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

Anatomical changes of Tenebrio molitor and Tribolium castaneum during complete metamorphosis

In holometabolous insects, extensive reorganisation of tissues and cells occurs at the pupal stage. The remodelling of the external exoskeleton and internal organs that intervenes during metamorphosis has been traditionally studied in many insect species based on histological or ultrastructural methods. This study demonstrates the use of synchrotron X-ray phase-contrast micro-computed tomography as a powerful, non-destructive tool for in situ morphological observation of anatomical structures at the pupal stage in two Tenebrionid beetles, i.e. Tribolium castaneum and Tenebrio molitor, known as important pests, as well as emerging and promising models in experimental biology. Virtual sections and three-dimensional reconstructions were performed on both males and females at early, intermediate, and late pupal stage. The dataset allowed us to observe the remodelling of the gut and nervous system as well as the shaping of the female and male reproductive system at different pupal ages in both mealworm and red flour beetles. Moreover, we observed that the timing and duration pattern of organ development varied between the species analysed, likely related to the species-specific adaptations of the pre-imaginal stages to environmental conditions, which ultimately affect their life cycle. This research provides new knowledge on the morphological modifications that occur during the pupal stage of holometabolous insects and provides a baseline set of information on beetle metamorphosis that may support future research in forensics, physiology, and ecology as well as an image atlas for educational purposes.

Temporal changes in the physical and mechanical properties of beetle elytra during maturation

Changes in physical properties of Tenebrio molitor and Tribolium castaneum elytra (hardened forewings) were studied to understand how the development of microstructure and chemical interactions determine cuticle mechanical properties. Analysis of these properties supports a model in which cuticular material is continuously secreted from epidermal cells to produce an extracellular matrix so that the outermost layers mature first. It is hypothesized that enzymatic crosslinking and pigmentation reactions along with dehydration help to stabilize the protein-chitin network within the initial layers of cuticle shortly after eclosion. Mature layers are proposed to bear most of the mechanical loads. The frequency dependence of the storage modulus and the tan δ values decreased during the beginning of maturation, reaching constant values after 48 h post-eclosion. A decrease of tan δ indicates an increase in crosslinking of the material. The water content declined from 75% to 31%, with a significant portion lost from within the open spaces between the dorsal and ventral cuticular layers. Dehydration had a less significant influence than protein crosslinking on the mechanical properties of the elytron during maturation. When Tribolium cuticular protein TcCP30 expression was decreased by RNAi, the tan δ and frequency dependence of E' of the elytron did not change during maturation. This indicates that TcCP30 plays a role in the crosslinking process of the beetle's exoskeleton. This study was inspired by previous work on biomimetic multicomponent materials and helps inform future work on creating robust lightweight materials derived from natural sources. STATEMENT OF SIGNIFICANCE: Examination of changes in the physical properties of the elytra (hardened forewings) of two beetle species advanced understanding of how the molecular interactions influence the mechanical properties of the elytra. Physical characterization, including dynamic mechanical analysis, determined that the outer portion of the elytra matured first, while epidermal cells continued to secrete reactive components until the entire structure reached maturation. RNA interference was used to identify the role of a key protein in the elytra. Suppression of its expression reduced the formation of crosslinked polymeric components in the elytra. Identifying the molecular interactions in the matrix of proteins and polysaccharides in the elytra together with their hierarchical architecture provides important design concepts in the development of biomimetic materials.

Involvement of the transcription factor E75 in adult cuticular formation in the red flour beetle Tribolium castaneum

