Structure and regulation of insect plasma membrane H(+)V-ATPase

Molecular strategies of the pygmy grasshopper Eucriotettix oculatus adapting to long-term heavy metal pollution

To study the heavy metal accumulation and its impact on insect exterior and chromosome morphology, and reveal the molecular mechanism of insects adapting to long-term heavy metal compound pollution habitats, this study, in the Diaojiang river basin, which has been polluted by heavy metals(HMs) for nearly a thousand years, two Eucriotettix oculatus populations was collected from mining and non-mining areas. It was found that the contents of 7 heavy metals (As, Cd, Pb, Zn, Cu, Sn, Sb) in E. oculatus of the mining area were higher than that in the non-mining 1-11 times. The analysis of morphology shows that the external morphology, the hind wing type and the chromosomal morphology of E. oculatus are significant differences between the two populations. Based on the heavy metal accumulation，morphological change, and stable population density, it is inferred that the mining area population has been affected by heavy metals and has adapted to the environment of heavy metals pollution. Then, by analyzing the transcriptome of the two populations, it was found that the digestion, immunity, excretion, endocrine, nerve, circulation, reproductive and other systems and lysosomes, endoplasmic reticulum and other cell structure-related gene expression were suppressed. This shows that the functions of the above-mentioned related systems of E. oculatus are inhibited by heavy metal stress. However, it has also been found that through the significant up-regulation of genes related to the above system, such as ATP2B, pepsin A, ubiquitin, AQP1, ACOX, ATPeV0A, SEC61A, CANX, ALDH7A1, DLD, aceE, Hsp40, and catalase, etc., and the down-regulation of MAPK signalling pathway genes, can enhanced nutrient absorption, improve energy metabolism, repair damaged cells and degrade abnormal proteins, maintain the stability of cells and systems, and resist heavy metal damage so that E. oculatus can adapt to the environment of heavy metal pollution for a long time.

Proteomic Analysis of the Midgut Contents of Silkworm in the Pupal Stage

The silkworm Bombyx mori, a lepidopteran insect, possesses an 8-10-day pupal stage, during which significant changes occur in the midgut, where it first condenses into the yellow body, and then undergoes decomposition. To gain insights into this transformation process, proteomics was performed on Bombyx mori midgut contents on day 2 and day 7 after pupation. The results revealed the identification of 771 proteins with more than one unique peptide. An analysis using AgriGO demonstrated that these proteins were predominantly associated with catalytic activity. Among the identified proteins, a considerable number were found to be involved in carbohydrate metabolism, amino acid metabolism, lipid metabolism, nucleic acid degradation, and energy support. Additionally, variations in the levels of certain proteases were observed between the midgut contents on day 2 and day 7 after pupation. An in-depth analysis of the two-dimensional electrophoresis of the midgut contents on day 7 after pupation led to the identification of twelve protein spots with potential gelatinolytic activity. Among these, six proteases were identified through mass spectrometry, including the p37k protease, vitellin-degrading protease, chymotrypsin-2, etc. These proteases may be responsible for the digestion of the yellow body during the later stages of pupal development.

Periplocoside P affects synaptic transmission at the neuromuscular junction and reduces synaptic excitability in Drosophila melanogaster by inhibiting V-ATPase

BACKGROUND

Periplocoside P (PSP) is a major component of Periploca sepium Bunge known for its potent insecticidal activity. V-Type adenosine triphosphatase (V-ATPase), which is widely distributed in the cytoplasmic membranes and organelles of eukaryotic cells, plays a crucial role in synaptic excitability conduction. Previous research has shown that PSP targets the apical membrane of goblet cells in the insect midgut. However, the effects of PSP on synaptic transmission at the neuromuscular junction are often overlooked.

RESULTS

The bioassay revealed that Drosophila adults with different genetic backgrounds showed varying levels of susceptibility to PSP in the order: parats1  > parats1 ;DSC1-/-  ≈ w1118  > DSC1-/- . Intracellular electrode recording demonstrated that PSP, similar to bafilomycin A1, had an impact on the amplitude of the excitatory junction potential (EJP) and accelerated excitability decay. Furthermore, the alteration in EJP amplitude is concentration-dependent. Another surprising discovery was that the knockout DSC1 channel showed insensitivity to PSP.

CONCLUSION

Our findings confirm that PSP can influence synaptic transmission at the neuromuscular junction of Drosophila larvae by targeting V-ATPase. These results provide a basis for investigating the mechanism of action of PSP and its potential application in designing novel insecticides. © 2023 Society of Chemical Industry.

Heterologous production of the insecticidal pea seed albumin PA1 protein by Pichia pastoris and protein engineering to potentiate aphicidal activity via fusion to snowdrop lectin Galanthus nivalis agglutinin; GNA)

BACKGROUND

New bioinsecticides with novel modes of action are urgently needed to minimise the environmental and safety hazards associated with the use of synthetic chemical pesticides and to combat growing levels of pesticide resistance. The pea seed albumin PA1b knottin peptide is the only known proteinaceous inhibitor of insect vacuolar adenosine triphosphatase (V-ATPase) rotary proton pumps. Oral toxicity towards insect pests and an absence of activity towards mammals makes Pa1b an attractive candidate for development as a bioinsecticide. The purpose of this study was to investigate if Pichia pastoris could be used to express a functional PA1b peptide and if it's insecticidal activity could be enhanced via engineering to produce a fusion protein comprising the pea albumin protein fused to the mannose-specific snowdrop lectin (Galanthus nivalis agglutinin; GNA).

RESULTS

We report the production of a recombinant full-length pea albumin protein (designated PAF) and a fusion protein (PAF/GNA) comprised of PAF fused to the N-terminus of GNA in the yeast Pichia pastoris. PAF was orally toxic to pea (Acyrthosiphon pisum) and peach potato (Myzus persicae) aphids with respective, Day 5 LC50 values of 54 µM and 105 µM derived from dose-response assays. PAF/GNA was significantly more orally toxic as compared to PAF, with LC50 values tenfold (5 µM) and 3.3-fold (32 µM) lower for pea and peach potato aphids, respectively. By contrast, no phenotypic effects were observed for worker bumble bees (Bombus terristrus) fed PAF, GNA or PAF/GNA in acute toxicity assays. Confocal microscopy of pea aphid guts after pulse-chase feeding fluorescently labelled proteins provides evidence that enhanced efficacy of the fusion protein is attributable to localisation and retention of PAF/GNA to the gut epithelium. In contact assays the fusion protein was also found to be significantly more toxic towards A. pisum as compared to PAF, GNA or a combination of the two proteins.

CONCLUSIONS

Our results suggest that GNA mediated binding to V-type ATPase pumps acts to potentiate the oral and contact aphicidal activity of PAF. This work highlights potential for the future commercial development of plant protein-based bioinsecticides that offer enhanced target specificity as compared to chemical pesticides, and compatibility with integrated pest management strategies.

Structural and Comparative Analyses of Insects Suggest the Presence of an Ultra-Conserved Regulatory Element of the Genes Encoding Vacuolar-Type ATPase Subunits and Assembly Factors

Gene and genome comparison represent an invaluable tool to identify evolutionarily conserved sequences with possible functional significance. In this work, we have analyzed orthologous genes encoding subunits and assembly factors of the V-ATPase complex, an important enzymatic complex of the vacuolar and lysosomal compartments of the eukaryotic cell with storage and recycling functions, respectively, as well as the main pump in the plasma membrane that energizes the epithelial transport in insects. This study involves 70 insect species belonging to eight insect orders. We highlighted the conservation of a short sequence in the genes encoding subunits of the V-ATPase complex and their assembly factors analyzed with respect to their exon-intron organization of those genes. This study offers the possibility to study ultra-conserved regulatory elements under an evolutionary perspective, with the aim of expanding our knowledge on the regulation of complex gene networks at the basis of organellar biogenesis and cellular organization.

