A palmitoyltransferase Approximated gene Bm-app regulates wing development in Bombyx mori

Bursicon regulates wing expansion via PKA in the oriental fruit fly, Bactrocera dorsalis

BACKGROUND

Bursicon is a heterodimeric neuropeptide that is involved in many physiological activities such as cuticle tanning, wing expansion, reproduction and immunity in insects. In this study, the role of bursicon in the wing expansion was investigated in Bactrocera dorsalis, an important invasive insect pest in agriculture.

RESULTS

The cDNA sequences and deduced amino acids of bursicon genes (named BdBurs-α and BdBurs-β) were determined, and two proteins typically contained 11 cysteine residues in conserved positions that were highly conserved in other insect species. The spatiotemporal expressions of bursicon genes showed that higher expression occurred at the pupal, early adult stage and ovaries, and lower expression at the late larval stage and in wing tissue (8-day-old pupae). Dysfunction of bursicon genes by dsRNA microinjection into 5-day-old pupae reduced PKA (a downstream component of the bursicon pathway) activity and resulted in malformed adult wings. PKA inhibitor injection into 5-day-old pupae also resulted in similar phenotypes. Hematoxylin & eosin staining of the adult wing showed that RNAi and PKA inhibitor treatment reduced the thickness of the wing cuticle, which wing cuticle thickness were ≈50% thinner than in the control. Furthermore, the expression of hedgehog (Bdhh) (one of 10 tested genes related to wing development) was significantly upregulated after RNAi and PKA inhibitor application.

CONCLUSION

The results indicate that bursicon plays a crucial role in the wing expansion of B. dorsalis, suggesting bursicon genes have potential to be the targets for B. dorsalis control. © 2023 Society of Chemical Industry.

Cytokine receptor DOME controls wing disc development in Bombyx mori

In multicellular organisms, the JAK/STAT signaling pathway is involved in cell proliferation, differentiation, apoptosis, and immune regulation. Through activation of the Stat92E transcription factor, JAK/STAT signaling induced proper wing development in Drosophila. Domeless (DOME) was the first identified invertebrate JAK/STAT receptor. However, the function of DOME in Bombyx mori development remains unclear, especially in wing morphogenesis. In this study, we isolated the cytokine receptor DOME gene in B. mori and evaluated its function in DOME-knockout models. We found that overexpression of DOME at the cellular level upregulated the expression of JAK/STAT pathway-related genes, promoted proliferation, and inhibited apoptosis. The results of the interference with DOME had the opposite effects with those of overexpression at the cellular level. Using CRISPR/Cas9 technology, we constructed a DOME-knockout transgenic silkworm strain (KO-DOME) and found that the wings of the pupa and moth stages were vesicle-shaped and smaller than those of the wild-type silkworm. Some KO-DOME silkworms were unable to extend their wings from the pupal case after eclosion. We detected the expression of cyclin and apoptosis-related genes in the wing disc of the moth stage and found that some cyclin genes, such as CyclinA, CyclinB, and CyclinD, were downregulated, whereas apoptotic genes, such as Caspase1, Caspase3, and Caspase8, were upregulated. We propose that DOME regulates cell proliferation and apoptosis by affecting the JAK/STAT signaling pathway, ultimately influencing the development of wing discs. Our study provides empirical evidence for the biological function of the silkworm DOME gene, which is essential for the normal development of wings.

Bombyx mori Vps13d is a key gene affecting silk yield

Bombyx mori is an important economic insect, its economic value mainly reflected in the silk yield. The major functional genes affecting the silk yield of B. mori have not been determined yet. Bombyx mori vacuolar protein sorting-associated protein 13d (BmVps13d) has been identified, but its function is not reported. In this study, BmVps13d protein shared 30.84% and 34.35% identity with that of in Drosophila melanogaster and Homo. sapiens, respectively. The expressions of BmVps13d were significantly higher in the midgut and silk gland of JS (high silk yield) than in that of L10 (low silk yield). An insertion of 9 bp nucleotides and two deficiencies of adenine ribonucleotides in the putative promoter region of BmVps13d gene in L10 resulted in the decline of promoter activity was confirmed using dual luciferase assay. Finally, the functions of BmVps13d in B. mori were studied using the CRISPR/Cas9 system, and the mutation of BmVps13d resulted in a 24.7% decline in weight of larvae, as well as a 27.1% (female) decline and a 11.8% (male) decline in the silk yield. This study provides a foundation for studying the molecular mechanism of silk yield and breeding the silkworm with high silk yield.

