Characterization and expression of the beta-N-acetylhexosaminidase gene family of Tribolium castaneum

Structure-Based High-Efficiency Homogeneous Antibody Platform by Endoglycosidase Sz Provides Insights into Its Transglycosylation Mechanism

Monoclonal antibodies (mAbs) have gradually dominated the drug markets for various diseases. Improvement of the therapeutic activities of mAbs has become a critical issue in the pharmaceutical industry. A novel endo-β-N-acetylglucosaminidase, EndoSz, from Streptococcus equisubsp. zooepidemicus Sz105 is discovered and applied to enhance the activities of mAbs. Our studies demonstrate that the mutant EndoSz-D234M possesses an excellent transglycosylation activity to generate diverse glycoconjugates on mAbs. We prove that EndoSz-D234M can be applied to various marketed therapeutic antibodies and those in development for antibody remodeling. The remodeled homogeneous antibodies (mAb-G2S2) produced by EndoSz-D234M increase the relative ADCC activities by 3-26-fold. We further report the high-resolution crystal structures of EndoSz-D234M in the apo-form at 2.15 Å and the complex form with a bound G2S2-oxazoline intermediate at 2.25 Å. A novel pH-jump method was utilized to obtain the complex structure with a high resolution. The detailed interactions of EndoSz-D234M and the carried G2S2-oxazoline are hence delineated. The oxazoline sits in a hole, named the oxa-hole, which stabilizes the G2S2-oxazoline in transit and catalyzes the further transglycosylation reaction while targeting Asn-GlcNAc (+1) of Fc. In the oxa-hole, the H-bonding network involved with oxazoline dominates the transglycosylation activity. A mobile loop2 (a.a. 152-159) of EndoSz-D234M reshapes the binding grooves for the accommodation of G2S2-oxazoline upon binding, at which Trp154 forms a hydrogen bond with Man (-2). The long loop4 (a.a. 236-248) followed by helix3 is capable of dominating the substrate selectivity of EndoSz-D234M. In addition, the stepwise transglycosylation behavior of EndoSz-D234M is elucidated. Based on the high-resolution structures of the apo-form and the bound form with G2S2-oxazoline as well as a systematic mutagenesis study of the relative transglycosylation activity, the transglycosylation mechanism of EndoSz-D234M is revealed.

Identification and functional analysis of two potential RNAi targets for chitin degradation in Holotrichia parallela Motschulsky (Insecta Coleoptera)

Chitin metabolism enzymes are safe and desirable targets for pest management. β-N-acetylglucosaminidase (NAG) and N-acetylglucosamine kinase (NAGK) are involved in chitin degradation. NAG is the main glycosidase that works synergistically with chitinases. NAGK is a key enzyme for the generation of UDP-Nacetylglucosamine (UDP-GlcNAc) and for the conversion of GlcNAc into GlcNAc 6-phosphate (GlcNAc-6-P). In this study, NAG and NAGK genes were identified from Holotrichia parallela, a polyphagous soil pest that causes serious damage to crops. The spatiotemporal expression investigated by RT-qPCR indicated that the two genes are expressed in all larval developmental stages. HpNAG is highly expressed in the integument and HpNAGK overexpressed in the midgut. After injection of dsHpNAG and dsHpNAGK, a significant RNAi effect was found after 72 h and larvae stopped growing. The survival rates of larvae were 13.3% and 16.7%, respectively. RNAi of HpNAG and HpNAGK regulated the expression levels of chitin metabolism-related genes, indicating that these two genes could be critical in the chitin metabolism. Furthermore, silencing HpNAG and HpNAGK reduced the thickness of the cuticle, and decreased its content of chitin. The study will lay a foundation for further clarifying the mechanism of chitin metabolism and provide potential targets for the biological control of H. parallela larvae.

Genomic and transcriptomic analyses of chitin metabolism enzymes in Tenebrio molitor

Chitin is of great importance in the cuticle and inner cuticular linings of insects. Chitin synthases (CHSs), chitin deacetylases (CDAs), chitinases (CHTs), and β-N-acetylhexosaminidases (HEXs) are important enzymes required for chitin metabolism, and play essential roles in development and metamorphosis. Although chitin metabolism genes have been well characterized in limited insects, the information in the yellow mealworm, Tenebrio molitor, a model insect, is presently still unavailable. With the help of bioinformatics, we identified 54 genes that encode putative chitin metabolism enzymes, including 2 CHSs, 10 CDAs, 32 CHTs, and 10 HEXs in the genome of T. molitor. All these genes have the conserved domains and motifs of their corresponding protein family. Phylogenetic analyses indicated that CHS genes were divided into two groups. CDA genes were clustered into five groups. CHT genes were phylogenetically grouped into 11 clades, among which 1 in the endo-β-N-acetylglucosaminidases group and the others were classified in the glycoside hydrolase family 18 groups. HEX genes were assorted into six groups. Developmental and tissue-specific expression profiling indicated that the identified chitin metabolism genes showed dynamical expression patterns concurrent with specific instar during molting period, suggesting their significant roles in molting and development. They were predominantly expressed in different tissues or body parts, implying their functional specialization and diversity. The results provide important information for further clarifying their biological functions using the yellow mealworm as an ideal experimental insect.

Nuclear receptor HR3 mediates transcriptional regulation of chitin metabolic genes during molting in Tribolium castaneum

BACKGROUND

Chitin, a major component of insect cuticles, plays a critical role in insect molting and morphogenesis. Thus, coordination of chitin remodeling during insect development requires tight transcriptional control of the chitin metabolism genes involved in chitin synthesis, assembly and degradation. However, the molecular mechanism underlying transcriptional coordination of chitin metabolism genes during beetle development is not yet completely understood.

RESULTS

We cloned the full-length cDNA encoding hormone receptor 3 (TcHR3) from Tribolium castaneum and showed a critical role of TcHR3 in modulating chitin metabolism gene expression during molting. Genome-wide transcriptome analysis of HR3-deficient old larvae using RNA sequencing analysis revealed a positive correlation between TcHR3 and transcription of chitin metabolism genes involved in chitin synthesis and degradation. In addition, HR3 overexpression significantly induced the gene promoter activity of N-acetylglucosaminidase 1 (NAG1) involved in chitin degradation and UDP-N-acetylglucosamine pyrophosphorylase 1 (UAP1) involved in chitin synthesis. Chromatin immunoprecipitation analysis revealed that HR3 could directly bind to HR3-response element of NAG1 and UAP1 promoters. Finally, HR3-deficient late instar larvae and prepupae exhibited defects in larval-larval and larval-pupal molting, respectively, leading to eventual larval death because developing larvae were trapped inside the old cuticle as a result of abnormal chitin metabolism.

CONCLUSION

TcHR3 is a transcriptional regulator of chitin metabolic genes for molting of T. castaneum. Controlling the molting system by TcHR3 might be a new management strategy for selective control of red flour beetle infestation. © 2022 Society of Chemical Industry.

A midgut-specific lytic polysaccharide monooxygenase of Locusta migratoria is indispensable for the deconstruction of the peritrophic matrix

Lytic polysaccharide monooxygenases (LPMOs) are important enzymes that boost the hydrolysis of recalcitrant polysaccharides, such as chitin. They are found extensively in different insect species and are classified as auxiliary activities family 15 (AA15) LPMOs (LPMO15). Some of them were identified from the insect midgut and proven to act on chitin. However, knowledge about their physiological roles during insect growth and development remains limited. Here, we found that midgut-specific LPMO15s are widely distributed in different insect orders, such as the orthopteran Locusta migratoria and the lepidopteran Bombyx mori. Using L. migratoria as a model insect, the function of midgut-specific LmLPMO15-3 during development was investigated. Double-stranded RNA-mediated downregulation of LmLPMO15-3 expression at the 4th or 5th instar nymph stage severely decreased the survival rate and resulted in lethal phenotypes. Hematoxylin and eosin staining results indicated that the deficient individuals exhibited incompletely digested peritrophic matrix (PM), which suggested that LmLPMO15-3 is essential for the deconstruction of the PM during molting. This study provides direct evidence of the physiological importance of a midgut-specific LPMO15 during insect development. As L. migratoria is one of the most destructive agricultural pests, LmLPMO15-3 is a potential target for pest management.