Silencing of V-ATPase-E gene causes midgut apoptosis of Diaphorina citri and affects its acquisition of Huanglongbing pathogen

The Asian citrus psyllid, Diaphorina citri Kuwayama, is among the most important pests of citrus. It is the main vector of the Huanglongbing (HLB) pathogen Candidatus Liberibacter asiaticus (CLas), which causes severe losses in citrus crops. Control of D. citri is therefore of paramount importance to reduce the spread of HLB. In this regard, using RNA interference (RNAi) to silence target genes is a useful strategy to control psyllids. In this study, using RNAi, we examined the biological functions of the V-ATPase subunit E (V-ATP-E) gene of D. citri, including its effect on acquisition of CLas. The amino acid sequence of V-ATP-E from D. citri had high homology with proteins from other insects. V-ATP-E was expressed at all D. citri life stages analyzed, and the expression level in mature adults was higher than that of teneral adults. Silencing of V-ATP-E resulted in a significant increase in mortality, reduced body weight, and induced cell apoptosis of the D. citri midgut. The reduced expression of V-ATP-E was indicated to inhibit CLas passing through the midgut and into the hemolymph, leading to a majority of CLas being confined to the midgut. In addition, double-stranded RNA of D. citri V-ATP-E was safe to non-target parasitic wasps. These results suggest that V-ATP-E is an effective RNAi target that can be used in D. citri control to block CLas infection.

Beyond being an energy supplier, ATP synthase is a sculptor of mitochondrial cristae

Mitochondrial F₁F_O-ATP synthase plays a key role in cellular bioenergetics; this enzyme is present in all eukaryotic linages except in amitochondriate organisms. Despite its ancestral origin, traceable to the alpha proteobacterial endosymbiotic event, the actual structural diversity of these complexes, due to large differences in their polypeptide composition, reflects an important evolutionary divergence between eukaryotic lineages. We discuss the effect of these structural differences on the oligomerization of the complex and the shape of mitochondrial cristae.

Vacuolar (H+ )-ATPase subunit c is essential for the survival and systemic RNA interference response in Locusta migratoria

BACKGROUND

Vacuolar (H⁺ )-ATPase (V-ATPase) is a multi-subunit enzyme that hydrolyzes adenosine triphosphate (ATP) to transport protons across a cellular membrane, and it plays an important role in numerous biological processes, including in growth, development and immune responses. The c subunit of V-ATPase is a highly conserved subunit of the rotatory proteolipid ring that is required for binding and transporting protons. To date, there are only a few published reports on V-ATPase-c functions in insects.

RESULTS

We identified and characterized the V-ATPase-c gene in Locusta migratoria, one of the most destructive agricultural insect pests in the world. LmV-ATPase-c was predominately expressed in Malpighian tubules of nymphs, followed by the hindgut and ovary, while the other tissues showed relatively low expression levels. Silencing of LmV-ATPase-c caused severe molting defects in nymphs and a high mortality rate of > 90%. Histological staining and microscopic examination of sections from the abdominal cuticle revealed the absence of newly formed cuticle in nymphs that were injected with dsLmV-ATPase-c. In addition, silencing of LmV-ATPase-c transcript levels significantly impaired RNA interference (RNAi) efficiency of a reporter gene. By quantifying double-stranded RNA (dsRNA) amounts by quantitative polymerase chain reaction (PCR), we found that RNAi against LmV-ATPase-c provoked a dramatic accumulation of dsRNA in the endosomes of epidermal and midgut cells of Locusta migratoria.

CONCLUSION

Our results indicate that LmV-ATPase-c is indispensable for the formation of new cuticle during the molting process and has pivotal functions in dsRNA escape from endosomes. LmV-ATPase-c might be a valuable target for developing new strategies for insect pest management. © 2022 Society of Chemical Industry.

Na+/K+-ATPase Activation by cAMP in the Midgut of Lutzomyia longipalpis (Lutz & Neiva, 1912; Diptera: Psychodidae)

Lutzomyia longipalpis (Lutz & Neiva, 1912) females have been intensively studied regarding the regulation of midgut pH. The mechanisms involved in pH regulation are complex, and some aspects remain to be clarified. Here, we investigated the role of the Na+/K+-ATPase pump as an electrochemical potential generator and its modulation by the second messenger cAMP in the midgut of female L. longipalpis. Our results suggest that not only may Na+/K+-ATPase be the main generator of an electrochemical potential across membranes in the midgut of female L. longipalpis, but also its activity is positively regulated by cAMP. cAMP-mediated Na+/K+-ATPase pump activity might be necessary to maintain the transport of the nutrients produced during blood digestion.

V-ATPase subunit a is required for survival and midgut development of Locusta migratoria

The vacuolar-type H⁺ -ATPase (V-ATPase) is an ATP-dependent proton pump, which regulates various cellular processes. To date, most functional studies on V-ATPases of insects have focused on subunits of the V1 complex, and there is little information on the VO genes. In this study, two cDNA sequences of LmV-ATPase a were identified in Locusta migratoria. RT-qPCR analysis revealed that LmV-ATPase a1 and LmV-ATPase a2 are differentially expressed in various tissues and developmental stages. Injection of dsRNA for the common region of LmV-ATPase a1 and LmV-ATPase a2 into third-instar nymphs resulted in a significant suppression of LmV-ATPase a. The injected nymphs ceased feeding, lost body weight and finally died at a mortality of 98.6%. Furthermore, aberrations of midgut epithelial cells, the accumulation of electron-lucent vesicles in the cytoplasm, and a partially damaged brush border were observed in dsLmV-ATPase a-injected nymphs using transmission electron microscopy. Especially, the mRNA level of wingles, and notch genes were dramatically down-regulated in the dsLmV-ATPase a-injected nymphs. Taken together, our results suggest that LmV-ATPase a is required for survival and midgut development of L. migratoria. Hence, this gene could be a good target for RNAi-based control against locusts.

Genome-wide analysis of V-ATPase genes in Plutella xylostella (L.) and the potential role of PxVHA-G1 in resistance to Bacillus thuringiensis Cry1Ac toxin

The rapid development of insecticide resistance has hampered the use of Bacillus thuringiensis (Bt), a widely used bio-pesticide. Plutella xylostella (L.) is a globally distributed lepidopteran pest of cruciferous vegetables and has developed severe field resistance to the Bt toxin. Vacuolar H⁺-ATPases (VHA) are multi-subunit complexes and participate in multiple physiological processes. However, the characterization and functional studies of VHA genes are lacking in insects. This study performed a genome-wide analysis and identified 35 VHA gene family members divided into 15 subfamilies in P. xylostella. We cloned a V-ATPase subunit G gene, PxVHA-G1, in our previous midgut transcriptome profiles. Quantitative reverse transcriptase-polymerase chain reaction results showed that PxVHA-G1 was upregulated in the Cry1S1000-resistant strain than in the G88-susceptible strain, and its expression profile revealed that the midgut, Malpighian tubules, and larva stages generally showed high expression levels. RNAi-mediated knockdown of the PxVHA-G1 gene increased the susceptibility of P. xylostella (G88 and Cry1S1000) to Cry1Ac toxin. Our study is the first to explore the role of PxVHA-G1 on regulating Cry1Ac toxicity in P. xylostella, thus, providing new insights into the role of VHAs in the development of Cry1Ac resistance and sustainable development of pest management.

Docking-based generation of antibodies mimicking Cry1A/1B protein binding sites as potential insecticidal agents against diamondback moth (Plutella xylostella)

BACKGROUND

Broad use of insecticidal Cry proteins from Bacillus thuringiensis in biopesticides and transgenic crops has resulted in cases of practical field resistance, highlighting the need for novel approaches to insect control. Previously we described an anti-Cry1Ab idiotypic-antibody (B12-scFv) displaying toxicity against rice leafroller (Cnaphalocrocis medinalis) larvae, supporting the potential of antibodies for pest control. The goal of the present study was to generate insecticidal antibodies against diamondback moth (Plutella xylostella) larvae.

