Tweedle cuticular protein BmCPT1 is involved in innate immunity by participating in recognition of Escherichia coli

RNAi of nuclear receptor E78 inhibits the cuticle formation in the molting process of spider mite, Tetranychus urticae

BACKGROUND

The two-spotted spider mite, Tetranychus urticae, is an important pest mite in agriculture worldwide. E78, as a member of the nuclear receptor superfamily and a downstream responsive gene of ecdysteroids, plays a crucial role in regulating physiological behaviors such as development and reproduction in insects. However, its function in mites remains unclear. The aim of this study was to explore how E78 functions in the molting process of spider mites.

RESULTS

In this study, reverse transcription quantitative polymerase chain reaction (RT-qPCR) experiments to analyze the expression pattern of TuE78 during the development of Tetranychus urticae, demonstrated that the expression level of TuE78 was higher during the molting state than that after the completion of molting, and it reached a peak expression level when the deutonymph mites entered the molting stage. RNA interference (RNAi)-mediated gene-silencing of TuE78 resulted in 95% deutonymph mite molt failure. A series of analysis under a light microscope, and scanning and transmission electron microscopy revealed that RNAi mites died within the exuvium without ecdysis, and that apolysis had started but the new cuticle was thin and the typical cuticular lamellae were absent, indicating blockage of the post-apolysial processes and explaining molt failure. Hence, transcriptome sequencing confirmed that the expression of cuticle protein and lipid metabolism-related genes was significantly affected after TuE78 silencing.

CONCLUSION

This study demonstrated that TuE78 participates in the molting process of Tetranychus urticae by regulating the post-apolysial processes with the formation of new cuticle and successful ecdysis. This in turn suggests the potential of TuE78 as a target for pest mite control and provides a theoretical basis for further exploration of the molecular regulatory mechanism of spider mite molting. © 2024 Society of Chemical Industry.

Sgabd-2 plays specific role in immune response against biopesticide Metarhizium anisopliae in Aphis citricola

Metarhizium anisopliae is an effective biopesticide for controlling Aphis citricola, which has developed resistance to many chemical pesticides. However, the powerful immune system of A. citricola has limited the insecticidal efficacy of M. anisopliae. The co-evolution between insects and entomogenous fungi has led to emergence of new antifungal immune genes, which remain incompletely understood. In this study, an important immune gene Sgabd-2 was identified from A. citricola through transcriptome analysis. Sgabd-2 gene showed high expression in the 4th instar nymph and adult stages, and was mainly distributed in the abdominal region of A. citricola. The recombinant protein (rSgabd-2) exhibited no antifungal activity but demonstrated clear agglutination activity towards the conidia of M. anisopliae. RNA interference of Sgabd-2 by dsRNA feeding resulted in decreased phenoloxidase (PO) activity and weakened defense for A. citricola against M. anisopliae. Simultaneous silence of GNBP-1 and Sgabd-2 effectively reduced the immunity of A. citricola against M. anisopliae more than the individual RNAi of GNBP-1 or Sgabd-2. Furthermore, a genetically engineered M. anisopliae expressing double-stranded RNA (dsSgabd-2) targeting Sgabd-2 in A. citricola successfully suppressed the expression of Sgabd-2 and demonstrated increased virulence against A. citricola. Our findings elucidated Sgabd-2 as a critical new antifungal immune gene and proposed a genetic engineering strategy to enhance the insecticidal virulence of entomogenous fungi through RNAi-mediated inhibition of pest immune genes.

Reduced cold tolerance of viral-infected leafhoppers attenuates viral persistent epidemics

Most arthropod-borne viruses produce intermittent epidemics in infected plants. However, the underlying mechanisms of these epidemics are unclear. Here, we demonstrated that rice stripe mosaic virus (RSMV), a viral pathogen, significantly increases the mortality of its overwintering vector, the leafhopper species Recilia dorsalis. Cold-stress assays indicated that RSMV reduces the cold tolerance of leafhoppers, a process associated with the downregulation of leafhopper cuticular protein genes. An RSMV-derived small RNA (vsiR-t00355379) was found to facilitate the downregulation of a leafhopper endocuticle gene that is mainly expressed in the abdomen (named RdABD-5) and is conserved across dipteran species. The downregulation of RdABD-5 expression in R. dorsalis resulted in fewer and thinner endocuticle lamellae, leading to decreased cold tolerance. This effect was correlated with a reduced incidence rate of RSMV in early-planted rice plants. These findings contribute to our understanding of the mechanism by which viral pathogens reduce cold tolerance in arthropod vectors and suggest an approach to managing the fluctuating prevalence of arboviruses.

