examine evidence for linkage by calculating the maximum lod score under the hypothesis that the two loci are linked over the likelihood under the hypothesis that the two loci assort independently, and then determine multilocus linkage maps for groups of putatively syntenic loci by calculating the maximum likelihood estimate of the recombination fractions and the log likelihood using the EM algorithm for a specified order of loci along the chromosome. In addition, the possibility of spurious linkage was exhaustively tested by searching for genotypes forbidden by the absence of crossing-over in one sex.

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.

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.

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.

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.

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.

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.

Pupal commitment and its hormonal control in wing imaginal discs

The timing of pupal commitment of the forewing imaginal discs of the silkworm, Bombyx mori, was determined by a transplantation assay using fourth instar larvae. The wing discs were not pupally committed at the time of ecdysis to the fifth instar. Pupal commitment began shortly after the ecdysis and was completed in 14 h. When the discs of newly molted larvae (0-h discs) were cultured in medium containing no hormone, they were pupally committed in 26 h. In vitro exposure of 0-h discs to 20-hydroxyecdysone accelerated the progression of pupal commitment. Methoprene, a juvenile hormone analog (JHA), did not suppress the change in commitment in vitro at physiological concentrations. Thus the wing discs at the time of the molt have lost their sensitivity to JH, and 20E is not a prerequisite for completion of pupal commitment. These results suggest that the change in commitment in the forewing discs may begin before the last larval molt.

Studies on proteins in post-ecdysial nymphal cuticle of locust, Locusta migratoria, and cockroach, Blaberus craniifer

Proteins were extracted from the cuticle of mid-instar nymphs of locusts, Locusta migratoria, and cockroaches, Blaberus craniifer. Seven proteins were purified from the locust extract and five from the cockroach extract, and their amino acid sequences were determined. Polyacrylamide gel electrophoresis indicates that the proteins are present only in the post-ecdysially deposited layer of the nymphal cuticles. One of the locust and one of the cockroach nymphal proteins contain a 68-residue motif, the RR-2 sequence, which has been reported for several proteins from the solid cuticles of other insect species. Two of the cockroach proteins contain a 75-residue motif, which is also present in a protein from the larval/pupal cuticle of a beetle, Tenebrio molitor, and in proteins from the exoskeletons of a lobster, Homarus americanus, and a spider, Araneus diadematus. The motif contains a variant of the Rebers-Riddiford consensus sequence, and is called the RR-3 motif. One of the locust and three of the cockroach post-ecdysial proteins contain one or more copies of an 18-residue motif, previously reported in a protein from Bombyx mori pupal cuticle. The nymphal post-ecdysial proteins from both species have features in common with pre-ecdysial proteins (pharate proteins) in cuticles destined to be sclerotised; they show little similarity to the post-ecdysial cuticular proteins from adult locusts or to proteins from soft, pliable cuticles. Possible roles for post-ecdysial cuticular proteins are discussed in relation to the reported structures.

Characterization of cuticular proteins in the red flour beetle, Tribolium castaneum

We are characterizing the cuticular proteins of Tribolium castaneum (Herbst) (Coleoptera:Tenebrionidae) to determine their role in the function of the exoskeleton. Based on qualitative analyses of cuticles, we focused on the sodium dodecyl sulfate (SDS)-extractable proteins. A small-scale cuticle "mini-prep" procedure was devised that yields preparations virtually free of contaminating cellular material compared to hand-dissected preparations, as assessed by fluorescent microscopy using DAPI to stain nuclei. Proteins extracted in 1% SDS from various developmental stages (last larval instar, pupal, adult) were analyzed by one-dimensional denaturing polyacrylamide gel electrophoresis and by two-dimensional gel electrophoresis. The cuticular protein profiles show both similarities and differences among the stages examined. The amino acid composition, glycosylation, and partial amino acid sequence of several abundant cuticular proteins indicate similarity to cuticular proteins of other insects.