RESULTS

Four genetically engineered antibodies (GEAbs) were designed in silico from B12-scFv using three-dimensional (3D) structure and docking predictions to alkaline phosphatase (ALP) as a Cry1Ac receptor in P. xylostella. Among these GEAbs, the GEAb-dV_L antibody consisting of two light chains had overlapping binding sites with Cry1A and Cry1B proteins and displayed high binding affinity to P. xylostella midgut brush border membrane (BBM) proteins. Proteins in BBM identified by pull-down assays as binding to GEAb-dV_L included an ABC transporter and V-ATPase subunit A protein. Despite lacking the α-helical structures in Cry1A that are responsible for pore formation, ingestion of GEAb-dV_L disrupted the P. xylostella larval midgut epithelium and resulted in toxicity. Apoptotic genes were activated in gut cells upon treatment with GEAb-dV_L .

CONCLUSION

This study describes the first insecticidal GEAb targeting P. xylostella by mimicking Cry proteins. Data support that GEAb-dV_L toxicity is associated to activation of intracellular cell death pathways, in contrast to pore-formation associated toxicity of Cry proteins. This work provides a foundation for the design of novel insecticidal antibodies for insect control. © 2021 Society of Chemical Industry.

Identification and Characterization of Aminopeptidase-N as a Binding Protein for Cry3Aa in the Midgut of Monochamus alternatus (Coleoptera: Cerambycidae)

Bacillus thuringiensis Cry proteins have been widely used over the past decades for many different insect pests, which are safe for users and the environment. The coleopteran-specific Cry3Aa toxin from B. thuringiensis exhibits toxicity to the larvae of Monochamus alternatus. Receptors play a key role in the mechanisms underlying the toxic action of Cry. However, the binding receptor for Cry3Aa has yet to be identified in the midgut of M. alternatus larvae. Therefore, the aim of this study was to identify the receptor for Cry3Aa toxin in the brush border membrane vesicles (BBMVs) of M. alternatus larvae. Our results indicate that the Cry3Aa toxin binds to the BBMVs (Kd = 247 nM) of M. alternatus via a 107 kDa aminopeptidase N (APN) (Kd = 57 nM). In silico analysis of the APN protein predicted that an 18 amino acid sequence in the N-terminal acted as a signal peptide, and that the Asn residue, located at position 918 in the C-terminus is an anchored site for glycosyl phosphatidyl inositol. Further analysis showed that M. alternatus APN exhibits 75% homology to the APN from Anoplophora glabripenis. Our work, therefore, confirmed that APN, which is localized in the BBMVs in the midgut of M. alternatus larvae, acts as a binding protein for Cry3Aa toxins.

Steroid hormone 20-hydroxyecdysone induces the transcription and complex assembly of V-ATPases to facilitate autophagy in Bombyx mori

Vacuolar-type H + -adenosine triphosphatases (V-ATPases) are indispensable for lysosome acidification and participate in autophagic processes. The steroid hormone 20-hydroxyecdysone (20E) predominantly induces autophagy and regulates insect larval molting and metamorphosis; however, the specific mechanism of lysosome acidification regulation by 20E remains unclear. Here, we showed that the developmental profiles of Bombyx V-ATPases were in accordance with autophagy occurrence and lysosome acidification in the fat body during larval-pupal metamorphosis. BmV-ATPase-A and BmV-ATPase-B were required for lysosome acidification and autophagic flux. Both 20E treatment and starvation were able to induce lysosome acidification. Furthermore, BmV-ATPase transcription was induced by 20E treatment and reduced by RNAi targeting the 20E receptor BmUsp. On the one hand, 20E upregulated the transcription of BmV-ATPases through inducing Bombyx transcription factor EB (TFEB) and its nuclear translocation; on the other hand, 20E inhibited mTOR signaling to induce the transcription and assembly of BmV-ATPase subunits. Overall, 20E induces lysosome acidification by upregulating the transcription and assembly of V-ATPase subunits via activating BmTFEB and cooperating with nutrient signaling. These findings improve our understanding of the regulatory mechanisms underlying lysosome acidification and autophagic flux in Bombyx mori.

The Inhibitory Effect of Celangulin V on the ATP Hydrolytic Activity of the Complex of V-ATPase Subunits A and B in the Midgut of Mythimna separata

Celangulin V (CV) is a compound isolated from Celastrus angulatus Max that has a toxic activity against agricultural insect pests. CV can bind to subunits a, H, and B of the vacuolar ATPase (V-ATPase) in the midgut epithelial cells of insects. However, the mechanism of action of CV is still unclear. In this study, the soluble complex of the V-ATPase A subunit mutant TSCA which avoids the feedback inhibition by the hydrolysate ADP and V-ATPase B subunit were obtained and then purified using affinity chromatography. The H⁺K⁺-ATPase activity of the complex and the inhibitory activity of CV on ATP hydrolysis were determined. The results suggest that CV inhibits the ATP hydrolysis, resulting in an insecticidal effect. Additionally, the homology modeling of the AB complex and molecular docking results indicate that CV can competitively bind to the AB complex at the ATP binding site, which inhibits ATP hydrolysis. These findings suggest that the AB subunits complex is one of the potential targets for CV and is important for understanding the mechanism of interaction between CV and V-ATPase.

Inhibition of silkworm vacuolar-type ATPase activity by its inhibitor Bafilomycin A1 induces caspase-dependent apoptosis in an embryonic cell line of silkworm

Vacuolar-type ATPase (V-ATPase) is a type of hydrogen ion transporter located in the vesicular membrane-like system, which mediates active transport and intracellular acidification in various compartments. In mammals, V-ATPase has been reported to play a key role in cell proliferation and apoptosis. The studies of V-ATPase in silkworm mainly focus on the acidification regulation of midgut and silk gland and immune resistance. However, there are few reports about the function of silkworm V-ATPase on cell proliferation, autophagy, and apoptosis. Thus, the function of V-ATPase in a cell line of Bombyx mori (BmE) was investigated by treating the cell line with bafilomycin A1, a specific inhibitor of V-ATPase. Cell counting kit 8 (CCK8) and flow cytometry analysis showed that bafilomycin A1 treatment decreased the cell proliferation activity, affected the cell cycle progression and induced cell apoptosis. LysoTracker Red staining showed that the target of bafilomycin A1 is lysosome. The expression of all autophagy-related genes ( BmATG5, BmATG6, and BmATG8) decreased, indicating that cell autophagy was inhibited. The analysis of the apoptosis pathway demonstrated that inhibiting the activity of V-ATPase of BmE cells could promote mitochondria to release cytochrome C, inhibit the expression of BmIAP, and activate the caspase cascade to induce apoptosis. All these findings systematically illustrate the effects of V-ATPase on the proliferation, autophagy, and apoptosis in BmE cells, and provide new ideas and a theoretical basis for further study on the function of V-ATPase in BmE.

RNAi-Mediated Knockdown of vATPase Subunits Affects Survival and Reproduction of Bed Bugs (Hemiptera: Cimicidae)

The common bed bug, Cimex lectularius L. (Hemiptera: Cimicidae) has resurged as one of the most troublesome household pests affecting people across the globe. Bed bug infestations have increased in recent years primarily due to the evolution of insecticide resistance and the insect's ability to hitchhike with travelers. vATPases are one of the most evolutionarily conserved holoenzymes in eukaryotes, which are mainly involved in proton transport across the plasma membranes and intracellular organelles. RNA interference (RNAi) has been developed as a promising tool for insect control. In this study, we used RNAi as an approach to knock down subunits A and E of the vATPase gene of bed bugs. Delivery of 0.2 µg/insect of dsRNA specific to vATPase-A and vATPase-E into female bed bugs dramatically impaired the laying and viability of eggs over time. Injection of the vATPase-E dsRNA decreased survival of the bed bugs over 30 d. Our results also showed that the knockdown of mRNA is highly effective and persistent up to 30 d post injection. This research demonstrated that silencing of the two vATPase subunits A and E offers a potential strategy to suppress bed bug populations.

