Disruption of the ovarian serine protease (Osp) gene causes female sterility in Bombyx mori and Spodoptera litura

CRISPR/Cas9-mediated Nap knockout affects female reproduction and egg shape in Bombyx mori

Insect reproductive capacity can affect effective pest control and infertility studies and has become an important focus in recent molecular genetic research. Nucleosome assembly protein (Nap) is highly conserved across multiple species and is involved in forming the sperm nucleus in many species. We used clustered regularly interspaced palindromic repeats/Cas9 technology to knockout BmNap in Bombyx mori and observed that the mutations caused female infertility, whereas male fertility was not affected. BmNap mutants grew and mated normally; however, female mutants laid smaller eggs that could not be fertilised and did not hatch. In addition, female sterility produced by the mutation could be inherited stably via male mutants; therefore, Nap could be used as a potential target for lepidopteran pest control through population regulation. In the current study, we elucidated a new function of BmNap, increased the understanding of the oogenesis regulation network in Lepidoptera and promoted the development of insect sterility technologies.

Exploring the role of the ovary-serine protease gene in the female fertility of the diamondback moth using CRISPR/Cas9

BACKGROUND

Oogenesis is a complex pathway necessary for proper female reproduction in insects. Ovary-serine protease (Osp) is a homologous gene of serine protease Nudel (SpNudel) and plays an essential role in the oogenesis and ovary development of Drosophila melanogaster. However, the function of Osp is not determined in Plutella xylostella, a highly destructive pest of cruciferous crops.

RESULTS

The PxOsp gene comprises a 5883-bp open-reading frame that encodes a protein consisting of 1994 amino acids, which contain four conserved domains. PxOsp exhibited a high relative expression in adult females with a specific expression in the ovary. Through the utilization of CRISPR/Cas9 technology, homozygous mutants of PxOsp were generated. These homozygous mutant females produced fewer eggs (average of 56 eggs/female) than wild-type (WT) females (average of 97 eggs/female) when crossed with WT males, and these eggs failed to hatch. Conversely, mutant males produced normal progeny when crossed with WT females. The ovarioles in homozygous mutant females were significantly shorter (5.02 mm in length) and contained fewer eggs (average of 3 eggs/ovariole) than WT ovarioles (8.09 mm in length with an average of 8 eggs/ovariole). Moreover, eggs laid by homozygous mutant females were fragile, with irregular shapes, and were unable to maintain structural integrity due to eggshell ruptures. However, no significant differences were observed between WT and mutant individuals regarding developmental duration, pupal weight, and mating behavior.

CONCLUSION

Our study suggesteds that PxOsp plays a vital role in female reproduction, particularly in ovary and egg development. Disrupting PxOsp results in recessive female sterility while leaving the male reproductive capability unaffected. This report represents the first study of a haplosufficient gene responsible for female fertility in lepidopteran insects. Additionally, these findings emphasize PxOsp as a potential target for genetically-based pest management of P. xylostella. © 2024 Society of Chemical Industry.

Knockout of ovary serine protease Leads to Ovary Deformation and Female Sterility in the Asian Corn Borer, Ostrinia furnacalis

Oogenesis in insects is a carefully orchestrated process, facilitating the formation of female gametes, which is regulated by multiple extrinsic and intrinsic factors, including ovary serine protease (Osp). As a member of the serine protease family, Osp is a homolog of Nudel, a maternally required protease defining embryonic dorsoventral polarity in Drosophila. In this study, we used CRISPR/Cas9-mediated mutagenesis to functionally characterize Osp in the Asian corn borer, Ostrinia furnacalis, a devastating maize pest throughout Asia and Australia. Building on previous knowledge, we hypothesized that knockout of Osp would disrupt embryonic development in O. furnacalis females. To examine this overarching hypothesis, we (1) cloned and characterized Osp from O. furnacalis, (2) designed target sites on exons 1 and 4 to construct a CRISPR/Cas9 mutagenesis system, and (3) documented phenotypic impacts among O. furnacalis Osp mutants. As a result, we (1) examined the temporal-spatial expression profiles of OfOsp, which has an open reading frame of 5648 bp in length and encodes a protein of 1873 amino acids; (2) established O. furnacalis Osp mutants; and (3) documented recessive, female-specific sterility among OfOspF mutants, including absent or deformed oviducts and reduced fertility in female but not male mutants. Overall, the combined results support our initial hypothesis that Osp is required for embryonic development, specifically ovarian maturation, in O. furnacalis females. Given its substantial impacts on female sterility, Osp provides a potential target for the Sterile Insect Technique (SIT) to manage Lepidoptera pests in general and the species complex Ostrinia in particular.