Map-based cloning and functional analysis revealed ABCC2 is responsible for Cry1Ac toxin resistance in Bombyx mori

Bt toxins are parasporal crystals produced by Bacillus thuringiensis (Bt). They have specific killing activity against various insects and have been widely used to control agricultural pests. However, their widespread use has developed the resistance of many target insects. To maintain the sustainable use of Bt products, the resistance mechanism of insects to Bt toxins must be fully clarified. In this study, Bt-resistant and Bt-susceptible silkworm strains were used to construct genetic populations, and the genetic pattern of silkworm resistance to Cry1Ac toxin was determined. Sequence-tagged site molecular marker technology was used to finely map the resistance gene and to draw a molecular genetic linkage map, and the two closest markers were T1590 and T1581, indicating the resistance gene located in the 155 kb genetic region. After analyzing the sequence of the predicted gene in the genetic region, an ATP binding cassette transporter (ABCC2) was identified as the candidate gene. Molecular modeling and protein-protein docking result showed that a tyrosine insertion in the mutant ABCC2 might be responsible for the interaction between Cry1Ac and ABCC2. Moreover, CRISPR/Cas9-mediated genome editing technology was used to knockout ABCC2 gene. The homozygous mutant ABCC2 silkworm was resistant to Cry1Ac toxin, which indicated ABCC2 is the key gene that controls silkworm resistance to Cry1Ac toxin. The results have laid the foundation for elucidating the molecular resistance mechanism of silkworms to Cry1Ac toxin and could provide a theoretical basis for the biological control of lepidopteran pests.

Sob gene is critical to wing development in Bombyx mori and Tribolium castaneum

The development of insect appendages requires the expression of multiple genes in a strict spatial and temporal order. The odd-skipped family genes are vital transcriptional factors involved in embryonic development. The development and morphogenesis of the insect wing requires multiple transcription factors to regulate the expression of wing patterning genes at the transcriptional level. However, the function of odd-related genes in insect wing morphogenesis and development during postembryonic stages is unclear. We focused on the roles of the sister of odd and bowl (sob) gene, a member of odd-skipped family genes, during the wing morphopoiesis in Bombyx mori using the clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein 9 system and in Tribolium castaneum by RNA interference. The results showed that the wings were significantly smaller and degenerated, and wing veins were indistinct in the sob gene loss-of-function group in both B. mori and T. castaneum. Quantitative real-time polymerase chain reaction revealed that the Tcsob gene regulated the expression of wing development genes, such as the cht 7 and the vg gene. The findings suggest the importance of sob gene in insect wing morphology formation during postembryonic stages.

Advances in Editing Silkworms (Bombyx mori) Genome by Using the CRISPR-Cas System

CRISPR (clustered regularly interspaced short palindromic repeats)-Cas (CRISPR-associated) represents a powerful genome editing technology that revolutionized in a short period of time numerous natural sciences branches. Therefore, extraordinary progress was made in various fields, such as entomology or biotechnology. Bombyx mori is one of the most important insects, not only for the sericulture industry, but for numerous scientific areas. The silkworms play a key role as a model organism, but also as a bioreactor for the recombinant protein production. Nowadays, the CRISPR-Cas genome editing system is frequently used in order to perform gene analyses, to increase the resistance against certain pathogens or as an imaging tool in B. mori. Here, we provide an overview of various studies that made use of CRISPR-Cas for B. mori genome editing, with a focus on emphasizing the high applicability of this system in entomology and biological sciences.

