Expression patterns of genes encoding proteins with peritrophin A domains and protein localization in Mamestra configurata

Boron compounds are effective on Tribolium castaneum (Coleoptera: Tenebrionidae): Reduced lipogenesis and induced body weight loss

In the current study, we investigated the insecticidal efficacy of two borates, disodium octaborate tetrahydrate (Etidot-67) and calcium metaborate (CMB) via surface application or diet delivery on the red flour beetle, Tribolium castaneum (Herbst, 1797) (Coleoptera: Tenebrionidae). The application method did not change the boron-related mortality, but CMB was more effective than Etidot-67. At the highest dose, it took around 13 days to reach the highest mortality (≥98.1%) for CMB, while it was 19 days for Etidot-67 (≥95.8%). Both boron compounds led to a significant reduction in triglyceride levels in parallel to the downregulation of acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), the two primary genes involved in de novo lipogenesis, while they also induced body weight loss. In conclusion, the current study indicated the insecticidal potential of boron compounds but CMB is more promising and more effective in controlling T. castaneum, while lipogenesis is inhibited and weight loss is induced by boron compounds.

Peritrophins are involved in the defense against Bacillus thuringiensis and nucleopolyhedrovirus formulations in Spodoptera littoralis (Lepidoptera: Noctuidae)

The peritrophic matrix (or peritrophic membrane, PM) is present in most insects where it acts as a barrier to mechanical insults and pathogens, as well as a facilitator of digestive processes. The PM is formed by the binding of structural PM proteins, referred to as peritrophins, to chitin fibrils and spans the entire midgut in lepidopterans. To investigate the role of peritrophins in a highly polyphagous lepidopteran pest, namely the cotton leafworm (Spodoptera littoralis), we generated Insect Intestinal Mucin (IIM-) and non-mucin Peritrophin (PER-) mutant strains via CRISPR/Cas9 mutagenesis. Both strains exhibited deformed PMs and retarded developmental rates. Bioassays conducted with Bacillus thuringiensis (Bt) and nucleopolyhedrovirus (SpliNPV) formulations showed that both the IIM- and PER- mutant larvae were more susceptible to these bioinsecticides compared to the wild-type (WT) larvae with intact PM. Interestingly, the provision of chitin-binding agent Calcofluor (CF) in the diet lowered the toxicity of Bt formulations in both WT and IIM- larvae and the protective effect of CF was significantly lower in PER- larvae. This suggested that the interaction of CF with PER is responsible for Bt resistance mediated by CF. In contrast, the provision of CF caused increased susceptibility to SpliNPV in both mutants and WT larvae. The study showed the importance of peritrophins in the defense against pathogens in S. littoralis and revealed novel insights into CF-mediated resistance to Cry toxin.

Two calcium-binding chaperones from the fat body of the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) involved in diapause

Molecular chaperones are crucial for the correct folding of newly synthesized polypeptides, in particular, under stress conditions. Various studies have revealed the involvement of molecular chaperones, such as heat shock proteins, in diapause maintenance and starvation; however, the role of other chaperones in diapause and starvation relatively is unknown. In the current study, we identified two lectin-type chaperones with calcium affinity, a calreticulin (LdCrT) and a calnexin (LdCnX), that were present in the fat body of the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) during diapause. Both proteins possessed an N-globular domain, a P-arm domain, and a highly charged C-terminal domain, while an additional transmembrane domain was present in LdCnX. Phylogenetic analysis revealed distinction at the order level. Both genes were expressed in multiple tissues in larval and adult stages, and constitutively throughout development, though a starvation response was detected only for LdCrT. In females, diapause-related expression analysis in the whole body revealed an upregulation of both genes by post-diapause, but a downregulation by diapause only for LdCrT. By contrast, males revealed no alteration in their diapause-related expression pattern in the entire body for both genes. Fat body-specific expression analysis of both genes in relation to diapause revealed the same expression pattern with no alteration in females and downregulation in males by post-diapause. This study suggests that calcium-binding chaperones play similar and possibly gender-specific roles during diapause.

