SEX DETERMINATION. A male-determining factor in the mosquito Aedes aegypti

LncRNA gene ANTSR coordinates complementary sex determination in the Argentine ant

Animals have evolved various sex determination systems. Here, we describe a newly found mechanism. A long noncoding RNA (lncRNA) transduces complementary sex determination (CSD) signal in the invasive Argentine ant. In this haplodiploid species, we identified a 5-kilobase hyper-polymorphic region underlying CSD: Heterozygous embryos become females, while homozygous and hemizygous embryos become males. Heterozygosity at the CSD locus correlates with higher expression of ANTSR, a gene that overlaps with the CSD locus and specifies an lncRNA transcript. ANTSR knockdown in CSD heterozygotes leads to male development. Comparative analyses indicated that, in Hymenoptera, ANTSR is an ancient yet rapidly evolving gene. This study reveals an lncRNA involved in genetic sex determination, alongside a previously unknown regulatory mechanism underlying sex determination based on complementarity among noncoding alleles.

Long non-coding RNAs as promising targets for controlling disease vector mosquitoes

Hematophagous female mosquitoes are important vectors of numerous devastating human diseases, posing a major public health threat. Effective prevention and control of mosquito-borne diseases rely considerably on progress in understanding the molecular mechanisms of various life activities, and accordingly, the molecules that regulate the various life activities of mosquitoes are potential targets for implementing future vector control strategies. Many long non-coding RNAs (lncRNAs) have been identified in mosquitoes and significant progress has been made in determining their functions. Here, we present a comprehensive overview of the research advances on mosquito lncRNAs, including their molecular identification, function, and interaction with other non-coding RNAs, as well as their synergistic regulatory roles in mosquito life activities. We also highlight the potential roles of competitive endogenous RNAs in mosquito growth and development, as well as in insecticide resistance and virus-host interactions. Insights into the biological functions and mechanisms of lncRNAs in mosquito life activities, viral replication, pathogenesis, and transmission will contribute to the development of novel drugs and safe vaccines.

Zygosity-based sex determination in a butterfly drives hypervariability of Masculinizer

Nature has devised many ways of producing males and females. Here, we report on a previously undescribed mechanism for Lepidoptera that functions without a female-specific gene. The number of alleles or allele heterozygosity in a single Z-linked gene (BaMasc) is the primary sex-determining switch in Bicyclus anynana butterflies. Embryos carrying a single BaMasc allele develop into WZ (or Z0) females, those carrying two distinct alleles develop into ZZ males, while (ZZ) homozygotes initiate female development, have mismatched dosage compensation, and die as embryos. Consequently, selection against homozygotes has favored the evolution of spectacular allelic diversity: 205 different coding sequences of BaMasc were detected in a sample of 246 females. The structural similarity of a hypervariable region (HVR) in BaMasc to the HVR in Apis mellifera csd suggests molecular convergence between deeply diverged insect lineages. Our discovery of this primary switch highlights the fascinating diversity of sex-determining mechanisms and underlying evolutionary drivers.

The Perpetual Vector Mosquito Threat and Its Eco-Friendly Nemeses

Mosquitoes are the most notorious arthropod vectors of viral and parasitic diseases for which approximately half the world's population, ~4,000,000,000, is at risk. Integrated pest management programs (IPMPs) have achieved some success in mitigating the regional transmission and persistence of these diseases. However, as many vector-borne diseases remain pervasive, it is obvious that IPMP successes have not been absolute in eradicating the threat imposed by mosquitoes. Moreover, the expanding mosquito geographic ranges caused by factors related to climate change and globalization (travel, trade, and migration), and the evolution of resistance to synthetic pesticides, present ongoing challenges to reducing or eliminating the local and global burden of these diseases, especially in economically and medically disadvantaged societies. Abatement strategies include the control of vector populations with synthetic pesticides and eco-friendly technologies. These "green" technologies include SIT, IIT, RIDL, CRISPR/Cas9 gene drive, and biological control that specifically targets the aquatic larval stages of mosquitoes. Regarding the latter, the most effective continues to be the widespread use of Lysinibacillus sphaericus (Ls) and Bacillus thuringiensis subsp. israelensis (Bti). Here, we present a review of the health issues elicited by vector mosquitoes, control strategies, and lastly, focus on the biology of Ls and Bti, with an emphasis on the latter, to which no resistance has been observed in the field.

