A cuticular protein from the moulting stages of an insect

Proteomic analysis of pharate pupal molting fluid from the tobacco hornworm, Manduca sexta

The insect cuticle is a key component of their success, being important for protection, communication, locomotion, and support. Conversely, as an exoskeleton, it also limits the size of the insect and must be periodically molted and a new one synthesized, to permit growth. To achieve this, the insect secretes a solution of chitinases, proteases and other proteins, known collectively as molting fluid, during each molting process to break down and recycle components of the old cuticle. Previous research has focused on the degradative enzymes in molting fluid and offered some characterization of their biochemical properties. However, identification of the specific proteins involved remained to be determined. We have used 2D SDS-PAGE and LC/MS-based proteomic analysis to identify proteins in the molting fluid of the tobacco hornworm, Manduca sexta, undergoing the larval to pupal molt. We categorized these proteins based on their proposed functions including chitin metabolism, proteases, peptidases, and immunity. This analysis complements previous reported work on M. sexta molting fluid and identifies candidate genes for enzymes involved in cuticle remodeling. Proteins classified as having an immune function highlight potential for molting fluid to act as an immune barrier to prevent infections during the cuticle degradation and ecdysis processes. Several proteins known to function in melanin synthesis as an immune response in hemolymph were present in molting fluid. We demonstrated that the bacterium Micrococcus luteus and the entomopathogenic fungus Beauveria bassiana can stimulate activation of phenoloxidase in molting fluid, indicating that the recognition proteins, protease cascade, and prophenoloxidase needed for melanin synthesis are present as a defense against infection during cuticle degradation. This analysis offers insights for proteins that may be important not only for molting in M. sexta but for insects in general.

Toxicogenomic differentiation of functional responses to fipronil and imidacloprid in Daphnia magna

Active substances of pesticides, biocides or pharmaceuticals can induce adverse side effects in the aquatic ecosystem, necessitating environmental hazard and risk assessment prior to substance registration. The freshwater crustacean Daphnia magna is a model organism for acute and chronic toxicity assessment representing aquatic invertebrates. However, standardized tests involving daphnia are restricted to the endpoints immobility and reproduction and thus provide only limited insights into the underlying modes-of-action. Here, we applied transcriptome profiling to a modified D. magna Acute Immobilization test to analyze and compare gene expression profiles induced by the GABA-gated chloride channel blocker fipronil and the nicotinic acetylcholine receptor (nAChR) agonist imidacloprid. Daphnids were expose to two low effect concentrations of each substance followed by RNA sequencing and functional classification of affected gene ontologies and pathways. For both insecticides, we observed a concentration-dependent increase in the number of differentially expressed genes, whose expression changes were highly significantly positively correlated when comparing both test concentrations. These gene expression fingerprints showed virtually no overlap between the test substances and they related well to previous data of diazepam and carbaryl, two substances targeting similar molecular key events. While, based on our results, fipronil predominantly interfered with molecular functions involved in ATPase-coupled transmembrane transport and transcription regulation, imidacloprid primarily affected oxidase and oxidoreductase activity. These findings provide evidence that systems biology approaches can be utilized to identify and differentiate modes-of-action of chemical stressors in D. magna as an invertebrate aquatic non-target organism. The mechanistic knowledge extracted from such data will in future contribute to the development of Adverse Outcome Pathways (AOPs) for read-across and prediction of population effects.

Transcriptome profiling of maternal stress-induced wing dimorphism in pea aphids

Wing dimorphism, that is, wingless and winged forms, can be induced by maternal stress signals and is an adaptive response of aphids to environmental changes. Here, we investigated the ecological and molecular effects of three kinds of stress, namely crowding, predation, and aphid alarm pheromone, on wing dimorphism. These three stressors induced high proportion of up to 60% of winged morphs in offspring. Transcriptome analysis of stress-treated female aphids revealed different changes in maternal gene expression induced by the three stressors. Crowding elicited widespread changes in the expression of genes involved in nutrient accumulation and energy mobilization. Distinct from crowding, predation caused dramatic expression changes in cuticle protein (CP) genes. Twenty-three CP genes that belong to CP RR2 subfamily and are highly expressed in legs and embryos were greatly repressed by the presence of ladybird. By contrast, application of alarm pheromone, E-β-farnesene, caused slight changes in gene expression. The three factors shared a responsive gene, cuticle protein 43. This study reveals the adaptive response of aphids to environmental stresses and provides a rich resource on genome-wide expression genes for exploring molecular mechanisms of ecological adaptation in aphids.

