CRISPR/Cas9 mediated knockout of Amyellow-y gene results in melanization defect of the cuticle in adult Apis mellifera

Transcriptomic Analysis of Genes Associated with Stinger Development at Different Life Stages of Apis mellifera

Stingers, evolved from ovipositors, are an important defense organ for the Apidae, Vespidae, and Formicidae species. However, the molecular mechanism of stinger development remains unclear. Here, we show that the earliest time point for the appearance of stingers in Apis mellifera is at the 1-day-old worker pupal stage based on morphological observations and anatomy from the pre-pupal to adult stages. To discover the genes related to stinger development, we first comprehensively compared the stinger transcriptome at different stages and screened 1282, 186, and 166 highly expressed genes in the stingers of 1- and 5-day-old worker pupae and newly emerged worker bees (NEBs), respectively, then identified 25 DEGs involved in the early stage of stinger development. We found that Dll was a key candidate gene in the early development of A. mellifera stingers by combining analyses of the protein-protein interaction network and spatiotemporal expression patterns. An RNAi experiment showed that about 20% of individuals exhibited tip bending in the piercing parts of their stingers in the Dll-dsRNA-treated group, with the morphology presenting as side-side or front-back tip bending. This indicates that Dll plays a vital role in the early development of A. mellifera stingers. Together, our study provides insight into the molecular mechanism of Hymenoptera stinger development and an inspiration for the molecular breeding of gentle honeybee species with stinger abnormalities.

RNAi of yellow-y, required for normal cuticle pigmentation, impairs courtship behavior and oviposition in the German cockroach (Blattella germanica)

The insect cuticle plays a key role in maintaining the insect's physiological function and behavior. Herein, the yellow-y protein is required to produce black melanin, and is expressed in a pattern that correlates with the distribution of this pigment. However, yellow-y can also have other functions, for instance, in insect behavior, but not much is known. In this study, we have studied the yellow-y gene in one important model and pest species, namely the German cockroach (Blattella germanica), which is to our knowledge the first time reported. In essence, we identified the yellow-y gene (BgY-y) and characterized its function by using RNA interference (RNAi). Silencing of BgY-y gene led to different developmental abnormalities (body weight and wings) in both genders. Specifically, there was an abundant decrease in melanin, turning the body color in pale yellow and the cuticle softer and more transparent. Interestingly, we also observed that the knockdown of BgY-y impaired the male cockroaches to display a weaker response to female-emitted contact sex pheromones, and also that the oviposition ability was weakened in the RNAi females. This study comprehensively analyzed the biological functions of the yellow-y gene in German cockroaches from the perspectives of development, body color, courtship behavior and oviposition, and as a consequence, this may opens new avenues to explore it as a novel pest control gene.

Unveiling the Genetic Symphony: Harnessing CRISPR-Cas Genome Editing for Effective Insect Pest Management

Phytophagous insects pose a significant threat to global crop yield and food security. The need for increased agricultural output while reducing dependence on harmful synthetic insecticides necessitates the implementation of innovative methods. The utilization of CRISPR-Cas (Clustered regularly interspaced short palindromic repeats) technology to develop insect pest-resistant plants is believed to be a highly effective approach in reducing production expenses and enhancing the profitability of farms. Insect genome research provides vital insights into gene functions, allowing for a better knowledge of insect biology, adaptability, and the development of targeted pest management and disease prevention measures. The CRISPR-Cas gene editing technique has the capability to modify the DNA of insects, either to trigger a gene drive or to overcome their resistance to specific insecticides. The advancements in CRISPR technology and its various applications have shown potential in developing insect-resistant varieties of plants and other strategies for effective pest management through a sustainable approach. This could have significant consequences for ensuring food security. This approach involves using genome editing to create modified insects or crop plants. The article critically analyzed and discussed the potential and challenges associated with exploring and utilizing CRISPR-Cas technology for reducing insect pest pressure in crop plants.

