Analysis of the cuticular proteins of Hyalophora cecropia with two dimensional electrophoresis

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.

Immunolocalization of cuticular proteins in Johnston's organ and the corneal lens of Anopheles gambiae

Previous work with EM immunolocalization examined the intracuticular placement of several antibodies directed against cuticular proteins (CPs) in various structures of Anopheles gambiae. Those structures had long stretches of fairly uniform cuticle. We have now used 19 antibodies directed against members of five CP families on two adult structures with considerable complexity, Johnston's organ and the corneal lens of the compound eye. We also localized chitin with colloidal-gold labeled wheat germ agglutinin. Twelve of these antibodies recognized structures in Johnston's organ. Only 6 were detected in the outer pedicel wall, but the internal structures were more complex with distinct distributions of members of the five CP families in six different structures. The corneal lens had four distinct regions of laminar cuticle. Thirteen of the 15 members of the CPR family were detected, none from the other CP families. Specific antibodies were localized to different regions and in different laminae within a region. The specificity of deployment of cuticular proteins revealed in this study is helping to explain why An. gambiae allocates about 2% of its protein coding genes to structural CPs.

Temporal and spatial expression of cuticular proteins of Anopheles gambiae implicated in insecticide resistance or differentiation of M/S incipient species

Background

Published data revealed that two of the 243 structural cuticular proteins of Anopheles gambiae, CPLCG3 and CPLCG4, are implicated in insecticide resistance and a third, CPF3, has far higher transcript levels in M than in S incipient species. We studied the distribution of transcripts for these three genes in the tissues of An. gambiae and the location of the proteins in the cuticle itself to gain information about how these cuticular proteins contribute to their important roles. Our data are consistent with CPLCG3/4 contributing to a thicker cuticle thus slowing penetration of insecticides and CPF3 possibly having a role in the greater desiccation tolerance of the M form.

Methods

Using RT-qPCR, we established the temporal expression of the genes and by in situ hybridization we revealed the main tissues where their mRNAs are found. Electron microscopy immunolocalization, using secondary antibodies labeled with colloidal gold, allowed us to localize these proteins within different regions of the cuticle.

Results

The temporal expression of these genes overlaps, albeit with higher levels of transcripts from CPF3 in pharate adults and both CPLCG3 and CPLCG4 are higher in animals immediately after adult eclosion. The main location of mRNAs for all three genes is in appendages and genitalia. In contrast, the location of their proteins within the cuticle is completely different. CPF3 is found exclusively in exocuticle and CPLCG3/4 is restricted to the endocuticle. The other CPF gene expressed at the same times, CPF4, in addition to appendages, has message in pharate adult sclerites.

Conclusions

The temporal and spatial differences in transcript abundance and protein localization help to account for An. gambiae devoting about 2% of its protein coding genes to structural cuticular proteins. The location of CPLCG3/4 in the endocuticle may contribute to the thickness of the cuticle, one of the recently appreciated components of insecticide resistance, while the location of CPF3 might be related to the greater desiccation resistance of the M form.

Relationship between the successful infection by entomopathogenic nematodes and the host immune response