Alpha-mannosidase-2 modulates arbovirus infection in a pathogen- and Wolbachia-specific manner in Aedes aegypti mosquitoes

Multiple Wolbachia strains can block pathogen infection, replication and/or transmission in Aedes aegypti mosquitoes under both laboratory and field conditions. However, Wolbachia effects on pathogens can be highly variable across systems and the factors governing this variability are not well understood. It is increasingly clear that the mosquito host is not a passive player in which Wolbachia governs pathogen transmission phenotypes; rather, the genetics of the host can significantly modulate Wolbachia-mediated pathogen blocking. Specifically, previous work linked variation in Wolbachia pathogen blocking to polymorphisms in the mosquito alpha-mannosidase-2 (αMan2) gene. Here we use CRISPR-Cas9 mutagenesis to functionally test this association. We developed αMan2 knockouts and examined effects on both Wolbachia and virus levels, using dengue virus (DENV; Flaviviridae) and Mayaro virus (MAYV; Togaviridae). Wolbachia titres were significantly elevated in αMan2 knockout (KO) mosquitoes, but there were complex interactions with virus infection and replication. In Wolbachia-uninfected mosquitoes, the αMan2 KO mutation was associated with decreased DENV titres, but in a Wolbachia-infected background, the αMan2 KO mutation significantly increased virus titres. In contrast, the αMan2 KO mutation significantly increased MAYV replication in Wolbachia-uninfected mosquitoes and did not affect Wolbachia-mediated virus blocking. These results demonstrate that αMan2 modulates arbovirus infection in A. aegypti mosquitoes in a pathogen- and Wolbachia-specific manner, and that Wolbachia-mediated pathogen blocking is a complex phenotype dependent on the mosquito host genotype and the pathogen. These results have a significant impact for the design and use of Wolbachia-based strategies to control vector-borne pathogens.

Finding divergent sequences of homomorphic sex chromosomes via diploidized nanopore-based assembly from a single male

Although homomorphic sex chromosomes can have non-recombining regions with elevated sequence divergence between its complements, such divergence signals can be difficult to detect bioinformatically. If found in genomes of e.g. insect pests, these sequences could be targeted by the engineered genetic sexing and control systems. Here, we report an approach that can leverage long-read nanopore sequencing of a single XY male to identify divergent regions of homomorphic sex chromosomes. Long-read data are used for de novo genome assembly that is diploidized in a way that maximizes sex-specific differences between its haploid complements. We show that the correct assembly phasing is supported by the mapping of nanopore reads from the male's haploid Y-bearing sperm cells. The approach revealed a highly divergent region (HDR) near the centromere of the homomorphic sex chromosome of Aedes aegypti, the most important arboviral vector, for which there is a great interest in creating new genetic control tools. HDR is located ~5Mb downstream of the known male-determining locus on chromosome 1 and is significantly enriched for ovary-biased genes. While recombination in HDR ceased relatively recently (~1.4 MYA), HDR gametologs have divergent exons and introns of protein coding genes, and most lncRNA genes became X-specific. Megabases of previously invisible sex-linked sequences provide new putative targets for engineering the genetic systems to control this deadly mosquito. Broadly, our approach expands the toolbox for studying cryptic structure of sex chromosomes.

The chromosome-scale genome assembly for the West Nile vector Culex quinquefasciatus uncovers patterns of genome evolution in mosquitoes

BACKGROUND

Understanding genome organization and evolution is important for species involved in transmission of human diseases, such as mosquitoes. Anophelinae and Culicinae subfamilies of mosquitoes show striking differences in genome sizes, sex chromosome arrangements, behavior, and ability to transmit pathogens. However, the genomic basis of these differences is not fully understood.