Ovariole-specific Yellow-g and Yellow-g2 proteins are required for fecundity and egg chorion rigidity in the red flour beetle, Tribolium castaneum

Most insects reproduce by laying eggs that have an eggshell/chorion secreted by follicle cells, which serves as a protective barrier for developing embryos. Thus, eggshell formation is vital for reproduction. Insect yellow family genes encode for secreted extracellular proteins that perform different, context-dependent functions in different tissues at various stages of development involving, for example, cuticle/eggshell coloration and morphology, molting, courtship behavior and embryo hatching. In this study we investigated the function of two of this family's genes, yellow-g (TcY-g) and yellow-g2 (TcY-g2), on the formation and morphology of the eggshell of the red flour beetle, Tribolium castaneum. Real-time PCR analysis revealed that both TcY-g and TcY-g2 were specifically expressed in the ovarioles of adult females. Loss of function produced by injection of double-stranded RNA (dsRNA) for either TcY-g or TcY-g2 gene resulted in failure of oviposition. There was no effect on maternal survival. Ovaries dissected from those dsRNA-treated females exhibited ovarioles containing not only developing oocytes but also mature eggs in their egg chambers. However, the ovulated eggs were collapsed and ruptured, resulting in swollen lateral oviducts and calyxes. TEM analysis showed that lateral oviducts were filled with electron-dense material, presumably from some cellular content leakage out of the collapsed eggs. In addition, morphological abnormalities in lateral oviduct epithelial cells and the tubular muscle sheath were evident. These results support the hypothesis that both TcY-g and TcY-g2 proteins are required for maintaining the rigidity and integrity of the chorion, which is critical for resistance to mechanical stress and/or rehydration during ovulation and egg activation in the oviducts of T. castaneum. Because Yellow-g and Yellow-g2 are highly conserved among insect species, both genes are potential targets for development of gene-based insect pest population control methods.

Characterization of five pigmentation genes as transgenic markers in Spodoptera frugiperda (Lepidoptera: Noctuidae)

The fall armyworm, Spodoptera frugiperda (J. E. Smith), has become one of the most damaging pests worldwide since its invasion of Africa, Asia and Oceania from 2016, threatening plants in 76 families including important crops. Genetics-based methods have proved to be an efficient way to control pests, especially invasive species, but many difficulties must be overcome to develop a transgenic insect strain, especially for a non-model species. Here we thus sought to identify a visible marker that would facilitate the distinction between genetically modified (GM) and non-transgenic insects, thereby simplifying mutation identification and facilitating the broader application of genome editing tools in non-model insects. Five genes (sfyellow-y, sfebony, sflaccase2, sfscarlet, and sfok) that are orthologs of well-studied genes in pigment metabolism were knocked out using the CRISPR/Cas9 system to identify candidate gene markers. Two genes, Sfebony and Sfscarlet, were identified responsible for body and compound eye coloration, respectively, in S. frugiperda, and could be potential visual markers for genetics-based pest management strategies.

Honey bee functional genomics using symbiont-mediated RNAi

Honey bees are indispensable pollinators and model organisms for studying social behavior, development and cognition. However, their eusociality makes it difficult to use standard forward genetic approaches to study gene function. Most functional genomics studies in bees currently utilize double-stranded RNA (dsRNA) injection or feeding to induce RNAi-mediated knockdown of a gene of interest. However, dsRNA injection is laborious and harmful, and dsRNA feeding is difficult to scale cheaply. Further, both methods require repeated dsRNA administration to ensure a continued RNAi response. To fill this gap, we engineered the bee gut bacterium Snodgrassella alvi to induce a sustained host RNA interference response that reduces expression of a targeted gene. To employ this functional genomics using engineered symbionts (FUGUES) procedure, a dsRNA expression plasmid is cloned in Escherichia coli using Golden Gate assembly and then transferred to S. alvi. Adult worker bees are then colonized with engineered S. alvi. Finally, gene knockdown is verified through qRT-PCR, and bee phenotypes of interest can be further assessed. Expression of targeted genes is reduced by as much as 50-75% throughout the entire bee body by 5 d after colonization. This protocol can be accomplished in 4 weeks by bee researchers with microbiology and molecular cloning skills. FUGUES currently offers a streamlined and scalable approach for studying the biology of honey bees. Engineering other microbial symbionts to influence their hosts in ways that are similar to those described in this protocol may prove useful for studying additional insect and animal species in the future.