OPEN RESEARCH BADGES

This article has earned an Open Data Badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available at https://doi.org/10.5061/dryad.55b2b15.

The Fukushima nuclear accident and the pale grass blue butterfly: evaluating biological effects of long-term low-dose exposures

Background

On August 9th 2012, we published an original research article in Scientific Reports, concluding that artificial radionuclides released from the Fukushima Dai-ichi Nuclear Power Plant exerted genetically and physiologically adverse effects on the pale grass blue butterfly Zizeeria maha in the Fukushima area. Immediately following publication, many questions and comments were generated from all over the world. Here, we have clarified points made in the original paper and answered questions posed by the readers.

Results

The following points were clarified. (1) There are many advantages to using the pale grass blue butterfly as an indicator species. (2) The forewings of the individuals collected in Fukushima were significantly smaller than in the northern and southern localities. (3) We observed growth retardation in the butterflies from the Fukushima area. (4) The aberrant colour patterns in the butterflies obtained in the Fukushima area were different from the colour patterns induced by temperature and sibling crosses but similar to those induced by external and internal exposures to the artificial radionuclides and by a chemical mutagen, suggesting that genetic mutations caused the aberrations. (5) This species of butterfly has been plentiful in Fukushima area for at least half a century. We here present specimens collected from Fukushima Prefecture before the accident. (6) Mutation accumulation was detected by the increase in the abnormality rates from May 2011 to September 2011. (7) The abnormal traits were heritable. (8) Our sampling localities were not affected by the tsunami. (9) We used a high enough number of samples to obtain statistically significant results. (10) The standard rearing method was followed, producing normal adults in the control groups. (11) The exposure experiments successfully reproduced the results of the field work. This species of butterfly is vulnerable to long-term low-dose internal and external exposures; however, insect cells are known to be resistant to short-term high-dose irradiation. This discrepancy is reconcilable based on the differences in the experimental conditions.

Conclusions

We are just beginning to understand the biological effects of long-term low-dose exposures in animals. Further research is necessary to accurately assess the possible biological effects of the accident.

Characterization of six antibacterial response genes from the European corn borer (Ostrinia nubilalis) larval gut and their expression in response to bacterial challenge

Six cDNAs encoding putative antibacterial response proteins were identified and characterized from the larval gut of the European corn borer (Ostrinia nubilalis). These antibacterial response proteins include four peptidoglycan recognition proteins (PGRPs), one β-1,3-glucanase-1 (βglu-1), and one lysozyme. Tissue-specific expression analysis showed that these genes were highly expressed in the midgut, except for lysozyme. Analysis of expression of these genes in different developmental stage showed that they were expressed in larval stages, but little or no detectable expression was found in egg, pupa and adult. When larvae were challenged with Gram-negative bacteria (Enterobacter aerogenes), the expression of all six genes was up-regulated in the fatbodies. However, when larvae were challenged with Gram-positive bacteria (Micrococcus luteus), only PGRP-C and lysozyme genes were up-regulated. This study provides additional insights into the expression of antibacterial response genes in O. nubilalis larvae and helps us better understand the immune defense response in O. nubilalis.

Effects of microwave radiation and conductive heating on Tribolium castaneum microstructure

Microwave radiation and conductive heating were used to completely kill adult Tribolium castaneum (Coleoptera: Tenebrionidae) in wheat flour to protect the flour during storage without significantly effecting its quality. The microstructure of T. castaneum was analyzed to reveal the mechanisms leading to death under microwave and heat treatments. Microwave radiation and conductive heating had different effects on the microstructure of the cuticle of adult T. castaneum and on the ultrastructure of the cells of the epidermis, fat body, and midgut. Both treatments caused a large cavity to appear in the nucleus and the disappearance of mitochondria and the Golgi apparatus. After microwave treatment, there was little change in the surface microstructure but the epidermis was of uneven thickness and the four outer layers of the cuticle were thinner. Nuclear size was essentially unchanged, but fat body cells were fewer and coalesced together. In contrast, conductive heating led to a disordered arrangement of cells on the surface of T. castaneum and indistinct boundaries between layers of the cuticle. The nuclei were enlarged and the fat body cells noticeably fewer and indistinct with a scattered distribution. Thus, microwave treatment produced less severe effects on the surface microstructure and cellular ultrastructure of T. castaneum than did conductive heating. It is concluded that these cellular and surface changes were responsible for the death of T. castaneum.