IMPORTANCE

Increasing arthropod vector dispersal rates have increased the susceptibility of crop to epidemic viral diseases. However, the incidence of some viral diseases fluctuates annually. In this study, we demonstrated that a rice virus reduces the cold tolerance of its leafhopper vector, Recilia dorsalis. This effect is linked to the virus-derived small RNA-mediated downregulation of a gene encoding a leafhopper abdominal endocuticle protein. Consequently, the altered structural composition of the abdominal endocuticle reduces the overwinter survival of leafhoppers, resulting in a lower incidence of RSMV infection in early-planted rice plants. Our findings illustrate the important roles of RNA interference in virus-vector insect-environment interactions and help explain the annual fluctuations of viral disease epidemics in rice fields.

Controllably Self-Assembled Antibacterial Nanofibrils Based on Insect Cuticle Protein for Infectious Wound Healing

Developing self-assembled biomedical materials based on insect proteins is highly desirable due to their advantages of green, rich, and sustainable characters as well as excellent biocompatibility, which has been rarely explored. Herein, salt-induced controllable self-assembly, antibacterial performance, and infectious wound healing performance of an insect cuticle protein (OfCPH-2) originating from the Ostrinia furnacalis larva head capsule are investigated. Interestingly, the addition of salts could trigger the formation of beaded nanofibrils with uniform diameter, whose length highly depends on the salt concentration. Surprisingly, the OfCPH-2 nanofibrils not only could form functional films with broad-spectrum antibacterial abilities but also could promote infectious wound healing. More importantly, a possible wound healing mechanism was proposed, and it is the strong abilities of OfCPH-2 nanofibrils in promoting vascular formation and antibacterial activity that facilitate the process of infectious wound healing. Our exciting findings put forward instructive thoughts for developing innovative bioinspired materials based on insect proteins for wound healing and related biomedical fields.

Genome-Wide Identification and Transcriptome-Based Expression Profile of Cuticular Protein Genes in Antheraea pernyi

Antheraea pernyi is one of the most famous edible and silk-producing wild silkworms of Saturniidae. Structural cuticular proteins (CPs) are the primary component of insect cuticle. In this paper, the CPs in the genome of A. pernyi were identified and compared with those of the lepidopteran model species Bombyx mori, and expression patterns were analyzed based on the transcriptomic data from the larval epidermis/integument (epidermis in the following) and some non-epidermis tissues/organs of two silkworm species. A total of 217 CPs was identified in the A. pernyi genome, a comparable number to B. mori (236 CPs), with CPLCP and CPG families being the main contribution to the number difference between two silkworm species. We found more RR-2 genes expressed in the larval epidermis of fifth instar of A. pernyi than B. mori, but less RR-2 genes expressed in the prothoracic gland of A. pernyi than B. mori, which suggests that the hardness difference in the larval epidermis and prothoracic gland between the two species may be caused by the number of RR-2 genes expressed. We also revealed that, in B. mori, the number of CP genes expressed in the corpus allatum and prothoracic gland of fifth instar was higher than that in the larval epidermis. Our work provided an overall framework for functional research into the CP genes of Saturniidae.

Identification of the cuticle protein AccCPR2 gene in Apis cerana cerana and its response to environmental stress

Cuticular proteins (CPs) are known to play important roles in insect development and defence responses. The loss of CP genes can lead to changes in insect morphology and sensitivity to the external environment. In this study, we identified the AccCPR2 gene, which belongs to the CPR family (including the R&R consensus motif) of CPs, and explored its function in the response of Apis cerana cerana to adverse external stresses. Our results demonstrated that AccCPR2 was highly expressed in the late pupal stage and epidermis, and the expression of AccCPR2 may be induced or inhibited under different stressors. RNA interference experiments showed that knockdown of AccCPR2 reduced the activity of antioxidant enzymes, led to the accumulation of oxidative damage and suppressed the expression of several antioxidant genes. In addition, knockdown of AccCPR2 also reduced the pesticide resistance of A. cerana cerana. The overexpression of AccCPR2 in a prokaryotic system further confirmed its role in resistance to various stresses. In summary, AccCPR2 may play pivotal roles in the normal development and environmental stress response of A. cerana cerana. This study also enriched the theoretical knowledge of the resistance biology of bees.