The origin, transport and cleavage of the molt-associated cuticular protein CECP22 from Calpodes ethlius (Lepidoptera, Hesperiidae)

CECP22 (Calpodes ethlius Cuticular Protein 22 kDa) is a molt associated protein found in the cuticle of C. ethlius larvae and pupae. The mRNA for the CECP22 cuticular protein is expressed in the epidermis and fat body during the intermolt. The protein itself accumulates in intermolt hemolymph, but at molting, when the cuticle is being digested, it is also found in the cuticle of surface integument, tracheae, foregut and hindgut and in the molting fluid. CECP22 exists in two forms. The large form (19.17 kDa, pI 6.2) becomes smaller (16.1 kDa, pI 7.4) by cleavage at the proteolytic cleavage site (position 170) with amidation of the C-terminal. The small, more basic peptide, appears only at molting, first in the cuticle and then in the molting fluid. It is presumed to be the active form of an amidase involved in the earliest stages of cuticle degradation. The inactive form accumulates in the hemolymph during the long intermolt and probably represents an abundant source of precursor enzyme that can be provided to all cuticle containing organs for a precise initiation of cuticle degradation.

Molecular cloning and characterization of a cDNA encoding a larval cuticle protein of Bombyx mori

Cuticle proteins termed LCPs are the major protein components of the larval integument of the silkworm, Bombyx mori. We purified an 18 kDa LCP (LCP18) from the guanidine hydrochloride extract of the larval cuticle and identified an LCP18 cDNA clone. The deduced primary structure and mRNA expression pattern of LCP18 are similar to those of other Bombyx LCPs and to several cuticle proteins identified in other insect species. RNA blot analysis demonstrated that the biosynthesis of LCP18 is regulated in a stage-dependent manner at the level of mRNA in epidermal cells. An in vivo study using a juvenile hormone analogue suggested that juvenile hormone positively regulates expression of LCP18 mRNA during larval intermolt stages.

A hydrophobic peptide (VAP-peptide) of the silkworm, Bombyx mori: a unique role for adult activity proposed from gene expression and production at the terminal phase of metamorphosis

A unique hydrophobic peptide (VAP-peptide) isolated from male adult heads of the silkworm, Bombyx mori, has been shown to act as a synergist to the diapause hormone when administered exogenously. Here, we investigated the true role of the endogenous VAP-peptide on differentiation and development of adult organs in the silkworm. By northern blot analyses, the VAP-peptide gene was shown to be exclusively expressed at the terminal phase of adult development in epithelial tissues, especially in the wing and the thoracic integument. In situ hybridization analysis revealed that the gene was highly expressed in the epidermal cells of the wing vein and the thoracic integument. The stage- and tissue-dependent gene expression were clearly correlated to the accumulation profile of VAP-peptide. In the adult thoracic integument, VAP-peptide was predominantly deposited in the cuticle layer. Affinity chromatography indicated the ability of VAP-peptide to bind to chitin. Based on its expression patterns, localization, and chemical properties, VAP-peptide is conceived to be a structural protein that participates in mechanical strengthening of specific cuticle structures, supporting their physical requirements in the adult life of the silkworm.

A cuticular protein from the moulting stages of an insect

A 22 kDa peptide was purified from prepupal cuticles of 5th instar Calpodes ethlius caterpillars. It was absent earlier in the stadium and from the egg and adult, i.e. it is related to cuticle turnover rather than cuticle structure. It was present at larval and metamorphic moults, showing that it is related to moulting not just metamorphosis. The cDNA corresponding to the 22 kDa peptide was isolated by antibody screening of an epidermal cDNA expression library. Hybridization to Calpodes genomic DNA showed that the gene was present as a single copy. The deduced amino acid sequence is not like any of the sequences of cuticular structural proteins that have been published, but has a 47 amino acid sequence similar to bacteriophage T7 N-acetylmuramoyl-L-alanine amidase (34% identical, 51% similar). The amino acid sequence, the timing of expression in development, and the similarity between the substrate of the bacteriophage amidase and components of insect cuticle, all suggest that the 22 kDa protein may have a role in cleaving chitin-peptide bonds as a prerequisite for digestion of the cuticle by chitinases and proteases.

Characterization of exoskeletal proteins from the American lobster, Homarus americanus

Proteins from the calcified exoskeleton of the lobster, Homarus americanus, were extracted and separated by two-dimensional gel-electrophoresis. Electroblotting the proteins onto polyvinylidene difluoride (PVDF) membranes followed by sequence determination gave 16 N-terminal amino-acid sequences and revealed that further eight proteins were N-terminally blocked. The relative molecular mass, M(r), was obtained for most of the electrophoretically separated proteins by means of matrix-assisted laser desorption mass spectrometry (MALDIMS) after electroelution from Coomassie-stained two-dimensional polyacrylamide gels. Eleven proteins were purified from extracts of the exoskeleton by low pressure ion exchange chromatography and reversed-phase high performance chromatography, and their sequences were determined by combined use of Edman degradation and mass spectrometry. Good agreement was obtained between the M(r)-values measured by mass spectrometry and those calculated from the sequences. Five of the sequenced proteins contain two copies of a previously observed 18-residue sequence motif, while a couple of the remaining sequences show similarity to sequences of exoskeletal proteins from shrimps and spiders. Only limited similarity to insect cuticular proteins was observed.

