Structural analysis of gene encoding cuticle protein BMCP18, and characterization of its putative transcription factor in the silkworm, Bombyx mori

The regulation of expression of insect cuticle protein genes

The exoskeleton of insects (cuticle) is an assembly of chitin and cuticle proteins. Its physical properties are determined largely by the proteins it contains, and vary widely with developmental stages and body regions. The genes encoding cuticle proteins are therefore good models to study the molecular mechanisms of signalling by ecdysteroids and juvenile hormones, which regulate molting and metamorphosis in insects. This review summarizes the studies of hormonal regulation of insect cuticle protein genes, and the recent progress in the analysis of the regulatory sequences and transcription factors important for their expression.

Arthropod nuclear receptors and their role in molting

The molting process in arthropods is regulated by steroid hormones acting via nuclear receptor proteins. The most common molting hormone is the ecdysteroid, 20-hydroxyecdysone. The receptors of 20-hydroxyecdysone have also been identified in many arthropod species, and the amino acid sequences determined. The functional molting hormone receptors consist of two members of the nuclear receptor superfamily, namely the ecdysone receptor and the ultraspiracle, although the ecdysone receptor may be functional, in some instances, without the ultraspiracle. Generally, the ecdysone receptor/ultraspiracle heterodimer binds to a number of ecdysone response elements, sequence motifs that reside in the promoter of various ecdysteroid-responsive genes. In the ensuing transcriptional induction, the ecdysone receptor/ultraspiracle complex binds to 20-hydroxyecdysone or to a cognate ligand that, in turn, leads to the release of a corepressor and the recruitment of coactivators. 3D structures of the ligand-binding domains of the ecdysone receptor and the ultraspiracle have been solved for a few insect species. Ecdysone agonists bind to ecdysone receptors specifically, and ligand-ecdysone receptor binding is enhanced in the presence of the ultraspiracle in insects. The basic mode of ecdysteroid receptor action is highly conserved, but substantial functional differences exist among the receptors of individual species. Even though the transcriptional effects are apparently similar for ecdysteroids and nonsteroidal compounds such as diacylhydrazines, the binding shapes are different between them. The compounds having the strongest binding affinity to receptors ordinarily have strong molting hormone activity. The ability of the ecdysone receptor/ultraspiracle complex to manifest the effects of small lipophilic agonists has led to their use as gene switches for medical and agricultural applications.

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.

A cuticle protein gene from the Japanese oak silkmoth, Antheraea yamamai: gene structure and mRNA expression

A cuticle protein gene, AyCP12, from the Japanese oak silkmoth, Antheraea yamamai, was isolated and characterized. The gene spans 1107 bp and consists of one intron and two exons coding for a 112 amino acid polypeptide with a predicted molecular mass of 12,163 Da and a pI of 4.4. The AyCP12 protein contained a type-specific consensus sequence identifiable in other insect cuticle proteins and the deduced amino acid sequence of the AyCP12 cDNA is most homologous to another silkmoth, A. pernyi, cuticle protein ApCP13 (82% protein sequence identity). Northern blot analysis revealed that AyCP12 showed the epidermis-specific expression.

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.

Microarray analysis of gene expression profiles in wing discs of Bombyx mori during pupal ecdysis

Wing discs of holometabolous insects undergo dramatic morphological changes during metamorphosis, a process that is controlled by the actions of hundreds of gene products. Using cDNA microarrays constructed from 5086 ESTs, we monitored the gene expression profiles in wing discs of Bombyx mori at 13 time points during pupal ecdysis (day-4 fifth instar larvae to day-0 pupae). Of the 5086 ESTs on the microarrays, 2998 ESTs had significant signals in more than half of the experiments. Of the 2998 ESTs, genes represented by 683 ESTs showed significant perturbations during pupal ecdysis. Genes previously known to be induced during metamorphosis were identified, including E75, Urbain, Chitinases, and cuticle proteins. The expressions of genes represented by 59 ESTs induced at the beginning of wandering contained genes predicted to be involved in protein degradation, amino acid metabolism, and amino acid transport. The expressions of genes represented by 147 ESTs induced after the ecdysteroid peak had a role in cuticle synthesis, pigmentation, ion transport, protein transport, and transcription regulation. The expressions of genes represented by 85 ESTs repressed after the ecdysteroid peak were predicted to be involved in nucleotide and nucleic acid metabolism and cell cycle. This indicates the involvement of several biological processes in wing disc development during metamorphosis.