Insect adult metamorphosis generally proceeds with undetectable levels of juvenile hormone (JH). In adult development of the red flour beetle Tribolium castaneum, biosynthesis of adult cuticle followed by its pigmentation and sclerotization occurs, and dark coloration of the cuticle becomes visible in pharate adults. Here, we examined the molecular mechanism of adult cuticular formation in more detail. We noticed that an exogenous JH mimic (JHM) treatment of Day 0 pupae did not inhibit pigmentation or sclerotization, but instead, induced precocious pigmentation of adult cuticle two days in advance. Quantitative RT-PCR analyses revealed that ecdysone-induced protein 75B (E75) is downregulated in JHM-treated pupae. Meanwhile, tyrosine hydroxylase (Th), an enzyme involved in cuticular pigmentation and sclerotization, was precociously induced, whereas a structural cuticular protein CPR27 was downregulated, by exogenous JHM treatment. RNA interference-mediated knockdown of E75 resulted in precocious adult cuticular pigmentation, which resembled the phenotype caused by JHM treatment. Notably, upregulation of Th as well as suppression of CPR27 were observed with E75 knockdown. Meanwhile, JHM treatment suppressed the expression of genes involved in melanin synthesis, such as Yellow-y and Laccase 2, but E75 knockdown did not result in marked reduction in their expression. Taken together, these results provided insights into the regulatory mechanisms of adult cuticular formation; the transcription of genes involved in adult cuticular formation proceeds in a proper timing with undetectable JH, and exogenous JHM treatment disturbs their transcription. For some of these genes such as Th and CPR27, E75 is involved in transcriptional regulation. This study shed light on the molecular mode of action of JHM as insecticides; exogenous JHM treatment disturbed the expression of genes involved in the adult cuticular formation, which resulted in lethality as pharate adults.

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

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

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

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

Formation of rigid, non-flight forewings (elytra) of a beetle requires two major cuticular proteins

Insect cuticle is composed primarily of chitin and structural proteins. To study the function of structural cuticular proteins, we focused on the proteins present in elytra (modified forewings that become highly sclerotized and pigmented covers for the hindwings) of the red flour beetle, Tribolium castaneum. We identified two highly abundant proteins, TcCPR27 (10 kDa) and TcCPR18 (20 kDa), which are also present in pronotum and ventral abdominal cuticles. Both are members of the Rebers and Riddiford family of cuticular proteins and contain RR2 motifs. Transcripts for both genes dramatically increase in abundance at the pharate adult stage and then decline quickly thereafter. Injection of specific double-stranded RNAs for each gene into penultimate or last instar larvae had no effect on larval–larval, larval–pupal, or pupal–adult molting. The elytra of the resulting adults, however, were shorter, wrinkled, warped, fenestrated, and less rigid than those from control insects. TcCPR27-deficient insects could not fold their hindwings properly and died prematurely approximately one week after eclosion, probably because of dehydration. TcCPR18-deficient insects exhibited a similar but less dramatic phenotype. Immunolocalization studies confirmed the presence of TcCPR27 in the elytral cuticle. These results demonstrate that TcCPR27 and TcCPR18 are major structural proteins in the rigid elytral, dorsal thoracic, and ventral abdominal cuticles of the red flour beetle, and that both proteins are required for morphogenesis of the beetle's elytra.

Primitive insects have two pairs of membranous flight wings, but during the evolution of the beetle lineage the forewings lost their flight function and became modified as hard, rigid covers called elytra for protection of soft body parts of the abdomen and also the delicate flexible hindwings, which retained their flight function. This transformation is manifested by a greatly thickened and rigid (sclerotized) exoskeletal cuticle secreted by the forewing epidermis. We demonstrate that this evolutionary modification is accompanied by the incorporation of two highly abundant structural proteins into the elytral cuticle, namely TcCPR18 and TcCPR27. Depletion of these proteins by RNA interference results in malformation and weakening of the elytra, culminating in insect death. These proteins are also abundant in hard cuticle from other regions such as the pronotum and ventral abdomen, but are absent in soft cuticles, and therefore may function as key determinants of rigid cuticle. Expression of such proteins at high levels in the modified forewing appears to have been a fundamental evolutionary step in the transformation of the membranous wing into a thickened and rigid elytron in the Coleoptera.

Transcription factors BmPOUM2 and BmβFTZ-F1 are involved in regulation of the expression of the wing cuticle protein gene BmWCP4 in the silkworm, Bombyx mori