Gene editing of the ABC Transporter/White locus using CRISPR/Cas9-mediated mutagenesis in the Indian Meal Moth

ATP binding cassette (ABC) proteins are involved in transport of substrates across membranes including eye pigments. Mutations of ABC transporter white, brown and scarlet genes of Drosophila and other insects result in visible eye color phenotypes. White locus was identified in a genome assembly of Plodia interpunctella and was found to extend for 16,670 bp comprising 13 exons. We report here recovery of heritable mutants in white in the Indian meal moth, P. interpunctella, using CRISPR/Cas9-mediated mutagenesis. A white eye strain of P. interpunctella c.737delC (Piw^-/-) was previously isolated in 1986. Guide RNA (sgRNA) was designed for exon 1 (sgRNA242). Microinjection of Cas9/sgRNA242 complex into Plodia wild type eggs (≤20 min post oviposition) produced 156 viable larvae of which 81 eclosed as adults. Forty-five (56 %) adults displayed wild type phenotype, while 26 females (32 %) and 10 males (12 %) showed full or partial white eye phenotype. The 26 white eye females were mated with Piw^-/- males and 21 matings resulted in F₁ white eye progeny. Thirteen of the Piw^-242 lines were established and sequencing showed indels at the CRISPR/Cas9 242AM site. Based on RT-PCR analysis, most white mutations resulted in suppressed levels of transcript. These results demonstrate the utility of CRISPR/Cas9 gene editing in Plodia which suggests this technology can be used to characterize the role of various genetic elements including those that encode novel targets or confer insecticide resistance mechanisms.

Multisite imaging of neural activity using a genetically encoded calcium sensor in the honey bee

Understanding of the neural bases for complex behaviors in Hymenoptera insect species has been limited by a lack of tools that allow measuring neuronal activity simultaneously in different brain regions. Here, we developed the first pan-neuronal genetic driver in a Hymenopteran model organism, the honey bee, and expressed the calcium indicator GCaMP6f under the control of the honey bee synapsin promoter. We show that GCaMP6f is widely expressed in the honey bee brain, allowing to record neural activity from multiple brain regions. To assess the power of this tool, we focused on the olfactory system, recording simultaneous responses from the antennal lobe, and from the more poorly investigated lateral horn (LH) and mushroom body (MB) calyces. Neural responses to 16 distinct odorants demonstrate that odorant quality (chemical structure) and quantity are faithfully encoded in the honey bee antennal lobe. In contrast, odor coding in the LH departs from this simple physico-chemical coding, supporting the role of this structure in coding the biological value of odorants. We further demonstrate robust neural responses to several bee pheromone odorants, key drivers of social behavior, in the LH. Combined, these brain recordings represent the first use of a neurogenetic tool for recording large-scale neural activity in a eusocial insect and will be of utility in assessing the neural underpinnings of olfactory and other sensory modalities and of social behaviors and cognitive abilities.

Feeding Asian honeybee queens with European honeybee royal jelly alters body color and expression of related coding and non-coding RNAs

Background and aims: The Asian honeybee (Apis cerana) and the European honeybee (Apis mellifera) are reproductively isolated. Previous studies reported that exchanging the larval food between the two species, known as nutritional crossbreeding, resulted in obvious changes in morphology, physiology and behavior. This study explored the molecular mechanisms underlying the honeybee nutritional crossbreeding. Methods: This study used full nutritional crossbreeding technology to rear A. cerana queens by feeding them with an A. mellifera royal jelly-based diet in an incubator. The body color and the expression of certain genes, microRNA, lncRNA, and circRNA among nutritional crossbred A. cerana queens (NQ), and control A. cerana queens (CQ) were compared. The biological functions of two target genes, TPH1 and KMO, were verified using RNA interference. Results: Our results showed that the NQ's body color turned yellow compared to the black control queens. Whole transcriptome sequencing results showed that a total of 1484, 311, 92, and 169 DEGs, DElncRNAs, DEmiRNAs, and DEcircRNAs, respectively, were identified in NQ and CQ, in which seven DEGs were enriched for three key pathways (tryptophan, tyrosine, and dopamine) involved in melanin synthesis. Interestingly, eight DElncRNAs and three DEmiRNAs were enriched into the key pathways regulating the above key DEGs. No circRNAs were enriched into these key pathways. Knocking down two key genes (KMO and TPH1) resulted in altered body color, suggesting that feeding NQ's an RNAi-based diet significantly downregulated the expression of TPH1 and KMO in 4-day-old larvae, which confirmed the function of key DEGs in the regulation of honeybee body color. Conclusion: These findings reveal that the larval diets from A. mellifera could change the body color of A. cerana, perhaps by altering the expression of non-coding RNAs and related key genes. This study serves as a model of epigenetic regulation in insect body color induced by environmental factors.