Purification and cDNA cloning of evolutionally conserved larval cuticle proteins of the silkworm, Bombyx mori

A specific set of structural proteins termed larval cuticle proteins (LCPs) accumulates in integuments during larval development of the silkworm, Bombyx mori. Two major larval cuticle proteins, LCP17 and LCP22, were purified from the guanidine hydrochloride extract of the larval cuticle, and specific antibodies were raised against these proteins. Immunoblot analysis revealed that both LCPs are actively synthesized during larval intermolt stages, whereas the LCP17 epitope is also slightly but significantly detectable in pupal integuments. cDNA clones for LCPs were isolated by immunoscreening of the cDNA expression library constructed from larval epidermal mRNA. Predicted amino acid sequences of LCP17 and LCP22 are homologous to cuticle proteins from other insect species, including Manduca sexta, Drosophila melanogaster and Locusta migratoria. This fact suggests that these cuticle protein genes originated from a common ancestral gene and have been conserved during evolution. Northern blot hybridization demonstrated that the expression of LCP17 as well as LCP22 mRNA is controlled in a stage-specific manner in the epidermis of the final instar larvae, suggesting a common regulatory mechanism for transcription of these two intermolt genes.

Sequence studies of proteins from larval and pupal cuticle of the yellow meal worm, Tenebrio molitor

Complete amino acid sequences have been determined for six larval-pupal cuticular proteins from Tenebrio molitor. The sequenced proteins are major components in both larval and pupal cuticle, and both basic and slightly acidic proteins are represented. The proteins show pronounced similarities to some of the proteins sequenced from other insect cuticles. Three slightly acidic larval-pupal Tenebrio cuticular proteins contain a 66-residue central, hydrophilic region, resembling regions in cuticular proteins from insect species of four different orders (Coleoptera, Diptera, Lepidoptera and Orthoptera), and three basic proteins from larval-pupal Tenebrio cuticle have a 51-residue hydrophilic region in common with two proteins from cuticle of pharate adult locusts (Locusta migratoria). The Tenebrio larval-pupal cuticular proteins are also similar to locust adult cuticular proteins, by frequent occurrence of the short sequence motif Ala-Ala-Pro-Ala/Val. The pronounced sequence similarities between cuticular proteins from different insect orders indicate that the conserved regions are functionally important.

Cuticular proteins from the giant cockroach, Blaberus craniifer

The extractable proteins from selected cuticular regions of nymphs and adults of the cockroach, Blaberus craniifer, have been compared by two-dimensional gel-electrophoresis. Only minor differences in protein patterns were observed when nymphal and adult pre-ecdysial cuticles (presumptive exocuticle) were compared, whereas the pattern obtained from nymphal mid-instar cuticle (mainly endocuticle) differed markedly from that obtained from mature adult cuticle. The pattern obtained from nymphal mid-instar cuticle depended upon the specific cuticular region analysed, but the differences within a stage were, to a large extent, quantitative and not qualitative. Seven nymphal endocuticular proteins have been purified to near homogeneity, and the complete amino acid sequence has been determined for three of them. One of the proteins, Bc-NCP1, contains a 16-residue motif repeated three times and containing a disulphide bridge. Protein Bc-NCP2 has a twice repeated motif in common with a pupal protein from Bombyx mori, and Bc-NCP4 contains a twice-repeated sequence of nine residues and is moreover characterized by an unusual high content of valine (22.0%). None of the protein sequences shows significant similarities to the sequences determined for locus endocuticular proteins, except that they all have pyroglutamate as the N-terminal residue.