In Bombyx mori, the wing cuticle protein gene BmWCP4 is expressed specifically in the epidermis at the onset and mid-stage of pupation and is responsible for the formation of the pupal cuticle during the larval-pupal metamorphosis. The gene consists of four exons and three introns and is present as a single copy in the genome. Its expression was up-regulated by 20-hydroxyecdysone (20E) and the 20E-induced expression was suppressed by juvenile hormone (JH) III. The upstream regulatory sequence region of the BmWCP4 gene was cloned and the regulatory elements responsible for 20E induction were identified. Two cis-regulatory elements (CREs) bound by the transcription factors BmPOUM2 and BmβFTZ-F1 were identified that mediated 20E-regulated expression of this gene. An electrophoretic mobility shift assay detected two nuclear proteins isolated from the epidermis and the BmN cell line that specifically bound to the POU and βFTZ-F1 CREs, respectively. BmPOUM2 recombinant protein explicitly bound to the POU CRE. Developmental and 20E-induced expression of the BmWCP4, BmPOUM2 and BmβFTZ-F1 genes showed that BmPOUM2 and BmβFTZ-F1 were initially expressed, followed by BmWCP4. These data suggest that the 20E-induced expression of BmWCP4 is mediated by the transcription factors BmPOUM2 and BmβFTZ-F1 binding to their CREs in the regulatory sequence region of the BmWCP4 gene.

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.

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.

Developmental regulation of the pheromone biosynthesis activating neuropeptide-receptor (PBAN-R): re-evaluating the role of juvenile hormone

Sex pheromone production in Helicoverpa armigera is regulated by pheromone-biosynthesis-activating neuropeptide (PBAN), which binds to a G-protein coupled receptor at the pheromone gland. We demonstrate the temporal differential expression levels of the PBAN receptor (PBAN-R) gene, reaching peak levels at a critical period of 5 h post-eclosion. Previous studies implied a possible regulatory role for juvenile hormone (JH). We herein demonstrate that PBAN-R expression levels increase normally when females are decapitated or head-ligated, removing the source of JH, before peak transcript levels are reached. Similarly, sex pheromone production can be induced by PBAN in such decapitated females. These results indicate that up-regulation, at this critical time, is not dependent on JH originating from the head. Conversely, JH injected in vivo at this critical period significantly inhibits PBAN-R transcript levels.

betaFTZ-F1 and Broad-Complex positively regulate the transcription of the wing cuticle protein gene, BMWCP5, in wing discs of Bombyx mori

The present study was undertaken to clarify the mechanism regulating cuticle protein gene expression. Expression of BMWCP5 was strong at around pupation and weak at the mid-pupal stage in wing tissues of Bombyx mori. We analyzed the upstream region of the BMWCP5 gene using a transient reporter assay with a gene gun system to identify the regulatory elements responsible for its unique expression pattern. We identified two betaFTZ-F1 binding sites to be important cis-acting elements for the transcription activation of the luciferase reporter gene by an ecdysone pulse. Site-directed mutagenesis of these sites, followed by introduction into wing discs, significantly decreased the reporter activity. We also found that the regions carrying the binding sites for the ecdysone-responsive factor BR-C Z4 (BR-Z4) were responsible for the hormonal enhancement of the reporter gene activity in wing discs. Mutation of the BR-Z4 binding sites decreased the reporter activity. The nuclear proteins that bound to these betaFTZ-F1 and BR-Z4 sites were identified by an electrophoretic mobility shift assay (EMSA). The results demonstrate for the first time that the BR-Z4 isoform can bind to the upstream region of the cuticle protein gene, BMWCP5, and activate its expression. The results also suggest that the BMWCP5 transcription is primarily regulated by the ecdysone pulse through betaFTZ-F1, and the stage-specific enhancement is brought about through BR-Z4.

Activation of BMWCP10 promoter and regulation by BR-C Z2 in wing disc of Bombyx mori

The cuticle protein gene BMWCP10 is transcriptionally upregulated by ecdysone during development. In the present study, using a transient reporter assay, the activity of various genomic segments at the 5'-flanking region of the BMWCP10 gene in driving gene expression and their involvement in ecdysone-mediated activation were assessed in the Bombyx wing disc. The promoter activity of BMWCP10 was responsive to 20-hydroxyecdysone (20E) in a dose-dependent manner, and the highest luciferase activity was observed in the presence of 2 microg/ml 20E. Furthermore, the upstream BMWCP10 promoter was activated by 20E in a stage-specific manner, and the 2.9-kb promoter contained essential elements for the temporal regulation of BMWCP10 in the Bombyx wing disc. Deletion studies revealed that the -598/-387 bp region was required for high-level transcription. In this region, a BR-C Z2 binding element was identified by electrophoretic mobility shift assay (EMSA). Site-directed mutagenesis of this element in the context of the 598-bp promoter fragment significantly decreased the reporter activity in response to ecdysone treatment. The results confirmed the role of BmBR-C Z2 in the transcription regulation of BMWCP10 and suggested the contribution of BmBR-C Z2 to BMWCP10 induction by 20E.