Vibrio cholerae high cell density quorum sensing activates the host intestinal innate immune response

Quorum sensing fundamentally alters the interaction of Vibrio cholerae with aquatic environments, environmental hosts, and the human intestine. At high cell density, the quorum-sensing regulator HapR represses not only expression of cholera toxin and the toxin co-regulated pilus, virulence factors essential in human infection, but also synthesis of the Vibrio polysaccharide (VPS) exopolysaccharide-based matrix required for abiotic and biotic surface attachment. Here, we describe a feature of V. cholerae quorum sensing that shifts the host-pathogen interaction toward commensalism. By repressing pathogen consumptive anabolic metabolism and, in particular, tryptophan uptake, V. cholerae HapR stimulates host intestinal serotonin production. This, in turn, activates host intestinal innate immune signaling to promote host survival.

Nuclear Factor Kappa B Promotes Ferritin Heavy Chain Expression in Bombyx mori in Response to B. mori Nucleopolyhedrovirus Infection

Ferritin heavy chain (FerHCH) is a major component of ferritin and plays an important role in maintaining iron homeostasis and redox equilibrium. Our previous studies have demonstrated that the Bombyx mori ferritin heavy chain homolog (BmFerHCH) could respond to B. mori nucleopolyhedrovirus (BmNPV) infection. However, the mechanism by which BmNPV regulates the expression of BmFerHCH remains unclear. In this study, BmFerHCH increased after BmNPV infection and BmNPV infection enhanced nuclear factor kappa B (NF-κB) activity in BmN cells. An NF-κB inhibitor (PDTC) reduced the expression of the virus-induced BmFerHCH in BmN cells, and overexpression of BmRelish (NF-κB) increased the expression of virus-induced BmFerHCH in BmN cells. Furthermore, BmNPV infection enhanced BmFerHCH promoter activity. The potential NF-κB cis-regulatory elements (CREs) in the BmFerHCH promoter were screened by using the JASPAR CORE database, and two effective NF-κB CREs were identified using a dual luciferase reporting system and electrophoretic mobility shift assay (EMSA). BmRelish (NF-κB) bound to NF-κB CREs and promoted the transcription of BmFerHCH. Taken together, BmNPV promotes activation of BmRelish (NF-κB), and activated BmRelish (NF-κB) binds to NF-κB CREs of BmFerHCH promoter to enhance BmFerHCH expression. Our study provides a foundation for future research on the function of BmFerHCH in BmNPV infection.

Cuticular protein genes involve heat acclimation of insect larvae under global warming

Cuticular proteins (CPs) play important roles in insect growth and development. However, it is unknown whether CPs are related to heat tolerance. Cnaphalocrocis medinalis, a serious pest of rice, occurs in summer and exhibits strong adaptability to high temperature, but the underlying mechanism is unclear. Here, the role of CP genes in heat acclimation was studied. Heat tolerance of the heat-acclimated larvae was significantly stronger than the unacclimated larvae. The cuticular protein content in the heat-acclimated larvae was higher than that of the unacclimated larvae. 191 presumed CP genes of C. medinalis (CmCPs) were identified. Expression patterns of 14 CmCPs were different between the heat acclimated (S39) and unacclimated (S27) larvae under heat stress. CmCPs were specifically expressed in epidermis and the head except CmCPR20 mainly expressed in Malpighian tubules. CmCPR20 was upregulated in S39 while downregulated in S27, but CmTweedle1 and CmCPG1 were upregulated in S27 and downregulated in S39. RNAi CmTweedle1 or CmCPG1 remarkably decreased heat tolerance and cuticular protein content of the heat-acclimated larvae but not the unacclimated larvae. RNAi CmCPR20 decreased heat tolerance and cuticular protein content of the unacclimated larvae but not the heat-acclimated larvae. CmTweedle1 and CmCPG1 genes involve heat acclimation of C. medinalis.