Identification of Potential Gene Targets for Suppressing Oviposition in Holotrichia parallela Using Comparative Transcriptome Analysis

Holotrichia parallela is an important plant pest. Comparative feeding experiments showed that the egg production, oviposition duration and survival rate of H. parallela beetles were significantly higher when they fed on elm leaves than when they fed on willow or purpus privet leaves. RNA sequencing was used to determine transcriptomic changes associated with oviposition. Comparative transcriptome analysis revealed that the beetles that fed on elm and willow had a total of 171 genes with differential expression. When the beetles fed on elm and purpus privet, 3568 genes had differential expression. The vitellogenesis, ovarian serine protease, odorant-binding proteins, acyl-CoA synthetase and follicle cell proteins were commonly upregulated genes in elm-fed beetles compared with those fed on willow/purpus privet leaves. The involvement of the follicle cell protein 3C gene in the regulation of oviposition was confirmed using RNA interference. The results provide insights into the molecular mechanisms underlying oviposition in H. parallela feeding on different host plants. This study also describes a method for identifying potentially effective genes for pest control.

Transcriptomic analysis of the fat body of resistant and susceptible silkworm strains, Bombyx mori (Lepidoptera), after oral treatment with fenpropathrin

The widespread use of pyrethroid pesticides has brought serious economic losses in sericulture, but there is still no viable solution. The key to solving the problem is to improve silkworm resistance to pesticides, which depends on understanding the resistance mechanism of silkworms to pesticides. This study aimed to use transcriptomes to understand the underlying mechanism of silkworm resistance to fenpropathrin, which will provide a theoretical molecular reference for breeding pesticide-resistant silkworm varieties. In this study, the fat bodies of two strains with differential resistance after 12 h of fenpropathrin feeding were analyzed using RNA-Seq. After feeding fenpropathrin, 760 differentially expressed genes (DEGs) were obtained in the p50(r) strain and 671 DEGs in the 8y strain. The DEGs involved in resistance to fenpropathrin were further identified by comparing the two strains, including 207 upregulated DEGs in p50(r) and 175 downregulated DEGs in 8y. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that these fenpropathrin-related DEGs are mainly enriched in the metabolism and transporter pathways. Moreover, 28 DEGs involved in the metabolic pathway and 18 in the transporter pathway were identified. Furthermore, organic cation transporter protein 6 (BmOCT6), a transporter pathway member, was crucial in enhancing the tolerance of BmN cells to fenpropathrin. Finally, the knockdown of the expression of the homologs of BmOCT6 in Glyphodes pyloalis (G. pyloalis) significantly decreased the resistant level of larvae to fenpropathrin. The findings showed that the metabolism and transporter pathways are associated with resistance to fenpropathrin in silkworm, and OCT6 is an effective and potential target not only for silkworm breeding but also for pest biocontrol.

The effects of phosphate fertilizer on the growth and reproduction of Pardosa pseudoannulata and its potential mechanisms

In fields, the natural enemy spider, Pardosa pseudoannulata, plays important roles in insect pest control. Agrochemicals, such as phosphate fertilizer, disturb the ecosystem and weaken the pest control efficiency of the spider. According to the usual habitat of the spider in soil cracks, the soil-application of phosphate fertilizer was carried out to determine its effects on the growth and reproduction of P. pseudoannulata. Phosphate fertilizer treatment prolonged longevity and increased mortality in subadults. The treatment also negatively affected reproduction of P. pseudoannulata adults even with removing phosphate fertilizer stress before adult emergence, leading to a lower mating rate, fewer eggsacs and eggs per female, and fewer offsprings in the first eggsac. The transcriptomic sequencing analysis revealed the up-regulation of unigenes related to stress resistance and down-regulation of unigenes associated with protein processing and proteasomal degradation in phosphate fertilizer-treated P. pseudoannulata. Decline in proper protein processing by E3 ubiquitin-protein ligase complex and endopeptidase activity might provide a partial explanation for negative effects of phosphate fertilizer on the spider reproduction. The study put a notice on negative effects of phosphate fertilizer on beneficial arthropods, which provide a great potential in the protection of P. pseudoannulata and other predator spider species.