Genomic structure and expression analysis of the RNase kappa family ortholog gene in the insect Ceratitis capitata

Cc RNase is the founding member of the recently identified RNase kappa family, which is represented by a single ortholog in a wide range of animal taxonomic groups. Although the precise biological role of this protein is still unknown, it has been shown that the recombinant proteins isolated so far from the insect Ceratitis capitata and from human exhibit ribonucleolytic activity. In this work, we report the genomic organization and molecular evolution of the RNase kappa gene from various animal species, as well as expression analysis of the ortholog gene in C. capitata. The high degree of amino acid sequence similarity, in combination with the fact that exon sizes and intronic positions are extremely conserved among RNase kappa orthologs in 15 diverse genomes from sea anemone to human, imply a very significant biological function for this enzyme. In C. capitata, two forms of RNase kappa mRNA (0.9 and 1.5 kb) with various lengths of 3' UTR were identified as alternative products of a single gene, resulting from the use of different polyadenylation signals. Both transcripts are expressed in all insect tissues and developmental stages. Sequence analysis of the extended region of the longer transcript revealed the existence of three mRNA instability motifs (AUUUA) and five poly(U) tracts, whose functional importance in RNase kappa mRNA decay remains to be explored.

Juvenile hormone resistance gene Methoprene-tolerant controls entry into metamorphosis in the beetle Tribolium castaneum

Besides being a spectacular developmental process, metamorphosis is key to insect success. Entry into metamorphosis is controlled by juvenile hormone (JH). In larvae, JH prevents pupal and adult morphogenesis, thus keeping the insect in its immature state. How JH signals to preclude metamorphosis is poorly understood, and a JH receptor remains unknown. One candidate for the JH receptor role is the Methoprene-tolerant (Met) Per-Arnt-Sim (PAS) domain protein [also called Resistance to JH, Rst (1)JH], whose loss confers tolerance to JH and its mimic methoprene in the fruit fly Drosophila melanogaster. However, Met deficiency does not affect the larval-pupal transition, possibly because this process does not require JH absence in Drosophila. By contrast, the red flour beetle Tribolium castaneum is sensitive to developmental regulation by JH, thus making an ideal system to examine the role of Met in the antimetamorphic JH action. Here we show that impaired function of the Met ortholog TcMet renders Tribolium resistant to the effects of ectopic JH and, in a striking contrast to Drosophila, causes early-stage beetle larvae to undergo precocious metamorphosis. This is evident as TcMet-deficient larvae pupate prematurely or develop specific heterochronic phenotypes such as pupal-like cuticular structures, appendages, and compound eyes. Our results demonstrate that TcMet functions in JH response and provide the critical evidence that the putative JH receptor Met mediates the antimetamorphic effect of JH.

Molecular cloning and tissue-specific transcriptional regulation of the first peroxidase family member, Udp1, in stinging nettle (Urtica dioica)

A full-length cDNA clone, designated Udp1, was isolated from Urtica dioica (stinging nettle), using a polymerase chain reaction based strategy. The putative Udp1 protein is characterized by a cleavable N-terminal signal sequence, likely responsible for the rough endoplasmic reticulum entry and a 310 amino acids mature protein, containing all the important residues, which are evolutionary conserved among different members of the plant peroxidase family. A unique structural feature of the Udp1 peroxidase is defined into the short carboxyl-terminal extension, which could be associated with the vacuolar targeting process. Udp1 peroxidase is differentially regulated at the transcriptional level and is specifically expressed in the roots. Interestingly, wounding and ultraviolet radiation stress cause an ectopic induction of the Udp1 gene expression in the aerial parts of the plant. A genomic DNA fragment encoding the Udp1 peroxidase was also cloned and fully sequenced, revealing a structural organization of three exons and two introns. The phylogenetic relationships of the Udp1 protein to the Arabidopsis thaliana peroxidase family members were also examined and, in combination with the homology modelling approach, dictated the presence of distinct structural elements, which could be specifically involved in the determination of substrate recognition and subcellular localization of the Udp1 peroxidase.