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.

Molecular cloning and characterization of a cDNA encoding a novel cuticle protein in the silkworm, Bombyx mori

We have cloned the full length of a novel cDNA named Bombyx mori cuticle protein that contains an AlaAlaProAla/Val-repeat (BMCPA) from a cDNA library of integument in the larval silkworm. Both a typical tandem repeat (A-A-P-A/V) for cuticle protein and a unique tandem repeat with Ser, Ala, Gly, Pro, Val, Tyr and Thr were observed in the predicted amino acid sequence of the cDNA encoding BMCPA. Approximately 80% of the amino acids in BMCPA were composed of Ser, Ala, Gly, Pro, Val and Tyr. Northern-hybridization analysis indicated that BMCPA mRNA is expressed only in the larval epidermis and that the expression pattern of the BMCPA gene in the developmental stage was observed mainly at the larval stage. We propose BMCPA may be a novel component of cuticle, and may play an important role in the integument of the larval silkworm.

Sequence, structure and expression of the hemolymph juvenile hormone binding protein gene in the tobacco hornworm, Manduca sexta

The hemolymph juvenile hormone binding protein (hJHBP) gene of Manduca sexta is a key target of its specific ligand, juvenile hormone (JH). While the cDNA for hJHBP has been partially characterized, little is known about the hJHBP gene structure or its promoter(s) and enhancers(s). Previous studies have demonstrated that JH stimulates a rapid accumulation of hJHBP mRNA in the fat body. To better understand the underlying molecular events affecting regulation, we sequenced the M. sexta hJHBP gene and its mRNA transcript, characterized its genomic organization, and determined the spatial and temporal expression patterns of the hJHBP gene. The gene is composed of 5 exons spanning 6.7 kb. Southern blot analysis indicates that the gene is present as a single copy. The earliest expression of hJHBP occurs 24 to 48 h after fertilization. Distribution studies indicate that fat body is the only site for hJHBP expression. Elements displaying similarity with sequences of other lepidopteran genes were discovered outside the open reading frame and may represent mobile insertion elements.

Identification and characterization of genes abnormally expressed in wing-deficient mutant (flügellos) of the silkworm, Bombyx mori

The wing-deficient mutant, flügellos (fl), of the silkworm lacks four wings in the pupa and the adult, due to aberrant wing morphogenesis during metamorphosis. To elucidate the mechanisms of wing-specific deficiencies in the fl mutant, we used mRNA differential display and identified five genes abnormally expressed in the fl wing discs. Northern blot and RT-PCR analyses revealed that four genes were overexpressed, but the fifth one was not transcribed in the fl wing discs. The expression level of ribosome-associated protein p40 in the fl wing discs was elevated approximately 10 times compared to the wild-type (WT) discs. Another overexpressed gene CB10 encodes a novel wing-specific protein with a putative zinc-finger motif. Overexpression of two components of extracellular matrix, cuticle protein 18 (BMCP18) and a fibrillin-like protein AD10, may result in the abnormal wing morphogenesis in the fl mutant. In contrast, a novel member of multifunctional Ca2+-binding protein annexins, designated as annexin b13 (Anx b13), was expressed dominantly in the wing discs of WT but completely repressed in the fl tissues. Strong expression of Anx b13 in wing discs during the fourth and fifth instar indicates that ANX B13 plays an important role in wing morphogenesis.