A Systematic Study of RNAi Effects and dsRNA Stability in Tribolium castaneum and Acyrthosiphon pisum, Following Injection and Ingestion of Analogous dsRNAs

RNA interference (RNAi) effects in insects are highly variable and may be largely dependent upon the stability of introduced double-stranded RNAs to digestion by nucleases. Here, we report a systematic comparison of RNAi effects in susceptible red flour beetle (Tribolium castaneum) and recalcitrant pea aphid (Acyrthosiphon pisum) following delivery of dsRNAs of identical length targeting expression of V-type ATPase subunit E (VTE) and inhibitor of apoptosis (IAP) genes. Injection and ingestion of VTE and IAP dsRNAs resulted in up to 100% mortality of T. castaneum larvae and sustained suppression (>80%) of transcript levels. In A. pisum, injection of VTE but not IAP dsRNA resulted in up to 65% mortality and transient suppression (ca. 40%) of VTE transcript levels. Feeding aphids on VTE dsRNA reduced growth and fecundity although no evidence for gene suppression was obtained. Rapid degradation of dsRNAs by aphid salivary, haemolymph and gut nucleases contrasted with stability in T. castaneum larvae where it appears that exo-nuclease activity is responsible for relatively slow digestion of dsRNAs. This is the first study to directly compare RNAi effects and dsRNA stability in receptive and refractory insect species and provides further evidence that dsRNA susceptibility to nucleases is a key factor in determining RNAi efficiency.

Comparative Proteomic Analysis of the Effect of Periplocoside P from Periploca sepium on Brush Border Membrane Vesicles in Midgut Epithelium of Mythimna separata Larvae

Periplocoside P (PSP), a novel compound isolated from Periploca sepium Bunge, possesses insecticidal activity against some lepidopterans, such as Mythimna separata. In M. separata, the brush border membrane vesicles of the midgut epithelium are the initial site of action of periplocosides. We conducted two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization time of flight/time of flight mass spectrometry analysis to analyze differentially expressed proteins (DEPs) from periplocoside P (PSP)-treated M. separata. We successfully isolated seven up-regulated and three down-regulated DEPs that have been previously identified, as well as a novel DEP. The DEPs are implicated in protein degradation, transporter, folding, and synthesis, and in juvenile hormone biosynthesis. DEPs involved in the oxidative phosphorylation energy metabolism pathway are enriched. Through real-time polymerase chain reaction assay, we confirmed that vma1 expression is significantly up-regulated expression levels in PSP-treated M. separata larvae. Enzymology validation further indicated that PSP can significantly inhibit V-type ATPase activity in a concentration-dependent manner. Given these results, we speculate that in M. separata, the V-type ATPase A subunit in the midgut epithelium is the putative target binding site of periplocosides. This finding provides preliminary evidence for the mode of action of periplocosides.

Proteomic analysis of Cry2Aa-binding proteins and their receptor function in Spodoptera exigua

The bacterium Bacillus thuringiensis produces Crystal (Cry) proteins that are toxic to a diverse range of insects. Transgenic crops that produce Bt Cry proteins are grown worldwide because of their improved resistance to insect pests. Although Bt "pyramid" cotton that produces both Cry1A and Cry2A is predicted to be more resistant to several lepidopteran pests, including Spodoptera exigua, than plants that produce Cry1Ac alone, the mechanisms responsible for the toxicity of Cry2Aa in S. exigua are not well understood. We identified several proteins that bind Cry2Aa (polycalin, V-ATPase subunits A and B, actin, 4-hydroxybutyrate CoA-transferase [4-HB-CoAT]), and a receptor for activated protein kinase C (Rack), in S. exigua. Recombinant, expressed versions of these proteins were able to bind the Cry2Aa toxin in vitro assays. RNA interference gene knockdown of the Se-V-ATPase subunit B significantly decreased the susceptibility of S. exigua larvae to Cry2Aa, whereas knockdown of the other putative binding proteins did not. Moreover, an in vitro homologous competition assay demonstrated that the Se-V-ATPase subunit B binds specifically to the Cry2Aa toxin, suggesting that this protein acts as a functional receptor of Cry2Aa in S. exigua. This the first Cry2Aa toxin receptor identified in S. exigua brush-border membrane vesicles.

Systemic RNAi in the small hive beetle Aethina tumida Murray (Coleoptera: Nitidulidae), a serious pest of the European honey bee Apis mellifera

BACKGROUND

Aethina tumida is a serious pest of the European honey bee (Apis mellifera) in North America and Australia. Here we investigate whether Laccase 2, the phenoloxidase gene essential for cuticle sclerotisation and pigmentation in many insects, and vacuolar-ATPase V-type subunit A, vital for the generation of proton gradients used to drive a range of transport processes, could be potential targets for RNAi-mediated control of A. tumida.

RESULTS

Injection of V-ATPase subunit A (5 ng) and Laccase 2 (12.5 ng) dsRNAs resulted in 100% larval mortality, and qPCR confirmed significant decreases and enhanced suppression of transcript levels over time. Oral delivery of V-ATPase subunit A dsRNA in solutions resulted in 50% mortality; however, gene suppression could not be verified. We suggest that the inconsistent RNAi effect was a consequence of dsRNA degradation within the gut owing to the presence of extracellular nucleases. Target specificity was confirmed by a lack of effect on survival or gene expression in honey bees injected with A. tumida dsRNAs.

CONCLUSION

This is the first study to show evidence for systemic RNAi in A. tumida in response to injected dsRNA, but further research is required to develop methods to induce RNAi effects via ingestion. © 2016 Crown copyright. Pest Management Science © 2016 Society of Chemical Industry.

Proteomics-based identification of midgut proteins correlated with Cry1Ac resistance in Plutella xylostella (L.)

The diamondback moth, Plutella xylostella (L.), is a worldwide pest of cruciferous crops and can rapidly develop resistance to many chemical insecticides. Although insecticidal crystal proteins (i.e., Cry and Cyt toxins) derived from Bacillus thuringiensis (Bt) have been useful alternatives to chemical insecticides for the control of P. xylostella, resistance to Bt in field populations of P. xylostella has already been reported. A better understanding of the resistance mechanisms to Bt should be valuable in delaying resistance development. In this study, the mechanisms underlying P. xylostella resistance to Bt Cry1Ac toxin were investigated using two-dimensional differential in-gel electrophoresis (2D-DIGE) and ligand blotting for the first time. Comparative analyses of the constitutive expression of midgut proteins in Cry1Ac-susceptible and -resistant P. xylostella larvae revealed 31 differentially expressed proteins, 21 of which were identified by mass spectrometry. Of these identified proteins, the following fell into diverse eukaryotic orthologous group (KOG) subcategories may be involved in Cry1Ac resistance in P. xylostella: ATP-binding cassette (ABC) transporter subfamily G member 4 (ABCG4), trypsin, heat shock protein 70 (HSP70), vacuolar H(+)-ATPase, actin, glycosylphosphatidylinositol anchor attachment 1 protein (GAA1) and solute carrier family 30 member 1 (SLC30A1). Additionally, ligand blotting identified the following midgut proteins as Cry1Ac-binding proteins in Cry1Ac-susceptible P. xylostella larvae: ABC transporter subfamily C member 1 (ABCC1), solute carrier family 36 member 1 (SLC36A1), NADH dehydrogenase iron-sulfur protein 3 (NDUFS3), prohibitin and Rap1 GTPase-activating protein 1. Collectively, these proteomic results increase our understanding of the molecular resistance mechanisms to Bt Cry1Ac toxin in P. xylostella and also demonstrate that resistance to Bt Cry1Ac toxin is complex and multifaceted.