Transcriptomic analysis of Mythimna separata ovaries and identification of genes involved in reproduction

The migratory insect Mythimna separata is a major pest of grain crops in Asia. Unfortunately, the molecular mechanisms that control and regulate reproduction in this species remain unclear. In this study, transcriptome sequencing was utilized to identify genes associated with ovary development and oogenesis. Clean sequences totaling 117.71 Gb were assembled into 178,534 unigenes with a mean length of 647.37 bp and N50 length of 837 bp. Transcriptome analysis showed that 7921 unigenes were significantly expressed in ovaries with 4403 and 3518 unigenes up- and down-regulated, respectively. Enrichment analysis with the Kyoto Encyclopedia of Genes and Genomes database suggested that 729 differentially expressed genes were significantly enriched in the top 20 pathways (q-values <0.05). Twenty genes were associated with ovary development and oogenesis and included lipases, Nanos, small heat shock proteins (sHsps) and histones; these were further verified by qRT-PCR and may play essential roles in M. separata reproduction. Collectively, our findings reveal underlying mechanisms of M.separata reproduction and may lead to RNAi-based management strategies targeting reproductive physiology.

Identification and expression profiling of serine protease-related genes in Tenebrio molitor

In insects, serine proteases and serine protease homologs (SPs/SPHs) are involved in a variety of physiological processes including digestion, development, and immunity. Here, we identified 112 SP and 88 SPH genes in the genome of the yellow mealworm, Tenebrio molitor. Based on the features of domain structure, they were divided into "S" group containing single Tryp-SPc or Tryp-SPHc domain, "C" group containing 1-4 CLIP domain (CLIPA-D) and "M" group containing the CBD, CUB, EGF, Fz, Gd, LDLa, PAN, SEA, SR, Sushi, and TSP domains, and have 115, 48, and 37 gene members, respectively. According to the active sites in the catalytic triad, the putative trypsin, chymotrypsin, or elastase-like enzyme specificity of the identified SPs/SPHs were predicted. Phylogenetic and genomic location analyses revealed that gene duplication exists in the large amount of SPs/SPHs. Gene expression profiling using RNA-seq data along with real time reverse transcription-polymerase chain reaction analysis showed that most SP/SPH genes display life stage specific expression patterns, indicating their important roles in development. Many SP/SPH genes are specifically or highly expressed in the gut, salivary gland, fat body, hemocyte, ovary, and testis, suggesting that they participate in digestion, immunity, and reproduction. The findings lay the foundation for further functional characterization of SPs/SPHs in T. molitor.

piggyBac-based transgenic RNAi of serine protease 2 results in male sterility in Hyphantria cunea

Fall webworm, Hyphantria cunea, is a global invasive forest pest that causes serious damage to the economy and ecosystem of agriculture and forestry. Due to the extent of the problem and the difficulty of conventional chemical control, new technologies must be pursued, such as genetic-based inheritable insect sterile technology (gSIT), which exhibits promise for pest control. In the present study, we established a piggyBac-based transgenic system in fall webworm and generated a dominant male-sterile strain by targeting the seminal fluid protein serine protease 2 (Hcser2), displaying an outstanding trait of gSIT. First, an RNA polymerase type III (Pol III) promoter, the HcU62 small nuclear RNA (snRNA) gene promoter, was identified and characterized through direct injection of RNAi plasmids in vivo. Quantitative real-time PCR revealed that HcU62 had the greatest knockdown efficiency of the Hcyellow gene among five short hairpin RNA (shRNA) plasmids tested, designated HcU61-HcU65. Second, subsequent application of piggyBac-based transgenic RNAi (HcU62: shHcyellow, Ysh2) significantly reduced the expression level of the Hcyellow gene, resulting in a stable yellow observable phenotype from the larval to pupal stages in Ysh2 transgenic mutants. Finally, an HcU62-driven transgenic RNAi strain targeting the Hcser2 gene was obtained, resulting in a dominant male-sterile phenotype. Significantly, this process did not affect the growth, development, mating behavior or egg laying of the mutants, and the dominant sterile trait could be inherited in the next generation through female Hcser2 mutants. Furthermore, CRISPR/Cas9-mediated disruption of the Hcser2 gene further confirmed the dominant sterile phenotype, supporting it as a generalized target for genetic control of H. cunea. This study reports the first piggyBac-mediated transgenic system in H. cunea, providing a promising genetic method for controlling this pest by targeting Hcser2 gene.