AA15 lytic polysaccharide monooxygenase is required for efficient chitinous cuticle turnover during insect molting

Microbial lytic polysaccharide monooxygenases (LPMOs) catalyze the oxidative cleavage of crystalline polysaccharides including chitin and cellulose. The discovery of a large assortment of LPMO-like proteins widely distributed in insect genomes suggests that they could be involved in assisting chitin degradation in the exoskeleton, tracheae and peritrophic matrix during development. However, the physiological functions of insect LPMO-like proteins are still undetermined. To investigate the functions of insect LPMO15 subgroup I-like proteins (LPMO15-1s), two evolutionarily distant species, Tribolium castaneum and Locusta migratoria, were chosen. Depletion by RNAi of T. castaneum TcLPMO15-1 caused molting arrest at all developmental stages, whereas depletion of the L. migratoria LmLPMO15-1, prevented only adult eclosion. In both species, LPMO15-1-deficient animals were unable to shed their exuviae and died. TEM analysis revealed failure of turnover of the chitinous cuticle, which is critical for completion of molting. Purified recombinant LPMO15-1-like protein from Ostrinia furnacalis (rOfLPMO15-1) exhibited oxidative cleavage activity and substrate preference for chitin. These results reveal the physiological importance of catalytically active LPMO15-1-like proteins from distant insect species and provide new insight into the enzymatic mechanism of cuticular chitin turnover during molting.

Advances in Optical Sensors of N-Acetyl-β-d-hexosaminidase (N-Acetyl-β-d-glucosaminidase)

N-Acetyl-β-d-hexosaminidases (EC 3.2.1.52) are exo-acting glycosyl hydrolases that remove N-acetyl-β-d-glucosamine (Glc-NAc) or N-acetyl-β-d-galactosamine (Gal-NAc) from the nonreducing ends of various biomolecules including oligosaccharides, glycoproteins, and glycolipids. The same enzymes are sometimes called N-acetyl-β-d-glucosaminidases, and this review article employs the shorthand descriptor HEX(NAG) to indicate that the terms HEX or NAG are used interchangeably in the literature. The wide distribution of HEX(NAG) throughout the biosphere and its intracellular location in lysosomes combine to make it an important enzyme in food science, agriculture, cell biology, medical diagnostics, and chemotherapy. For more than 50 years, researchers have employed chromogenic derivatives of N-acetyl-β-d-glucosaminide in basic assays for biomedical research and clinical chemistry. Recent conceptual and synthetic innovations in molecular fluorescence sensors, along with concurrent technical improvements in instrumentation, have produced a growing number of new fluorescent imaging and diagnostics methods. A systematic summary of the recent advances in optical sensors for HEX(NAG) is provided under the following headings: assessing kidney health, detection and treatment of infectious disease, fluorescence imaging of cancer, treatment of lysosomal disorders, and reactive probes for chemical biology. The article concludes with some comments on likely future directions.

The Role of Chitooligosaccharidolytic β-N-Acetylglucosamindase in the Molting and Wing Development of the Silkworm Bombyx mori

The insect glycoside hydrolase family 20 β-N-acetylhexosaminidases (HEXs) are key enzymes involved in chitin degradation. In this study, nine HEX genes in Bombyx mori were identified by genome-wide analysis. Bioinformatic analysis based on the transcriptome database indicated that each gene had a distinct expression pattern. qRT-PCR was performed to detect the expression pattern of the chitooligosaccharidolytic β-N-acetylglucosaminidase (BmChiNAG). BmChiNAG was highly expressed in chitin-rich tissues, such as the epidermis. In the wing disc and epidermis, BmChiNAG has the highest expression level during the wandering stage. CRISPR/Cas9-mediated BmChiNAG deletion was used to study the function. In the BmChiNAG-knockout line, 39.2% of female heterozygotes had small and curly wings. The ultrastructure of a cross-section showed that the lack of BmChiNAG affected the stratification of the wing membrane and the formation of the correct wing vein structure. The molting process of the homozygotes was severely hindered during the larva to pupa transition. Epidermal sections showed that the endocuticle of the pupa was not degraded in the mutant. These results indicate that BmChiNAG is involved in chitin catabolism and plays an important role in the molting and wing development of the silkworm, which highlights the potential of BmChiNAG as a pest control target.

Transcriptome dynamics during metamorphosis of imaginal discs into wings and thoracic dorsum in Apis mellifera castes

BACKGROUND

Much of the complex anatomy of a holometabolous insect is built from disc-shaped epithelial structures found inside the larva, i.e., the imaginal discs, which undergo a rapid differentiation during metamorphosis. Imaginal discs-derived structures, like wings, are built through the action of genes under precise regulation.

RESULTS

We analyzed 30 honeybee transcriptomes in the search for the gene expression needed for wings and thoracic dorsum construction from the larval wing discs primordia. Analyses were carried out before, during, and after the metamorphic molt and using worker and queen castes. Our RNA-seq libraries revealed 13,202 genes, representing 86.2% of the honeybee annotated genes. Gene Ontology analysis revealed functional terms that were caste-specific or shared by workers and queens. Genes expressed in wing discs and descendant structures showed differential expression profiles dynamics in premetamorphic, metamorphic and postmetamorphic developmental phases, and also between castes. At the metamorphic molt, when ecdysteroids peak, the wing buds of workers showed maximal gene upregulation comparatively to queens, thus underscoring differences in gene expression between castes at the height of the larval-pupal transition. Analysis of small RNA libraries of wing buds allowed us to build miRNA-mRNA interaction networks to predict the regulation of genes expressed during wing discs development.

CONCLUSION

Together, these data reveal gene expression dynamics leading to wings and thoracic dorsum formation from the wing discs, besides highlighting caste-specific differences during wing discs metamorphosis.

Release of Mediator Enzyme β-Hexosaminidase and Modulated Gene Expression Accompany Hemocyte Degranulation in Response to Parasitism in the Silkworm Bombyx mori

In insects infections trigger hemocyte-mediated immune reactions including degranulation by exocytosis; however, involvement of mediator enzymes in degranulation process is unknown in insects. We report here that in silkworm Bombyx mori, infection by endoparasitoid Exorista bombycis and microsporidian Nosema bombycis activated granulation in granulocytes and promoted degranulation of accumulated structured granules. During degranulation the mediator lysosomal enzyme β-hexosaminidase showed increased activity and expression of β-hexosaminidase gene was enhanced. The events were confirmed in vitro after incubation of uninfected hemocytes with E. bombycis larval tissue protein. On infection, cytotoxicity marker enzyme lactate dehydrogenase (LDH) was released from the hemocytes illustrating cell toxicity. Strong positive correlation (R² = 0.71) between LDH activity and β-hexosaminidase released after the infection showed parasitic-protein-induced hemocyte damage and accompanied release of the enzymes. Expression of β-hexosaminidase gene was enhanced in early stages after infection followed by down regulation. The expression showed positive correlation (R² = 0.705) with hexosaminidase activity pattern. B. mori hexosaminidase showed 98% amino acid similarity with that of B. mandarina showing origin from same ancestral gene; however, 45-60% varied from other lepidopterans showing diversity. The observation signifies the less known association of hexosaminidase in degranulation of hemocytes induced by parasitic infection in B. mori and its divergence in different species.

Leishmania infection induces a limited differential gene expression in the sand fly midgut

BACKGROUND

Sand flies are the vectors of Leishmania parasites. To develop in the sand fly midgut, Leishmania multiplies and undergoes various stage differentiations giving rise to the infective form, the metacyclic promastigotes. To determine the changes in sand fly midgut gene expression caused by the presence of Leishmania, we performed RNA-Seq of uninfected and Leishmania infantum-infected Lutzomyia longipalpis midguts from seven different libraries corresponding to time points which cover the various Leishmania developmental stages.