Reproduction of entomopathogenic nematodes requires that they escape recognition by a host's immune system or that they have mechanisms to escape encapsulation and melanization. We investigated the immune responses of larvae for the greater wax moth (Galleria mellonella), tobacco hornworm (Manduca sexta), Japanese beetle (Popillia japonica), northern masked chafer (Cyclocephala borealis), oriental beetle (Exomala orientalis) and adult house crickets (Acheta domesticus), challenged with infective juveniles from different species and strains of entomopathogenic nematodes. The in vivo immune responses of hosts were correlated with nematode specificity and survival found by infection assays. In P. japonica, 45% of injected infective juveniles from Steinernema glaseri NC strain survived; whereas the hemocytes from the beetle strongly encapsulated and melanized the Heterorhabditis bacteriophora HP88 strain, S. glaseri FL strain, Steinernema scarabaei and Steinernema feltiae. Overall, H. bacteriophora was intensively melanized in resistant insect species (E. orientalis, P. japonica and C. borealis) and had the least ability to escape the host immune response. Steinernema glaseri NC strain suppressed the immune responses in susceptible hosts (M. sexta, E. orientalis and P. japonica), whereas S. glaseri FL strain was less successful. Using an in vitro assay, we found that hemocytes from G. mellonella, P. japonica, M. sexta and A. domestica recognized both nematode species quickly. However, many S. glaseri in M. sexta and H. bacteriophora in G. mellonella escaped from hemocyte encapsulation by 24h. These data indicate that, while host recognition underlies some of the differences between resistant and susceptible host species, escape from encapsulation following recognition can also allow successful infection. Co-injected surface-coat proteins from S. glaseri did not protect H. bacteriophora in M. sexta but did protect H. bacteriophora in E. orientalis larva; therefore, surface coat proteins do not universally convey host susceptibility. Comparisons of surface coat proteins by native and SDS-PAGE demonstrated different protein compositions between H. bacteriophora and S. glaseri and between the two strains of S. glaseri.

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.

Characteristic properties of proteins from pre-ecdysial cuticle of larvae and pupae of the mealworm Tenebrio molitor

Proteins extracted from the cuticle of pharate larvae and pupae of the mealworm Tenebrio molitor are more soluble at low temperatures than at higher temperatures, a behaviour characteristic of hydrophobic proteins. When the temperature of an unfractionated cuticular extract is raised from 4 to 25 degrees C the solution becomes turbid, droplets of a heavy, protein-rich phase are formed, which gradually settles, leaving an upper protein-poor phase, indicating that the aggregation process is a coacervation. The aggregation of the dissolved cuticular proteins is influenced by changes in temperature, pH, and ionic strength. The process has been studied by measuring development of turbidity in unfractionated cuticular extracts and in solutions of three purified proteins from Tenebrio pharate larvae and pupae (TmLPCP-A1a, TmLPCP-E1a, and TmLPCP-G1a), while temperature, pH or ionic strength of the solutions were varied. Protein aggregation was also studied by determination of changes in fluorescence intensity, when the hydrophobicity probe, 8-anilinonaphthalenesulfonic acid (ANS) was added to solutions of the cuticular proteins. Only when the protein solutions had developed a measurable turbidity was an increase in ANS-fluorescence observed, indicating formation of tightly packed clusters of hydrophobic amino acid residues during aggregation. The temperature range for aggregation depends upon protein concentration: the higher the concentration the lower and more narrow is the temperature range within which aggregation occurs. The tendency for the individual cuticular proteins to aggregate is most pronounced near their isoelectric points, and most of the cuticular proteins have alkaline isoelectric points. The influence of salts on the tendency of the proteins to aggregate varies among the proteins and depends upon how close they are to their isoelectric point. A solution containing both protein TmLPCP-A1a and TmLPCP-E1a becomes more turbid and develops a more intense ANS-fluorescence when warmed from 10 to 30 degrees C than corresponding to the sum of measurements performed on separate solutions of the two proteins, indicating that the two proteins interact during aggregation. The Tenebrio larval/pupal cuticular proteins are characterized by an abundance of hydrophobic amino acid residues, and especially their contents of alanine and proline are high. The behaviour of the cuticular proteins in solution resembles that of another hydrophobic protein, tropoelastin, and it seems reasonable to suggest that similar interactions govern the folding and aggregation of the peptide chains in the two types of proteins. The proline and alanine rich chain segments in the pharate cuticular proteins are suggested to form a series of beta-turns and to fold into a relatively open structure at low temperatures, giving water access to the hydrophobic residues and making the proteins water soluble. At increased temperatures the structure of the ordered water layer surrounding the hydrophobic groups breaks down, and the peptide chains tend to collapse into a more closed structure and to interact more tightly with hydrophobic regions in neighbouring molecules. In dilute solutions in the test tube this results in aggregation and precipitation of the proteins; in intact, pharate cuticle at ambient temperatures the proteins will preferably be in an aggregated, easily dissociated state. Accordingly, small changes in intercuticular pH and ionic strength can produce pronounced changes in the mechanical properties of unsclerotized solid cuticle by interference with protein interactions, in agreement with reports that some cuticles undergo plasticization during and/or immediately after ecdysis.