Purification and characterization of five cuticular proteins from the spider Araneus diadematus

Urea-extractable proteins have been purified from the cephalothoracic cuticle of mature Araneus diadematus spiders. Two-dimensional gel electrophoresis showed at least 12 major proteins, with pIs between 4.5 and 8.5. Five proteins were purified and their primary structure determined, using a combination of mass spectrometry and Edman degradation. Based on the amino acid sequence the proteins can be divided into two groups, both characterized by hydrophobic regions dominated by Ala, Pro and Val. Sequence similarity was observed between all the spider cuticle proteins and a number of proteins from other arthropod cuticles. Although the similarity seemed to be confined only to a region in the central part of the molecules, it does link these very distantly related species.

Cloning and sequencing of a cDNA encoding a larval-pupal-specific cuticular protein in Tenebrio molitor (Insecta, Coleoptera). Developmental expression and effect of a juvenile hormone analogue

A cDNA clone encoding a larval-pupal cuticular protein, named TMLPCP-22, has been isolated by screening a library in expression vector with a monoclonal antibody made against pupal cuticular proteins of Tenebrio molitor. Northern-blot and in situ hybridization analyses showed that the expression of TMLPCP-22 is regulated in a stage-specific and tissue-specific manner; the transcript was present during the secretion of preecdysial larval and pupal cuticles and was restricted to epidermal cells. No expression was observed during adult cuticle deposition. In supernumerary pupae obtained after application of a juvenile hormone analogue, which is known to inhibit the adult programme, TMLPCP-22 mRNA was expressed again, confirming its larval-pupal specificity.

Proteins of crustacean exoskeleton: IV. Partial amino acid sequences of exoskeletal proteins from the Bermuda land crab, Gecarcinus lateralis, and comparisons to certain insect proteins

As in all decapod Crustacea, the exoskeleton of the land crab Gecarcinus lateralis consists of four layers. Prior electrophoretic analysis of proteins extracted from these layers revealed an abundance of small M(r) proteins with acidic pIs are found in insect cuticle (O'Brien et al. [1991 Biol. Bull., 181:427-441). Further, immunological cross-reactivity between crab exoskeletal proteins and insect cuticular proteins has been demonstrated (Kumari and Skinner [1993] J. Exp. Zool., 265:195-210). Partial amino acid sequences of a number of proteins from the four exoskeletal layers are described here. Proteins were electrophoresed on two-dimensional (2D) gels, transferred to polyvinylidene difluoride (PVDF) membranes, and stained; individual spots were recovered and their N-termini were sequenced. In addition, a 14-kDa protein (pI = 5.4) from membranous layer (ML14) was eluted from 2D gels and digested with endoproteinase Lys-C; N-termini of its constituent peptides were sequenced. The two epicuticular proteins differed from each other. Three proteins with identical electrophoretic mobility isolated from exocuticle, endocuticle, and membranous layer appeared to have identical N termini, while another electrophoretically identical set from the three layers appeared identical with each other but differed in three positions from the first set. Two proteins from the membranous layer both had a mass of 25 kDa but different isoelectric points. Their sequences were indistinguishable from each other but clearly distinct from another membranous layer protein. Another distinct sequence was found in a 14-kDa protein from endocuticle, while a less acidic pair of 14-kDa proteins from endocuticle and membranous layer were quite similar to one another. The three internal peptide fragments from ML14 were distinct, but one had regions similar to the ML14 N terminus. One crab exoskeletal protein sequence was similar to some structural proteins of vertebrates, whereas others had motifs found in insect cuticular proteins. The sequence similarities identified did not account for the antibody cross-reactivity.

Identification, sequence and mRNA expression pattern during metamorphosis of a cDNA encoding a glycine-rich cuticular protein in Tenebrio molitor

The study of insect cuticular proteins and their sequences is of interest because they are involved in protein-protein and protein-chitin interactions which confer the mechanical properties and fine architecture of the cuticle. Moreover, in the coleopteran Tenebrio molitor there is a dramatic change in cuticular architecture between pre- and postecdysial secretion. We report the isolation, by differential screening, and the sequence characterization of a cDNA clone encoding a cuticular protein of T. molitor, ACP17. After insertion in the expression vector pEX1, the recognition of the fusion protein by an anti-cuticular monoclonal antibody confirmed the cuticular nature of ACP17. Northern hybridization analysis showed that ACP17 mRNA expression begins weakly 3 days before adult ecdysis and strongly increases during the secretion of postecdysial adult cuticle, with a maximum just after ecdysis. In situ hybridization revealed that the ACP17 mRNA is only present in the epidermis which secretes hard cuticle. The deduced amino acid (aa) composition exhibits a high content of Gly (28%) and Ala (20%) and, particularly, two poly(Gx) stretches separated by repetitive motifs with proline AAPVA. A comparison is made with other cuticle aa sequences.