Identification of Peritrophins and Antiviral Effect of Bm01504 against BmNPV in the Silkworm, Bombyx mori

The insect midgut secretes a semi-permeable, acellular peritrophic membrane (PM) that maintains intestinal structure, promotes digestion, and protects the midgut from food particles and pathogenic microorganisms. Peritrophin is an important PM protein (PMP) in the PM. Here, we identified 11 peritrophins with 1–16 chitin binding domains (CBDs) comprising 50–56 amino acid residues. Multiple CBDs in the same peritrophin clustered together, rather than by species. The CBD contained six highly conserved cysteine residues, with the key feature of amino acids between them being CX_11-15CX₅CX_9-14CX_11-12CX_6-7C. Peritrophins with 2 and 4 CBDs (Bm09641 and Bm01504, respectively), and with 1, 8, and 16 CBDs (Bm11851, Bm00185, and Bm01491, respectively) were mainly expressed in the anterior midgut, and throughout the midgut, respectively. Survival rates of transgenic silkworms with Bm01504 overexpression (Bm01504-OE) and knockout (Bm01504-KO) infected with B. morinucleopolyhedrovirus (BmNPV) were significantly higher and lower, whereas expression of the key viral gene, p10, were lower and higher, respectively, compared with wild type (WT). Therefore, Bm01504-OE and Bm01504-KO transgenic silkworms were more and less resistant, respectively, to BmNPV. Bm01504 plays important roles in resisting BmNPV invasion. We provide a new perspective for studying PM function, and reveal how the silkworm midgut resists invasive exogenous pathogenic microorganisms.

A journey into the world of insect lipid metabolism

Lipid metabolism is fundamental to life. In insects, it is critical, during reproduction, flight, starvation, and diapause. The coordination center for insect lipid metabolism is the fat body, which is analogous to the vertebrate adipose tissue and liver. Fat body contains various different cell types; however, adipocytes and oenocytes are the primary cells related to lipid metabolism. Lipid metabolism starts with the hydrolysis of dietary lipids, absorption of lipid monomers, followed by lipid transport from midgut to the fat body, lipogenesis or lipolysis in the fat body, and lipid transport from fat body to other sites demanding energy. Lipid metabolism is under the control of hormones, transcription factors, secondary messengers and posttranscriptional modifications. Primarily, lipogenesis is under the control of insulin-like peptides that activate lipogenic transcription factors, such as sterol regulatory element-binding proteins, whereas lipolysis is coordinated by the adipokinetic hormone that activates lipolytic transcription factors, such as forkhead box class O and cAMP-response element-binding protein. Calcium is the primary-secondary messenger affecting lipid metabolism and has different outcomes depending on the site of lipogenesis or lipolysis. Phosphorylation is central to lipid metabolism and multiple phosphorylases are involved in lipid accumulation or hydrolysis. Although most of the knowledge of insect lipid metabolism comes from the studies on the model Drosophila; other insects, in particular those with obligatory or facultative diapause, also have great potential to study lipid metabolism. The use of these models would significantly improve our knowledge of insect lipid metabolism.

A peritrophin mediates the peritrophic matrix permeability in the workers of the bees Melipona quadrifasciata and Apis mellifera

The permeability of the peritrophic matrix, essential for its function, depends on its chemical composition. The objective was to determine if the permeability of the peritrophic matrix varies along the midgut and in the presence of anti-peritrophin-55 antibody in Melipona quadrifasciata and Apis mellifera bees. The thickness of the peritrophic matrix in both species varies between the anterior and posterior midgut regions in workers. In A. mellifera dextran molecules with 40 kDa cross the peritrophic matrix, whereas those ≥70 kDa are retained in the endoperitrophic space. In M. quadrifasciata the peritrophic matrix permeability was for molecules <40 kDa. Bees fed on anti-peritrophin-55 antibody showed an increase in peritrophic matrix permeability, but survival was not affected. In the bees studied, the peritrophic matrices have morphological differences between midgut regions, but there is no difference in their permeability along the midgut, which is affected by peritrophin 55.

Functional expression of a peritrophin A-like SfPER protein is required for larval development in Spodoptera frugiperda (Lepidoptera: Noctuidae)

Peritrophins are associated with structural and functional integrity of peritrophic membranes (PM), structures composed of chitin and proteins. PM lines the insect midgut and has roles in digestion and protection from toxins. We report the full-length cDNA cloning, molecular characterization and functional analysis of SfPER, a novel PM peritrophin A protein, in Spodoptera frugiperda. The predicted amino acid sequence indicated SfPER's domain structure as a CMCMC-type, consisting of a signal peptide and three chitin-binding (C) domains with two intervening mucin-like (M) domains. Phylogenetic analysis determined a close relationship between SfPER and another S. frugiperda PM peritrophin partial sequence. SfPER transcripts were found in larvae and adults but were absent from eggs and pupae. Chitin affinity studies with a recombinant SfPER-C1 peritrophin A-type domain fused to SUMO/His-tag confirmed that SfPER binds to chitin. Western blots of S. frugiperda larval proteins detected different sized variants of SfPER along the PM, with larger variants found towards the posterior PM. In vivo suppression of SfPER expression did not affect susceptibility of larvae to Bacillus thuringiensis toxin, but significantly decreased pupal weight and adult emergence, possibly due to PM structural alterations impairing digestion. Our results suggest SfPER could be a novel target for insect control.