CRISPR/Cas9 in lepidopteran insects: Progress, application and prospects

Clustered regularly spaced short palindrome repeats (CRISPR) structure family forms the acquired immune system in bacteria and archaea. Recent advances in CRISPR/Cas genome editing as derived from prokaryotes, confirmed the characteristics of robustness, high target specificity and programmability, and also revolutionized the insect sciences field. The successful application of CRISPR in a wide variety of lepidopteran insects, with a high genetic diversity, provided opportunities to explore gene functions, insect modification and pest control. In this review, we present a detailed overview on the recent progress of CRISPR in lepidopteran insects, and described the basic principles of the system and its application. Major interest is on wing development, pigmentation, mating, reproduction, sex determination, metamorphosis, resistance and silkworm breeding innovation. Finally, we outlined the limitations of CRISPR/Cas system and discussed its application prospects in lepidopteran insects.

CRISPR/Cas9-based knockout reveals that the clock gene timeless is indispensable for regulating circadian behavioral rhythms in Bombyx mori

Circadian rhythms, which are ubiquitous and adaptive, occur across all species, from microbes to humans, in which they organize and modify behavior and physiology. timeless (tim) is a canonical clock gene. The core composition of the Drosophila melanogaster endogenous circadian clock has been extensively investigated; however, in lepidopteran insects, including Bombyx mori, the mechanism is complicated and little is known regarding the participation of tim in the negative feedback loop responsible for behavioral activities. To arrive at a comprehensive understanding of the role of tim in the B. mori endogenous circadian clock, we exploited the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 gene editing system. We attempted to elucidate the functions of tim in the circadian clock of B. mori using Bmtim mutants. The knockouts affected two circadian behavioral activities: adult emergence and embryo hatching rhythms. Quantitative real-time polymerase chain reaction results confirmed that tim-knockouts induced relative reductions in the expression levels, and thereby the oscillation amplitudes, of Bmper and Bmclk messenger RNAs during both the photophase and scotophase. Additionally, the daily rhythmic expression of Bmdbt was upregulated in the photophase and downregulated in the scotophase in a tim-knockout. Our study reveals that tim is integral to the B. mori circadian clock and may be involved in regulating eclosion and hatching rhythms.

Porcupine/Wntless-dependent trafficking of the conserved WntA ligand in butterflies

Wnt ligands are key signaling molecules in animals, but little is known about the evolutionary dynamics and mode of action of the WntA orthologs, which are not present in the vertebrates or in Drosophila. Here we show that the WntA subfamily evolved at the base of the Bilateria + Cnidaria clade, and conserved the thumb region and Ser209 acylation site present in most other Wnts, suggesting WntA requires the core Wnt secretory pathway. WntA proteins are distinguishable from other Wnts by a synapomorphic Iso/Val/Ala216 amino-acid residue that replaces the otherwise ubiquitous Thr216 position. WntA embryonic expression is conserved between beetles and butterflies, suggesting functionality, but the WntA gene was lost three times within arthropods, in podoplean copepods, in the cyclorrhaphan fly radiation, and in ensiferan crickets and katydids. Finally, CRISPR mosaic knockouts (KOs) of porcupine and wntless phenocopied the pattern-specific effects of WntA KOs in the wings of Vanessa cardui butterflies. These results highlight the molecular conservation of the WntA protein across invertebrates, and imply it functions as a typical Wnt ligand that is acylated and secreted through the Porcupine/Wntless secretory pathway.

The biological characters of Bmelav-like genes in the development of Bombyx mori

The ELAV/Hu family is a conserved multigene family of pan-neuronal RNA-binding protein involved in post-transcriptional regulation in metazoans. In Drosophila, three members of this family, ELAV, RBP9 and FNE, are involved in neuronal differentiation, gene expression regulation and so on. This family is less well characterized in Bombyx mori. Two orthologs BmELAV-like-1 (BmEL-1) and BmELAV-like-2 (BmEL-2) share 55%-71% and 47%-62% identity with that of in Drosophila and humans, respectively. Bmel-1 is ubiquitously expressed while Bmel-2 is expressed in the head and ovaries specifically. Proteins encoded by both genes are localized in nuclear and cytoplasm. The weight of body, cocoon, pupae and cocoon shell are differently affected in Bmel-1^- /-2^- mutants created using CRISPR/Cas9 technology. Mutations of both genes increase the expression of four silk protein genes, Fib-L, Fib-H, P25 and Ser-1. In addition, the oviposition ability of Bmel-2^- females is decreased. This study not only provides valuable insights into the functional roles of Bmelav-like genes in the growth, cocoon characters and regulation of silk protein genes expression, but also provides useful information for silkworm variety breeding.