Expression cloning and characterization of a pupal cuticle protein cDNA of Galleria mellonella L

Epidermal mRNA of freshly ecdysed pupae of Galleria mellonella was used to establish a cDNA library in phage lambda gt11. A cDNA clone was isolated by means of a pupal cuticle protein (PCP) specific antibody. Nucleic acid sequence data show an insert of 1212 bp with an open reading frame of 1062 bp. The presence of start, stop, and polyadenylation sites suggests, that this insert represents a full length transcript. Conceptual translation resulted in a protein of 353 amino acids including a signal peptide. The final processed protein product is rich in alanine and charged amino acids like glutamic acid. It has a calculated pI of 4.19 and a molecular mass of 34.272 kDa. In hybrid selection/in vitro translation and in vitro transcription/translation experiments a translational product of 54 kDa was synthesized. The difference between apparent and calculated molecular mass is thought to be due to the relatively high amount of glutamic acid residues clustered in two regions. The developmental profile of expression of the corresponding gene was analyzed by northern blot hybridization using a cDNA probe. The time course of expression is coincident with developmentally regulated metamorphic changes in the integument.

Primary structure of proteins from the wing cuticle of the migratory locust, Locusta migratoria

Wing cuticle from pharate adult locusts, Locusta migratoria, contains several prominent proteins which occur as minor components or are completely absent in other cuticular regions. Six of the wing-specific proteins have been purified and their amino acid sequences determined by combined use of mass spectrometry and automated Edman degradation. During the sequence determination very long sequence runs (90-121 residues) were necessary in order to establish the primary structure. All the wing-specific cuticular proteins from locusts contain the repeated short sequence motif -Ala-Ala-Pro-Ala/Val-, which is common for all hitherto sequenced cuticular proteins from pharate locusts. Several of the wing-specific proteins also possess an N-terminal region rich in glycine, tyrosine and leucine, characteristic for many locust cuticular proteins. Two of the analysed proteins have a conserved 61-residue sequence in common with a previously sequenced protein from locust wing cuticle and with two proteins from the pharate cuticle of adult Tenebrio molitor. Possible roles for the various sequence motifs are discussed.

Insect cuticular proteins

Insect cuticles are composite structural materials with mechanical properties optimal for their biological functions. The bulk properties of cuticles are to a large extent determined by the interactions between the various components, mainly the chitin filament system and the proteins. The various cuticular types show pronounced differences in mechanical properties, and it is suggested that these differences can be related to the properties of the individual proteins and to the degree of secondary stabilization (sclerotization). The amino acid sequences, which have been obtained for insect cuticular proteins either by direct sequencing of purified proteins or by deduction from corresponding DNA-sequences, are listed according to insect order and species. Extensive sequence similarity is observed among several cuticular proteins obtained from different insect orders. Other cuticular proteins are characterized by repeated occurrence of a few small motifs consisting mainly of hydrophobic residues. The latter group of proteins has so far only been reported from stiff cuticles. The possible relevance of the various motifs and repeats for protein interaction and the mechanical properties of cuticles is discussed.

Comparison of larval and pupal cuticular proteins in Tenebrio molitor

Protein extracts from pupal and larval pharate cuticle from the meal worm, Tenebrio molitor, gave nearly identical patterns by two-dimensional electrophoresis and by ion-exchange chromatography. The main components in the cuticular extracts from the two metamorphic stages were also identical with respect to molecular mass according to electrospray ionization mass spectrometry. The complete amino acid sequence for one of the pupal cuticular proteins was determined; according to partial amino acid sequences and the mass spectrometric peptide map for the corresponding larval cuticular protein, it was concluded that the larval protein has the same amino acid sequence as the pupal protein. The sequence is characterized by a high content of alanine, proline, valine, and tyrosine and the complete absence of acidic amino acid residues, the sulphur containing amino acids and tryptophan. The sequence is further characterized by a high frequency of repeated sequence motifs, among which the Ala-Ala-Pro-Ala motif is the most abundant, but also longer sequence motifs are repeated. The sequence shows striking resemblance to sequences of proteins isolated from pharate locust cuticle.