A Blueprint of Microstructures and Stage-Specific Transcriptome Dynamics of Cuticle Formation in Bombyx mori

Insect cuticle is critical for the environmental adaptability and insecticide resistance of insects. However, there is no clear understanding of the structure and protein components of the cuticle during each developmental stage of holometabolous insects, and knowledge about the protein components within each layer is vague. We conducted serial sectioning, cuticular structure analysis, and transcriptome sequencing of the larval, pupal, and adult cuticles of Bombyx mori. The deposition processes of epicuticle, exocuticle, and endocuticle during larval, pupal, and adult cuticle formation were similar. Transcriptome analysis showed that these cuticle formations share 74% of the expressed cuticular protein (CP) genes and 20 other structural protein genes, such as larval serum protein and prisilkin. There are seven, six, and eleven stage-specific expressed CP genes in larval, pupal, and adult cuticles, respectively. The types and levels of CP genes may be the key determinants of the properties of each cuticular layer. For example, the CPs of the RR-2 protein family with high contents of histidine (His) are more essential for the exocuticle. Functional analysis suggested that BmorCPAP1-H is involved in cuticle formation. This study not only offers an in-depth understanding of cuticle morphology and protein components but also facilitates the elucidation of molecular mechanisms underlying cuticle formation in future studies.

U1 small nuclear ribonucleoprotein is essential for early larval development in silkworm, Bombyx mori

U1 small nuclear ribonucleoproteins (U1 snRNP) associates with 5' splice sites in the form of ribonucleoprotein particles and is highly conserved among species. The physiological functions of U1 snRNP in a lepidopteran model insect Bombyx mori is mostly unknown. Here, we showed that U1 snRNP plays an important role in the development of silkworm. Knockout of U1 snRNP in silkworm showed either delayed or stationary 1st instar larva development compared with the wild-type group. U1 snRNP deletion mutants exhibited abnormal cellular phenotypes with enlarged cell nucleus, scant cytoplasm and enlarged nuclei. RNA-seq analysis revealed that genes involved in metabolic pathway, biosynthesis of secondary metabolites and steroid hormone biosynthesis were significantly affected by U1 snRNP depletion. Taken together, our study suggests that U1 snRNP homeostasis plays an important role in silkworm development.

Identification and expression analysis of cuticular protein genes in the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

Structural cuticular proteins (CPs) are major components of the insect cuticle, and they play critical roles in insect development and insecticide resistance. Here, a total of 196 CP genes were successfully annotated in the Plutella xylostella genome. On the basis of motif analysis, these CPs were classified into 10 different families, including 122 CPR, 12 CPAP1, 8 CPAP3, 9 CPLCP, 2 Tweedle, 1 CPF, 1 CPFL, 1 CPCFC, 17 CPG and 2 18 aa proteins, and the remaining 21 unclassified CPs were classed as cuticular proteins hypothetical (CPH). A phylogenetic analysis of CPs from different insects revealed species-specific clades of RR-1 and RR-2 genes, suggesting that CP gene duplication might occur independently among insect taxa, while we also found that some other CPs (such as CPAP1 and CPAP3) had a closer relationship based on their conserved domain architecture. Using available RNAseq libraries, the expression profiles of the CPs were analyzed over the four developmental stages of the insect (i.e., egg, larva, pupa, and adult), revealing stage-specific expression patterns for the CPs. In a chlorpyrifos resistant strain, 18 CP genes were found to be more than two-fold upregulated compared to the susceptible control strain, and qRT-PCR analysis showed that these CP genes were overexpressed after exposure to chlorpyrifos, suggesting a potential role in the molecular mechanism of insecticide resistance in P. xylostella. This study provides the tools and molecular basis to study the role of CPs in the post-embryonal development and the mechanisms of insecticide resistance of P. xylostella.

RNA-seq analysis of gene expression changes in cuticles during the larval-pupal metamorphosis of Plutella xylostella

The diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae) is a holometabolous insect that its cuticles must undergo the significant changes during the larval-pupal metamorphosis development. To elucidate these changes at molecular levels, RNA-seq analysis of cuticles from LLS (later fourth instar larval stage), PPS (prepupal stage) and PS (pupal stage) were performed in P. xylostella. In this paper, a total of 17,710 transcripts were obtained in the larval-pupal transition of P. xylostella, and out of which 2293 (881 up-regulated and 1412 down-regulated) and 2989 transcripts (2062 up-regulated and 927 down-regulated) were identified to be differentially expressed between LLS and PPS, as well as PPS and PS, respectively. The further GO and KEGG analysis of differentially expressed genes (DEGs) revealed that the 'structural constituent of cuticle', 'chitin metabolic process', 'chitin binding', 'tyrosine metabolism' and 'insect hormone biosynthesis' pathways were significantly enriched, indicating these pathways might be involved in the process of larval pupation in P. xylostella. Then, we found some genes that encoded cuticular proteins, chitinolytic enzymes, chitin synthesis enzymes, and cuticle tanning proteins changed their expression levels remarkably, indicating these genes might play important roles in the restruction (degradation and biosynthesis) of insect cuticles during the larval metamorphosis. Additionally, the significant changes in the mRNA levels of 20-hydroxyecdysone (20E) and juvenile hormone (JH) related genes suggested their crucial roles in regulating cuticle remodeling during the larval metamorphosis of P. xylostella. In conclusion, the present study provide us the comprehensive gene expression profiles to explore the molecular mechanisms of cuticle metamorphosis in P. xylostella, which laid a molecular basis to study roles of specific pathways and genes in insect development.

Antimicrobial peptides fromBombyx mori: a splendid immune defense response in silkworms

Bombyx mori L., a primary producer of silk, is the main tool in the sericulture industry and provides the means of livelihood to a large number of people. Silk cocoon crop losses due to bacterial infection pose a major threat to the sericulture industry. Bombyx mori L., a silkworm of the mulberry type, has a sophisticated inherent innate immune mechanism to combat such invasive pathogens. Among all the components in this defense system, antimicrobial peptides (AMPs) are notable due to their specificity towards the invading pathogens without harming the normal host cells. Bombyx mori L. so far has had AMPs identified that belong to six different families, namely cecropin, defensin, moricin, gloverin, attacin and lebocin, which are produced by the Toll and immune deficiency (IMD) pathways. Their diverse modes of action depend on microbial pathogens and are still under investigation. This review examines the recent progress in understanding the immune defense mechanism of Bombyx mori based on AMPs.

AMPs produced by B. mori induced by microbial challenge in the fat body.

Identification of Cuticular Protein Genes in the Colorado Potato Beetle Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Structural cuticular proteins (CPs) are the primary components of insect cuticle, linings of salivary gland, foregut, hindgut and tracheae, and midgut peritrophic membrane. Variation of CPs in insect cuticle can cause penetration resistance to insecticides. Moreover, depletion of specific CP by RNA interference may be a suitable way for the development of potential pest control traits. Leptinotarsa decemlineata (Say) CPs are poorly characterized at present, and therefore, we mined the genome and transcriptome data to better annotate and classify L. decemlineata CPs in this study, by comparison with the annotated CPs of Tribolium castaneum Browse (Coleoptera: Tenebrionidae). We identified 175 CP genes. Except one miscellaneous CP with an 18-amino acid motif, these CPs were classified into 7 families based on motifs and phylogenetic analyses (CPs with a Rebers and Riddiford motif, CPR; CPs analogous to peritrophins, CPAP3 and CPAP1; CPs with a tweedle motif, TWDL; CPs with a 44-amino acid motif, CPF; CPs that are CPF-like, CPFL; and CPs with two to three copies of C-X5-C motif, CPCFC). Leptinotarsa decemlineata CPRs could be categorized into three subfamilies: RR-1 (50), RR-2 (85), and RR-3 (2). The RR-1 proteins had an additional motif with a conserved YTADENGF sequence. The RR-2 members possessed a conserved RDGDVVKG region and three copes of G-x(3)-VV. Few genes were found in TWDL (9), CPAP1 (9), CPAP3 (8), CPF (5), CPFL (4), and CPCFC (2) families. The findings provide valuable information to explore molecular modes of penetration resistance to insecticides and to develop dsRNA-based control method in L. decemlineata.

Hormonal control and target genes of ftz-f1 expression in the honeybee Apis mellifera: a positive loop linking juvenile hormone, ftz-f1, and vitellogenin

Ftz-f1 is an orphan member of the nuclear hormone receptor superfamily. A 20-hydroxyecdysone pulse allows ftz-f1 gene expression, which then regulates the activity of downstream genes involved in major developmental progression events. In honeybees, the expression of genes like vitellogenin (vg), prophenoloxidase and juvenile hormone-esterase during late pharate-adult development is known to be hormonally controlled in both queens and workers by increasing juvenile hormone (JH) titres in the presence of declining levels of ecdysteroids. Since Ftz-f1 is known for mediating intracellular JH signalling, we hypothesized that ftz-f1 could mediate JH action during the pharate-adult development of honeybees, thus controlling the expression of these genes. Here, we show that ftz-f1 has caste-specific transcription profiles during this developmental period, with a peak coinciding with the increase in JH titre, and that its expression is upregulated by JH and downregulated by ecdysteroids. RNAi-mediated knock down of ftz-f1 showed that the expression of genes essential for adult development (e.g. vg and cuticular genes) depends on ftz-f1 expression. Finally, a double-repressor hypothesis-inspired vg gene knock-down experiment suggests the existence of a positive molecular loop between JH, ftz-f1 and vg.