Molecular mechanism and functional significance of acid generation in the Drosophila midgut

The gut of Drosophila melanogaster includes a proximal acidic region (~pH 2), however the genome lacks the H⁺/K⁺ ATPase characteristic of the mammalian gastric parietal cell, and the molecular mechanisms of acid generation are poorly understood. Here, we show that maintenance of the low pH of the acidic region is dependent on H⁺ V-ATPase, together with carbonic anhydrase and five further transporters or channels that mediate K⁺, Cl⁻ and HCO₃⁻ transport. Abrogation of the low pH did not influence larval survival under standard laboratory conditions, but was deleterious for insects subjected to high Na⁺ or K⁺ load. Insects with elevated pH in the acidic region displayed increased susceptibility to Pseudomonas pathogens and increased abundance of key members of the gut microbiota (Acetobacter and Lactobacillus), suggesting that the acidic region has bacteriostatic or bacteriocidal activity. Conversely, the pH of the acidic region was significantly reduced in germ-free Drosophila, indicative of a role of the gut bacteria in shaping the pH conditions of the gut. These results demonstrate that the acidic gut region protects the insect and gut microbiome from pathological disruption, and shed light on the mechanisms by which low pH can be maintained in the absence of H⁺, K⁺ ATPase.

Intestinal regeneration as an insect resistance mechanism to entomopathogenic bacteria

The intestinal epithelium of insects is exposed to xenobiotics and entomopathogens during the feeding developmental stages. In these conditions, an effective enterocyte turnover mechanism is highly desirable to maintain integrity of the gut epithelial wall. As in other insects, the gut of lepidopteran larvae have stem cells that are capable of proliferation, which occurs during molting and pathogenic episodes. While much is known on the regulation of gut stem cell division during molting, there is a current knowledge gap on the molecular regulation of gut healing processes after entomopathogen exposure. Relevant information on this subject is emerging from studies of the response to exposure to insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) as model intoxicants. In this work we discuss currently available data on the molecular cues involved in gut stem cell proliferation, insect gut healing, and the implications of enhanced healing as a potential mechanism of resistance against Bt toxins.

The Legs Have It: In Situ Expression of Ion Transporters V-Type H(+)-ATPase and Na(+)/K(+)-ATPase in the Osmoregulatory Leg Organs of the Invading Copepod Eurytemora affinis

The copepod Eurytemora affinis has an unusually broad salinity range, as some populations have recently invaded freshwater habitats independently from their ancestral saline habitats. Prior studies have shown evolutionary shifts in ion transporter activity during freshwater invasions and localization of ion transporters in newly discovered "Crusalis organs" in the swimming legs. The goals of this study were to localize and quantify expression of ion transport enzymes V-type H(+)-ATPase (VHA) and Na(+)/K(+)-ATPase (NKA) in the swimming legs of E. affinis and determine the degree of involvement of each leg in ionic regulation. We confirmed the presence of two distinct types of ionocytes in the Crusalis organs. Both cell types expressed VHA and NKA, and in the freshwater population the location of VHA and NKA in ionocytes was, respectively, apical and basal. Quantification of in situ expression of NKA and VHA established the predominance of swimming leg pairs 3 and 4 in ion transport in both saline and freshwater populations. Increases in VHA expression in swimming legs 3 and 4 of the freshwater population (in fresh water) relative to the saline population (at 15 PSU) arose from an increase in the abundance of VHA per cell rather than an increase in the number of ionocytes. This result suggests a simple mechanism for increasing ion uptake in fresh water. In contrast, the decline in NKA expression in the freshwater population arose from a decrease in ionocyte area in legs 4, likely resulting from decreases in number or size of ionocytes containing NKA. Such results provide insights into mechanisms of ionic regulation for this species, with added insights into evolutionary mechanisms underlying physiological adaptation during habitat invasions.

Validation of the Target Protein of Insecticidal Dihydroagarofuran Sesquiterpene Polyesters

A series of insecticidal dihydroagarofuran sesquiterpene polyesters were isolated from the root bark of Chinese bittersweet (Celastrus angulatus Max). A previous study indicated that these compounds affect the digestive system of insects, and aminopeptidase N3 and V-ATPase have been identified as the most putative target proteins by affinity chromatography. In this study, the correlation between the affinity of the compounds to subunit H and the insecticidal activity or inhibitory effect on the activity of V-ATPase was analyzed to validate the target protein. Results indicated that the subunit H of V-ATPase was the target protein of the insecticidal compounds. In addition, the possible mechanism of action of the compounds was discussed. The results provide new ideas for developing pesticides acting on V-ATPase of insects.

Predominant expression and activity of vacuolar H(+)-ATPases in the mixed segment of the wood-feeding termite Nasutitermes takasagoensis

The mixed segment is a unique part of the gut present only in the most apical lineage of termites and consists of a complex of overlapping mesenteric and proctodeal epithelia. In spite of its unique structure, the physiological functions of the mixed segment have been poorly studied. We performed transcriptome analysis to identify functional enzymes acting in the mixed segment of the wood-feeding higher termite Nasutitermes takasagoensis. We sequenced the transcripts (4563 isotigs) of the mixed segment and compared them with those of the midgut (4813 isotigs) and the first proctodeal segment (3629 isotigs). We found that vacuolar H(+)-ATPase (V-ATPase) subunits were predominant in the mixed segment, which was confirmed by RT-qPCR analysis. The V-ATPase activity in these three tissues was in a good agreement with the expression patterns, suggesting that V-ATPase is a prevalent enzyme in the mixed segment of the termites. The results confirmed the proposed role of the mixed segment as a transporting epithelium.

RNA interference tools for the western flower thrips, Frankliniella occidentalis

The insect order Thysanoptera is exclusively comprised of small insects commonly known as thrips. The western flower thrips, Frankliniella occidentalis, is an economically important pest amongst thysanopterans due to extensive feeding damage and tospovirus transmission to hundreds of plant species worldwide. Geographically-distinct populations of F. occidentalis have developed resistance against many types of traditional chemical insecticides, and as such, management of thrips and tospoviruses are a persistent challenge in agriculture. Molecular methods for defining the role(s) of specific genes in thrips-tospovirus interactions and for assessing their potential as gene targets in thrips management strategies is currently lacking. The goal of this work was to develop an RNA interference (RNAi) tool that enables functional genomic assays and to evaluate RNAi for its potential as a biologically-based approach for controlling F. occidentalis. Using a microinjection system, we delivered double-stranded RNA (dsRNA) directly to the hemocoel of female thrips to target the vacuolar ATP synthase subunit B (V-ATPase-B) gene of F. occidentalis. Gene expression analysis using real-time quantitative reverse transcriptase-PCR (qRT-PCR) revealed significant reductions of V-ATPase-B transcripts at 2 and 3 days post-injection (dpi) with dsRNA of V-ATPase-B compared to injection with dsRNA of GFP. Furthermore, the effect of knockdown of the V-ATPase-B gene in females at these two time points was mirrored by the decreased abundance of V-ATPase-B protein as determined by quantitative analysis of Western blots. Reduction in V-ATPase-B expression in thrips resulted in increased female mortality and reduced fertility, i.e., number of viable offspring produced. Survivorship decreased significantly by six dpi compared to the dsRNA-GFP control group, which continued decreasing significantly until the end of the bioassay. Surviving female thrips injected with dsRNA-V-ATPase-B produced significantly fewer offspring compared to those in the dsRNA-GFP control group. Our findings indicate that an RNAi-based strategy to study gene function in thrips is feasible, can result in quantifiable phenotypes, and provides a much-needed tool for investigating the molecular mechanisms of thrips-tospovirus interactions. To our knowledge, this represents the first report of RNAi for any member of the insect order Thysanoptera and demonstrates the potential for translational research in the area of thrips pest control.