METHODS

In this study, we used a combination of advanced genome technologies such as Oxford Nanopore Technology sequencing, Hi-C scaffolding, Bionano, and cytogenetic mapping to develop an improved chromosome-scale genome assembly for the West Nile vector Culex quinquefasciatus.

RESULTS

We then used this assembly to annotate odorant receptors, odorant binding proteins, and transposable elements. A genomic region containing male-specific sequences on chromosome 1 and a polymorphic inversion on chromosome 3 were identified in the Cx. quinquefasciatus genome. In addition, the genome of Cx. quinquefasciatus was compared with the genomes of other mosquitoes such as malaria vectors An. coluzzi and An. albimanus, and the vector of arboviruses Ae. aegypti. Our work confirms significant expansion of the two chemosensory gene families in Cx. quinquefasciatus, as well as a significant increase and relocation of the transposable elements in both Cx. quinquefasciatus and Ae. aegypti relative to the Anophelines. Phylogenetic analysis clarifies the divergence time between the mosquito species. Our study provides new insights into chromosomal evolution in mosquitoes and finds that the X chromosome of Anophelinae and the sex-determining chromosome 1 of Culicinae have a significantly higher rate of evolution than autosomes.

CONCLUSION

The improved Cx. quinquefasciatus genome assembly uncovered new details of mosquito genome evolution and has the potential to speed up the development of novel vector control strategies.

Identification and functional verification of Y-chromosome-specific gene typo-gyf in Bactrocera dorsalis

Genes on the Y chromosome play important roles in male sex determination and development. The identification of Y-chromosome-specific genes not only provides a theoretical basis for the study of male reproductive development, but also offers genetic control targets for agricultural pests. However, Y-chromosome genes are rarely characterized due to their high repeatability and high heterochromatinization, especially in the oriental fruit fly. In this study, 1 011 Y-chromosome-specific candidate sequences were screened from 2 to 4 h Bactrocera dorsalis embryo datasets with the chromosome quotient method, 6 of which were identified as Y-chromosome-specific sequences by polymerase chain reaction, including typo-gyf, a 19 126-bp DNA sequence containing a 575-amino acid open reading frame. Testicular deformation and a significant reduction in sperm number were observed after typo-gyf knockdown with RNA interference in embryos. After typo-gyf knockout with clustered regularly interspaced palindromic repeats (CRISPR) / CRISPR-associated protein 9 in the embryonic stage, the sex ratio of the emergent adults was unbalanced, with far more females than males. A genotype analysis of these females with the Y-chromosome gene MoY revealed no sex reversal. Typo-gyf knockout led to the death of XY individuals in the embryonic stage. We conclude that typo-gyf is an essential gene for male survival, and is also involved in testicular development and spermatogenesis. The identification of typo-gyf and its functional verification provide insight into the roles of Y-chromosome genes in male development.

On the Origin and Evolution of the Mosquito Male-determining Factor Nix

The mosquito family Culicidae is divided into 2 subfamilies named the Culicinae and Anophelinae. Nix, the dominant male-determining factor, has only been found in the culicines Aedes aegypti and Aedes albopictus, 2 important arboviral vectors that belong to the subgenus Stegomyia. Here we performed sex-specific whole-genome sequencing and RNAseq of divergent mosquito species and explored additional male-inclusive datasets to investigate the distribution of Nix. Except for the Culex genus, Nix homologs were found in all species surveyed from the Culicinae subfamily, including 12 additional species from 3 highly divergent tribes comprising 4 genera, suggesting Nix originated at least 133 to 165 million years ago (MYA). Heterologous expression of 1 of 3 divergent Nix open reading frames (ORFs) in Ae. aegypti resulted in partial masculinization of genetic females as evidenced by morphology and doublesex splicing. Phylogenetic analysis suggests Nix is related to femaleless (fle), a recently described intermediate sex-determining factor found exclusively in anopheline mosquitoes. Nix from all species has a conserved structure, including 3 RNA-recognition motifs (RRMs), as does fle. However, Nix has evolved at a much faster rate than fle. The RRM3 of both Nix and fle are distantly related to the single RRM of a widely distributed and conserved splicing factor transformer-2 (tra2). The RRM3-based phylogenetic analysis suggests this domain in Nix and fle may have evolved from tra2 or a tra2-related gene in a common ancestor of mosquitoes. Our results provide insights into the evolution of sex determination in mosquitoes and will inform broad applications of mosquito-control strategies based on manipulating sex ratios toward nonbiting males.

