Pupal and larval cuticle proteins of Drosophila melanogaster

Smoothened antagonist sonidegib affects the development of D. melanogaster larvae via suppression of epidermis formation

Hedgehog (Hh) signaling is essential for the regulation of embryonic growth and development, the maintenance of stem cell autostasis, and tissue formation, whether in vertebrates or invertebrates. However, exploration into the Hh pathway antagonists in Drosophila or other pests of agricultural importance has been scant. In order to gain a better understanding of the potential utility of the antagonists in insect investigations, a conventional Hh antagonist, sonidegib, was used to evaluate the effects on the development of Drosophila larvae. The results showed that early instar larvae exposed to sonidegib exhibited new epidermal abnormalities and decreased motility after molting. Transcriptome analysis revealed that Sonidegib had a profound effect on chitin-based cuticle development throughout all stages of larvae. Physiological experiments revealed that sonidegib suppressed the epidermis formation and decreased the chitin content. The results of this study shed new light on the potential use of Hh antagonists in agricultural pest management.

Cuticle protein gene LmCP8 is involved in the structural development of the ovipositor in the migratory locust Locusta migratoria

The ovipositor comprises the external genitalia of female insects, which plays an important role in the mating and ovipositing process of insects. However, it remains rudimentary of regional gene expression and physiological function in the ovipositor during structural development. Here, we analysed the basic structure and characteristics of the ovipositor in the migratory locust Locusta migratoria. RNA-seq analysis revealed the specialization of chitin metabolism, lipids synthesis and transport, tanning and cuticular protein genes in the ovipositor. Among them, two cuticle protein genes, LmCP8 and LmACP79, were identified, which are specifically expressed in the ovipositor. Functional analysis based on RNA interference showed that deficiency of LmCP8 affected the structural development of the ovipositor resulting in the retention of a large number of remaining unproduced oocysts in the ovary of the locusts. Our results provide a fundamental resource to investigate the structural development and physiological function of the ovipositor in L. migratoria.

Near infrared spectroscopy (NIRS) coupled with chemometric methods to identify and estimate taxonomic relationships of flies with forensic potential (Diptera: Calliphoridae and Sarcophagidae)

Infrared spectroscopy has been gaining prominence in entomology, such as for solving taxonomic problems, sexing adult specimens, determining the age of immature specimens, detecting drugs of abuse in fly larvae, and can be an important technique in Forensic Entomology. In order to help identify the species of Calliphoridae and Sarcophagidae families, the present study aimed to evaluate the use of near infrared spectroscopy (NIRS) coupled with chemometric methods for separating fly specimens into taxonomic categories and understanding the taxonomic relationship between them. Spectra collected from nine species of flies were subjected to unsupervised principal component analysis (PCA) and hierarchical cluster analysis (HCA), in which we sought to visualize the relationship between the samples (segregation of genera and families) with subsequent identification. In PCA, the best model was achieved using five principal components (PCs), which explained 99.16% of total variance of the original data set. The first principal component (PC1) and the fourth principal component (PC4) provided the best segregation, the latter being more important in the segregation of the species Chrysomya albiceps, Lucilia eximia, and Ravinia belforti from the others. In the HCA dendrogram, there was a clear separation between the specimens by family (Calliphoridae and Sarcophagidae) and genera (Chrysomya, Lucilia, Oxysarcodexia, Peckia and Ravinia). This study shows that NIRS is efficient to identify flies' taxonomic properties, such as family and genera, providing quick evidence for the tested species identity.