RESULTS

The combined transcriptomes resulted in the de novo assembly of 13,841 sand fly midgut transcripts. Importantly, only 113 sand fly transcripts, about 1%, were differentially expressed in the presence of Leishmania parasites. Further, we observed distinct differentially expressed sand fly midgut transcripts corresponding to the presence of each of the various Leishmania stages suggesting that each parasite stage influences midgut gene expression in a specific manner. Two main patterns of sand fly gene expression modulation were noted. At early time points (days 1-4), more transcripts were down-regulated by Leishmania infection at large fold changes (> 32 fold). Among the down-regulated genes, the transcription factor Forkhead/HNF-3 and hormone degradation enzymes were differentially regulated on day 2 and appear to be the upstream regulators of nutrient transport, digestive enzymes, and peritrophic matrix proteins. Conversely, at later time points (days 6 onwards), most of the differentially expressed transcripts were up-regulated by Leishmania infection with small fold changes (< 32 fold). The molecular functions of these genes have been associated with the metabolism of lipids and detoxification of xenobiotics.

CONCLUSION

Overall, our data suggest that the presence of Leishmania produces a limited change in the midgut transcript expression profile in sand flies. Further, Leishmania modulates sand fly gene expression early on in the developmental cycle in order to overcome the barriers imposed by the midgut, yet it behaves like a commensal at later time points where a massive number of parasites in the anterior midgut results only in modest changes in midgut gene expression.

The beta-1, 4-N-acetylglucosaminidase 1 gene, selected by domestication and breeding, is involved in cocoon construction of Bombyx mori

Holometabolous insects have distinct larval, pupal, and adult stages. The pupal stage is typically immobile and can be subject to predation, but cocoon offers pupal protection for many insect species. The cocoon provides a space in which the pupa to adult metamorphosis occurs. It also protects the pupa from weather, predators and parasitoids. Silk protein is a precursor of the silk used in cocoon construction. We used the silkworm as a model species to identify genes affecting silk protein synthesis and cocoon construction. We used quantitative genetic analysis to demonstrate that β-1,4-N-acetylglucosaminidase 1 (BmGlcNase1) is associated with synthesis of sericin, the main composite of cocoon. BmGlcNase1 has an expression pattern coupled with silk gland development and cocoon shell weight (CSW) variation, and CSW is an index of the ability to synthesize silk protein. Up-regulated expression of BmGlcNase1 increased sericin content by 13.9% and 22.5% while down-regulation reduced sericin content by 41.2% and 27.3% in the cocoons of females and males, respectively. Genomic sequencing revealed that sequence variation upstream of the BmGlcNase1 transcriptional start site (TSS) is associated with the expression of BmGlcNase1 and CSW. Selective pressure analysis showed that GlcNase1 was differentially selected in insects with and without cocoons (ω₁ = 0.044 vs. ω₂ = 0.154). This indicates that this gene has a conserved function in the cocooning process of insects. BmGlcNase1 appears to be involved in sericin synthesis and silkworm cocooning.

The cocoon provides a protected space for the metamorphosis of many insect species. Silk protein is a precursor of the fiber used for cocoon construction. Deciphering the genetic basis underlying silk protein synthesis will improve our understanding of cocoon construction and the adaptations of species that construct cocoons. We used the silkworm (Bombyx mori) as a model to identify genes affecting silk protein synthesis and cocoon construction. Quantitative genetic analysis was used to show that β-1,4-N-acetylglucosaminidase 1 (BmGlcNase1), a gene selected during silkworm domestication and breeding, is associated with sericin synthesis. Transgenic-based functional validation confirmed that BmGlcNase1 positively regulates sericin content in the silkworm cocoon. The selective pressure of GlcNase1 in the evolution of insects with cocoons is higher than those without cocoons. This indicates that it has a conserved function in the cocooning process. These results reveal aspects of the genetic basis of silk protein synthesis and the cocoon construction of insects.

Insect Cuticular Chitin Contributes to Form and Function

Chitin contributes to the rigidity of the insect cuticle and serves as an attachment matrix for other cuticular proteins. Deficiency of chitin results in abnormal embryos, cuticular structural defects and growth arrest. When chitin is not turned over during molting, the developing insect is trapped inside the old cuticle. Partial deacetylation of cuticular chitin is also required for proper laminar organization of the cuticle and vertical pore canals, molting, and locomotion. Thus, chitin and its modifications strongly influence the structure of the exoskeleton as well as the physiological functions of the insect. Internal tendons and specialized epithelial cells called "tendon cells" that arise from the outer layer of epidermal cells provide attachment sites at both ends of adult limb muscles. Membrane processes emanating from both tendon and muscle cells interdigitate extensively to strengthen the attachment of muscles to the extracellular matrix (ECM). Protein ligands that bind to membrane-bound integrin complexes further enhance the adhesion between muscles and tendons. Tendon cells contain F-actin fiber arrays that contribute to their rigidity. In the cytoplasm of muscle cells, proteins such as talin and other proteins provide attachment sites for cytoskeletal actin, thereby increasing integrin binding and activation to mechanically couple the ECM with actin in muscle cells. Mutations in integrins and their ligands, as well as depletion of chitin deacetylases, result in defective locomotion and muscle detachment from the ECM. Thus, chitin in the cuticle and chitin deacetylases strongly influence the shape and functions of the exoskeleton as well as locomotion of insects.

Gene Expression in the Salivary Gland of Rhipicephalus (Boophilus) microplus Fed on Tick-Susceptible and Tick-Resistant Hosts

The success of cattle tick fixation largely depends on the secretion of substances that alter the immune response of the host. The majority of these substances are expressed by the parasite salivary gland and secreted in tick saliva. It is known that hosts can mount immune responses against ticks and bovine European breeds, and bovine industrial crossbreeds are more susceptible to infestations than are Bos indicus cattle. To identify candidates for the development of novel control strategies for the cattle tick Rhipicephalus (Boophilus) microplus, a salivary gland transcriptome analysis of engorged females fed on susceptible or resistant hosts was performed. Using RNA-Seq, transcriptomes were de novo assembled and produced a total of 235,451 contigs with 93.3% transcriptome completeness. Differential expression analysis identified 137 sequences as differentially expressed genes (DEGs) between ticks raised on tick-susceptible or tick-resistant cattle. DEGs predicted to be secreted proteins include innexins, which are transmembrane proteins that form gap junction channels; the transporters Na⁺/dicarboxylate, Na⁺/tricarboxylate, and phosphate transporter and a putative monocarboxylate transporter; a phosphoinositol 4-phosphate adaptor protein; a cysteine-rich protein containing a trypsin inhibitor-like (TIL) domain; a putative defense protein 3 containing a reeler domain; and an F-actin-uncapping protein LRRC16A with a CARMIL_C domain; these genes were upregulated in ticks fed on tick-susceptible cattle. DEGs predicted to be non-secreted proteins included a small heat shock protein and the negative elongation factor B-like, both acting in a coordinated manner to increase HSP transcript levels in the salivary glands of the ticks fed on tick-susceptible cattle; the 26S protease regulatory subunit 6B and another chaperone with similarity to calnexin, also upregulated in ticks fed on tick-susceptible cattle; an EF-hand calcium binding protein and a serine carboxypeptidase (SCP), both involved in the blood coagulation cascade and upregulated in ticks fed on tick-susceptible cattle; and two ribosomal proteins, the 60S acidic ribosomal protein P2 and the 60S ribosomal protein L19. These results help to characterize cattle tick salivary gland gene expression in tick-susceptible and tick-resistant hosts and suggest new putative targets for the control of tick infestations, as those genes involved in the mechanism of stress response during blood feeding.

Transcriptome of pleuropodia from locust embryos supports that these organs produce enzymes enabling the larva to hatch

Background

Pleuropodia are limb-derived glandular organs that transiently appear on the first abdominal segment in embryos of insects from majority of “orders”. They are missing in the genetic model Drosophila and little is known about them. Experiments carried out on orthopteran insects 80 years ago indicated that the pleuropodia secrete a “hatching enzyme” that digests the serosal cuticle to enable the larva to hatch, but evidence by state-of-the-art molecular methods is missing.

