We developed a novel antiviral strategy by combining transposon-based transgenesis and the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9) system for the direct cleavage of Bombyx mori nucleopolyhedrovirus (BmNPV) genome DNA to promote virus clearance in silkworms. We demonstrate that transgenic silkworms constitutively expressing Cas9 and guide RNAs targeting the BmNPV immediate early-1 (ie-1) and me53 genes effectively induce target-specific cleavage and subsequent mutagenesis, especially large (∼7-kbp) segment deletions in BmNPV genomes, and thus exhibit robust suppression of BmNPV proliferation. Transgenic animals exhibited higher and inheritable resistance to BmNPV infection than wild-type animals. Our approach will not only contribute to modern sericulture but also shed light on future antiviral therapy.IMPORTANCE Pathogen genome targeting has shown its potential in antiviral research. However, transgenic CRISPR/Cas9 system-mediated viral genome targeting has not been reported as an antiviral strategy in a natural animal host of a virus. Our data provide an effective approach against BmNPV infection in a real-world biological system and demonstrate the potential of transgenic CRISPR/Cas9 systems in antiviral research in other species.
Custom-designed nuclease technologies such as the clustered regularly interspaced short palindromic repeat (CRISPR)-associated (Cas) system provide attractive genome editing tools for insect functional genetics. The targeted gene mutagenesis mediated by the CRISPR/Cas9 system has been achieved in several insect orders including Diptera, Lepidoptera and Coleoptera. However, little success has been reported in agricultural pests due to the lack of genomic information and embryonic microinjection techniques in these insect species. Here we report that the CRISPR/Cas9 system induced efficient gene mutagenesis in an important Lepidopteran pest Spodoptera litura. We targeted the S. litura Abdominal-A (Slabd-A) gene which is an important embryonic development gene and plays a significant role in determining the identities of the abdominal segments of insects. Direct injection of Cas9 messenger RNA and Slabd-A-specific single guide RNA (sgRNA) into S. litura embryos successfully induced the typical abd-A deficient phenotype, which shows anomalous segmentation and ectopic pigmentation during the larval stage. A polymerase chain reaction-based analysis revealed that the Cas9/sgRNA complex effectively induced a targeted mutagenesis in S. litura. These results demonstrate that the CRISPR/Cas9 system is a powerful tool for genome manipulation in Lepidopteran pests such as S. litura.
Sex-specific regulatory elements are key components for developing insect genetic sexing systems. The current insect genetic sexing system mainly uses a female-specific modification system whereas little success was reported on male-specific genetic modification. In the silkworm Bombyx mori, a lepidopteran model insect with economic importance, a transgene-based, female-specific lethality system has been established based on sex-specific alternative splicing factors and a female-specific promoter BmVgp (vitellogenin promoter) has been identified. However, no male-specific regulatory elements have yet been identified. Here we report the transgenic identification of two promoters that drive reporter gene expression in a testis-specific manner in B. mori. Putative promoter sequences from the B. mori Radial spoke head 1 gene (BmR1) and beta-tubulin 4 gene (Bmβ4) were introduced using piggybac-based germline transformation. In transgenic silkworms, expression of the reporter gene enhanced green fluorescent protein (EGFP) directed by either BmR1 promoter (BmR1p) or Bmβ4p showed precisely testis-specific manners from the larval to adult stage. Furthermore, EGFP expression of these two transgenic lines showed different localization in the testis, indicating that BmR1p or Bmβ4p might be used as distinct regulatory elements in directing testis-specific gene expression. Identification of these testis-specific promoters not only contributes to a better understanding of testis-specific gene function in insects, but also has potential applications in sterile insect techniques for pest management.
Insect body pigmentation and coloration are critical to adaption to the environment. To explore the mechanisms that drive pigmentation, we used the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR‐associated protein 9 (Cas9) genome editing system to target the ebony gene in the non‐model insect Spodoptera litura. Ebony is crucial to melanin synthesis in insects. By directly injecting Cas9 messenger RNA and ebony‐specific guide RNAs into S. litura embryos, we successfully induced a typical ebony‐deficient phenotype of deep coloration of the puparium and induction of melanin formation during the pupal stage. Polymerase chain reaction‐based genotype analysis demonstrated that various mutations had occurred at the sites targeted in ebony. Our study clearly demonstrates the function of ebony in the puparium coloration and also provides a potentially useful marker gene for functional studies in S. litura as well as other lepidopteran pests.
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