Revealing phosphorylation regulatory networks during embryogenesis of honey bee worker and drone (Apis mellifera)

Protein phosphorylation is known to regulate a comprehensive scenario of critical cellular processes. However, phosphorylation-mediated regulatory networks in honey bee embryogenesis are mainly unknown. We identified 6342 phosphosites from 2438 phosphoproteins and predicted 168 kinases in the honey bee embryo. Generally, the worker and drone develop similar phosphoproteome architectures and major phosphorylation events during embryogenesis. In 24 h embryos, protein kinases A play vital roles in regulating cell proliferation and blastoderm formation. At 48–72 h, kinase subfamily dual-specificity tyrosine-regulated kinase, cyclin-dependent kinase (CDK), and induced pathways related to protein synthesis and morphogenesis suggest the centrality to enhance the germ layer development, organogenesis, and dorsal closure. Notably, workers and drones formulated distinct phosphoproteome signatures. For 24 h embryos, the highly phosphorylated serine/threonine-protein kinase minibrain, microtubule-associated serine/threonine-protein kinase 2 (MAST2), and phosphorylation of mitogen-activated protein kinase 3 (MAPK3) at Thr564 in workers, are likely to regulate the late onset of cell proliferation; in contrast, drone embryos enhanced the expression of CDK12, MAPK3, and MAST2 to promote the massive synthesis of proteins and cytoskeleton. In 48 h, the induced serine/threonine-protein kinase and CDK12 in worker embryos signify their roles in the construction of embryonic tissues and organs; however, the highly activated kinases CDK1, raf homolog serine/threonine-protein kinase, and MAST2 in drone embryos may drive the large-scale establishment of tissues and organs. In 72 h, the activated pathways and kinases associated with cell growth and tissue differentiation in worker embryos may promote the configuration of rudimentary organs. However, kinases implicated in cytoskeleton organization in drone embryos may drive the blastokinesis and dorsal closure. Our hitherto most comprehensive phosphoproteome offers a valuable resource for signaling research on phosphorylation dynamics in honey bee embryos.

Understanding of Waggle Dance in the Honey Bee (Apis mellifera) from the Perspective of Long Non-Coding RNA

The ethological study of dance behaviour has yielded some findings since Karl Von Frisch discovered and interpreted the ‘dance language’ in the honey bee. However, the function and role of long non-coding RNAs on dance behaviour are hardly known until now. In this study, the differential expression patterns of lncRNAs in the brains of waggling dancers and non-dancing bees were analysed by RNA sequencing. Furthermore, lncRNA-mRNA association analysis was constructed to decipher the waggle dance. The results of RNA sequencing indicated that a total of 2877 lncRNAs and 9647 mRNAs were detected from honey bee brains. Further comparison analysis displayed that two lncRNAs, MSTRG.6803.3 and XR_003305156.1, may be involved in the waggle dance. The lncRNA-mRNA association analysis showed that target genes of differentially expressed lncRNAs in the brains between waggling dancers and non-dancing bees were mainly annotated in biological processes related to metabolic process, signalling and response to stimulus and in molecular function associated with signal transducer activity, molecular transducer activity and binding. Nitrogen metabolism was likely implicated in the modulation of the waggle dance. Our findings contribute to further understanding the occurrence and development of waggle dance.

Nosema apis and N. ceranae Infection in Honey bees: A Model for Host-Pathogen Interactions in Insects

There has been increased focus on the role of microbial attack as a potential cause of recent declines in the health of the western honey bee, Apis mellifera. The Nosema species, N. apis and N. ceranae, are microsporidian parasites that are pathogenic to honey bees, and infection by these species has been implicated as a key factor in honey bee losses. Honey bees infected with both Nosema spp. display significant changes in their biology at the cellular, tissue, and organismal levels impacting host metabolism, immune function, physiology, and behavior. Infected individuals lead to colony dysfunction and can contribute to colony disease in some circumstances. The means through which parasite growth and tissue pathology in the midgut lead to the dramatic physiological and behavioral changes at the organismal level are only partially understood. In addition, we possess only a limited appreciation of the elements of the host environment that impact pathogen growth and development. Critical for answering these questions is a mechanistic understanding of the host and pathogen machinery responsible for host-pathogen interactions. A number of approaches are already being used to elucidate these mechanisms, and promising new tools may allow for gain- and loss-of-function experiments to accelerate future progress.