The wing-specific cuticular protein LmACP7 is essential for normal wing morphogenesis in the migratory locust

Wings are an indispensable structure in many insects for their foraging, courtship, escape from predators, and migration. Cuticular proteins are major components of the insect cuticle and wings, but there is limited information on how cuticular proteins may play an essential role in wing morphogenesis. We identified a wing-specific cuticular protein, LmACP7, which belongs to the RR-2 subfamily of CPR chitin-binding proteins in the migratory locust. LmACP7 was initially produced in epidermal cells and subsequently migrated to the exocuticle at the pre-ecdysial stage in adult wings. Depletion of LmACP7 transcripts by RNA interference markedly reduced its protein amounts, which consequently led to abnormal wing morphogenesis. The deformed wings were curved, wrinkled, and failed to fully expand. We further demonstrated that the deformation was caused by both severe damage of the endocuticle and death of the epidermal cells in the wings. Based on these data, we propose that LmACP7 not only serves as an essential structural protein in the wing but is also required for the integrity of wing epithelial cells. LmACP7 contributes to production of the wing endocuticle and to the morphogenesis of functional wings in the migratory locust.

Evolutionarily conserved, multitasking TRP channels: lessons from worms and flies

The Transient Receptor Potential (TRP) channel family is comprised of a large group of cation-permeable channels, which display an extraordinary diversity of roles in sensory signaling. TRPs allow animals to detect chemicals, mechanical force, light, and changes in temperature. Consequently, these channels control a plethora of animal behaviors. Moreover, their functions are not limited to the classical senses, as they are cellular sensors, which are critical for ionic homeostasis and metabolism. Two genetically tractable invertebrate model organisms, Caenorhabditis elegans and Drosophila melanogaster, have led the way in revealing a wide array of sensory roles and behaviors that depend on TRP channels. Two overriding themes have emerged from these studies. First, TRPs are multitasking proteins, and second, many functions and modes of activation of these channels are evolutionarily conserved, including some that were formerly thought to be unique to invertebrates, such as phototransduction. Thus, worms and flies offer the potential to decipher roles for mammalian TRPs, which would otherwise not be suspected.

Genomic and proteomic studies on the effects of the insect growth regulator diflubenzuron in the model beetle species Tribolium castaneum

Several benzoylphenyl urea-derived insecticides such as diflubenzuron (DFB, Dimilin) are in wide use to control various insect pests. Although this class of compounds is known to disrupt molting and to affect chitin content, their precise mode of action is still not understood. To gain a broader insight into the mechanism underlying the insecticidal effects of benzoylphenyl urea compounds, we conducted a comprehensive study with the model beetle species and stored product pest Tribolium castaneum (red flour beetle) utilizing genomic and proteomic approaches. DFB was added to a wheat flour-based diet at various concentrations and fed to larvae and adults. We observed abortive molting, hatching defects and reduced chitin amounts in the larval cuticle, the peritrophic matrix and eggs. Electron microscopic examination of the larval cuticle revealed major structural changes and a loss of lamellate structure of the procuticle. We used a genomic tiling array for determining relative expression levels of about 11,000 genes predicted by the GLEAN algorithm. About 6% of all predicted genes were more than 2-fold up- or down-regulated in response to DFB treatment. Genes encoding enzymes involved in chitin metabolism were unexpectedly unaffected, but many genes encoding cuticle proteins were affected. In addition, several genes presumably involved in detoxification pathways were up-regulated. Comparative 2D gel electrophoresis of proteins extracted from the midgut revealed 388 protein spots, of which 7% were significantly affected in their levels by DFB treatment as determined by laser densitometry. Mass spectrometric identification revealed that UDP-N-acetylglucosamine pyrophosphorylase and glutathione synthetase were up-regulated. In summary, the red flour beetle turned out to be a good model organism for investigating the global effects of bioactive materials such as insect growth regulators and other insecticides. The results of this study recapitulate all of the different DFB-induced symptoms in a single model insect, which have been previously found in several different insect species, and further illustrate that DFB treatment causes a wide range of effects at the molecular level.

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.