A conserved domain in arthropod cuticular proteins binds chitin

Many insect cuticular proteins include a 35-36 amino acid motif known as the R&R consensus. The extensive conservation of this region led to the suggestion that it functions to bind chitin. Provocatively, it has no sequence similarity to the well-known cysteine-containing chitin-binding domain found in chitinases and some peritrophic membrane proteins. Using fusion proteins expressed in E. coli, we show that an extended form of the R&R consensus from proteins of hard cuticles is necessary and sufficient for chitin binding. Recombinant AGCP2b, a putative cuticular protein from the mosquito Anopheles gambiae, was expressed in E. coli and the purified protein shown to bind to chitin beads. A stretch of 65 amino acids from AGCP2b, including the R&R consensus, conferred chitin binding to glutathione-S-transferase (GST). Directed mutagenesis of some conserved amino acids within this extended R&R consensus from hard cuticle eliminated chitin binding. Thus arthropods have two distinct classes of chitin binding proteins, those with the chitin-binding domain found in lectins, chitinases and peritrophic membranes (cysCBD) and those with the cuticular protein chitin-binding domain (non-cysCBD).

Vector specificity of barley yellow dwarf virus (BYDV) transmission: identification of potential cellular receptors binding BYDV-MAV in the aphid, Sitobion avenae

Two proteins (SaM35 and SaM50) isolated from head tissues of the aphid vector, Sitobion avenae, were identified as potential receptors for barley yellow dwarf virus MAV isolate (Luteoviridae) based on MAV virus overlay assays and immunoblots of urea SDS 2-D gels. An anti-idiotypic antibody (MAV4 anti-ID) that mimics an epitope on MAV virions and competes with MAV in antibody binding assays also bound to SaM50 and SaM35 and to six additional proteins including a GroEL homolog. No MAV-binding proteins were detected from the nonvector aphid, Rhopalosiphum maidis, although MAV4 anti-ID did react with four proteins from R. maidis. It is hypothesized that SaM35 and SaM50 may be MAV receptors involved in MAV transmission based on their high affinity for MAV and their unique association with the vector, S. avenae. The additional aphid proteins binding the MAV4 anti-ID may represent less specific virus-binding proteins facilitating transmission through different aphid tissues.

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.

A family of pupal-specific cuticular protein genes in the mosquito Anopheles gambiae

We have cloned and sequenced members of a cuticular protein multi-gene family from the mosquito Anopheles gambiae. Three genes (agcp2a-c), each approximately 1 kb in length, were found in a 17.4 kb genomic phage clone. Analysis of ten cDNAs revealed that at least four related genes are present. The open reading frame of the genes and cDNAs showed 95% sequence identity. Divergence was observed in the sequence of the 3' ends and the number of copies of two repeated coding sequences. In situ hybridizations with a probe prepared from one of these circular protein genes physically mapped to two loci, 26B on chromosome 2L and 37A on 3R. Transcription of these An. gambiae cuticular protein genes appears to be limited to pharate pupae and the expressed protein(s) is found in early pupae. The deduced amino acid sequence of these proteins contains a hydrophilic region with significant similarity to other cuticular proteins including the pupal-specific cuticular protein, EDG84, of Drosophila melanogaster (Apple and Fristrom).

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.

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.

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.

Characterization of four pupal wing cuticular protein genes of the silkmoth Antheraea polyphemus

Three different clones have been isolated from a genomic library of the silkmoth Antheraea polyphemus by employing a subtractive hybridization technique. The clones with inserts of 13-16 kb of DNA each, code for mRNAs expressed in the wing epidermis during JH induced second pupal cuticle deposition. While two of the clones code for a single mRNA each, the third one codes for two mRNAs. All the four mRNAs code for distinct polypeptides that can be precipitated with antibodies raised against pupal cuticular proteins. These genes are activated at the same period of pupal development and their transcripts follow similar patterns of accumulation. Although these genes are expressed in a tissue and time specific manner attesting to their pupal wing epidermal specificity, three of them are expressed in the adult wing epidermis also, but not at the larval stage. While DNAs from other silkmoths and insects hybridize to these genes, only one of the A. polyphemus genes hybridizes to RNA from second pupal wings of two other silkmoths tested.