Results

We used high-throughput RNA-sequencing to identify the genes expressed in the pleuropodia of the locust Schistocerca gregaria (Orthoptera). First, using transmission electron microscopy we studied the development of the pleuropodia during 11 stages of the locust embryogenesis. We show that the glandular cells differentiate and start secreting just before the definitive dorsal closure of the embryo and the secretion granules outside the cells become more abundant prior to hatching. Next, we generated a comprehensive embryonic reference transcriptome for the locust and used it to study genome wide gene expression across ten morphologicaly defined stages of the pleuropodia. We show that when the pleuropodia have morphological markers of functional organs and produce secretion, they are primarily enriched in transcripts associated with transport functions. They express genes encoding enzymes capable of digesting cuticular protein and chitin. These include the potent cuticulo-lytic Chitinase 5, whose transcript rises just before hatching. Unexpected finding was the enrichment in transcripts for immunity-related enzymes. This indicates that the pleuropodia are equipped with epithelial immunity similarly as barrier epithelia in postembryonic stages.

Conclusions

These data provide transcriptomic support for the historic hypothesis that pleuropodia produce cuticle-degrading enzymes and function in hatching. They may also have other functions, such as facilitation of embryonic immune defense. By the genes that they express the pleuropodia are specialized embryonic organs and apparently an important though neglected part of insect physiology.

Knockdown of β-N-acetylglucosaminidase 2 Impairs Molting and Wing Development in Lasioderma serricorne (Fabricius)

β-N-acetylglucosaminidases (NAGs) are carbohydrate enzymes that degrade chitin oligosaccharides into N-acetylglucosamine monomers. This process is important for chitin degradation during insect development and metamorphosis. We identified and evaluated a β-N-acetylglucosaminidase 2 gene (LsNAG2) from the cigarette beetle, Lasioderma serricorne (Fabricius). The full-length open reading frame of LsNAG2 was 1776 bp and encoded a 591 amino acid protein. The glycoside hydrolase family 20 (GH20) catalytic domain and an additional GH20b domain of the LsNAG2 protein were highly conserved. Phylogenetic analysis revealed that LsNAG2 clustered with the group II NAGs. Quantitative real-time PCR analyses showed that LsNAG2 was expressed in all developmental stages and was most highly expressed in the late larval and late pupal stages. In the larval stage, LsNAG2 was predominantly expressed in the integument. Knockdown of LsNAG2 in fifth instar larvae disrupted larval-pupal molting and reduced the expression of four chitin synthesis genes (trehalase 1 (LsTRE1), UDP-N-acetylglucosamine pyrophosphorylase 1 and 2 (LsUAP1 and LsUAP2), and chitin synthase 1 (LsCHS1)). In late pupae, LsNAG2 depletion resulted in abnormal adult eclosion and wing deformities. The expression of five wing development-related genes (teashirt (LsTSH), vestigial (LsVG), wingless (LsWG), ventral veins lacking (LsVVL), and distal-less (LsDLL)) significantly declined in the LsNAG2-depleted beetles. These findings suggest that LsNAG2 is important for successful molting and wing development of L. serricorne.

Progress and prospects of arthropod chitin pathways and structures as targets for pest management

Chitin is a structural component of the arthropod cuticular exoskeleton and the peritrophic matrix of the gut, which play crucial roles in growth and development. In the past few decades, our understanding of the composition, biosynthesis, assembly, degradation, and regulation of chitinous structures has increased. Many chemicals have been developed that target chitin biosynthesis (benzoyphenyl ureas, etoxazole), chitin degradation (allosamidin, psammaplin), and chitin regulation (benzoyl hydrazines), thus resulting in molting deformities and lethality. In addition, proteins that disrupt chitin structures, such as lectins, proteases, and chitinases have been utilized to halt feeding and induce mortality. Chitin-degrading enzymes, such as chitinases are also useful for improving the efficacy of bio-insecticides. Transgenic plants, baculoviruses, fungi, and bacteria have been engineered to express chitinases from a variety of organisms for control of arthropod pests. In addition, RNA interference targeting genes involved in chitin pathways and structures are now being investigated for the development of environmentally friendly pest management strategies. This review describes the chemicals and proteins used to target chitin structures and enzymes for arthropod pest management, as well as pest management strategies based upon these compounds, such as plant-incorporated-protectants and recombinant entomopathogens. Recent advances in RNA interference-based pest management, and how this technology can be used to target chitin pathways and structures are also discussed.

Knockdown of β-N-acetylglucosaminidase gene disrupts molting process in Heortia vitessoides Moore

β-N-acetylglucosaminidase (NAG) is a key enzyme in insect chitin metabolism and plays an important role in many physiological activities of insects. The HvNAG1 gene was identified from the Heortia vitessoides Moore (Lepidoptera: Crambidae) cDNA library and its expression patterns were determined using quantitative real-time polymerase chain reaction. The results indicated that HvNAG1 mRNA levels were high in the midgut and before molting, and 20E could induce its expression. Subsequently, the HvNAG1 gene was knocked down via RNA interference to identify its functions. We found that 3 μg of dsNAG1 resulted in optimal interference at 48 and 72 hr after injection, causing a decrease in NAG1 protein content, which resulted in abnormal or lethal phenotypes, and a sharp decrease in the survival rate. These results indicate that HvNAG1 plays a key role in the molting process of H. vitessoides. However, the silencing of HvNAG1 had no significant effect on the chitin metabolism-related genes tested in this study. Our present study provides a reference for further research on the utility of key genes involved in the chitin metabolic pathway in the insect molting process.

Novel Glycosylated Naphthalimide-Based Activatable Fluorescent Probe: A Tool for the Assessment of Hexosaminidase Activity and Intracellular Hexosaminidase Imaging

The development of effective detection methods for hexosaminidase is of great importance for the rapid screening of potential inhibitors in vitro and for the early diagnosis of related diseases ex vivo. In this study, the activatable fluorescent probes that are based on naphthalimide decorated with ethylene glycol units were synthesized using N-acetyl-β-d-glucosaminide as a hexosaminidase-responsive group. When exposed to this enzyme, the glucoside-linked naphthalimide moiety of 1c can be cleaved quickly with significant changes in both color (from colorless to yellow) and fluorescence (from blue to green). Probe 1c shows better water-solubility and fluorescence properties than common substrate 4-methylumbelliferyl N-acetyl-β-d-glucosaminide. Furthermore, the response mechanism of 1c to hexosaminidase was evaluated using HPLC analysis and TD-DFT calculations. Molecular docking was performed to investigate the interaction mode. In addition, 1c has successfully achieved the straightforward rapid discovery of effective hexosaminidase inhibitors. Fluorescence imaging experiments indicate that 1c has good cell safety and can be employed as a useful tool for detecting intracellular hexosaminidase activity.

Biosynthesis, modifications and degradation of chitin in the formation and turnover of peritrophic matrix in insects

The peritrophic matrix (PM) is an extracellular, semi-permeable biocomposite that lines the midgut of most insects. The PM serves as the first defense in the midgut to resist microorganisms such as viruses, bacteria and other pathogens, and to protect epithelial cells from mechanical damage. The PM also separates the midgut lumen into different compartments, which play important roles in nutrient ingestion and digestion. The PM is a highly dynamic structure that consists mainly of chitin fibers cross-linked by proteins, glycoproteins, and proteoglycans. The PM is continuously biosynthesized, assembled, and degraded in response to feeding and development. Chitin chains are synthesized by several enzymes and organized in several hierarchical levels, in which various PM-associated proteins appear to be essential for maintaining the structural integrity and physiological function of the PM. This review summarizes research advances on molecular components of the PM and their functions, as well as related proteins and enzymes that contribute to PM formation and modification. Crucial gaps in our current understanding of the PM are also addressed.

Key factors determining variations in RNA interference efficacy mediated by different double-stranded RNA lengths in Tribolium castaneum

Double-stranded RNA (dsRNA) length may affect RNA interference (RNAi) efficacy. Herein, variation in RNAi efficacy associated with dsRNA molecular length was confirmed via comparison of knockdown results following dsRNA injection into Tribolium castaneum. Through in vitro experiments with T. castaneum midgut, dsRNA accumulation in the midgut, degradation by midgut homogenates and persistence in haemolymph after injection were tested to determine the causes of RNAi efficacy variation. The comparative efficacies of dsRNAs were 480 bp ≈ 240 bp > 120 bp > 60 bp >> 21 bp. The combined midgut dsRNA accumulation and midgut homogenate-induced degradation analyses suggested cellular uptake to be the key barrier for 21 bp dsRNA functioning, but was likely not the main determinant of the variation in longer dsRNAs' (≥60 bp) bioactivity. In vitro RNAi experiment with T. castaneum midgut showed that long dsRNAs all significantly depleted the expression of corresponding genes, suggesting little variation in intracellular RNAi machinery's affinity for different dsRNA lengths. In vivo haemolymph content dynamics of different dsRNAs following injection indicated higher persistence of longer dsRNAs. In addition, comparison of the in vivo and in vitro RNAi efficacy also indicated the importance of haemolymph degradation. Thus, the varied efficacy of long dsRNAs resulted from their degradation by nucleases, which varied with dsRNA length.