Amino acid sequence studies on endocuticular proteins from the desert locust, Schistocerca gregaria

Seven proteins from the abdominal cuticle of sexually mature locusts, Schistocerca gregaria, have been extracted, purified and sequenced. None of the proteins have been obtained from the pharate adult cuticle of the same species, and they probably represent post-ecdysially deposited endocuticular proteins. All the proteins contain the Rebers-Riddiford consensus sequence commonly found in cuticular proteins. The proteins are all N-terminally blocked by a pyroglutamine residue, and most of them contain one or more N-acetylhexosamine residues, presumably N-acetylgalactosamine (GalNAc), O-linked to either threonine or serine residues. One of the proteins is C-terminally blocked by an amide group. The unglycosylated forms of the proteins have molecular masses in the range from 9 to 20 kDa. The structures of the endocuticular proteins are discussed in relation to the special mechanical properties of locust abdominal cuticle.

Catecholamine-containing proteins from the pharate pupal cuticle of the tobacco hornworm, Manduca sexta

Three catecholamine-containing proteins from tanning, pharate pupal, abdominal cuticle of the tobacco hornworm, Manduca sexta, have been purified to apparent homogeneity and characterized. These proteins have apparent molecular masses of 32, 41 and 48 kDa and were shown by liquid chromatography-electrochemical analysis, after heating in 1 M acetic acid at 110 degrees C, to release nu-beta-alanylnorepinephrine (NBANE). NBANE is a hydrolysis product of N-beta-alanyldopamine (NBAD) that is bonded covalently at the beta-side-chain carbon to amino acid residues of cuticular proteins. Amino acid compositional analysis revealed that MS-PCP32 (32 KDa) has a high content of alanine (25.6%), valine (13.1%), proline (10.8%) and glycine (10%), a low level of phenylalanine, and no detectable tyrosine or methionine. In contrast, MS-PCP41 (41 kDa) had a much higher content of glycine (31.2%) and substantial levels of serine (9.2%), proline (10.2%) and glutamate/glutamine (10.6%), whereas tyrosine and phenylalanine were not detected. Two of the three purified proteins showed apparent similarities to each other in nu-terminal amino acid sequences, and to several other known insect cuticular proteins. Proteins MS-PCP41 and MS-PCP48 had the characteristic GGX triplet repeat, which is found in a variety of cuticular proteins and may be important for protein folding appropriate for cuticular functions. Therefore, a diversity of cuticular proteins with different amino acid sequences and properties apparently are secreted into the presumptive pupal exocuticle. These then can form adducts and possible cross-links with NBAD through its quinonoid intermediates during cuticular sclerotization.

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.

Characterization of two high molecular weight catechol-containing glycoproteins from pharate pupal cuticle of the tobacco hornworm, Manduca sexta

Two high molecular weight cuticular proteins (MSCP120 and MSCP246) were extracted in acidic guanidine hydrochloride solution from tanning abdominal cuticle of Manduca sexta pharate pupae and purified by size exclusion high performance liquid chromatography. The apparent molecular weights were ca. 120 and 246 kDa as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Both proteins contained high levels of glutamate/glutamine, glycine, serine, alanine and aspartate/asparagine. MSCP120 was enriched in histidine relative to MSCP246, but the reverse was true for valine and proline. Small quantities of beta-alanine and 3,4-dihydroxyphenylalanine (DOPA), as well as other catechols and carbohydrates, also were detected in the hydrolysates. The proteins became radiolabeled when [1-14C]-beta-alanine was injected into pharate pupae, presumably by the formation of adducts with N-beta-alanyldopamine metabolites during sclerotization. Mild acid hydrolysis released N-beta-alanylnorepinephrine and 3,4-dihydroxyphenylketoethanol from both proteins. Strong acid hydrolysis yielded predominantly 3,4-dihydroxyphenylketoethylamine (arterenone), but also DOPA and dopamine. The N-terminal amino acid sequences of the two cuticular proteins were dissimilar, and that of MSCP246 was more hydrophobic than MSCP120. Both of these proteins were glycosylated with glucose, N-acetylglucosamine and traces of N-acetylgalactosamine, and MSCP246 also contained galactose. These structural glycoproteins, which occur in cuticle undergoing sclerotization, apparently react post-translationally with quinonoid tanning agents to yield catecholamine-protein adducts. Small amounts of peptidyl DOPA probably are formed by hydroxylation of tyrosyl residues. Results from this study are consistent with the hypothesis that these catechol-containing glycoproteins participate in cross-linking reactions in M. sexta pupal cuticle during sclerotization.