Cc RNase: the Ceratitis capitata ortholog of a novel highly conserved protein family in metazoans

Complementary DNA encoding a protein, designated Cc RNase, was isolated from the insect Ceratitis capitata. Deduced amino acid sequence analysis demonstrates that the Cc RNase has strong sequence homology with other uncharacterized proteins predicted from EST sequences belonging to different animal species, therefore defining a new protein family, which is conserved from Caenorhabditis elegans to humans. Phylogenetic analysis data in addition to extensive homolog searches in all available complete genomes suggested that all family members are true orthologs. Proteins belonging to this family are composed of 95-101 amino acids. The C.capitata orthologous protein was expressed in Escherichia coli. Despite the fact that the amino acid sequence of Cc RNase does not share any significant similarities with other known ribonucleases, our data give strong evidence in support of the assignment of enzymatic activity to the recombinant protein. The expressed molecule exhibits ribonucleolytic activity against poly(C) and poly(U) synthetic substrates, as well as rRNA. It is also demonstrated that expression of Cc RNase in E.coli inhibits growth of the host cells.

A novel putative insect chitinase with multiple catalytic domains: hormonal regulation during metamorphosis

We have used differential display to identify genes that are regulated by juvenile hormone in the epidermis of the beetle Tenebrio molitor. One of the genes encodes T. molitor chitinase 5 (TmChit5), a chitinase possessing an unusual structure. Sequence analysis of TmChit5 identified five 'chitinase units' of approx. 480 amino acids with similarity to chitinase family 18. These units are separated by less conserved regions containing putative PEST (rich in proline, glutamic acid, serine and threonine) sequences, putative chitin-binding domains and mucin domains. Northern-blot analysis identified a single transcript of approx. 9 kb, whose abundance correlated with that of 20-hydroxyecdysone during metamorphosis. Injection of pupae with 20-hydroxyecdysone alone, or in combination with cycloheximide, indicated that TmChit5 expression is directly induced by the hormone. Further experiments indicated that methoprene (a juvenile hormone analogue) indirectly induced TmChit5 mRNA expression. On the basis of the present results and previous studies, we propose a molecular mechanism for cuticle digestion during the moulting process.

Hormone-dependent protein patterns in integument and cuticular pigmentation in Apis mellifera during pharate adult development

The epidermal proteins from staged Apis mellifera pupae and pharate adults and the progress of cuticular pigmentation until adult eclosion were used as parameters to study integument differentiation under hormonal treatment. Groups of bees were treated at the beginning of the pupal stage with the juvenile hormone analog pyriproxyfen (PPN) or as pharate adults with 20-hydroxyecdysone (20E). Another group was treated with both hormones applied successively at these same developmental periods. Controls were maintained without treatment. The epidermal proteins, separated by SDS-PAGE and identified by silver staining, were studied at seven intervals during the pupal and pharate adult stages. The initiation and progress of cuticular pigmentation was also monitored and compared to controls. The results showed that PPN reduced the interval of expression of some epidermal proteins, whereas 20E had an antagonistic effect, promoting a prolongation in the time of expression of the same proteins. In PPN-treated bees, cuticular pigmentation started precociously, whereas in 20E-treated individuals this developmental event was postponed. The double hormonal treatment restored the normal progress of cuticular pigmentation and, to a large extent, the temporal epidermal protein pattern. These results are discussed in relation to the 20E titer modulation and morphogenetic hormone interaction.

Expression and function of the Drosophila melanogaster ADH in male Ceratitis capitata adults: a potential strategy for medfly genetic sexing based on gene-transfer technology

The aim of development of a Mediterranean fruit fly Ceratitis capitata genetic sexing strain derives from the large scale SIT programmes being carried out to control this pest. Toward this direction, we present here the male-specific expression of the Drosophila melanogaster alcohol dehydrogenase (ADH) in medfly transgenic adults generated by Minos-mediated germ line transformation. This expression pattern is obtained by using a promoter fragment of the male-specific gene MSSP-alpha2 of the medfly. We show that the heterologous enzyme is functional in the medfly oxidizing both ethanol and 2-propanol. Although leading to an approximately twofold increase of total ADH activity in male compared to female transgenic adults, these expression levels are not enough for performing genetic sexing when high doses of environmental alcohol are applied. This could be achieved either by further enhancement of the transgene expression or by generating an Adh- line to host the Minos insertions.