Comparison of newly isolated cuticular protein genes from six aphid species

This paper reports on the first aphids' cuticular proteins. One gene (Mpcp1) was obtained by screening a cDNA library of Myzus persicae with antibodies to a lepidopteran cuticle protein. MpCP1 presents a putative signal peptide, a central extended R&R domain, flanked by N- and C-terminal repeats of alanine, tyrosine and proline. The mRNA of Mpcp1 could be detected in a larval and in adult stages. Primers based on Mpcp1 allowed isolating and comparing cuticle protein genes from five aphid species, but not from whitefly or thrips. Comparison revealed a high degree of similarity. Data from this paper suggest that this cuticle protein family is typical and predominant to aphids. The conformation of these cuticle proteins and the significance on particular properties of aphid cuticle is discussed.

Drosophila melanogaster antimicrobial defense

The Drosophila melanogaster host defense is complex but remarkably efficient. It is a multifaceted response to a variety of fungal, bacterial, and parasitic invaders. Current knowledge is discussed on recognition of infectious microorganisms and on the activation of intracellular signaling cascades that concur with the expression of numerous immune-responsive genes, among which, to date, the most prominent appear to encode potent antimicrobial peptides.

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

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

Surface membranes, Golgi complexes, and vacuolar systems

In the absence of fossils, the cells of vertebrates are often described in lieu of a general animal eukaryote model, neglecting work on insects. However, a common ancestor is nearly a billion years in the past, making some vertebrate generalizations inappropriate for insects. For example, insect cells are adept at the cell remodeling needed for molting and metamorphosis, they have plasma membrane reticular systems and vacuolar ferritin, and their Golgi complexes continue to work during mitosis. This review stresses the ways that insect cells differ from those of vertebrates, summarizing the structure of surface membranes and vacuolar systems, especially of the epidermis and fat body, as a prerequisite for the molecular studies needed to understand cell function. The objective is to provide a structural base from which molecular biology can emerge from biochemical description into a useful analysis of function.

Isolation, characterization, and antimicrobial properties of bovine oligosaccharide-binding protein. A microbicidal granule protein of eosinophils and neutrophils

Peptidoglycan recognition proteins (PGRPs) constitute a recently characterized family of pattern-recognition molecules that are conserved from insects to humans and are implicated in mammalian innate immunity. Here we report the isolation, characterization, cDNA cloning, and antimicrobial activities of a bovine PGRP ortholog termed bovine oligosaccharide-binding protein (bOBP). Milligram quantities of bOBP were purified from peripheral leukocytes, thus allowing for the characterization of the disulfide array and for determining the in vitro antimicrobial activities of the native protein. Of the tissues analyzed, bOBP mRNA was detected only in bone marrow where the protein is synthesized as a 190 amino acid precursor. The mature 169 amino acid protein is stored in the cytoplasmic granules of neutrophils and eosinophils but is absent from lymphocytes, monocytes, and platelets. bOBP was microbicidal for Gram-positive and Gram-negative bacteria and yeast at low micromolar concentrations. The finding that bOBP was microbicidal for organisms in which peptidoglycan is absent (Cryptococcus neoformans) or buried (Salmonella typhimurium) indicates that previous conclusions about the specificity of peptidoglycan recognition proteins must be reevaluated and suggests that other envelope components may mediate the antimicrobial action of PGRP family members.

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

BMCP18(2) is one of the major cuticle proteins identified in the larval cuticle of the silkworm, Bombyx mori. A genomic clone coding for BMCP18 was isolated from a B. mori genomic library, and its structure was analyzed. The BMCP18 gene consists of three exons interspersed by two introns. Bm1 element-like sequences were identified around this gene, suggesting possible involvement of this retroposon in the duplication of B. mori cuticle protein genes during evolution. A structural comparison of the BMCP18 gene and related cuticle protein genes of other lepidopteran species (MSCP14.6 and HCCP12) showed that the 5' upstream region of the BMCP18, MSCP14.6, and HCCP12 genes has a 12-bp identical sequence matching the recognition sequence for transcription factors COUP-TF and HNF-4. This implies that molecular mechanisms regulating expression of these cuticle protein genes are also conserved. mRNAs coding for Bmsvp, the B. mori homolog of Drosophila Seven-up, which is known as a homolog of vertebrate COUP-TF, and BmHNF-4, a homolog of vertebrate HNF-4, were detected in the larval epidermis. Bmsvp bound to the 12-bp sequence in vitro, suggesting that Bmsvp regulates the BMCP18 gene expression.