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.

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

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

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

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

Gene expression patterns in the black blowfly (Phormia regina) as revealed by two-dimensional electrophoresis of proteins. I. Developmental stage-specific and sex-specific differences

The black blowfly, Phormia regina, has been implicated in human myiasis and as a contact vector of viral and bacterial diseases present in carrion to which female flies are attracted for egg deposition. Inbred strains of P. regina are an excellent model system for studying gene expression in the developmental stages of such holometabolous dipteran parasites. However, information regarding gene and protein expression patterns in P. regina is limited. We used ISO-DALT high-resolution, two-dimensional electrophoresis with silver staining to establish fundamental protein maps for examination of the stage-specific gene expression patterns in the 615 most abundant proteins of the eggs, first- and third-instar larvae, pupae, and male and female adults. We also used a differential extraction technique to identify the major cuticular proteins of the adults. The results show 48 clearly identifiable stage-specific and sex-specific proteins. Thus, approximately 8% of the most abundant proteins exhibit developmental changes. These analyses serve as an initial data base for further studies of ontogenetic regulation, organellar origin, and physiologic function of the stage-specific proteins in the life cycle of these opportunistically parasitic dipterans.

Determination of the covalent structure of an N- and C-terminally blocked glycoprotein from endocuticle of Locusta migratoria. Combined use of plasma desorption mass spectrometry and Edman degradation to study post-translationally modified proteins

The complete structure of protein isolated from endocuticle of sexually mature locusts, Locusta migratoria, has been determined by a combination of automatic Edman degradation and plasma desorption mass spectrometry. The protein is extensively post-translationally modified. The N-terminal is 5-oxoproline (pyroglutamic acid) and the C-terminal proline residue is amidated. Furthermore, the protein is glycosylated by a single N-acetyl-galactosamine residue at one, two or three threonines. The N-terminal sequence was obtained by analysing the N-acetylated N,O-permethylated derivative using plasma desorption mass spectrometry. The position and type of carbohydrate were determined by combining an HPLC-based carbohydrate analysis with the peak pattern of the phenylthiohydantoin derivative in automatic sequencing and with mass information on peptides. The protein has pronounced similarity to cuticular proteins from larvae of diptera and lepidoptera, but only slight resemblance to the previously sequenced locust exocuticular proteins. This indicates a similarity between soft larval cuticles and locust endocuticle, a similarity which may extend to their mechanical properties.

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.

Structure of O-glycosidically linked oligosaccharides synthesized by the insect cell line Sf9

The O-glycosidically linked oligosaccharides on the pseudorabies virus (PRV) glycoprotein gp50 synthesized by three different cell lines were studied. The intact membrane protein (gp50) was expressed in Vero cells and in the insect cell line Sf9. In addition, a truncated, secreted form lacking the transmembrane and cytoplasmic domains (gp50T), was expressed in CHO and Sf9 cells. The protein, both in intact and truncated form, synthesized by the two mammalian cells contained only the disaccharide Gal beta 1-3GalNAc, either unsubstituted or substituted with one or two sialic acid residues. By contrast, the major O-linked structure on gp50 and gp50T synthesized by Sf9 cells was the monosaccharide GalNAc. The Sf9 cells also linked lower amounts of Gal beta 1-3GalNAc to gp50 (12%) and gp50T (26%). None of the structures synthesized by Sf9 cells contained sialic acid. Measurements of the two relevant glycosyltransferases revealed that while all three cell lines contain comparable levels of UDP-GalNAc:polypeptide, N-acetylgalactosaminyltransferase activity, there is a greater variation in the levels of UDP-Gal:N-acetylgalactosamine, beta 1-3 galactosyltransferase, with the Sf9 cells containing the lowest level.