Primary structure of a 14 kDa basic structural protein (Lm-76) from the cuticle of the migratory locust, Locusta migratoria

The complete amino acid sequence of a 14 kDa structural protein (LM-76) isolated from pharate cuticle of the locust, Locusta migratoria, was determined by Edman degradation of the intact protein and enzymatically derived peptides. Plasma desorption and electrospray mass spectrometry was used as an integrated part of the structure determination. Protein Lm-76 has characteristics similar to proteins previously isolated from the pharate locust. The amino acid composition shows a high content of alanine (32%) and absence of the amino acids Glu, Cys, Met, Phe and Trp. The sequence has a central hydrophilic region surrounded by two hydrophobic regions with 7 repeats of a (Tyr)-Ala-Ala-Pro-Ala/Val motif. The conservation around the prolyl residues within this sequence motif is demonstrated for the hitherto sequenced presumptive exocuticle proteins from L. migratoria. The N-terminal region of protein Lm-76 is enriched in the amino acids Gly, Leu and Tyr located in the conserved sequence NH2-Gly-Tyr-Leu-Gly-Gly-(Tyr)-.

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.

High resolution two-dimensional mapping of tissue-specific polypeptides in the desert locust, Schistocerca gregaria

High resolution two-dimensional gel electrophoresis (2-DE) using immobilized pH gradients was used to map the tissue-specific polypeptides of the desert locust, Schistocerca gregaria. Highly specific comprehensive 2-DE reference maps ("master gels") were developed for the brain, corpus cardiacum, subesophageal ganglion, and hemolymph. The polypeptides were well resolved within the pH 4-7 range in the first dimension and within the 14-94 kDa molecular mass range in the second dimension.

Hormonal regulation of epidermal metamorphosis in vitro: control of expression of a larval-specific cuticle gene

Fourth (penultimate) instar larval epidermis of the tobacco hornworm, Manduca sexta, was used to develop an in vitro culture system to study the hormonal control of metamorphosis at both the cellular and the molecular level. Immediate exposure to 4 x 10(-6) M 20-hydroxyecdysone (20-HE) for more than 8 hr, followed by hormone-free medium for 24 hr, caused the formation of a new larval cuticle. By contrast, incubation in hormone-free medium for more than 24 hr prior to exposure to 20-HE allowed pupal cuticle synthesis. The cessation of expression of the larval-specific cuticular gene LCP-14 occurred rapidly in response to 20-HE during the larval molt in vitro (half-life: ca. 6 hr), even in the presence of 3 x 10(-8) M JH I. This suppression by 20-HE was prevented by cycloheximide, indicating that 20-HE does not act directly on this gene. Incubation with alpha-amanitin showed that the half-life of LCP-14 was more than 10 hr. Thus, 20-HE must both suppress gene transcription and destabilize the mRNA. LCP-14 mRNA subsequently reappeared 24 hr after exposure to hormone-free medium, indicating that suppression was temporary. By contrast, when JH and its effects were absent after preincubation in hormone-free medium for 48 hr, 20-HE caused permanent suppression of LCP-14 mRNA, since the mRNA did not reappear after removal of 20-HE. Exposure of Day 2 fifth instar larval epidermis to 3 x 10(-7) M 20-HE, which causes pupal commitment in the absence of JH I, also permanently suppressed LCP-14 gene expression.

The urea-soluble low molecular weight cuticle proteins from the different developmental stages of Dacus oleae

The cuticle proteins of the insect Dacus oleae have been isolated by extraction with a solution of 7 M urea. The affinity properties of cuticle proteins, isolated from the third instar larvae (L3DCPs 1-7), to chitin have been studied. Purified cuticle antigens were polymerized by glutaraldehyde and used for raising antibodies. The developmental appearance of the cuticle proteins has been studied by two-dimensional electrophoresis.