Distribution of Glycan Motifs at the Surface of Midgut Cells in the Cotton Leafworm (Spodoptera littoralis) Demonstrated by Lectin Binding

Glycans are involved in many biological phenomena, including signal transduction, cell adhesion, immune response or differentiation. Although a few papers have reported on the role of glycans in the development and proper functioning of the insect midgut, no data are available regarding the localization of the glycan structures on the surface of the cells in the gut of insects. In this paper, we analyzed the spatial distribution of glycans present on the surface of the midgut cells in larvae of the cotton leafworm Spodoptera littoralis, an important agricultural pest insect worldwide. For this purpose, we established primary midgut cell cultures, probed these individual cells that are freely suspended in liquid medium with a selection of seven fluorescently labeled lectins covering a range of different carbohydrate binding specificities [mannose oligomers (GNA and HHA), GalNAc/Gal (RSA and SSA), GlcNAc (WGA and Nictaba) and Neu5Ac(α-2,6)Gal/GalNAc (SNA-I)], and visualized the interaction of these lectins with the different zones of the midgut cells using confocal microscopy. Our analysis focused on the typical differentiated columnar cells with a microvillar brush border at their apical side, which are dominantly present in the Lepidopteran midgut and function in food digestion and absorption, and as well as on the undifferentiated stem cells that are important for midgut development and repair. Confocal microscopy analyses showed that the GalNAc/Gal-binding lectins SSA and RSA and the terminal GlcNAc-recognizing WGA bound preferentially to the apical microvillar zone of the differentiated columnar cells as compared to the basolateral pole. The reverse result was observed for the mannose-binding lectins GNA and HHA, as well as Nictaba that binds preferentially to GlcNAc oligomers. Furthermore, differences in lectin binding to the basal and lateral zones of the cell membranes of the columnar cells were apparent. In the midgut stem cells, GNA and Nictaba bound more strongly to the membrane of these undifferentiated cells compared to the microvillar pole of the columnar cells, while SSA, HHA, WGA, and SNA-I showed stronger binding to the microvilli. Our results indicated that polarization of the midgut cells is also reflected by a specific distribution of glycans, especially between the basal and microvillar pole. The data are discussed in relation to the functioning and development of the insect midgut.

Autographa californica Multiple Nucleopolyhedrovirus AC83 is a Per Os Infectivity Factor (PIF) Protein Required for Occlusion-Derived Virus (ODV) and Budded Virus Nucleocapsid Assembly as well as Assembly of the PIF Complex in ODV Envelopes

Baculovirus occlusion-derived virus (ODV) initiates infection of lepidopteran larval hosts by binding to the midgut epithelia, which is mediated by per os infectivity factors (PIFs). Autographa californica multiple nucleopolyhedrovirus (AcMNPV) encodes seven PIF proteins, of which PIF1 to PIF4 form a core complex in ODV envelopes to which PIF0 and PIF6 loosely associate. Deletion of any pif gene results in ODV being unable to bind or enter midgut cells. AC83 also associates with the PIF complex, and this study further analyzed its role in oral infectivity to determine if it is a PIF protein. It had been proposed that AC83 possesses a chitin binding domain that enables transit through the peritrophic matrix; however, no chitin binding activity has ever been demonstrated. AC83 has been reported to be found only in the ODV envelopes, but in contrast, the Orgyia pseudotsugata MNPV AC83 homolog is associated with both ODV nucleocapsids and envelopes. In addition, unlike known pif genes, deletion of ac83 eliminates nucleocapsid formation. We propose a new model for AC83 function and show AC83 is associated with both ODV nucleocapsids and envelopes. We also further define the domain required for nucleocapsid assembly. The cysteine-rich region of AC83 is also shown not to be a chitin binding domain but a zinc finger domain required for the recruitment or assembly of the PIF complex to ODV envelopes. As such, AC83 has all the properties of a PIF protein and should be considered PIF8. In addition, pif7 (ac110) is reported as the 38th baculovirus core gene.IMPORTANCE ODV is essential for the per os infectivity of the baculovirus AcMNPV. To initiate infection, ODV binds to microvilli of lepidopteran midgut cells, a process which requires a group of seven virion envelope proteins called PIFs. In this study, we reexamined the function of AC83, a protein that copurifies with the ODV PIFs, to determine its role in the oral infection process. A zinc finger domain was identified and a new model for AC83 function was proposed. In contrast to previous studies, AC83 was found to be physically located in both the envelope and nucleocapsid of ODV. By deletion analysis, the AC83 domain required for nucleocapsid assembly was more finely delineated. We show that AC83 is required for PIF complex formation and conclude that it is a true per os infectivity factor and should be called PIF8.