Organization, evolution and expression of a multigene family encoding putative members of the odourant binding protein family in the medfly Ceratitis capitata

A multigene family encoding male specific serum polypeptides (MSSPs) that show significant structural similarity to the family of insect odourant binding proteins, has been characterized in the medfly Ceratitis capitata. This family comprises seven members classified in three subgroups, MSSP-alpha, MSSP-beta and MSSP-gamma. The genes of subgroups alpha and beta are clustered in tandem in a 35-kb genomic region, and present an exceptionally high degree of similarity not only in their coding but also in the surrounding regions, while the genes of the gamma subgroup are drastically divergent. Although MSSPs are predominantly expressed in the male fat body, detailed expression studies suggest that individual members of this family are expressed in a distinct sex- and tissue-specific manner.

DEC: a new miniature inverted-repeat transposable element from the genome of the beetle Tenebrio molitor

In this paper we describe a novel family of miniature inverted-repeat transposable elements (MITEs), named DEC, isolated from the genome of the beetle Tenebrio molitor. These elements are highly reiterated and their number is estimated to be around 3500 per haploid genome. Two of them have been isolated and the two sequences are 84% identical. Like other MITEs, they are characterized by their small size, their A + T richness, the presence of terminal inverted repeats and the absence of open reading frames. These data suggest that MITEs are probably widely distributed in arthropods.

Cloning and characterization of new orphan nuclear receptors and their developmental profiles during Tenebrio metamorphosis

Five PCR fragments corresponding to a part of the DNA-binding domain of different hormone nuclear receptors were isolated from Tenebrio molitor mRNAs. The sequence identity of three of them with known Drosophila nuclear receptors strongly suggests that they are the Tenebrio orthologs of seven-up, DHR3 and beta-FTZ-F1, and thus named Tmsvp, TmHR3 and TmFTZ-F1. The full-length sequences of the other two were established. TmHR78 is either a new receptor of the DHR78 family or the same gene which has evolved rapidly, particularly in the E domain. TmGRF belongs to the GCNF1 family and its in vitro translated product binds to the extended half site TCAAGGTCA with high affinity. The periods of expression of the corresponding transcripts in epidermal cells during Tenebrio metamorphosis were analyzed as a function of 20-hydroxyecdysone titers measured in the hemolymph of the animals taken for RNA extraction. Comparison of the expression profiles of these nuclear receptors with those observed during Drosophila metamorphosis revealed similar temporal correlations as a function of ecdysteroid variations, which further supported the sequence identity data for TmSVP, TmHR3, TmFTZ-F1 and TmHR78.

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.

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 two new cuticular genes specifically expressed during the post-ecdysial molting period in Tenebrio molitor

In a previous study, we have isolated a cDNA, TM-ACP17, coding for a post-ecdysial adult protein of Tenebrio molitor. After screening of a genomic library with TM-ACP17, we report isolation and sequencing of TM-ACP17 gene and a new gene, TM-LPCP29, coding for a larval-pupal protein. These two genes exhibit a common sequence of 15 nucleotides and a characteristic of most cuticular protein genes so far described: an intron interrupting the signal peptide. The deduced aa sequence of TM-LPCP29 exhibits a high percentage of Ala (26.5%) and Val (17.5%) and is highly hydrophobic. In the N-terminal part, the motif VAAPV is repeated ten times. Numerous histidine residues are present in the C- and N-terminal regions. A comparison is made with other cuticle protein sequences. Northern hybridization analysis showed that TM-LPCP29 is present during larval and mainly pupal post-ecdysial cuticle secretion. In-situ hybridization revealed that TM-LPCP29 mRNA is expressed in epidermis and not in muscles or fat body.