Walter J, Liu Z, Xu J, Huang Y. Gtsf1 is essential for proper female sex determination and transposon silencing in the silkworm, Bombyx mori

Sex determination pathways are astoundingly diverse in insects. For instance, the silk moth Bombyx mori uniquely use various components of the piRNA pathway to produce the Fem signal for specification of the female fate. In this study, we identified BmGTSF1 as a novel piRNA factor which participates in B. mori sex determination. We found that BmGtsf1 has a distinct expression pattern compared to Drosophila and mouse. CRISPR/Cas9 induced mutation in BmGtsf1 resulted in partial sex reversal in genotypically female animals by shifting expression of the downstream targets BmMasc and Bmdsx to the male pattern. As levels of Fem piRNAs were substantially reduced in female mutants, we concluded that BmGtsf1 plays a critical role in the biogenesis of the feminizing signal. We also demonstrated that BmGTSF1 physically interacted with BmSIWI, a protein previously reported to be involved in female sex determination, indicating BmGTSF1 function as the cofactor of BmSIWI. BmGtsf1 mutation resulted in piRNA pathway dysregulation, including piRNA biogenesis defects and transposon derepression, suggesting BmGtsf1 is also a piRNA factor in the silkworm. Furthermore, we found that BmGtsf1 mutation leads to gametogenesis defects in both male and female. Our data suggested that BmGtsf1 is a new component involved in the sex determination pathway in B. mori.

Sex determination is a fundamentally important process in most sexually reproducing metazoan. Nevertheless, the underlying mechanisms of sex determination are highly diverse. In B. mori, piRNAs derived from the W-chromosome-linked Fem precursor serve as the primary female determining signal. However, we still know little about the initiation of B. mori sex determination and its relationship with piRNA pathway. Here, we provided evidence that BmGTSF1 is a novel piRNA factor which is indispensable for B.mori female sex determination. Mutations in BmGtsf1 resulted in dysregulation of the piRNA pathway and caused partial female-male sex reversal. We also detected dramatic diminution of Fem piRNA in female mutant, indicating BmGTSF1 regulates B. mori sex determination via piRNA pathway. More importantly, we showed that BmGTSF1 interacted with BmSIWI, which protein had been reported to be involved in piRNA pathway and sex determination in B. mori, supporting the conclusion that BmGTSF1 is a novel factor for piRNA pathway and sex determination.

Bmapaf-1 is Involved in the Response against BmNPV Infection by the Mitochondrial Apoptosis Pathway

Simple Summary

Apaf-1 is involved in the apoptosis pathway and Bmapaf-1 showed a significant response to BmNPV infection in our previous transcriptome data. In this study, the underlying mechanism of Bmapaf-1 in response to BmNPV infection was studied. To preliminarily determine the relationship of Bmapaf-1 with BmNPV, the expression pattern of Bmapaf-1 was analyzed in different tissues of differentially resistant silkworm strains following virus infection. To further define the role of Bmapaf-1 in BmNPV infection, the alteration of BmNPV infection in BmN cells and the expression patterns of Bmcas-Nc and Bmcas-1 were analyzed following knockdown and overexpression of Bmapaf-1 using siRNA and the pIZT/V5-His-mCherry insect vector, respectively. Furthermore, to analyze whether Bmapaf-1 is involved in BmNPV infection by apoptosis, the inducer NSC348884 and inhibitor Z-DEVD-FMK were used.