Cloning, expression and purification of subunit H of vacuolar H⁺-ATPase from Mythimna separata Walker (Lepidoptera: Noctuidae)

The vacuolar (H+)-ATPase (V-ATPase) of insect, which is composed of membrane-bound V0 complex and peripheral V1 complex, participates in lots of important physiological process. Subunit H, as a subunit of V1 complex, plays a vital role in bridging the communication between V1 and V0 complexes and interaction with other proteins. Yeast subunit H has been successfully crystallized through expression in E. coli, but little is known about the structure of insect subunit H. In this study, we cloned, expressed and purified the subunit H from midgut of Mythimna separata Walker. Through RACE (rapidly amplification of cDNA ends) technique, we got 1807 bp full length of subunit H, and to keep the nature structure of subunit H, we constructed Baculovirus expression vector with His-tag in the C-terminal and expressed the recombinant protein in insect sf9 cells, thereafter, purified the recombinant protein by Ni-NTA columns. Results of SDS-PAGE, western blotting and mass spectrometry showed that the recombinant protein was successfully expressed. The method of expressing and purifying M. separata subunit H will provide a foundation for obtaining the crystal of subunit H and further study of the design of novel insecticides based on its structure and function.

Enhanced whitefly resistance in transgenic tobacco plants expressing double stranded RNA of v-ATPase A gene

BACKGROUND

Expression of double strand RNA (dsRNA) designed against important insect genes in transgenic plants have been shown to give protection against pests through RNA interference (RNAi), thus opening the way for a new generation of insect-resistant crops. We have earlier compared the efficacy of dsRNAs/siRNAs, against a number of target genes, for interference in growth of whitefly (Bemisia tabaci) upon oral feeding. The v-ATPase subunit A (v-ATPaseA) coding gene was identified as a crucial target. We now report the effectiveness of transgenic tobacco plants expressing siRNA to silence v-ATPaseA gene expression for the control of whitefly infestation.

METHODOLOGY/PRINCIPAL FINDINGS

Transgenic tobacco lines were developed for the expression of long dsRNA precursor to make siRNA and knock down the v-ATPaseA mRNA in whitefly. Molecular analysis and insecticidal properties of the transgenic plants established the formation of siRNA targeting the whitefly v-ATPaseA, in the leaves. The transcript level of v-ATPaseA in whiteflies was reduced up to 62% after feeding on the transgenic plants. Heavy infestation of whiteflies on the control plants caused significant loss of sugar content which led to the drooping of leaves. The transgenic plants did not show drooping effect.

CONCLUSIONS/SIGNIFICANCE

Host plant derived pest resistance was achieved against whiteflies by genetic transformation of tobacco which generated siRNA against the whitefly v-ATPaseA gene. Transgenic tobacco lines expressing dsRNA of v-ATPaseA, delivered sufficient siRNA to whiteflies feeding on them, mounting a significant silencing response, leading to their mortality. The transcript level of the target gene was reduced in whiteflies feeding on transgenic plants. The strategy can be taken up for genetic engineering of plants to control whiteflies in field crops.

Development of RNAi methods for Peregrinus maidis, the corn planthopper

The corn planthopper, Peregrinus maidis, is a major pest of agronomically-important crops. Peregrinus maidis has a large geographical distribution and transmits Maize mosaic rhabdovirus (MMV) and Maize stripe tenuivirus (MSpV). The objective of this study was to develop effective RNAi methods for P. maidis. Vacuolar-ATPase (V-ATPase) is an essential enzyme for hydrolysis of ATP and for transport of protons out of cells thereby maintaining membrane ion balance, and it has been demonstrated to be an efficacious target for RNAi in other insects. In this study, two genes encoding subunits of P. maidis V-ATPase (V-ATPase B and V-ATPase D) were chosen as RNAi target genes. The open reading frames of V-ATPase B and D were generated and used for constructing dsRNA fragments. Experiments were conducted using oral delivery and microinjection of V-ATPase B and V-ATPase D dsRNA to investigate the effectiveness of RNAi in P. maidis. Real-time quantitative reverse transcriptase-PCR (qRT-PCR) analysis indicated that microinjection of V-ATPase dsRNA led to a minimum reduction of 27-fold in the normalized abundance of V-ATPase transcripts two days post injection, while ingestion of dsRNA resulted in a two-fold reduction after six days of feeding. While both methods of dsRNA delivery resulted in knockdown of target transcripts, the injection method was more rapid and effective. The reduction in V-ATPase transcript abundance resulted in observable phenotypes. Specifically, the development of nymphs injected with 200 ng of either V-ATPase B or D dsRNA was impaired, resulting in higher mortality and lower fecundity than control insects injected with GFP dsRNA. Microscopic examination of these insects revealed that female reproductive organs did not develop normally. The successful development of RNAi in P. maidis to target specific genes will enable the development of new insect control strategies and functional analysis of vital genes and genes associated with interactions between P. maidis and MMV.

Effects of period RNAi on V-ATPase expression and rhythmic pH changes in the vas deferens of Spodoptera littoralis (Lepidoptera: Noctuidae)

Circadian clocks (oscillators) regulate multiple aspects of insect behaviour and physiology. The circadian system located in the male reproductive tract of Lepidoptera orchestrates rhythmic sperm release from testis and sperm maturation in the upper vas deferens (UVD). Our previous research on the cotton leafworm, Spodoptera littoralis, suggested rhythmic changes in the V-ATPase levels in the UVD epithelium, which correlated with rhythmic pH fluctuations in the UVD lumen. However, it was not known whether UVD cells contain clock mechanism that generates these daily fluctuations. In the current paper, we show circadian rhythm in the expression of clock gene period at the mRNA and protein level in the UVD epithelium. To determine the role of PER in V-ATPase and pH regulation, testes-UVD complexes were treated in vitro with double-stranded fragments of per mRNA (dsRNA). This treatment, which transiently lowered per mRNA and protein in the UVD, altered expression of V-ATPase c subunit. In addition, per RNAi caused a significant delay in the UVD lumen acidification. These data demonstrate that the UVD molecular oscillator involving the period gene plays an essential role in the regulation of rhythmic V-ATPase activity and periodic acidification of the UVD lumen.

Insights into the insect salivary gland proteome: diet-associated changes in caterpillar labial salivary proteins

The primary function of salivary glands is fluid and protein secretion during feeding. Compared to mammalian systems, little is known about salivary protein secretion processes and the effect of diet on the salivary proteome in insect models. Therefore, the effect of diet nutritional quality on caterpillar labial salivary gland proteins was investigated using an unbiased global proteomic approach by nanoLC/ESI/tandem MS. Caterpillars of the beet armyworm, Spodoptera exigua Hübner, were fed one of three diets: an artificial diet containing their self-selected protein to carbohydrate (p:c) ratio (22p:20c), an artificial diet containing a higher nutritional content but the same p:c ratio (33p:30c) or the plant Medicago truncatula Gaertn. As expected, most identified proteins were associated with secretory processes and not influenced by diet. However, some diet-specific differences were observed. Nutrient stress-associated proteins, such as peptidyl-propyl cis-trans isomerase and glucose-regulated protein94/endoplasmin, and glyceraldehyde 3-phosphate dehydrogenase were identified in the labial salivary glands of caterpillars fed nutritionally poor diets, suggesting a link between nutritional status and vesicular exocytosis. Heat shock proteins and proteins involved in endoplasmic reticulum-associated protein degradation were also abundant in the labial salivary glands of these caterpillars. In comparison, proteins associated with development, such as arylphorin, were found in labial salivary glands of caterpillars fed 33p:30c. These results suggest that caterpillars fed balanced or nutritionally-poor diets have accelerated secretion pathways compared to those fed a protein-rich diet.

Lysosomal acidification mechanisms

Lysosomes, the terminal organelles on the endocytic pathway, digest macromolecules and make their components available to the cell as nutrients. Hydrolytic enzymes specific to a wide range of targets reside within the lysosome; these enzymes are activated by the highly acidic pH (between 4.5 and 5.0) in the organelles' interior. Lysosomes generate and maintain their pH gradients by using the activity of a proton-pumping V-type ATPase, which uses metabolic energy in the form of ATP to pump protons into the lysosome lumen. Because this activity separates electric charge and generates a transmembrane voltage, another ion must move to dissipate this voltage for net pumping to occur. This so-called counterion may be either a cation (moving out of the lysosome) or an anion (moving into the lysosome). Recent data support the involvement of ClC-7, a Cl(-)/H(+) antiporter, in this process, although many open questions remain as to this transporter's involvement. Although functional results also point to a cation transporter, its molecular identity remains uncertain. Both the V-ATPase and the counterion transporter are likely to be important players in the mechanisms determining the steady-state pH of the lysosome interior. Exciting new results suggest that lysosomal pH may be dynamically regulated in some cell types.

