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

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.

STAT transcription factor is indispensable for oogenesis in silkworm

Signal Transducer and Activator of Transcription (STAT) proteins represent a critical transcription factor family with multifaceted roles in diverse fundamental eukaryotic processes. In Drosophila, STAT exerts a pivotal regulatory influence on oogenesis, governing the early differentiation of follicular cells and ensuring proper encapsulation of germ-line cells. However, the role of STAT in egg development in silkworms remains unknown. In the present study, using CRISPR/Cas9 technology, we successfully generated a strain of silkworms with targeted deletion of the STAT-L gene, which resulted in significant reproductive abnormalities observed in female moths, including shortened fallopian tubes and reduced egg production. The ovaries dissected from STAT-L knockout silkworms during the pupal stage of silkworm exhibited varying degrees of fusion among egg chambers. Additionally, paraffin sections of prepupal ovaries also revealed evidence of egg chambers fusion. To elucidate the molecular mechanism underlying the role of the STAT-L gene regulation on egg development in silkworm, we performed ovarian transcriptomic analysis following STAT-L knockout. Our findings indicated that STAT-L gene can modulate Notch signaling pathway by down-regulating APH-1 gene expression. These results suggest that STAT-L gene plays a crucial role in normal egg chamber formation in silkworms, potentially through its influence on Notch signaling pathway expression.

Cytotoxin-mediated silk gland organ dysfunction diverts resources to enhance silkworm fecundity by potentiating nutrient-sensing IIS/TOR pathways

Energy reserves, primarily stored in the insect's fat body, are essential for physiological processes such as reproduction and cocoon formation. However, whether these processes are mutually constraining is unknown. Here, we showed that cocoon-free silkworms accumulate amino acid constituents of silk proteins in the hemolymph and maintain lipid and sugar reserves in the pupal fat body by repressing the expression of sericin and fibroin genes in the middle and posterior silk glands, respectively, via butterfly pierisin-1A catalytic domain expression. This, in turn, upregulates insulin/insulin-like signaling and target of rapamycin (IIS/TOR) signaling, which enhances vitellogenesis and accelerates ovarian development, thus contributing to increased fecundity. The impacts of semi-starvation on fecundity and egg hatchability were also less pronounced in cocoon-free silkworms compared with wildtype silkworms. These data uncover the resource allocation trade-off between cocoon formation and fecundity and demonstrate that nutritional signaling plays a role in regulating silkworm reproduction.

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.

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.

lncR26319/miR-2834/EndophilinA axis regulates oogenesis of the silkworm, Bombyx mori

Oocyte maturation is critical for insect reproduction. Vitellogenesis, the timely production and uptake of vitellogenin (Vg), is crucial for female fecundity. Vg is synthesized in fat body and absorbed by the oocytes through endocytosis during insect oogenesis. In the silkworm, Bombyx mori, we discovered that a nucleus-enriched long-noncoding RNA (lncRNA) lncR26319 regulates Endophilin A (EndoA) - a member of the endophilin family of endocytic proteins - through competitive binding to miR-2834. The lncR26319-miR-2834-EndoA axis was required for Vg endocytosis in the silkworm; loss of EndoA or overexpression of miR-2834 significantly reduced egg numbers in virgin moths. In addition, accumulation of miR-2834 resulted in pupal and adult deformation and reduced fecundity in females. The expression of Vg, 30-kDa (30K) protein, and egg-specific protein (Esp) decreased after knockdown of EndoA or overexpression of miR-2834, while knockdown of miR-2834 had an opposite effect on the expression of Vg, 30K protein gene, and Esp. These results suggest that the lncR26319-miR-2834-EndoA axis contributes to the endocytic activity in the Vg uptake and leads to the normal progression of oogenesis in the silkworm. Thus, miR-2834 and EndoA are crucial for female reproduction and could be potential targets for new pest management strategies in lepidopterans.

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.

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.

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.