A family of peptidoglycan recognition proteins in the fruit fly Drosophila melanogaster

Peptidoglycans from bacterial cell walls trigger immune responses in insects and mammals. A peptidoglycan recognition protein, PGRP, has been cloned from moths as well as vertebrates and has been shown to participate in peptidoglycan-mediated activation of prophenoloxidase in the silk moth. Here we report that Drosophila expresses 12 PGRP genes, distributed in 8 chromosomal loci on the 3 major chromosomes. By analyzing cDNA clones and genomic databases, we grouped them into two classes: PGRP-SA, SB1, SB2, SC1A, SC1B, SC2, and SD, with short transcripts and short 5'-untranslated regions; and PGRP-LA, LB, LC, LD, and LE, with long transcripts and long 5'-untranslated regions. The predicted structures indicate that the first group encodes extracellular proteins and the second group, intracellular and membrane-spanning proteins. Most PGRP genes are expressed in all postembryonic stages. Peptidoglycan injections strongly induce five of the genes. Transcripts from the different PGRP genes were found in immune competent organs such as fat body, gut, and hemocytes. We demonstrate that at least PGRP-SA and SC1B can bind peptidoglycan, and a function in immunity is likely for this family.

L-Glutamate retrieved with the moulting fluid is processed by a glutamine synthetase in the pupal midgut of Calpodes ethlius

From apolysis until pupal ecdysis, the pharate pupa of the Brazilian Skipper (Calpodes ethlius) lies wrapped in a prepupal shell composed of the larval cuticle and an ecdysial space (ES) filled with enzyme-rich moulting fluid (MF). In the 4h before ecdysis the pharate pupa drinks the moulting fluid through its mouth and anus, and transfers the cuticular degradation products to its midgut (MG). At the same time, extra fluid passes across the body wall of the pharate pupa and flushes out the ES. The MF is recovered at an overall rate of 70µl/h and reabsorbed across the pharate pupal midgut at about 26µl/h. L-Glutamate was found to be the dominant amino acid in the moulting fluid. Total MF glutamate peaked at 850nmol about 8h before pupal ecdysis (P-8), but by ecdysis it had dropped to nearly zero as the MF became diluted with new fluid and was consumed. The drop in glutamate in the ES coincided with a rise in the glutamine content of the fluid in the midgut lumen. The highest rate of glutamine synthesis occurred in midguts isolated from pharate pupae actively drinking MF (P</=-4). The enzyme glutamine synthetase (GS) was found to be active in glutamate metabolism in the pharate pupal midgut. Glutamine synthesis in the midgut was L-glutamate-dependent and inhibited by two selective competitive inhibitors of GS activity, L-methionine sulfoximine (MSO) and glufosinate ammonium (GLA). Injection of GS inhibitors into the prepupal ES greatly reduced the glutamine content of the midgut epithelium by P+24. Although a corresponding increase in midgut glutamate levels was not seen, midgut serine levels in treated animals rose, suggesting that GS inhibitors shunted the MF-derived glutamate along an alternative metabolic pathway. GLA was much more toxic to pupae than MSO. Midgut GS appears to play a central role in the recycling of L-glutamate across the pupal MG epithelium at pupation.

The origin, transport and cleavage of the molt-associated cuticular protein CECP22 from Calpodes ethlius (Lepidoptera, Hesperiidae)

CECP22 (Calpodes ethlius Cuticular Protein 22 kDa) is a molt associated protein found in the cuticle of C. ethlius larvae and pupae. The mRNA for the CECP22 cuticular protein is expressed in the epidermis and fat body during the intermolt. The protein itself accumulates in intermolt hemolymph, but at molting, when the cuticle is being digested, it is also found in the cuticle of surface integument, tracheae, foregut and hindgut and in the molting fluid. CECP22 exists in two forms. The large form (19.17 kDa, pI 6.2) becomes smaller (16.1 kDa, pI 7.4) by cleavage at the proteolytic cleavage site (position 170) with amidation of the C-terminal. The small, more basic peptide, appears only at molting, first in the cuticle and then in the molting fluid. It is presumed to be the active form of an amidase involved in the earliest stages of cuticle degradation. The inactive form accumulates in the hemolymph during the long intermolt and probably represents an abundant source of precursor enzyme that can be provided to all cuticle containing organs for a precise initiation of cuticle degradation.