Advances and challenges in synthetic biology for mosquito control

Mosquito-borne illnesses represent a significant global health peril, resulting in approximately one million fatalities annually. West Nile, dengue, Zika, and malaria are continuously expanding their global reach, driven by factors that escalate mosquito populations and pathogen transmission. Innovative control measures are imperative to combat these catastrophic ailments. Conventional approaches, such as eliminating breeding sites and using insecticides, have been helpful, but they face challenges such as insecticide resistance and environmental harm. Given the mounting severity of mosquito-borne diseases, there is promise in exploring innovative approaches using synthetic biology to bolster mosquitoes' resistance to pathogens, or even eliminate the mosquito vectors, as a means of control. This review outlines current strategies, future goals, and the importance of gene editing for global health defenses against mosquito-borne diseases.

The Scorpionfly (Panorpa cognata) Genome Highlights Conserved and Derived Features of the Peculiar Dipteran X Chromosome

Many insects carry an ancient X chromosome-the Drosophila Muller element F-that likely predates their origin. Interestingly, the X has undergone turnover in multiple fly species (Diptera) after being conserved for more than 450 My. The long evolutionary distance between Diptera and other sequenced insect clades makes it difficult to infer what could have contributed to this sudden increase in rate of turnover. Here, we produce the first genome and transcriptome of a long overlooked sister-order to Diptera: Mecoptera. We compare the scorpionfly Panorpa cognata X-chromosome gene content, expression, and structure to that of several dipteran species as well as more distantly related insect orders (Orthoptera and Blattodea). We find high conservation of gene content between the mecopteran X and the dipteran Muller F element, as well as several shared biological features, such as the presence of dosage compensation and a low amount of genetic diversity, consistent with a low recombination rate. However, the 2 homologous X chromosomes differ strikingly in their size and number of genes they carry. Our results therefore support a common ancestry of the mecopteran and ancestral dipteran X chromosomes, and suggest that Muller element F shrank in size and gene content after the split of Diptera and Mecoptera, which may have contributed to its turnover in dipteran insects.

Efficient sex separation by exploiting differential alternative splicing of a dominant marker in Aedes aegypti

Only female mosquitoes consume blood giving them the opportunity to transmit deadly human pathogens. Therefore, it is critical to remove females before conducting releases for genetic biocontrol interventions. Here we describe a robust sex-sorting approach termed SEPARATOR (Sexing Element Produced by Alternative RNA-splicing of A Transgenic Observable Reporter) that exploits sex-specific alternative splicing of an innocuous reporter to ensure exclusive dominant male-specific expression. Using SEPARATOR, we demonstrate reliable sex selection from early larval and pupal stages in Aedes aegypti, and use a Complex Object Parametric Analyzer and Sorter (COPAS) to demonstrate scalable high-throughput sex-selection of first instar larvae. Additionally, we use this approach to sequence the transcriptomes of early larval males and females and find several genes that are sex-specifically expressed. SEPARATOR can simplify mass production of males for release programs and is designed to be cross-species portable and should be instrumental for genetic biocontrol interventions.

Recognition of polymorphic Csd proteins determines sex in the honeybee

Sex in honeybees, Apis mellifera, is genetically determined by heterozygous versus homo/hemizygous genotypes involving numerous alleles at the single complementary sex determination locus. The molecular mechanism of sex determination is however unknown because there are more than 4950 known possible allele combinations, but only two sexes in the species. We show how protein variants expressed from complementary sex determiner (csd) gene determine sex. In females, the amino acid differences between Csd variants at the potential-specifying domain (PSD) direct the selection of a conserved coiled-coil domain for binding and protein complexation. This recognition mechanism activates Csd proteins and, thus, the female pathway. In males, the absence of polymorphisms establishes other binding elements at PSD for binding and complexation of identical Csd proteins. This second recognition mechanism inactivates Csd proteins and commits male development via default pathway. Our results demonstrate that the recognition of different versus identical variants of a single protein is a mechanism to determine sex.