Identification of the Mamestra configurata (Lepidoptera: Noctuidae) peritrophic matrix proteins and enzymes involved in peritrophic matrix chitin metabolism

The peritrophic matrix (PM) is essential for insect digestive system physiology as it protects the midgut epithelium from damage by food particles, pathogens, and toxins. The PM is also an attractive target for development of new pest control strategies due to its per os accessibility. To understand how the PM performs these functions, the molecular architecture of the PM was examined using genomic and proteomic approaches in Mamestra configurata (Lepidoptera: Noctuidae), a major pest of cruciferous oilseed crops in North America. Liquid chromatography-tandem mass spectrometry analyses of the PM identified 82 proteins classified as: (i) peritrophins, including a new class with a CBDIII domain; (ii) enzymes involved in chitin modification (chitin deacetylases), digestion (serine proteases, aminopeptidases, carboxypeptidases, lipases and α-amylase) or other reactions (β-1,3-glucanase, alkaline phosphatase, dsRNase, astacin, pantetheinase); (iii) a heterogenous group consisting of polycalin, REPATs, serpin, C-Type lectin and Lsti99/Lsti201 and 3 novel proteins without known orthologs. The genes encoding PM proteins were expressed predominantly in the midgut. cDNAs encoding chitin synthase-2 (McCHS-2), chitinase (McCHI), and β-N-acetylglucosaminidase (McNAG) enzymes, involved in PM chitin metabolism, were also identified. McCHS-2 expression was specific to the midgut indicating that it is responsible for chitin synthesis in the PM, the only chitinous material in the midgut. In contrast, the genes encoding the chitinolytic enzymes were expressed in multiple tissues. McCHS-2, McCHI, and McNAG were expressed in the midgut of feeding larvae, and NAG activity was present in the PM. This information was used to generate an updated model of the lepidopteran PM architecture.

GUT GENES ASSOCIATED WITH THE PERITROPHIC MATRIX IN Reticulitermes flavipes (Blattodea: Rhinotermitidae): IDENTIFICATION AND CHARACTERIZATION

The peritrophic matrix (PM) is an acellular structure that lines the gut of most insects. It is an attractive target for pest management strategies because of its close involvement in digestive processes and role as a barrier against pathogens and toxins. The purpose of this study was to identify and characterize the genes that translate for principal components of the Reticulitermes flavipes PM. Genes encoding a gut chitin synthase (CHS), two proteins with peritrophin-A domains, and a chitin deacetylase were identified from an R. flavipes symbiont-free gut cDNA library, a pyrosequencing study of termite lignocellulose digestion, and a metatranscriptomic analysis of R. flavipes fed on agricultural biomass. Quantitative expression analysis of the identified genes, in the termite digestive tract, revealed that the transcripts coding for a CHS (RfCHSB) and the proteins with peritrophin-A domains (RfPPAD1 and RfPPAD2) were predominantly expressed in the midgut, suggesting an association with the PM. The peritrophin identity of the RfPPAD2 gene was confirmed by immunodetection of its translated peptide in the midgut and PM. The discovery and characterization of PM components of R. flavipes provides a basis for further investigation of the viability of this structure as a target for candidate termiticides.

Spatial and temporal synthesis of Mamestra configurata peritrophic matrix through a larval stadium

The structure and synthesis of the Mamestra configurata peritrophic matrix (PM) was examined at various time points during a larval stadium. Bright field and confocal fluorescence microscopy revealed major differences between the PM of feeding and molting larvae. The PM from feeding larvae was thinner and composed of approximately 5-10 layers. In contrast, mid-molt larvae had a chitinaceaous PM composed of multiple thick layers which filled most of the midgut lumen. PM synthesis initiates in the anterior midgut, based on the expression of genes encoding chitin synthase-2 (CHS-2), coincident with the incorporation of the major structural PM proteins (McIIM1, McIIM2 and McPM1). This is followed by reinforcement with other PM proteins (McIIM3 and McIIM4) as it moves toward the posterior of the midgut. Chitin deacetylase (McCDA1) was associated only with the anterior PM. Collectively, these findings indicate that the structural properties of the PM differ along the length of the midgut. Genes encoding chitinolytic enzymes (McCHI and McNAG) were expressed and exochitinase activity was present when the PM had degraded (pre-molt) and when the new PM was forming (mid-molt), indicating that they are involved in either PM turnover and/or maintenance dependent upon the stage.