Amino acid sequence determination of a protein purified from the shell of the shrimp, Pandalus borealis

One of the urea-extractable proteins in the shell of the shrimp Pandalus borealis has been purified, and the complete amino acid sequence has been determined by the combined use of mass spectrometry and Edman degradation of the intact protein as well as of enzymatically derived peptides. Characteristic features of the sequence are discussed and compared to sequences from insect cuticular proteins and other structural proteins.

The primary structure of an endocuticular protein from two locus species, Locusta migratoria and Schistocerca gregaria, determined by a combination of mass spectrometry and automatic Edman degradation

The complete primary structures of two variants of a protein, Abd-5, isolated from the endocuticles of the migratory locust Locusta migratoria and the desert locust Schistocerca gregaria, have been determined. The proteins from the two species are N-terminally blocked with pyroglutamic acid. Their sequences differed only in two positions. Comparison of the sequences to those of other cuticular proteins shows that moderate homologies exist to 11 other cuticular proteins from insects representing four different orders. Amino acid residues in certain positions appear to be strictly conserved.

Structure and expression of mRNA for vitellogenin in Bombyx mori

Vitellogenin, a precursor of major yolk protein of the silkworm, Bombyx mori is a tetramer composed of each two molecules of heavy and light subunits. We cloned mRNA sequence for the B. mori vitellogenin and analyzed its structure. Sequence alignment of several overlapping cDNA clones indicated that the vitellogenin mRNA is approx. 5.7 kb, containing an open reading frame for a peptide with 1782 amino acid residues. By comparing the deduced amino acid sequence with the amino-terminal primary structures of vitellogenin subunits, it is suggested that the heavy and light subunits of the B. mori vitellogenin are encoded by a single contiguous mRNA. The primary translation product of the vitellogenin mRNA was detected in the microsomal fraction prepared from the fat body of vitellogenic females. Northern blot analysis of the fat body RNA demonstrated that the biosynthesis of vitellogenin in B. mori is regulated in a tissue-, sex- and stage-specific manner at the level of mRNA. Possible cause for discrepancy between the present results and our previous proposal (Izumi, S. and Tomino, S. (1983) Insect Biochem. 13, 81-85) on the biosynthesis of B. mori vitellogenin is also discussed.

Structure and developmental expression of a larval cuticle protein gene of the silkworm, Bombyx mori

Structure and expression of the gene for a larval cuticle protein of the silkworm, Bombyx mori were studied. A major cuticle protein, termed 'LCP30' was purified from the urea extract of integuments of the fifth (final) instar larvae. Immunoblot analysis by use of the anti-LCP30 antibody revealed that LCP30 begins to accumulate in larvae as early as 10 h after hatch and is present throughout the larval stages. The LCP30 epitope is also detectable in the adult abdominal integument but is absent from pupal integument and adult wing. Screening of an epidermal cDNA expression library with the antibody probe yielded a cDNA clone for LCP30. Primary structure deduced from the cDNA sequence showed that LCP30 bears an arginine-glycine-aspartate (RGD) sequence. The region around this domain exhibits striking similarity with the amino acid sequences found in vertebrate collagens. The genomic DNA clone coding for LCP30 was isolated by screening a B. mori gene library with the LCP30 cDNA probe. The gene consists of five exons interspersed by four introns spanning over 2.7 kb region of chromosomal DNA. The LCP30 mRNA is detectable at high levels at larval intermolt stages, gradually declines after the fourth molt and totally disappears at mid-fifth larval instar, indicating that the expression of LCP30 gene is regulated in a stage-specific fashion in the epidermal cells. Topical application of a juvenile hormone analogue (methoprene) to the fifth instar larvae followed by RNA blot and S1 nuclease mapping analyses of the epidermal RNA proved that juvenile hormone activates transcription of the LCP30 gene.

Characterization of a cDNA and gene encoding a cuticular protein from rigid cuticles of the giant silkmoth, Hyalophora cecropia

We have isolated a cDNA and gene encoding a protein (HCCP66) found in the rigid cuticles of both larvae and pupae of the silkmoth, Hyalophora cecropia. The cDNA encoded a protein similar to cuticle proteins isolated from several other insects and contained a sequence motif similar to one present in a "family" of cuticular proteins from flexible cuticles. The gene had a structure similar to that of cuticle protein genes isolated from Drosophila melanogaster, albeit with a much larger intron that contained three copies of a transposable element-like sequence similar to short interspersed repeated DNA elements (SINEs). A sequence found 5' to the transcription start site matched the Octamer (Oct) cis-acting element. This sequence was capable of binding protein(s) from whole cell extracts of wing epidermis with high affinity and sequence specificity suggesting a role in transcriptional regulation.