Chitinous Structures as Potential Targets for Insect Pest Control

Chitinous structures are physiologically fundamental in insects. They form the insect exoskeleton, play important roles in physiological systems and provide physical, chemical and biological protections in insects. As critically important structures in insects, chitinous structures are attractive target sites for the development of new insect-pest-control strategies. Chitinous structures in insects are complex and their formation and maintenance are dynamically regulated with the growth and development of insects. In the past few decades, studies on insect chitinous structures have shed lights on the physiological functions, compositions, structural formation, and regulation of the chitinous structures. Current understanding of the chitinous structures has indicated opportunities for exploring new target sites for insect control. Mechanisms to disrupt chitinous structures in insects have been studied and strategies for the potential development of new means of insect control by targeting chitinous structures have been proposed and are practically to be explored.

Chitin in Arthropods: Biosynthesis, Modification, and Metabolism

Chitin is a structural constituent of extracellular matrices including the cuticle of the exoskeleton and the peritrophic matrix (PM) of the midgut in arthropods. Chitin chains are synthesized through multiple biochemical reactions, organized in several hierarchical levels and associated with various proteins that give their unique physicochemical characteristics of the cuticle and PM. Because, arthropod growth and morphogenesis are dependent on the capability of remodeling chitin-containing structures, chitin biosynthesis and degradation are highly regulated, allowing ecdysis and regeneration of the cuticle and PM. Over the past 20 years, much progress has been made in understanding the physiological functions of chitinous matrices. In this chapter, we mainly discussed the biochemical processes of chitin biosynthesis, modification and degradation, and various enzymes involved in these processes. We also discussed cuticular proteins and PM proteins, which largely determine the physicochemical properties of the cuticle and PM. Although rapid advances in genomics, proteomics, RNA interference, and other technologies have considerably facilitated our research in chitin biosynthesis, modification, and metabolism in recent years, many aspects of these processes are still partially understood. Further research is needed in understanding how the structural organization of chitin synthase in plasma membrane accommodate chitin biosynthesis, transport of chitin chain across the plasma membrane, and release of the chitin chain from the enzyme. Other research is also needed in elucidating the roles of chitin deacetylases in chitin organization and the mechanism controlling the formation of different types of chitin in arthropods.

Comparative Proteome Analysis Reveals that Cuticular Proteins Analogous to Peritrophin-Motif Proteins are Involved in the Regeneration of Chitin Layer in the Silk Gland of Bombyx mori at the Molting Stage

The silk gland of silkworm produces silk proteins during larval development. Many studies have long focused on the silk gland of the fifth instar larvae, but few have investigated this gland at other larval stages. In the present study, the silk gland proteomes of the fourth instar and fourth molt are analyzed using liquid chromatography-tandem mass spectrometry. In total, 2654 proteins are identified from the silk gland. A high abundance of ribosomal proteins and RR-motif chitin-binding proteins is identified during day 2 of the fourth instar (IV-2) larval developmental stage, and the expression of cuticular proteins analogous to peritrophin (CPAP)-motif chitin-binding proteins is higher during the fourth molt (IV-M). In all, nine enzymes are found to be involved in the chitin regeneration pathway in the silk gland. Among them, two chitinase and two chitin deacetylases are identified as CPAP-motif proteins. Furthermore, the expression of CPAP3-G, the most abundant CPAP-motif cuticular protein in the silk gland during the IV-M stage, is investigated using western blot and immunofluorescence analyses; CPAP3-G shows a reverse changing trend with chitin in the silk gland. The findings of this study suggest that CPAP-motif chitin-binding proteins are involved in the degradation of the chitin layer in the silk gland. The data have been deposited to the ProteomeXchange with identifier PXD008677.

Glycoside hydrolase family 18 and 20 enzymes are novel targets of the traditional medicine berberine

Berberine is a traditional medicine that has multiple medicinal and agricultural applications. However, little is known about whether berberine can be a bioactive molecule toward carbohydrate-active enzymes, which play numerous vital roles in the life process. In this study, berberine and its analogs were discovered to be competitive inhibitors of glycoside hydrolase family 20 β-N-acetyl-d-hexosaminidase (GH20 Hex) and GH18 chitinase from both humans and the insect pest Ostrinia furnacalis Berberine and its analog SYSU-1 inhibit insect GH20 Hex from O. furnacalis (OfHex1), with K_i values of 12 and 8.5 μm, respectively. Co-crystallization of berberine and its analog SYSU-1 in complex with OfHex1 revealed that the positively charged conjugate plane of berberine forms π-π stacking interactions with Trp⁴⁹⁰, which are vital to its inhibitory activity. Moreover, the 1,3-dioxole group of berberine binds an unexplored pocket formed by Trp³²², Trp⁴⁸³, and Val⁴⁸⁴, which also contributes to its inhibitory activity. Berberine was also found to be an inhibitor of human GH20 Hex (HsHexB), human GH18 chitinase (HsCht and acidic mammalian chitinase), and insect GH18 chitinase (OfChtI). Besides GH18 and GH20 enzymes, berberine was shown to weakly inhibit human GH84 O-GlcNAcase (HsOGA) and Saccharomyces cerevisiae GH63 α-glucosidase I (ScGluI). By analyzing the published crystal structures, berberine was revealed to bind with its targets in an identical mechanism, namely via π-π stacking and electrostatic interactions with the aromatic and acidic residues in the binding pockets. This paper reports new molecular targets of berberine and may provide a berberine-based scaffold for developing multitarget drugs.

Molecular characterization and function of β-N-acetylglucosaminidase from ridgetail white prawn Exopalaemon carinicauda

Chitin degradation is catalyzed by a two-component chitinolytic enzyme system, chitinase and β-N-acetylglucosaminidase (NAGase). In this paper, the full-length cDNA sequence encoding NAGase (EcNAG) was obtained from Exopalaemon carinicauda. The deduced amino acid sequence of EcNAG open reading frame (ORF) contained one Glycohydro_20b2 domain and one Glyco_hydro_20 domain. Based on the cDNA sequence, the genomic structure of EcNAG was characterized and it was composed of six exons and five introns. EcNAG mRNA majorly expressed in the hepatopancreas and epidermis. During the molting stages, EcNAG mRNA expression was well-regulated and its expression reached the highest level at the molting stage E. In addition, EcNAG was recombinant expressed in Pichia pastoris and the partial enzymatic characterization of recombinant EcNAG was confirmed. After being challenged with Vibrio parahaemolyticus and Aeromonas hydrophila, the expression of EcNAG was up-regulated significantly at 6 h and reached the peak at 12 h. And then, the expression began to down-regulated and came to the normal level at 72 h. It is helpful to research the relationship between the molt-related hormones and chitinlytic enzymes.

Protein Discovery: Combined Transcriptomic and Proteomic Analyses of Venom from the Endoparasitoid Cotesia chilonis (Hymenoptera: Braconidae)

Many species of endoparasitoid wasps provide biological control services in agroecosystems. Although there is a great deal of information on the ecology and physiology of host/parasitoid interactions, relatively little is known about the protein composition of venom and how specific venom proteins influence physiological systems within host insects. This is a crucial gap in our knowledge because venom proteins act in modulating host physiology in ways that favor parasitoid development. Here, we identified 37 possible venom proteins from the polydnavirus-carrying endoparasitoid Cotesia chilonis by combining transcriptomic and proteomic analyses. The most abundant proteins were hydrolases, such as proteases, peptidases, esterases, glycosyl hydrolase, and endonucleases. Some components are classical parasitoid venom proteins with known functions, including extracellular superoxide dismutase 3, serine protease inhibitor and calreticulin. The venom contains novel proteins, not recorded from any other parasitoid species, including tolloid-like proteins, chitooligosaccharidolytic β-N-acetylglucosaminidase, FK506-binding protein 14, corticotropin-releasing factor-binding protein and vascular endothelial growth factor receptor 2. These new data generate hypotheses and provide a platform for functional analysis of venom components.