Transcription profiling of resistance to Bti toxins in the mosquito Aedes aegypti using next-generation sequencing

The control of mosquitoes transmitting infectious diseases relies mainly on the use of chemical insecticides. However, resistance to most chemical insecticides threatens mosquito control programs. In this context, the spraying of toxins produced by the bacteria Bacillus thuringiensis subsp. israelensis (Bti) in larval habitats represents an alternative to chemical insecticides and is now widely used for mosquito control. Recent studies suggest that resistance of mosquitoes to Bti toxin may occur locally but mechanisms have not been characterized so far. In the present study, we investigated gene transcription level variations associated with Bti toxin resistance in the mosquito Aedes aegypti using a next-generation sequencing approach. More than 6 million short cDNA tags were sequenced from larvae of two strains sharing the same genetic background: a Bti toxins-resistant strain and a susceptible strain. These cDNA tags were mapped with a high coverage (308 reads per position in average) to more than 6000 genes of Ae. aegypti genome and used to quantify and compare the transcription level of these genes between the two mosquito strains. Among them, 86 genes were significantly differentially transcribed more than 4-fold in the Bti toxins resistant strain comparatively to the susceptible strain. These included gene families previously associated with Bti toxins resistance such as serine proteases, alkaline phosphatase and alpha-amylase. These results are discussed in regards of potential Bti toxins resistance mechanisms in mosquitoes.

Effects of hormone agonists on Sf9 cells, proliferation and cell cycle arrest

Methoxyfenozide and methoprene are two insecticides that mimic the action of the main hormones involved in the control of insect growth and development, 20-hydroxyecdysone and juvenile hormone. We investigated their effect on the Spodoptera frugiperda Sf9 cell line. Methoxyfenozide was more toxic than methoprene in cell viability tests and more potent in the inhibition of cellular proliferation. Cell growth arrest occurred in the G2/M phase after a methoprene treatment and more modestly in G1 after methoxyfenozide treatment. Microarray experiments and real-time quantitative PCR to follow the expression of nuclear receptors ultraspiracle and ecdysone receptor were performed to understand the molecular action of these hormone agonists. Twenty-six genes were differentially expressed after methoxyfenozide treatment and 55 genes after methoprene treatment with no gene in common between the two treatments. Our results suggest two different signalling pathways in Sf9 cells.

Histopathology and ultrastructure of midgut of Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) fed Bt-cotton

The interaction of Cry toxins from Bacillus thuringiensis in the midgut of some insect larvae determines their efficacies as insecticides, due to the expression and availability of sites of action of the toxin in the midgut. Researches point out cases of resistance to Cry toxin due to alterations in the binding sites in columnar cell membrane. We analyzed the effects of Cry1Ac toxin expressed by Bt-cotton plants on Alabama argillacea midgut morphophysiology clarifying in levels of morphological and ultrastructural. Larvae in the 4th instar of A. argillacea after 20 min from ingesting Bt-cotton leaves expressing 0.183 ng of Cry1Ac exhibited ultrastructural and morphological modifications in the columnar cells with significant changes in the mitochondrial polymorphism, cytoplasmic vacuolization, microvillus and basal labyrinth. Expressive morphological alterations were also observed in the goblet cells indicating that the columnar cells are not the only target of the Cry1Ac toxin. The regenerative cells did not modify their structures and exhibited decrease in regeneration capacity. In conclusion, the ingestion of 0.183 ± 0.077 ng of Cry1Ac was enough to promote alterations in the columnar and goblet cells, besides reducing significantly the number of regenerative cells, which may have contributed to larval death. Nevertheless, further studies are necessary to determine the true cause of death.

The effect of soil pH and temperature on Folsomia candida transcriptional regulation

Differences in abiotic factors like temperature and soil pH can have a significant physiological impact on soil dwelling invertebrates and may confound results in ecotoxicological testing. In this study we exposed Folsomia candida to a range of two abiotic stress treatments (pH and temperature) for 3 days and measured gene expression of a panel of nine stress response genes with real-time Q-PCR. The exposure to different pH values had a minimal effect on the expression of the nine selected genes: only V-ATPase expression was significantly increased due to decreasing pH. ATPase expression was up-regulated, possibly due to increased proton trafficking across the cell membrane, at a lower pH. HSP70 was up-regulated in collembolans exposed to 30 degrees C, and along with HSP40 at 0 degrees C. We speculate that the minor pH effect on gene expression, compared to the temperature treatment, can be explained by the spatial restricted exposure to the external pH in the gut. Our data showed that only 1 or 2 stress response genes were transcriptionally affected by pH and temperature thus exerting minimal effects. The physiological effects of these treatments on F. candida might indicate interesting novel molecular mechanisms.

Effect of entomocidal proteins from Bacillus thuringiensis on ion permeability of apical membranes of Tenebrio molitor larvae gut epithelium

Effects of entomocidal Cry-type proteins, delta-endotoxins Cry3A and Cry11A produced by Bacillus thuringiensis, on ion permeability of the apical membranes of intestinal epithelium from Tenebrio molitor larvae midgut were studied. Using potential-sensitive dyes safranine O and oxonol VI and DeltapH indicator acridine orange, it was shown that placing brush border membrane vesicles (BBMV) (loaded with Mg2+ during their preparation) into a salt-free buffer medium resulted in spontaneous generation of transmembrane electric potential on the vesicular membrane (negative inside the vesicles) accompanied by acidification of the aqueous phase inside the vesicles. The generation of transmembrane ion gradients on the vesicular membrane was a result of an electrogenic efflux of Mg2+ from the vesicles as shown by abolishing of the membrane potential by such agents as MgSO4 or CaCl2 in centimolar concentrations, a highly lipophilic cation tetraphenylphosphonium, and some blockers of cell membrane Ca2+-channels in submillimolar concentrations. A passive generation of membrane potential on the vesicular membrane (but positive inside the vesicles) was also observed upon addition of centimolar concentrations of K2SO4. Addition of delta-endotoxins Cry3A and Cry11A to the vesicle suspension in a salt-free buffer medium or in the same medium supplemented with centimolar concentrations of K2SO4 exerted a pronounced hyperpolarization of the vesicular membrane. This hyperpolarization was sensitive to the same agents, which abolished the membrane potential generation in the absence of delta-endotoxin. It is concluded that Cry proteins induced in BBMV from T. molitor opening pores or ion channels, which were considerably more permeable for alkaline- and alkaline-earth metal cations than for the accompanying anions.

Chromatographic and electrophoretic resolution of proteins and protein complexes from the larval midgut microvilli of Manduca sexta

The microvillar proteome of Manduca sexta larval midguts was analyzed by subjecting brush border membrane vesicles (BBMV) to two different two-dimensional approaches: (i) Anion exchange chromatography followed by SDS-PAGE and (ii) Blue Native-PAGE followed by SDS-PAGE. The first technique was superior to conventional 2-D gel electrophoresis in resolving the most abundant proteins associated with the midgut microvilli. Twenty of them were successfully identified as digestive enzymes, binding targets of the insecticidal Cry1A toxins from Bacillus thuringiensis (Bt), and signal transduction proteins. A homolog of the chlorophyllide A binding protein from the silkworm and several aminopeptidases N represent the most abundant proteins associated with the BBMV. The second technique revealed protein oligomeric complexes associated with midgut microvilli in vivo. Two such complexes contained subunits of the vacuolar ATP synthase complex, and one was an oligomer of the chlorophyllide A binding protein. An additional complex consisted of homo- or hetero-tetramers of three different aminopeptidases N (APNs). As APNs are well-known binding partners of Cry1A toxins, their quaternary structure has implications for Bt toxin mode of action. Both techniques provide a useful complement to conventional 2-D gel electrophoresis in analyzing the complex proteome of the microvillar membrane fraction.