Current Status of Omics Studies Elucidating the Features of Reproductive Biology in Blood-Feeding Insects

Female insects belonging to the genera Anopheles, Aedes, Glossina, and Rhodnius account for the majority of global vector-borne disease mortality. In response to mating, these female insects undergo several molecular, physiological, and behavioral changes. Studying the dynamic post-mating molecular responses in these insects that transmit human diseases can lead to the identification of potential targets for the development of novel vector control methods. With the continued advancements in bioinformatics tools, we now have the capability to delve into various physiological processes in these insects. Here, we discuss the availability of multiple datasets describing the reproductive physiology of the common blood-feeding insects at the molecular level. Additionally, we compare the male-derived triggers transferred during mating to females, examining both shared and species-specific factors. These triggers initiate post-mating genetic responses in female vectors, affecting not only their reproductive success but also disease transmission.

Masculinizer gene controls male sex determination in the codling moth, Cydia pomonella

The molecular mechanisms of sex determination in moths and butterflies (Lepidoptera) with female heterogamety (WZ/ZZ) are poorly understood, except in the silkworm Bombyx mori. However, the Masculinizer (Masc) gene that controls male development and dosage compensation in B. mori, appears to be conserved in Lepidoptera, as its masculinizing function was recently confirmed in several moth species. In this work, we investigated the role of the Masc gene in sex determination of the codling moth Cydia pomonella (Tortricidae), a globally important pest of pome fruits and walnuts. The gene structure of the C. pomonella Masc ortholog, CpMasc, is similar to B. mori Masc. However, unlike B. mori, we identified 14 splice variants of CpMasc in the available transcriptomes. Subsequent screening for sex specificity and genetic variation using publicly available data and RT-PCR revealed three male-specific splice variants. Then qPCR analysis of these variants revealed sex-biased expression showing a peak only in early male embryos. Knockdown of CpMasc by RNAi during early embryogenesis resulted in a shift from male-to female-specific splicing of the C. pomonella doublesex (Cpdsx) gene, its downstream effector, in ZZ embryos, leading to a strongly female-biased sex ratio. These data clearly demonstrate that CpMasc functions as a masculinizing gene in the sex-determining cascade of C. pomonella. Our study also showed that CpMasc transcripts are provided maternally, as they were detected in unfertilized eggs after oviposition and in mature eggs dissected from virgin females. This finding is unique, as maternal provision of mRNA has rarely been studied in Lepidoptera.

Intersex is required for female sexual development in Hermetia illucens

Sex-determination pathways are extremely diverse. Understanding the mechanism of sex determination in insects is important for genetic manipulation of the pest population and for breeding of economically valuable insects. Although sex determination has been well characterized in the model species Drosophila melanogaster, little is known about this pathway in Stratiomyidae. In the present study, we first identified the Drosophila intersex (ix) homolog in Hermetia illucens, also known as the black soldier fly, which belongs to the Stratiomyidae family and which is an important insect for the conversion of various organic wastes. Phylogenetic analyses and multiple sequence alignment revealed that Hiix is conserved compared with Drosophila. We showed that Hiix is highly expressed in internal genitalia. Disruption of the Hiix gene using CRISPR/Cas9 resulted in female-specific defects in external genitalia and abnormal and undersized ovaries. Taken together, our study furthers our understanding of sex determination in insects and could facilitate breeding of H. illucens.