Efficient and Regioselective Synthesis of β-GalNAc/GlcNAc-Lactose by a Bifunctional Transglycosylating β-N-Acetylhexosaminidase from Bifidobacterium bifidum

β-N-Acetylhexosaminidases have attracted interest particularly for oligosaccharide synthesis, but their use remains limited by the rarity of enzyme sources , low efficiency, and relaxed regioselectivity of transglycosylation. In this work, genes of 13 β-N-acetylhexosaminidases, including 5 from Bacteroides fragilis ATCC 25285, 5 from Clostridium perfringens ATCC 13124, and 3 from Bifidobacterium bifidum JCM 1254, were cloned and heterogeneously expressed in Escherichia coli The resulting recombinant enzymes were purified and screened for transglycosylation activity. A β-N-acetylhexosaminidase named BbhI, which belongs to glycoside hydrolase family 20 and was obtained from B. bifidum JCM 1254, possesses the bifunctional property of efficiently transferring both GalNAc and GlcNAc residues through β1-3 linkage to the Gal residue of lactose. The effects of initial substrate concentration, pH, temperature, and reaction time on transglycosylation activities of BbhI were studied in detail. With the use of 10 mM pNP-β-GalNAc or 20 mM pNP-β-GlcNAc as the donor and 400 mM lactose as the acceptor in phosphate buffer (pH 5.8), BbhI synthesized GalNAcβ1-3Galβ1-4Glc and GlcNAcβ1-3Galβ1-4Glc at maximal yields of 55.4% at 45°C and 4 h and 44.9% at 55°C and 1.5 h, respectively. The model docking of BbhI with lactose showed the possible molecular basis of strict regioselectivity of β1-3 linkage in β-N-acetylhexosaminyl lactose synthesis.

IMPORTANCE

Oligosaccharides play a crucial role in many biological events and therefore are promising potential therapeutic agents. However, their use is limited because large-scale production of oligosaccharides is difficult. The chemical synthesis requires multiple protecting group manipulations to control the regio- and stereoselectivity of glycosidic bonds. In comparison, enzymatic synthesis can produce oligosaccharides in one step by using glycosyltransferases and glycosidases. Given the lower price of their glycosyl donor and their broader acceptor specificity, glycosidases are more advantageous than glycosyltransferases for large-scale synthesis. β-N-Acetylhexosaminidases have attracted interest particularly for β-N-acetylhexosaminyl oligosaccharide synthesis, but their application is affected by having few enzyme sources, low efficiency, and relaxed regioselectivity of transglycosylation. In this work, we describe a microbial β-N-acetylhexosaminidase that exhibited strong transglycosylation activity and strict regioselectivity for β-N-acetylhexosaminyl lactose synthesis and thus provides a powerful synthetic tool to obtain biologically important GalNAcβ1-3Lac and GlcNAcβ1-3Lac.

The De Novo Transcriptome and Its Functional Annotation in the Seed Beetle Callosobruchus maculatus

Despite their unparalleled biodiversity, the genomic resources available for beetles (Coleoptera) remain relatively scarce. We present an integrative and high quality annotated transcriptome of the beetle Callosobruchus maculatus, an important and cosmopolitan agricultural pest as well as an emerging model species in ecology and evolutionary biology. Using Illumina sequencing technology, we sequenced 492 million read pairs generated from 51 samples of different developmental stages (larvae, pupae and adults) of C. maculatus. Reads were de novo assembled using the Trinity software, into a single combined assembly as well as into three separate assemblies based on data from the different developmental stages. The combined assembly generated 218,192 transcripts and 145,883 putative genes. Putative genes were annotated with the Blast2GO software and the Trinotate pipeline. In total, 33,216 putative genes were successfully annotated using Blastx against the Nr (non-redundant) database and 13,382 were assigned to 34,100 Gene Ontology (GO) terms. We classified 5,475 putative genes into Clusters of Orthologous Groups (COG) and 116 metabolic pathways maps were predicted based on the annotation. Our analyses suggested that the transcriptional specificity increases with ontogeny. For example, out of 33,216 annotated putative genes, 51 were only expressed in larvae, 63 only in pupae and 171 only in adults. Our study illustrates the importance of including samples from several developmental stages when the aim is to provide an integrative and high quality annotated transcriptome. Our results will represent an invaluable resource for those working with the ecology, evolution and pest control of C. maculatus, as well for comparative studies of the transcriptomics and genomics of beetles more generally.

Biosynthesis, Turnover, and Functions of Chitin in Insects

Chitin is a major component of the exoskeleton and the peritrophic matrix of insects. It forms complex structures in association with different assortments of cuticle and peritrophic matrix proteins to yield biocomposites with a wide range of physicochemical and mechanical properties. The growth and development of insects are intimately coupled with the biosynthesis, turnover, and modification of chitin. The genes encoding numerous enzymes of chitin metabolism and proteins that associate with and organize chitin have been uncovered by bioinformatics analyses. Many of these proteins are encoded by sets of large gene families. There is specialization among members within each family, which function in particular tissues or developmental stages. Chitin-containing matrices are dynamically modified at every developmental stage and are under developmental and/or physiological control. A thorough understanding of the diverse processes associated with the assembly and turnover of these chitinous matrices offers many strategies to achieve selective pest control.

The β-N-acetylhexosaminidase gene family in the brown planthopper, Nilaparvata lugens

β-N-Acetylhexosaminidases (HEXs) are enzymes that can degrade the chitin oligosaccharides that are produced by the activity of chitinases on chitin in insects. Using bioinformatic methods based on genome and transcriptome databases, 11 β-N-acetylhexosaminidase genes (NlHexs) in Nilaparvata lugens were identified and characterized. Phylogenetic analysis revealed a six-grouped tree topology. The O-Linked N-acetylglucosaminidase (O-GlcNAcase) group includes NlHex11, which harbours a catalytic domain that differs from that of the other 10 NlHexs. Observations of the expression of NlHexs during different developmental stages revealed that NlHex4 is expressed with periodicity during moulting. Although the tissue-specific expression patterns of most NlHexs were nonspecific, NlHex4 was found to be expressed mainly in the female reproductive system as well as in the integument. RNA interference (RNAi) demonstrated failure to shed the old cuticle only in the nymphs treated with double-stranded RNA (dsRNA) targeting NlHex4, and these nymphs eventually died; no observable morphological abnormalities were found in insects treated with dsRNAs targeting the other 10 NlHexs. Based on this study and our previous analyses, a '5 + 1 + 3' pattern of chitinolytic enzymes is proposed, in which five chitinases, one NlHEX and three chitin deacetylases are required for moulting in N. lugens. A better understanding of chitin metabolism in the hemimetabolous insect, N. lugens, would be achieved by considering three chitinolytic enzyme families: chitinase, chitin deacetylase and β-N-acetylhexosaminidase.

Two Chitin Biosynthesis Pathway Genes in Bactrocera dorsalis (Diptera: Tephritidae): Molecular Characteristics, Expression Patterns, and Roles in Larval-Pupal Transition

Glucose-6-phosphate isomerase (G6PI) and UDP-N-acetylglucosamine pyrophosphorylase (UAP), two key components in the chitin biosynthesis pathway, are critical for insect growth and metamorphosis. In this study, we identified the genes BdG6PI and BdUAP from the oriental fruit fly, Bactrocera dorsalis (Hendel). The open reading frames (ORFs) of BdG6PI (1,491 bp) and BdUAP (1,677 bp) encoded 496 and 558 amino acid residues, respectively. Multiple sequence alignments showed that BdG6PI and BdUAP had high amino acid sequence identity with other insect homologues. Quantitative real-time polymerase chain reaction (qPCR) analysis indicated that BdG6PI was mainly expressed in the early stages of third-instar larvae and adults, while significantly higher expression of BdUAP was observed in adults. Both transcripts were expressed highly in the Malpighian tubules, but only slightly in the tracheae. The expression of both BdG6PI and BdUAP was significantly up-regulated by 20-hydroxyecdysone exposure and down-regulated by starvation. Moreover, injection of double-stranded RNAs of BdG6PI and BdUAP into third-instar larvae significantly reduced the corresponding gene expressions. Additionally, silencing of BdUAP resulted in 65% death and abnormal phenotypes of larvae, while silencing of BdG6PI had a slight effect on insect molting. These findings provide some data on the roles of BdG6PI and BdUAP in B. dorsalis and demonstrate the potential role for BdUAP in larval-pupal transition.