In vivo biosynthesis of a stage-specific cuticle glycoprotein during early metamorphosis of the medfly Ceratitis capitata

Cuticle proteins of an insect pest, the Medfly Ceratitis capitata, were resolved in polyacrylamide gels and partially characterized. The pupal cuticle was found to be different from cuticles of other insects since more than 80% w/w of the protein is a single mannose-containing polypeptide (PCG-100). The temporally-regulated in vivo biosynthesis and deposition of cuticle proteins was studied by microinjection of [35S]methionine followed by hand dissection of pupal cuticles. The major pupal glycoprotein, PCG-100, is cuticle- and stage-specific and was the earliest to be labeled and deposited. Its synthesis was maximal at around 46 hours after pupariation and then it decreased. The deposited PCG-100 and other minor pupal cuticle proteins become non-extractable at the end of the instar (7 days after pupariation) probably by sclerotization phenomena. These results provide insight into the temporal control of gene expression programs involved in cuticle deposition during medfly metamorphosis.

Evolution of nested genes with special reference to cuticle proteins in Drosophila melanogaster

One of the pupal cuticle protein (PCP) genes has been found within an intron of a Drosophila housekeeping gene (the Gart locus) that encodes three enzymes involved in the purine pathway. This intronic gene has been described as a gene within a gene, and the gene is now called a "nested" gene. Because the intronic PCP gene has sequence similarity with the larval cuticle protein (LCP) gene, it may have been derived from one of the LCP genes or their ancestral gene. We have studied possible phylogenetic relationships among these five genes by comparing nucleotide sequences of four LCP genes with that of the PCP gene. The results obtained suggest that the PCP gene may have originated from an ancestral gene before duplication of the LCP genes occurred. Using the number of synonymous (silent) substitutions, we then estimated the divergence time between the PCP gene and the LCP genes to be about 70 million years (Myr). The divergence time estimated is much larger than that for the sibling species of D. melanogaster (about 2.5 Myr), indicating that the "nested" gene structure can be seen not only in Drosophila melanogaster, but also in other distantly related Drosophila species.

Regulation of larval cuticle protein gene expression in Drosophila melanogaster

Genes that encode 3rd instar larval cuticle proteins (LCP's) of Drosophila melanogaster are located in at least two chromosomal sites. The genes encoding four of the five predominant LCP's are located in a cluster at the chromosomal region 44D. They are organized in pairs that are transcribed divergently, and expressed with different timing during the third larval instar. Towards understanding the basis of gene regulation within the 44D cluster, we have analyzed genetic variants, including the 2-3 variant, which has an insertion of a copia-like transposable element, H.M.S. Beagle, within the 44D cluster. The Beagle element appears to inactivate the LCP-3 gene by inserting into its TATA box, but also may cause the precocious expression of two other LCP genes, LCP-1 and LCP-f2, in the cluster. The long terminal repeat (LTR) of the Beagle element apparently contains a sequence, perhaps an enhancer-like element, which causes altered expression of these genes. We have also investigated the cis-regulatory elements involved in expression of the LCP-2 gene in wild-type larvae. We have identified two upstream regions that may contain separate cis-regulatory elements. The region between -252 bp and -515 bp may be essential for any expression of LCP-2. Additionally, the region between -515 bp and -795 bp appears to be required for the normal level of expression of the LCP-2 gene.

An assembly zone antigen of the insect cuticle

The assembly zone is a morphologically distinct region in the insect integument that lies between the epidermis and its principal secretory product, the lamellate cuticle. Despite its central location in the process of cuticle formation, little is known about its structure or function. Using various antisera we have shown that in Drosophila melanogaster larvae and pupae the assembly zone is antigenically distinct from the overlying lamellate cuticle. This observation suggests that this region does not contain lamellae in the process of assembling but rather is a stable and permeable matrix through which lamellar components travel in the process of cuticle formation. Curiously an antigen present in the assembly zone was also contained in the moulting gel, indicating a heretofore unsuspected chemical relationship between these two materials.