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.

Yellow-y Functions in Egg Melanization and Chorion Morphology of the Asian Tiger Mosquito, Aedes albopictus

The Asian tiger mosquito, Aedes albopictus, is one of the most serious public health pests, which can transmit various vector-borne diseases. Eggs from this mosquito species become dark black shortly after oviposition and exhibit high desiccation resistance. Some of the Yellow proteins that act as dopachrome conversion enzymes (DCEs) are involved in the tyrosine-mediated tanning (pigmentation and sclerotization) metabolic pathway that significantly accelerates melanization reactions in insects. In this research, we analyzed the function of one of the yellow genes, yellow-y (AalY-y), in eggshell/chorion melanization of Ae. albopictus eggs. Developmental and tissue-specific expression measured by real-time PCR showed that AalY-y transcripts were detected at all stages of development analyzed, with significantly higher levels in the ovaries from blood-fed adult females. Injection of double-stranded RNA for AalY-y (dsAalY-y) had no significant effect on fecundity. However, unlike dsEGFP-treated control eggs that become black by 2–3 h after oviposition (HAO), dsAalY-y eggs were yellow-brown at 2 HAO, and reddish-brown even at 48 HAO. dsEGFP eggs exhibited resistance to desiccation at 48 HAO, whereas approximately 50% of the dsAalY-y eggs collapsed when they were moved to a low humidity condition. In addition, TEM analysis revealed an abnormal morphology and ultrastructure of the outer-endochorion in the dsAalY-y eggs. These results support the hypothesis that AalY-y is involved in the tyrosine-induced melanin biosynthetic pathway, plays an important role in black melanization of the chorion and functions in conferring proper morphology of the outer-endochorion, a structure that is presumably required for egg desiccation resistance in Ae. albopictus.

Expansion of CRISPR Targeting Sites Using an Integrated Gene-Editing System in Apis mellifera

Simple Summary

CRISPR/Cas9, a versatile gene manipulation tool, has been harnessed for targeted genome engineering in honeybees. However, until now, only SpCas9 that enables NGG recognition has been shown to manipulate the genome in A. mellifera, limiting the editable range to the NGG-included loci. In the current study, to evaluate the potential expansion when utilising Cpf1, SpCas9 and SaCas9, we predicted the distribution and number of targeting sites throughout the whole honeybee genome with a bioinformatic approach. The results of bioinformatics analysis suggest that the number of accessible targeting sites in A. mellifera could be significantly increased via the integrated CRISPR system. In addition, we measured the cleavage activity of these new CRISPR enzymes in A. mellifera, and it was found that both SaCas9 and Cpf1 can induce genome alternation in A. mellifera, albeit with relatively lower mutagenesis rates for Cpf1 and unstable editing for SaCas9. To our knowledge, our study provides the first evidence that SaCas9 and Cpf1 can efficiently mediate genome sequence mutation, thereby expanding the targetable spectrum in A. mellifera. The integrated CRISPR system will probably boost both fundamental studies and applied researches in A. mellifera and perhaps other insects.

Abstract

CRISPR/Cas9, a predominant gene-editing tool, has been utilised to dissect the gene function in Apis mellifera. However, only the genomic region containing NGG PAM could be recognised and edited in A. mellifera, seriously hampering the application of CRISPR technology in honeybees. In this study, we carried out the bioinformatics analysis for genome-wide targeting sites of NGG, TTN, and NNGRRT to determine the potential expansion of the SpCas9, SaCas9, Cpf1, and it was found that the targetable spectrum of the CRISPR editing system could be markedly extended via the integrated gene manipulation system. Meanwhile, the single guide RNA (sgRNA)/crRNA of different novel gene editing systems and the corresponding CRISPR proteins were co-injected into honeybee embryos, and their feasibility was tested in A. mellifera. The sequencing data revealed that both SaCas9 and Cpf1 are capable of mediating mutation in A. mellifera, albeit with relatively lower mutagenesis rates for Cpf1 and unstable editing for SaCas9. To our knowledge, our results provide the first demonstration that SaCas9 and Cpf1 can function to induce genome sequence alternation, which extended the editing scope to the targets with TTN and NNGRRT and enabled CRISPR-based genome research in a broader range in A. mellifera.