Immune responses to bacterial and fungal infections in the silkworm, Bombyx mori

The silkworm Bombyx mori, an economically important insect that is usually reared indoors, is susceptible to various pathogens, including bacteria, fungi, viruses, and microsporidia. As with other insects, the silkworm lacks an adaptive immune system and relies solely on innate immunity to defend itself against infection. Compared to other intensively studied insects, such as the fruit fly and tobacco hornworm, the principal immune pathways in the silkworm remain unclear. In this article, we review the literature concerning silkworm immune responses to bacteria and fungi and present our perspectives on future research into silkworm immunity.

Genome-wide annotation of cuticular proteins in the oriental fruit fly (Bactrocera dorsalis), changes during pupariation and expression analysis of CPAP3 protein genes in response to environmental stresses

Cuticular proteins (CPs) are essential components of the insect cuticle as they create a structural and protective shield and may have a role in insect development. In this paper, we studied the CPs in the oriental fruit fly (Bactrocera dorsalis), one of the most economically important pests in the Tephritidae family around the world. The availability of a complete genome sequence (NCBI Assembly: ASM78921v2) allowed the identification of 164 CP genes in B. dorsalis. Comparative analysis of the CPs in B. dorsalis with those in the model insect Drosophila melanogaster and the closely related Ceratitis capitata, and CPs from mosquitoes, Lepidoptera, Hymenoptera and Coleoptera identified Diptera-specific genes and cuticle development patterns. Analysis of their evolutionary relationship revealed that some CP families had evolved according to the phylogeny of the different insect species, while others shared a closer relationship based on domain architecture. Subsequently, transcriptome analysis showed that while most of the CPs (60-100% of the family members) are expressed in the epidermis, some were also present in internal organs such as the fat body and the reproductive organs. Furthermore, the study of the expression profiles throughout development revealed a profound change in the expression of CPs during the formation of the puparium (pupariation). Further analysis of the expression profiles of the CPAP3 genes under various environmental stresses revealed them to be involved in the response to pesticides and arid and extreme temperatures conditions. In conclusion, the data provide a particular overview of CPs and their evolutionary and transcriptional dynamics, and in turn they lay a molecular foundation to explore their roles in the unique developmental process of insect metamorphosis and stress responses.

Identifying the function of LvPI3K during the pathogenic infection of Litopenaeus vannamei by Vibrio alginolyticus

It is well known that PI3K regulates various processes in mammalian cells by generating a secondary messenger that later activates AKT. However, its innate immune function in crustaceans remains unclear. We report the characterization of Litopenaeus vannamei PI3K (LvPI3K) for investigating how PI3K participates in the innate immunity of crustaceans. Full-length LvPI3K cDNA was 3357 bp long, with a 3222 bp open reading frame (ORF) that encodes a putative protein of 1292 amino acids. The PI3K catalytic domain (PI3Kc) of LvPI3K was found to be rather conserved when the PI3Ks from other species were analyzed. The LvPI3K protein was shown to be localized to the cytoplasm of Drosophila S2 cells, while LvPI3K mRNA was ubiquitously expressed in healthy L. vannamei, with the highest expression found in hemolymph. A dual luciferase reporter gene assay demonstrated that LvPI3K overexpression activated the promoter of antibacterial peptide LvPEN4 in a dose-dependent manner. However, the addition of PDTC, a specific inhibitor of NF-κB, suppressed the LvPI3K-induced LvPEN4 promoter activation. Moreover, Vibrio alginolyticus challenge induced a rapid up-regulation of LvPI3K expression. Further experiments showed that LvPI3K silencing in shrimp challenged with V. alginolyticus significantly increased Vibrio number, ROS production and DNA damage in the hemolymph, as well as significantly decreased total hemocyte count. The mRNA levels of certain molecules related to LvPI3K signaling, such as LvAKT and LvPEN4, also decreased following LvPI3K silencing. Taken together, these results suggest that LvPI3K regulates the downstream signal component LvPEN4 and functions in V. alginolyticus resistance.