Voltage coupling of primary H+ V-ATPases to secondary Na+- or K+-dependent transporters

This review provides alternatives to two well established theories regarding membrane energization by H(+) V-ATPases. Firstly, we offer an alternative to the notion that the H(+) V-ATPase establishes a protonmotive force (pmf) across the membrane into which it is inserted. The term pmf, which was introduced by Peter Mitchell in 1961 in his chemiosmotic hypothesis for the synthesis of ATP by H(+) F-ATP synthases, has two parts, the electrical potential difference across the phosphorylating membrane, Deltapsi, and the pH difference between the bulk solutions on either side of the membrane, DeltapH. The DeltapH term implies three phases - a bulk fluid phase on the H(+) input side, the membrane phase and a bulk fluid phase on the H(+) output side. The Mitchell theory was applied to H(+) V-ATPases largely by analogy with H(+) F-ATP synthases operating in reverse as H(+) F-ATPases. We suggest an alternative, voltage coupling model. Our model for V-ATPases is based on Douglas B. Kell's 1979 'electrodic view' of ATP synthases in which two phases are added to the Mitchell model - an unstirred layer on the input side and another one on the output side of the membrane. In addition, we replace the notion that H(+) V-ATPases normally acidify the output bulk solution with the hypothesis, which we introduced in 1992, that the primary action of a H(+) V-ATPase is to charge the membrane capacitance and impose a Deltapsi across the membrane; the translocated hydrogen ions (H(+)s) are retained at the outer fluid-membrane interface by electrostatic attraction to the anions that were left behind. All subsequent events, including establishing pH differences in the outside bulk solution, are secondary. Using the surface of an electrode as a model, Kell's 'electrodic view' has five phases - the outer bulk fluid phase, an outer fluid-membrane interface, the membrane phase, an inner fluid-membrane interface and the inner bulk fluid phase. Light flash, H(+) releasing and binding experiments and other evidence provide convincing support for Kell's electrodic view yet Mitchell's chemiosmotic theory is the one that is accepted by most bioenergetics experts today. First we discuss the interaction between H(+) V-ATPase and the K(+)/2H(+) antiporter that forms the caterpillar K(+) pump, and use the Kell electrodic view to explain how the H(+)s at the outer fluid-membrane interface can drive two H(+) from lumen to cell and one K(+) from cell to lumen via the antiporter even though the pH in the bulk fluid of the lumen is highly alkaline. Exchange of outer bulk fluid K(+) (or Na(+)) with outer interface H(+) in conjunction with (K(+) or Na(+))/2H(+) antiport, transforms the hydrogen ion electrochemical potential difference, mu(H), to a K(+) electrochemical potential difference, mu(K) or a Na(+) electrochemical potential difference, mu(Na). The mu(K) or mu(Na) drives K(+)- or Na(+)-coupled nutrient amino acid transporters (NATs), such as KAAT1 (K(+) amino acid transporter 1), which moves Na(+) and an amino acid into the cell with no H(+)s involved. Examples in which the voltage coupling model is used to interpret ion and amino acid transport in caterpillar and larval mosquito midgut are discussed.

Cloning and sequencing of V-ATPase subunit d from mung bean and its function in passive proton transport

We have previously shown that vacuolar H+-ATPase subcomplex V(o) from mung bean contains subunit d, however, its sequence and function were unknown. In the present study, we report the cloning and recombinant over expression of subunit d from mung bean in E. coli. To study the function of subunit d, two vacuolar H+-ATPase subcomplexes V(o) from mung bean were purified-one containing subunits a and c(c',c") and the other containing subunits a, c(c',c") and d. After reconstitution of the purified V(o) subcomplexes into liposomes, the proton translocation was studied. Our results show that the V(o) subcomplex in the absence of subunit d is a passive proton channel, while the V(o) subcomplex in the presence of the subunit d is not. Taken together, our data supports the conclusion that the subunit d of the plant vacuolar H(+)-ATPase from mung bean is positioned at the central stalk and involved in the proton translocation across the tonoplast membrane.

Comparison of proton-specific ATPase activities in plume and root tissues of two co-occurring hydrocarbon seep tubeworm species Lamellibrachia luymesi and Seepiophila jonesi

Lamellibrachia luymesi and Seepiophila jonesi are co-occurring species of vestimentiferan tubeworms found at hydrocarbon seepage sites on the upper Louisiana slope of the Gulf of Mexico. Like all vestimentiferans, they rely on internal sulfide-oxidizing symbiotic bacteria for nutrition. These symbionts produce hydrogen ions as a byproduct of sulfide oxidation, which the host tubeworm needs to eliminate to prevent acidosis. The hydrothermal vent tubeworm Riftia pachyptila uses a high activity of P- and V-type H⁺-ATPases located in its plume epithelium to excrete protons. Unlike R. pachyptila, the seep species grow a posterior root, which they can use in addition to their plumes as a nutrient exchange surface. In this study we measured the ATPase activities of plume and root tissues collected from L. luymesi and S. jonesi, and used a combination of inhibitors to determine the relative activities of P- and V-type H⁺-ATPases. We found that the total H⁺-ATPase activity of their plumes was approximately 14 μmol h^-1 g^-1 wet weight, and that of their roots was between 5 and 7 μmol h^-1 g^-1 wet weight. These activities were more than ten times lower than those measured in R. pachyptila. We suggest that seep tubeworms might use passive channels to eliminate protons across their roots, in addition to ATP-dependant proton pumps located in their plumes and roots. In addition, we found strong differences between the types of ATPase activities in the plumes of L. luymesi and S. jonesi. While the H⁺-ATPase activity of L. luymesi plumes is dominated by P-type ATPases, S. jonesi has an unusually high activity of V-type H⁺-ATPases. We suggest that S. jonesi relies on its high V-type H⁺-ATPase activity to drive carbon dioxide uptake across its plume surface. L. luymesi, on the other hand, might rely partially on bicarbonate uptake across its root.

Global topology analysis of pancreatic zymogen granule membrane proteins

The zymogen granule is the specialized organelle in pancreatic acinar cells for digestive enzyme storage and regulated secretion and is a classic model for studying secretory granule function. Our long term goal is to develop a comprehensive architectural model for zymogen granule membrane (ZGM) proteins that would direct new hypotheses for subsequent functional studies. Our initial proteomics analysis focused on identification of proteins from purified ZGM (Chen, X., Walker, A. K., Strahler, J. R., Simon, E. S., Tomanicek-Volk, S. L., Nelson, B. B., Hurley, M. C., Ernst, S. A., Williams, J. A., and Andrews, P. C. (2006) Organellar proteomics: analysis of pancreatic zymogen granule membranes. Mol. Cell. Proteomics 5, 306-312). In the current study, a new global topology analysis of ZGM proteins is described that applies isotope enrichment methods to a protease protection protocol. Our results showed that tryptic peptides of ZGM proteins were separated into two distinct clusters according to their isobaric tag for relative and absolute quantification (iTRAQ) ratios for proteinase K-treated versus control zymogen granules. The low iTRAQ ratio cluster included cytoplasm-orientated membrane and membrane-associated proteins including myosin V, vesicle-associated membrane proteins, syntaxins, and all the Rab proteins. The second cluster having unchanged ratios included predominantly luminal proteins. Because quantification is at the peptide level, this technique is also capable of mapping both cytoplasm- and lumen-orientated domains from the same transmembrane protein. To more accurately assign the topology, we developed a statistical mixture model to provide probabilities for identified peptides to be cytoplasmic or luminal based on their iTRAQ ratios. By implementing this approach to global topology analysis of ZGM proteins, we report here an experimentally constrained, comprehensive topology model of identified zymogen granule membrane proteins. This model contributes to a firm foundation for developing a higher order architecture model of the ZGM and for future functional studies of individual ZGM proteins.