Functional analysis of insect molting fluid proteins on the protection and regulation of ecdysis

Molting fluid accumulates between the old and new cuticles during periodical ecdysis in Ecdysozoa. Natural defects in insect ecdysis are frequently associated with melanization (an immunity response) occurring primarily in molting fluids, suggesting that molting fluid may impact immunity as well as affect ecdysis. To address this hypothesis, proteomic analysis of molting fluids from Bombyx mori during three different types of ecdysis was performed. Many proteins were newly identified, including immunity-related proteins, in each molting fluid. Molting fluids inhibited the growth of bacteria in vitro. The entomopathogenic fungi Beauveria bassiana, which can escape immune responses in feeding larvae, is quickly recognized by larvae during ecdysis, followed by melanization in molting fluid and old cuticle. Fungal conidia germination was delayed, and no hyphae were detected in the hemocoels of pharate instar insects. Molting fluids protect the delicate pharate instar insects with extremely thin cuticles against microorganisms. To explore the function of molting fluids in ecdysis regulation, based on protein similarity, 32 genes were selected for analysis in ecdysis regulation through RNAi in Tribolium castaneum, a model commonly used to study integument development because RNAi is difficult to achieve in B. mori. We identified 24 molting proteins that affected ecdysis after knockdown, with different physiological functions, including old cuticle protein recycling, molting fluid pressure balance, detoxification, and signal detection and transfer of molting fluids. We report that insects secrete molting fluid for protection and regulation of ecdysis, which indicates a way to develop new pesticides through interrupting insect ecdysis in the future.

Improvement of glycosylation structure by suppression of β-N-acetylglucosaminidases in silkworm

The baculovirus-silkworm recombinant protein expression system is an excellent method for achieving high-level expression and post-translational modifications, especially glycosylation. However, the presence of paucimannosidic-type N-glycan in glycoproteins restricts their clinical use. Paucimannosidic-type N-glycan is produced by insect-specific membrane-binding-type β-N-acetylglucosaminidase (GlcNAcase). In the silkworm, BmGlcNAcase1, BmGlcNAcase2, and BmFDL are membrane-binding-type GlcNAcases. We investigated the localization of these GlcNAcases and found that BmFDL and BmGlcNAcase2 were mainly located in the fat body and hemolymph, respectively. The fat body is the main tissue of recombinant protein expression by baculovirus, and many glycoproteins are secreted into the hemolymph. These results suggest that inhibition of BmFDL and BmGlcNAcase2 could increase GlcNAc-type N-glycan levels. We therefore injected a GlcNAcase inhibitor into silkworms to investigate changes in the N-glycan structure of the glycoprotein expressed by baculovirus; modest levels of GlcNAc-type N-glycan were observed (0.8% of total N-glycan). Next, we generated a transgenic silkworm in which RNA interference (RNAi) reduced the BmFDL transcript level and enzyme activity to 25% and 50%, respectively, of that of the control silkworm. The proportion of GlcNAc-type N-glycan increased to 4.3% in the RNAi-transgenic silkworm. We conclude that the structure of N-glycan can be changed by inhibiting the GlcNAcases in silkworm.

Irreversible inhibitory kinetics of mercuric ion on N-acetyl-β-D-glucosaminidase from Nile tilapia (Oreochromis niloticus)

N-acetyl-β-D-glucosaminidase (EC 3.2.1.52, NAGase), hydrolyzes dimers or trimers of N-acetyl-β-D-glucosamine (NAG) into monomers and is shown to be important for the reproduction of male animals. NAGase is purified from the spermary of Nile tilapia, and its enzyme activity can be strongly inhibited by mercuric chloride (HgCl2). In this paper, we determined the kinetics of HgCl2-mediated inhibition of NAGase, and our results showed that it was irreversible inhibition with an IC50 value at 2.70±0.02 μM. Moreover, Hg(2+) reduced the thermal and pH stability of the enzyme. We determined the inhibition kinetics of Hg(2+) by using the kinetic method of substrate reaction. With this inhibition model, the microscopic rate constants for the reaction of Hg(2+) with free enzyme (k1) and the enzyme-substrate complex ( [Formula: see text] ) were determined to be 4.42×10(-4) mM(-1) s(-1) and 7.06×10(-5) mM(-1) s(-1), respectively, indicating that the presence of substrate can protect NAGase from Hg(2+) inhibition.

The expression profile and promoter analysis of β-N-acetylglucosaminidases in the silkworm Bombyx mori

β-N-acetylglucosaminidase (GlcNAcase) is a key enzyme in the chitin decomposition process. In this study, we investigated the gene expression profile of GlcNAcases and the regulation mechanism for one of these genes, BmGlcNAcase1, in the silkworm. We performed sequence analysis of GlcNAcase. Using dual-spike-in qPCR method, we examined the expression of Bombyx β-N-acetylglucosaminidases (BmGlcNAcases) in various tissues of silkworm as well as expression changes after stimulation with ecdysone. Using Bac-to-Bac system and luciferase reporter vectors, we further analyzed the promoter sequence of BmGlcNAcase1. The results showed that these proteins have a highly conserved catalytic domain. The expression levels of the BmGlcNAcase genes varied in different tissues, and were increased 48 h after exposure to ecdysone. BmGlcNAcase1 gene promoter with 5'-end serial deletions showed different levels of activity in various tissues, higher in the blood, skin and fat body. Deletion of the region from -347 to -223 upstream of BmGlcNAcase-1 gene abolished its promoter activity. This region contains the binding sites for key transcription factors including Hb, BR-C Z, the HSF and the typical TATA-box element. These results indicate that BmGlcNAcases are expressed at different levels in different tissues of the silkworm, but all are subjected to the regulation by ecdysone. BmGlcNAcase1 promoter analysis has paved a foundation for further study of the gene expression patterns.

Inactivation kinetics of formaldehyde on N-acetyl-β-D-glucosaminidase from Nile tilapia (Oreochromis niloticus)

Formaldehyde is a widely used sanitizer in aquaculture in China, while the appropriate concentration is not available to be used effectively and without damage to tilapia much less to its reproductive function. N-acetyl-β-D-glucosaminidase (EC 3.2.1.52, NAGase), hydrolyzing the oligomers of N-acetyl-β-D-glucosamine into monomer, is proved to be correlated with reproduction of male animals. In this paper, NAGase from spermary of tilapia was chosen as the material to study the effects of formaldehyde on its activity in order to further investigate the effects of formaldehyde use on tilapia reproduction. The results showed the relationship between the residual enzyme activity and the concentration of formaldehyde was concentration dependent, and the IC50 value was estimated to be 3.2 ± 0.1 %. Appropriate concentration of formaldehyde leaded to competitive reversible inhibition on tilapia NAGase. Moreover, formaldehyde could reduce the thermal and pH stability of the enzyme. The inactivation kinetics of formaldehyde on the enzyme was studied using the kinetic method of substrate reaction. The inactivation model was setup, and the rate constants were determined. The results showed that the inactivation of formaldehyde on tilapia NAGase was a slow, reversible reaction with partially residual activity. The results will give some basis to determine the concentration of formaldehyde used in tilapia culture.