Toward a CRISPR-Cas9-based Gene Drive in the Diamondback Moth Plutella xylostella

Promising to provide powerful genetic control tools, gene drives have been constructed in multiple dipteran insects, yeast, and mice for the purposes of population elimination or modification. However, it remains unclear whether these techniques can be applied to lepidopterans. Here, we used endogenous regulatory elements to drive Cas9 and single guide RNA (sgRNA) expression in the diamondback moth (DBM), Plutella xylostella, and test the first split gene drive system in a lepidopteran. The DBM is an economically important global agriculture pest of cruciferous crops and has developed severe resistance to various insecticides, making it a prime candidate for such novel control strategy development. A very high level of somatic editing was observed in Cas9/sgRNA transheterozygotes, although no significant homing was revealed in the subsequent generation. Although heritable Cas9-medated germline cleavage as well as maternal and paternal Cas9 deposition were observed, rates were far lower than for somatic cleavage events, indicating robust somatic but limited germline activity of Cas9/sgRNA under the control of selected regulatory elements. Our results provide valuable experience, paving the way for future construction of gene drives or other Cas9-based genetic control strategies in DBM and other lepidopterans.

Mutation of Serine protease 1 Induces Male Sterility in Bombyx mori

Serine proteases are important in reproduction, embryonic development, cell differentiation, apoptosis, and immunity. The genes encoding some serine proteases are essential for male fertility in both humans and rodents and are functionally conserved among metazoan. For example, the Serine protease 1 (Ser1) gene determines male reproductive success in the model lepidopteran insect Bombyx mori. In this study, we explored the function of BmSer1 through transgenic CRISPR/Cas9 technology-mediated mutations in silkworm. We found that the mutation of BmSer1 gene resulted in male sterility but had no effect on female fertility. Male mutants produce normal eupyrene sperm bundles, but the sperm bundles do not dissociate into single sperm. Male sterility caused by the BmSer1 gene mutation was inherited stably through female individuals. Therefore, the serine protease encoded by BmSer1 is essential for male reproductive success in lepidopterans and is a potential target gene for biological reproductive regulation.

Disruption of egg-specific protein causes female sterility in Bombyx mori

Yolk proteins are the main source of nutrients during embryonic and early larval development in oviparous animals. Therefore, vitellogenesis is crucial for reproduction. The silkworm, Bombyx mori, is a model lepidopteran insect in which there are three yolk proteins: vitellin, 30-kDa protein, and egg-specific protein (Esp). In this study, we explored the gene function of Esp through transgenic clustered regularly interspaced palindromic repeats (CRISPR) / CRISPR-associated protein 9 technology-mediated mutations in the silkworm. We found that Esp mutation resulted in female sterility but had no effect on male fertility. Female mutants could lay eggs after mating, but the eggs were smaller and lighter colored than those laid by wild-type females. The most important finding is that the eggs laid by female mutants did not hatch. Furthermore, we observed stable inheritance of female sterility caused by Esp mutation through successive generations. Thus, Esp encodes a yolk protein that is crucial for female reproductive success and is a potential target for pest control.

Proteolysis in Reproduction: Lessons From Gene-Modified Organism Studies

The physiological roles of proteolysis are not limited to degrading unnecessary proteins. Proteolysis plays pivotal roles in various biological processes through cleaving peptide bonds to activate and inactivate proteins including enzymes, transcription factors, and receptors. As a wide range of cellular processes is regulated by proteolysis, abnormalities or dysregulation of such proteolytic processes therefore often cause diseases. Recent genetic studies have clarified the inclusion of proteases and protease inhibitors in various reproductive processes such as development of gonads, generation and activation of gametes, and physical interaction between gametes in various species including yeast, animals, and plants. Such studies not only clarify proteolysis-related factors but the biological processes regulated by proteolysis for successful reproduction. Here the physiological roles of proteases and proteolysis in reproduction will be reviewed based on findings using gene-modified organisms.

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.

Functional conservation and diversification of yellow-y in lepidopteran insects

The diverse colors and patterns found in Lepidoptera are important for success of these species. Similar to the wings of adult butterflies, lepidopteran larvae exhibit diverse color variations to adapt to their habitats. Compared with butterfly wings, however, less attention has been paid to larval body colorations and patterns. In the present study, we focus on the yellow-y gene, which participates in the melanin synthesis pathway. We conducted CRISPR/Cas9-mediated targeted mutagenesis of yellow-y in the tobacco cutworm Spodoptera litura. We analyzed the role of S. litura yellow-y in pigmentation by morphological observation and discovered that yellow-y is necessary for normal black pigmentation in S. litura. We also showed species- and tissue-specific requirements of yellow-y in pigmentation in comparison with those of Bombyx mori yellow-y mutants. Furthermore, we found that almost none of the yellow-y mutant embryos hatched unaided. We provide evidence that S. litura yellow-y has a novel important function in egg hatching, in addition to pigmentation. The present study will enable a greater understanding of the functions and diversification of the yellow-y gene in insects.