Monoclonal antibodies recognizing larval- and pupal-specific cuticular proteins of Tenebrio molitor (Insecta, Coleoptera)

To study the sequential expression of insect epidermal cells during metamorphosis, a library of monoclonal antibodies (MABs) was prepared against the water-soluble proteins from preecdysial pupal cuticle of Tenebrio molitor. Six selected MABs recognizing only larval and pupal cuticular proteins (CPs) in immunoblot analysis were classified into three types. Type 1 recognized a 21.5 and a 22 kDa polypeptide, type 2, a 26 kDa polypeptide, and type 3, three polypeptides of 18.5, 19.5 and 21.5 kDa. They did not immunoreact with any protein of fat bodies or haemolymph from pharate pupae, suggesting that the antigens originate from the epidermis. The stage-specificity was confirmed by electron microscopic immunogold labelling. Type 1 and 3 MABs recognized antigens characterizing larval and pupal preecdysial sclerotized cuticles, while the antigens recognized by type 2 were localized in the first few lamellae of unsclerotized postecdysial cuticle. When the expression of the adult programme was inhibited by application of a juvenile hormone analogue, the larval-/pupal-specific CPs were detected in the supernumerary pupal cuticle. These results suggest that the genes encoding these proteins are juvenile hormone dependent. These MABs should be useful tools to isolate pupal-specific genes whose regulation sems to be different from that of the adult-specific ones.

Structure and expression of gene coding for a pupal cuticle protein of Bombyx mori

A specific protein termed as PCP accumulates in the newly synthesized pupal cuticle of the silkworm, Bombyx mori. We have cloned the genomic sequence encoding PCP and analyzed its structure. The PCP gene comprises two exons interspersed by a single intron approx. 5.8 kb in length. Transcription initiation sites of the PCP gene were located at nucleotide level. The 5' flanking region of the gene contains a sequence homologous to the Pit-1 DNA recognition element of the rat prolactin and growth hormone genes. The developmental profile of the PCP precursor RNA in epidermal cells showed that the biosynthesis of PCP is regulated at the transcriptional level in a stage- and tissue-specific fashion during post-embryonic development. Administration of 20-hydroxyecdysone to the isolated abdomens prepared from the early fifth instar larvae provoked the accumulation of PCP mRNA in epidermis, suggesting that the molting hormone triggers the expression of PCP gene.

Developmental profiles of epidermal mRNAs during the pupal-adult molt of Tenebrio molitor and isolation of a cDNA clone encoding an adult cuticular protein: effects of a juvenile hormone analogue

Changes in translatable mRNAs from the wing epidermis of the Coleoptera Tenebrio molitor have been investigated during metamorphosis by analysis of in vitro translated products. Striking differences between the patterns obtained from mRNAs extracted during pupal and adult cuticle secretion indicated that a drastic change in gene expression occurs during the pupal-adult transition. In addition to these stage-specific modifications, the mRNA patterns changed within each cuticular synthesis program (pupal or adult), especially at ecdysis. After tritiated leucine incorporation, some of the major radiolabeled cuticular proteins showed similar changes suggesting that the sequential appearance of mRNAs corresponds to sequential deposition of cuticular proteins. In supernumerary pupae obtained after juvenile hormone analogue (JHA) application on newly ecdysed pupae, translatable mRNA were very similar to those of pharate pupae. The JHA seemed, therefore, to prevent the expression of the adult program. By immunoblotting in vitro translated products with a monoclonal antibody recognizing an adult-specific cuticular protein, the developmental profile of the corresponding mRNA was studied. This mRNA was detected in anterior wing epidermis during the first 80 hr of the pharate adult stage. Using the same antibody, a cDNA clone was isolated from epidermal mRNA. The hybrid selected mRNA coded for only one protein with an apparent MW of 22 kDa which was, furthermore, recognized by the antibody. The Northern blot analysis performed with the clone confirmed the Western blot analysis of the in vitro translation products. JHA application at the beginning of the pupal-adult reprograming prevented the appearance of this mRNA; however, this transcript was present during the following molting cycle. This reversibility of the JHA action was confirmed by immunogold labeling of the cuticles formed in treated animals.