Enzymatic characterizations and activity regulations of N-acetyl-β-D-glucosaminidase from the spermary of Nile tilapia (Oreochromis niloticus)

N-Acetyl-β-D-glucosaminidase (NAGase) is proved to be correlated with reproduction of male animals. In this study, enzymatic characterizations of NAGase from spermary of Nile tilapia (Oreochromis niloticus) were investigated in order to further study its reproductive function in fish. Tilapia NAGase was purified to be PAGE homogeneous by the following techniques: (NH4)2SO4 fractionation (40-55%), DEAE-cellulose (DE-32) ion exchange chromatography, Sephadex G-200 gel filtration and DEAE-Sephadex (A-50). The specific activity of the purified enzyme was 4100 U/mg. The enzyme molecular weight was estimated as 118.0 kD. Kinetic studies showed that the hydrolysis of p-nitrophenyl-N-acetyl-β-D-glucosaminide (pNP-NAG) by the enzyme followed Michaelis-Menten kinetics. The Michaelis-Menten constant (Km) and maximum velocity (Vm) were determined to be 0.67 mM and 23.26 μM/min, respectively. The optimum pH and optimum temperature of the enzyme for hydrolysis of pNP-NAG was to be at pH 5.7 and 55°C, respectively. The enzyme was stable in a pH range from 3.3 to 8.1 at 37°C, and inactive at temperature above 45°C. The enzyme activity was regulated by the following ions in decreasing order: Hg(2+) > Zn(2+) > Cu(2+) > Pb(2+) > Mn(2+). The IC50 of Cu(2+), Zn(2+) and Hg(2+) was 1.23, 0.28, and 0.0027 mM, respectively. However, the ions Li(+), Na(+), K(+), Mg(2+) and Ca(2+) had almost no influence on enzyme activity. In conclusion, the enzymatic characterizations of NAGase from tilapia were special to the other animals, which were correlated with its living habit; besides, CuSO4 and ZnSO4 should used very carefully as insecticides in tilapia cultivation since they both had strong regulations on the enzyme.

Molecular and functional analysis of UDP-N-acetylglucosamine Pyrophosphorylases from the Migratory Locust, Locusta migratoria

UDP-N-acetylglucosamine pyrophosphorylases (UAP) function in the formation of extracellular matrix by producing N-acetylglucosamine (GlcNAc) residues needed for chitin biosynthesis and protein glycosylation. Herein, we report two UAP cDNA's derived from two different genes (LmUAP1 and LmUAP2) in the migratory locust Locusta migratoria. Both the cDNA and their deduced amino acid sequences showed about 70% identities between the two genes. Phylogenetic analysis suggests that LmUAP1 and LmUAP2 derive from a relatively recent gene duplication event. Both LmUAP1 and LmUAP2 were widely expressed in all the major tissues besides chitin-containing tissues. However, the two genes exhibited different developmental expression patterns. High expression of LmUAP1 was detected during early embryogenesis, then decreased greatly, and slowly increased before egg hatch. During nymphal development, the highest expression of LmUAP1 appeared just after molting but declined in each inter-molting period and then increased before molting to the next stage, whereas LmUAP2 was more consistently expressed throughout all these stages. When the early second- and fifth-instar nymphs (1-day-old) were injected with LmUAP1 double-stranded RNA (dsRNA), 100% mortality was observed 2 days after the injection. When the middle second- and fifth-instar nymphs (3- to 4-day-old) were injected with LmUAP1 dsRNA, 100% mortality was observed during their next molting process. In contrast, when the insects at the same stages were injected with LmUAP2 dsRNA, these insects were able to develop normally and molt to the next stage successfully. It is presumed that the lethality caused by RNAi of LmUAP1 is due to reduced chitin biosynthesis of the integument and midgut, whereas LmUAP2 is not essential for locust development at least in nymph stage. This study is expected to help better understand different functions of UAP1 and UAP2 in the locust and other insect species.

A sperm-plasma β-N-acetyl-D-hexosaminidase interacting with a Chitinolytic β-N-Acetyl-D-hexosaminidase in insect molting fluid

Insects require molting fluids to shed the old cuticle during molting. β-N-acetyl-D-hexosaminidase, known as Hex1, together with various chitinases, is responsible for degrading the chitin component of the old cuticle. This study showed that another β-N-acetyl-D-hexosaminidase, termed OfHex3, interacted with Hex1 and functioned in the molting fluid, although the homolog of OfHex3 was known as a sperm–plasma enzyme functioning in egg–sperm recognition. OfHex3 is an enzyme cloned from the insect Asian corn borer, Ostrinia furnacalis, which is one of the most destructive pests of maize. The enzymatic activity analysis indicated that OfHex3 was able to degrade chitooligosaccharides, but at a lower rate than that of OfHex1. Because OfHex3 did not have substrate inhibition, we deduced that the presence of OfHex3 might help OfHex1 relieve substrate inhibition during chitin degradation during molting. The expression patterns of OfHex3 during O. furnacalis development were studied by real-time PCR as well as western blot. The results showed that both gene transcription and protein translation levels of OfHex3 were up-regulated during larval–larval molting. The tissue-specific expression pattern analysis indicated that OfHex3 was mostly localized in the fat body and testis. All these data further supported that Hex3 was involved in molting as well as in fertilization. This study may help to understand the complexity of cuticle degradation during insect molting, and may provide a possible target for pest control.

Characterization of a spruce budworm chitin deacetylase gene: stage- and tissue-specific expression, and inhibition using RNA interference

Chitin deacetylase (CDA) catalyzes the conversion of chitin into chitosan, thereby modifying the physical properties of insect cuticles and peritrophic matrices. A lepidopteran chitin deacetylase gene (CfCDA2) was cloned from the spruce budworm, Choristoneura fumiferana, and found to generate two alternatively spliced transcripts, CfCDA2a and CfCDA2b. Transcriptional analysis using isoform-specific RT-PCR primers indicated that both isoforms were upregulated during the molt. Interestingly, CfCDA2b transcripts were most abundant in the head during the molting stage while those of CfCDA2a were predominant in the epidermis during the feeding period. Injection of CfCDA2-specific dsRNA into C. fumiferana larvae or pre-pupae induced both abnormal phenotypes and high mortality, which resulted from an inability to shed the old cuticle. These results suggest that CfCDA2 plays an important role in the molting process, and that the two alternatively spliced transcripts have different functions during insect development. This is the first detailed characterization of lepidopteran chitin deacetylase gene.

Chitin synthesis inhibitors: old molecules and new developments

Abstract  Chitin is the most abundant natural aminopolysaccharide and serves as a structural component of extracellular matrices. It is found in fungal septa, spores, and cell walls, and in arthropod cuticles and peritrophic matrices, squid pens, mollusk shells, nematode egg shells, and some protozoan cyst walls. As prokaryotes, plants and vertebrates including humans do not produce chitin, its synthesis is considered as an attractive target site for fungicides, insecticides, and acaricides. Although no chitin synthesis inhibitor has been developed into a therapeutic drug to treat fungal infections in humans, a larger number of compounds have been successfully launched worldwide to combat arthropod pests in agriculture and forestry. This review summarizes the latest advances on the mode of action of chitin synthesis inhibitors with a special focus on those molecules that act on a postcatalytic step of chitin synthesis.

RNA interference to reveal roles of β-N-acetylglucosaminidase gene during molting process in Locusta migratoria

β-N-acetylglucosaminidases are crucial enzymes involved in chitin degradation in insects. We identified a β-N-acetylglucosaminidase gene (LmNAG1) from Locusta migratoria. The full-length complementary DNA (cDNA) of LmNAG1 consists of 2 667 nucleotides, including an open reading frame (ORF) of 1 845 nucleotides encoding 614 amino acid residues, and 233- and 589-nucleotide non-coding regions at the 5'- and 3'-ends, respectively. Phylogenetic analysis grouped the cDNA-deduced LmNAG1 protein with the enzymatically characterized β-N-acetylglucosaminidases in group I. Analyses of stage- and tissue-dependent expression patterns of LmNAG1 were carried out by real-time quantitative polymerase chain reaction. Our results showed that LmNAG1 transcript level in the integument was significantly high in the last 2 days of the fourth and fifth instar nymphs. LmNAG1 was highly expressed in foregut and hindgut. RNA interference of LmNAG1 resulted in an effective silence of the gene and a significantly reduced total LmNAG enzyme activity at 48 and 72 h after the injection of LmNAG1 double-stranded RNA (dsRNA). As compared with the control nymphs injected with GFP dsRNA, 50% of the dsLmNAG1-injected nymphs were not able to molt successfully and eventually died. Our results suggest that LmNAG1 plays an essential role in molting process of L. migratoria.