Structure and spatial expression of the Manduca sexta MSCP14.6 cuticle gene

The genomic and cDNA sequences of the MSCP14.6 gene section, which encodes a Manduca sexta cuticle protein, have been determined. The genomic sequence presented here includes 1428 N of 5' flanking DNA, 1587 N of transcribed DNA, and 465 N of 3' flanking DNA. The intron/exon boundaries mapped by comparison of these sequences were confirmed by primer extension and SI nuclease mapping. Prior work showed that the RNA produced by this gene is regulated both temporally and spatially during larval, pupal, and adult development, and also showed that both 20-hydroxyecdysone (20E) and juvenile hormone (JH) are important in controlling the amount of RNA present in the epidermis (Riddiford et al., 1986). In situ hybridizations show that MSCP14.6 is expressed throughout the epidermis in larvae and is spatially restricted in pharate pupal and pharate adult stages. The results presented here delimiting the transcription unit and 5' flanking DNA of the MSCP14.6 gene will facilitate further research to determine the DNA elements necessary for regulation of gene expression.

Up-regulation of an adult cuticular gene by 20-hydroxyecdysone in insect metamorphosing epidermis cultured in vitro

Pupal forewing epidermis of the Coleoptera, Tenebrio molitor, was used to develop an in vitro system to study the hormonal control of metamorphosis at the cellular and molecular levels. Exposure to 1 microM 20-hydroxyecdysone for 48 h caused the formation of a typical adult cuticle. Under these conditions the expression of ACP-20, an adult-specific cuticular gene, was fivefold higher than in absence of exogenous hormone. This stimulation was also observed when a higher level of 20-hydroxyecdysone was maintained, and prevented by protein inhibitors, indicating that 20-hydroxyecdysone does not act directly on this gene. Exposure to 20-hydroxyecdysone followed by exposure in hormone-free medium caused the cessation of this stimulation, showing the requirement of the 20-hydroxyecdysone continuous presence for stimulating ACP-20 gene expression. Thus, unlike the other cuticular protein genes so far studied, its expression is not repressed by 20-hydroxyecdysone, and does not need the decline in ecdysteroids titer.

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.

Ecdysteroid-dependent protein synthesis in caste-specific development of the larval honey bee ovary

In the honey bee, Apis mellifera, the fifth larval instar is a critical period for caste differentiation. During this premetamorphic phase the hormonal milieu shows pronounced caste differences and several organs, particularly the ovaries, enter different developmental pathways leading to highly fertile queens and nearly sterile workers. Developmental profiles of total protein synthesis in larval ovaries showed marked caste differences starting with the early fifth instar. By two-dimensional electrophoresis, caste-specific patterns could be detected in the synthesis of a 29 kDa/pI 4.6 and two 24 kDa/pI 5.2-5.5. proteins (pI=isoelectric point). A marked decrease in the expression of these proteins was found to coincide with caste-specific differences in the haemolymph ecdysteroid titer. In vitro exposure of larval worker ovaries to physiological (10^-7 M) concentrations of synthetic makisterone A elicited an identical response. Juvenile hormone did not affect protein synthesis patterns in larval ovaries, and also did not inhibit or reverse the ecdysteroid-induced effects. Heat shock experiments revealed that the 29 kDa/pI 4.6 ecdysteroid-regulated protein belongs to the class of small heat shock proteins.

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.

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.

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.

cDNA cloning and deduced amino acid sequence of a major, glycine-rich cuticular protein from the coleopteran Tenebrio molitor. Temporal and spatial distribution of the transcript during metamorphosis

In Coleoptera, the elytra (forewings), with a very hard and thick cuticle, protect the membranous and delicate hindwings against mechanical stress. We have isolated and characterized a cDNA encoding a major cuticle protein in Tenebrio molitor, named ACP-20. The deduced amino acid sequence is roughly tripartite, with two terminal glycine-rich domains and a central region showing pronounced similarities with some other hard cuticle proteins. Northern blot and in situ hybridization analyses reveal that ACP-20 gene expression is developmentally regulated since transcript accumulation occurs only in epidermal regions synthesizing hard cuticle and is restricted to the period of preecdysial adult cuticle deposition. Moreover, application of a juvenile hormone analogue prevents the appearance of the transcript, indicating that juvenile hormone, a key molecule involved in the control of insect metamorphosis, negatively regulates the expression of the ACP-20 gene.