A monoclonal antibody against an adult-specific cuticular protein of Tenebrio molitor (Insecta, Coleoptera)

To study the sequential expression of the epidermal program in the mealworm Tenebrio molitor, monoclonal antibodies were prepared against the water-soluble proteins from preecdysial adult cuticle. Among the 16 clones obtained, one of them (named K2F6) recognized a 20-kDa antigen, found only in adult extracts but not in the larval or pupal ones, as revealed by immunoblot analysis. Our results strongly suggest an epidermal origin for this protein. The monoclonal antibody K2F6 fails to react with water-soluble proteins from fat body and hemolymph taken during the deposition of the 20-kDa antigen. Electron microscopic immunogold localization of this antigen showed that it is secreted, just after epicuticle deposition, in the 30 first-deposited preecdysial lamellae of sternal and elytral cuticles only. The sclerotizing process, which modifies the physicochemical properties of these cuticles, does not prevent the immunoreaction. When the expression of the adult program was inhibited by application of a juvenile hormone analog (ZR 515), the water-soluble proteins from different pupal-adult intermediates were never recognized by the monoclonal antibody K2F6 using immunoblot analysis. These results support the conclusion that this 20-kDa antigen is a protein specific for the sclerotized cuticle of the adult stage.

Expression and hormonal control of a new larval cuticular multigene family at the onset of metamorphosis of the tobacco hornworm

The pattern of cuticular protein synthesis by the epidermis of the tobacco hornworm larva changes during the final day of feeding, leading to an alteration in cuticular structure and a stiffening of the cuticle. We have isolated a small multigene family which codes for at least three of the new cuticular proteins made at this time. The five genes which were isolated from this family map to two different genomic regions. Sequencing shows that one of the genes is 1.9 kb and consists of three exons coding for a 12.2-kDa acidic (pI = 5.26) protein that is predominantly hydrophilic. The deduced amino acid sequence shows regions of similarity to proteins from flexible lepidopteran cuticles and from Drosophila larval and pupal cuticles, but not to proteins found in highly sclerotized cuticles. This gene family is first expressed late on the penultimate day (Day 2) of feeding in the final larval instar and ceases expression 2 days later when metamorphosis begins. In situ hybridization shows that this gene family is expressed in all the epidermal cells of Day 3 larvae except the bristle cells and those at the muscle attachment site. Expression can be induced in Day 1 epidermis by exposure to 50 ng/ml 20-hydroxyecdysone in vitro, but only if juvenile hormone is absent. Its developmental expression, tissue specificity, and hormonal regulation strongly suggest that this multigene family is involved in the structural changes that occur in the larval cuticle just prior to the onset of metamorphosis.

Stage and segment specificity of the secretory cell of the dermal glands of the tobacco hornworm, Manduca sexta

The pair of epidermally derived Verson's glands on each segment of the tobacco hornworm, Manduca sexta, secretes at ecdysis proteinaceous products which coat the epicuticle. These proteins are produced by a single secretory cell which displays both stage- and segment-specificity during development. Three major 12-kDa polypeptides are synthesized at the larval molts, while higher molecular weight (14-93 kDa) polypeptides are produced at the pupal molt. In the pupa, but not in the larva, there are three segment-specific protein patterns, each involving both qualitative and quantitative differences: (1) thoracic (T) segments 1 and 2; (2) T3 and abdominal (A) segment 1; (3) A2-A8. Larval-specific proteins were found to be synthesized in low amounts throughout the penultimate fourth instar, with enhanced synthesis occurring during the molt, coincident with the molting surge of ecdysteroids. Synthesis of the major pupal products commenced about the time of wandering, with enhanced synthesis occurring throughout prepupal development, coincident with the prepupal surge in ecdysteroids. The onset of synthesis of the major pupal products differed, both within and between segments. Culture of fifth instar Day 2 glands in vitro showed that this synthesis depended on 20-hydroxyecdysone. The differential regulation within and between segments observed in vivo was also seen in vitro.