A water-soluble protein specific to the adult cuticle in Tenebrio

A functional analysis of ACP-20, an adult-specific cuticular protein gene from the beetle Tenebrio: role of an intronic sequence in transcriptional activation during the late metamorphic period

A gene encoding the adult cuticular protein ACP-20 was isolated in Tenebrio. It consists of three exons interspersed by two introns, intron 1 interrupting the signal peptide. To understand the regulatory mechanisms of ACP-20 expression, ACP-20 promoter-luciferase reporter gene constructs were transfected into cultured pharate adult wing epidermis. Transfection assays needed the presence of 20-hydroxyecdysone, confirming that ACP-20 is up-regulated by ecdysteroids. Analysis of 5' deletion constructs revealed that three regions are necessary for high levels of transcription. Interaction experiments between intronic fragments and epidermal nuclear proteins confirmed the importance of intron 1 in ACP-20 transcriptional control, which results from the combined activity of regulatory cis-acting elements of the promoter and those of intron 1.

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.

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.

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.

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.

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.

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.

Temporal synthesis of cuticle proteins during larval development in Glossina morsitans

1. Larval development in Glossina species occurs in utero with the mature third instar larva being deposited after a developmental period of 7 days. 2. In this study, the patterns of cuticular protein synthesis during larval development were analysed by two-dimensional gel electrophoresis. 3. From the results, four types of cuticle proteins were identified: those specific to larval, pupal and adult cuticles, and others common to all the stages. 4. Few cuticular proteins were synthesized between the first and second larval instars. By the third larval instar (two days before larviposition), a large number of proteins (Mr < or = 30 kDa) were induced. These proteins persisted up to the brown pupal stage and showed a rapid decline thereafter. Most of the proteins with molecular weights Mr < or = 30 kDa were undetectable at apolysis (5 days after larviposition). 5. By day 15 of the pupal stage, the number of cuticle proteins was very small. The protein profile during the pupal stages remained relatively constant. This was probably due to the fact that the pupal cuticle does not provide any protection since it is itself enclosed at all times within the protective puparium.

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.

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.

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.