Transgenic characterization of two silkworm tissue-specific promoters in the haemocyte plasmatocyte cells

Haemocytes play crucial roles in insect metabolism, metamorphosis, and innate immunity. As a model of lepidopteran insects, the silkworm is a useful model to study the functions of both haematopoiesis and haemocytes. Tissue-specific promoters are excellent tools for genetic manipulation and are widely used in fundamental biological research. Herein, two haemocyte-specific genes, Integrin β2 and Integrin β3, were confirmed. Promoter activities of Integrin β2 and Integrin β3 were evaluated by genetic manipulation. Quantitative real-time PCR and western blotting suggested that both promoters can drive enhanced green fluorescent protein (EGFP) specifically expressed in haemocytes. Further evidence clearly demonstrated that the transgenic silkworm exhibited a high level of EGFP signal in plasmatocytes, but not in other detected haemocyte types. Moreover, EGFP fluorescence signals were observed in the haematopoietic organ of both transgenic strains. Thus, two promoters that enable plasmatocytes to express genes of interest were confirmed in our study. It is expected that the results of this study will facilitate advances in our understanding of insect haematopoiesis and immunity in the silkworm, Bombyx mori.

Identification, expression pattern, and feature analysis of cuticular protein genes in the pine moth Dendrolimus punctatus (Lepidoptera: Lasiocampidae)

Cuticular proteins (CPs) are vital components of the insects' cuticle that support movement and protect insect from adverse environmental conditions. The CPs exist in a large number and diversiform structures, thus, the accurate annotation is the first step to interpreting their roles in insect growth. The rapid development of sequencing technology has simplified the access to the information on protein sequences, especially for non-model species. Dendrolimus punctatus is a Lepidopteran defoliator, and its periodic outbreaks cause severe damage to the coniferous forests. The transcriptome of D. punctatus integrating the whole developmental periods are available for the potential investigation of CPs. In this study, we identified 216 CPs from D. punctatus, including 147 from CPR family, 4 from TWDL family, 3 from CPF/CPFL families, 22 from CPAP families, 8 low complexity proteins, 1 CPCPC and 31 from other CP families. The putative CPs were compared with homologs in other species such as Bombyx mori, Manduca sexta and Drosophila melanogaster. We further identified five co-orthologous groups have highly similar sequences of CRPs in nine lepidopteran species, which exclusively presented in RR-2 subfamily rather than RR-1. We inferred that in Lepidoptera the difference in RR-2 numbers was maintained by homologs in co-orthologous groups, coincided with observation in Drosophila and Anopheles that gene cluster was the model and source for the expansion of RR-2 genes. In combination with the variation of members in each CP family among different species, these results indicated the evolution of CPs was highly correlated to the adaptation of insect to environment. Furthermore, we compared the amino acid composition of the different types CPRs, and examined the expression patterns of CP genes in various developmental stages. The comprehensive overview of CPs from our study provides an insight into their evolution and the association between them and insect development.

Cuticular protein LmTwdl1 is involved in molt development of the migratory locust

The cuticle, an essential structure for insects, is produced from cuticular proteins and chitin via a series of biochemical reactions. Tweedle genes are important members of the cuticular protein family and have four conserved motifs binding to chitin. Tweedle family genes have been found to play a profound effect on cuticle development. Here, we report that the cuticular protein gene LmTwdl1 of Locusta migratoria belongs to the Tweedle family. In situ hybridization showed that LmTwdl1 is localized to epidermal cells of the cuticle. The expression patterns of LmTwdl1 showed low expression in the cuticle during the early and middle stages of the fifth-instar nymphs; in contrast, its expression rapidly increased in the late stages of fifth-instar nymphs. We performed RNA interference to examine the function of LmTwdl1 in locusts. Silencing of LmTwdl1 resulted in high mortality during the molting process before the next stage. Also, the epicuticle of nymphs failed to molt, tended to be thinner and the arrangement of chitin in the procuticle appeared to be disordered compare to the control group. These results demonstrate that LmTwdl1 plays a critical role in molting, which contributes to a better understanding of the distinct functions of the Tweedle family in locusts.