Abstract

Discovery of the anti-BmNPV (Bombyx mori nuclearpolyhedrovirus) silkworm strain suggests that some kind of antiviral molecular mechanism does exist but is still unclear. Apoptosis, as an innate part of the immune system, plays an important role in the response against pathogen infections and may be involved in the anti-BmNPV infection. Several candidate genes involved in the mitochondrial apoptosis pathway were identified from our previous study. Bombyx mori apoptosis protease-activating factor-1 (Bmapaf-1) was one of them, but the antiviral mechanism is still unclear. In this study, sequences of BmApaf-1 were characterized. It was found to contain a unique transposase_1 functional domain and share high CARD and NB-ARC domains with other species. Relatively high expression levels of Bmapaf-1 were found at key moments of embryonic development, metamorphosis, and reproductive development. Further, the significant difference in expression of Bmapaf-1 in different tissues following virus infection indicated its close relationship with BmNPV, which was further validated by RNAi and overexpression in BmN cells. Briefly, infection of budded virus with enhanced green fluorescent protein (BV-EGFP) was significantly inhibited at 72 h after overexpression of Bmapaf-1, which was confirmed after knockdown of Bmapaf-1 with siRNA. Moreover, the downstream genes of Bmapaf-1, including Bmnedd2-like caspase (BmNc) and Bmcaspase-1 (Bmcas-1), were upregulated after overexpression of Bmapaf-1 in BmN cells, which was consistent with the RNAi results. Furthermore, the phenomenon of Bmapaf-1 in response to BmNPV infection was determined to be related to apoptosis using the apoptosis inducer NSC348884 and inhibitor Z-DEVD-FMK. Therefore, Bmapaf-1 is involved in the response against BmNPV infection by the mitochondrial apoptosis pathway. This result provides valuable data for clarifying the anti-BmNPV mechanism of silkworms and breeding of resistant silkworm strains.

BmSd gene regulates the silkworm wing size by affecting the Hippo pathway

Insect wings are developed from the wing disc during metamorphosis. Bombyx mori, a model lepidopteran insect, loses flight ability after long-term domestication from the wild silkworm, Bombyx mandarina. The mw mutant (u11 strain) shows minute wings compared to wild type (e.g., p50 strain) wings. RNA sequencing analysis previously revealed differential Hippo-pathway-related gene expression between the u11 and p50 strains. The Hippo pathway is an evolutionarily conserved signaling cascade that controls organ size during development in animals. In this study, the function of BmSd which has been characterized as one of the Hippo-pathway-related genes was analyzed for silkworm wing development. We found that mats, warts, and hippo expression levels were higher in u11 compared to p50 wing discs. BmSd (scalloped) expression, which encodes a prominent transcriptional partner to Yorkie (Yki), gradually decreased during the wandering stage in u11, but exhibited the opposite expression pattern in p50. When BmSd was knocked down by small interfering RNA during the wandering stage in the p50 strain, 57.9% of the individuals showed minute wings. Additionally, ex, kibra, and wingless expression levels decreased in the BmSd knockdown mutant. Further, BmSd deletion mediated by clustered regularly interspaced short palindromic repeats (CRISPR) / CRISPR-associated protein 9 induced 50% of individuals with minute wings, a phenotype similar to the mw mutant. This result demonstrates that BmSd plays pivotal roles in silkworm wing development. Our results show that the Hippo signaling pathway participates and plays crucial roles in the regulation of silkworm wing development, and our findings provide a basis for further research on B. mori wing development.

Expressional analysis of the silkworm storage protein 1 and identification of its interacting proteins

Storage proteins are haemolymph-specific proteins in insects, mainly synthesized in the fat body, released into the haemolymph, and then selectively reabsorbed by the fat body before pupation. These storage proteins play an important role in insect metamorphosis and egg development. Some of these storage proteins are responsive to pathogen infection and can even suppress pathogen multiplication. However, the mechanisms of the physiological, biochemical and immune-responsive functions of storage proteins remain unclear. In this study, the expression patterns of Bombyx mori storage protein 1 (BmSP1) during the larval stage were analysed. Then, BmSP1 protein fused with enhanced green fluorescent protein (EGFP) was successfully expressed in a B. mori baculovirus vector expression system. Quantitative real-time PCR showed that the expression level of BmSP1 increased with the advance of instars and reached the highest level in the fifth instar, especially in the fat body. Recombinant BmSP1 expressed in silkworm larvae inhibited haemolymph melanization. Then, proteins that interact with BmSP1 were identified with EGFP used as an antigenic determinant by co-immunoprecipitation. A 30 kDa low molecular weight lipoprotein PBMHP-6 precursor (BmLP6) was shown to interact with BmSP1. Yeast two-hybrid experiments confirmed the interaction between BmSP1 and BmLP6. The results obtained in this study will be helpful for further study of the functions of BmSP1 and BmLP6 in the regulatory network of silkworm development and innate immunity.