Primary structure of a structural protein from the cuticle of the migratory locust, Locusta migratoria

The complete amino acid sequence of a structural protein isolated from pharate cuticle of the locust Locusta migratoria was determined. The protein has an unusual amino acid composition: 42% of the residues are alanine and only 14 of the 20 common amino acid residues are present. The primary structure consists of regions enriched in particular amino acid residues. The N-terminal region and a region close to the C-terminus are enriched in glycine. The rest of the protein is dominated by alanine, except for two short regions enriched in hydrophilic residues. Almost all the proline residues are situated in the alanine-rich regions in a conserved sequence 'A-A-P-A/V'. An internal duplication has taken place covering most of the protein except for the glycine-rich regions. Owing to the unusual features of the protein a combination of automated Edman degradations and plasma-desorption m.s. was used to determine the complete sequence. The protein does not show sequence homology to other proteins, but proteins divided into regions enriched in the same kind of amino acid residues have been isolated from other insect structures.

Gene within a gene: nested Drosophila genes encode unrelated proteins on opposite DNA strands

A pupal cuticle protein gene has been found within an intron of a Drosophila gene that encodes three purine pathway enzymatic activities. The intronic gene is encoded on the DNA strand opposite the purine pathway gene and is itself interrupted by an intron. Whereas the purine pathway gene is active throughout development, the intronic cuticle protein gene is expressed primarily over a 3 hr period in the abdominal epidermal cells of prepupae that secrete the pupal cuticle. Therefore, a housekeeping gene and a developmentally regulated gene function in a nested arrangement.

Procuticle proteins and chitin-like material in the inner epicuticle of the Drosophila pupal cuticle

The inner (protein) epicuticle of the pupal cuticle of Drosophila is shown to contain at least two hydrophobic proteins (19 and 21 kD) that are also present in the outer procuticle lamellae. An N-acetylglucosamine-containing carbohydrate is also present in the inner epicuticle. This represents the first attempt to characterize the non-lipid components of an insect epicuticle.

The pupal cuticle of Drosophila: differential ultrastructural immunolocalization of cuticle proteins

Precise ultrastructural localization of Drosophila melanogaster pupal cuticle proteins (PCPs) was achieved by the immunogold labeling of frozen thin sections. PCPs were found in lamellate cuticle and intracellular vesicles but, curiously, were absent from the assembly zone of the cuticle. Antibodies that distinguish between the two classes of PCPs--low molecular weight (L-PCPs) and high molecular weight (H-PCPs)--revealed that the morphologically distinct outer lamellae contained L-PCPs and the inner lamellae contained H-PCPs. The sharp boundary between these two antigenic domains coincides with the transition from the outer to the inner lamellae, which in turn is correlated with the cessation of L-PCP synthesis and the initiation of H-PCP synthesis in response to 20-hydroxyecdysone (Doctor, J., D. Fristrom, and J.W. Fristrom, 1985, J. Cell Biol. 101:189-200). Hence, differences in protein composition are associated with differences in lamellar morphology.

The pupal cuticle of Drosophila: biphasic synthesis of pupal cuticle proteins in vivo and in vitro in response to 20-hydroxyecdysone

We investigated the synthesis and localization of Drosophila pupal cuticle proteins by immunochemical techniques using both a complex antiserum and monoclonal antibodies. A set of low molecular weight (15,000-25,000) pupal cuticle proteins are synthesized by the imaginal disk epithelium before pupation. After pupation, synthesis of the low molecular weight proteins ceases and a set of unrelated high molecular weight proteins (40,000-82,000) are synthesized and incorporated into the pupal cuticle. Ultrastructural changes in the cuticle deposited before and after pupation correlate with the switch in cuticle protein synthesis. A similar biphasic accumulation of low and high molecular weight pupal cuticle proteins is also seen in imaginal discs cultured in vitro. The low molecular weight pupal cuticle proteins accumulate in response to a pulse of the insect steroid hormone 20-hydroxyecdysone and begin to appear 6 h after the withdrawal of the hormone from the culture medium. The high molecular weight pupal cuticle proteins accumulate later in culture; a second pulse of hormone appears to be necessary for the accumulation of two of these proteins.