Efficient Sex Separation by Exploiting Differential Alternative Splicing of a Dominant Marker in Aedes aegypti

Only female mosquitoes consume blood and transmit deadly human pathogens. Therefore, it is critical to remove females before conducting releases for genetic biocontrol interventions. Here we describe a robust sex-sorting approach termed SEPARATOR (Sexing Element Produced by Alternative RNA-splicing of A Transgenic Observable Reporter) that exploits sex-specific alternative splicing of an innocuous reporter to ensure exclusive dominant male-specific expression. Using SEPARATOR, we demonstrate reliable sex selection from larval and pupal stages in Aedes aegypti, and use a Complex Object Parametric Analyzer and Sorter (COPAS®) to demonstrate scalable high-throughput sex-selection of first instar larvae. Additionally, we use this approach to sequence the transcriptomes of early larval males and females and find several genes that are sex-specifically expressed in males. SEPARATOR can simplify mass production of males for release programs and is designed to be cross-species portable and should be instrumental for genetic biocontrol interventions.

Recovery of metagenomic data from the Aedes aegypti microbiome using a reproducible snakemake pipeline: MINUUR

Background: Ongoing research of the mosquito microbiome aims to uncover novel strategies to reduce pathogen transmission. Sequencing costs, especially for metagenomics, are however still significant. A resource that is increasingly used to gain insights into host-associated microbiomes is the large amount of publicly available genomic data based on whole organisms like mosquitoes, which includes sequencing reads of the host-associated microbes and provides the opportunity to gain additional value from these initially host-focused sequencing projects. Methods: To analyse non-host reads from existing genomic data, we developed a snakemake workflow called MINUUR (Microbial INsights Using Unmapped Reads). Within MINUUR, reads derived from the host-associated microbiome were extracted and characterised using taxonomic classifications and metagenome assembly followed by binning and quality assessment. We applied this pipeline to five publicly available Aedes aegypti genomic datasets, consisting of 62 samples with a broad range of sequencing depths. Results: We demonstrate that MINUUR recovers previously identified phyla and genera and is able to extract bacterial metagenome assembled genomes (MAGs) associated to the microbiome. Of these MAGS, 42 are high-quality representatives with >90% completeness and <5% contamination. These MAGs improve the genomic representation of the mosquito microbiome and can be used to facilitate genomic investigation of key genes of interest. Furthermore, we show that samples with a high number of KRAKEN2 assigned reads produce more MAGs. Conclusions: Our metagenomics workflow, MINUUR, was applied to a range of Aedes aegypti genomic samples to characterise microbiome-associated reads. We confirm the presence of key mosquito-associated symbionts that have previously been identified in other studies and recovered high-quality bacterial MAGs. In addition, MINUUR and its associated documentation are freely available on GitHub and provide researchers with a convenient workflow to investigate microbiome data included in the sequencing data for any applicable host genome of interest.

Giant Sex Chromosomes in Omophoita Species (Coleoptera, Chrysomelidae): Structural and Evolutionary Relationships Revealed by Zoo-FISH and Comparative Genomic Hybridization (CGH)

The beetles of the subtribe Oedionychina (Chrysomelidae, Alticinae) are the only ones that have the atypical giant and achiasmatic sex chromosomes, which are substantially larger than the autosomes. Previous cytogenetic analyses suggest a large accumulation of repetitive DNA in the sex chromosomes. In this study, we examined the similarity of X and Y chromosomes in four Omophoita species and compared genomic differentiation to better understand the evolutionary process and the giant sex chromosomes origin. Intraspecific genomic comparation using male and female genomes of O. octoguttata and interespecific analyses using genomic DNA of O. octoguttata, O. sexnotata, O. magniguttis, and O. personata were performed. In addition, whole chromosome painting (WCP) experiments were performed with X and Y chromosome probes of O. octogutatta. CGH analysis revealed great genomic similarity between the sexes and a sex-specific region on the Y chromosome, and interspecific analysis revealed a genomic divergence between species. In contrast, WCP results revealed that the sex chromosomes of O. octoguttata have high intra- and interspecific similarity with the studied species. Our data support a common origin under the canonical evolution of the sex chromosomes in this group, as they have high genomic similarity between them.

A DBHS family member regulates male determination in the filariasis vector Armigeres subalbatus

The initial signals governing sex determination vary widely among insects. Here we show that Armigeres subalbatus M factor (AsuMf), a male-specific duplication of an autosomal gene of the Drosophila behaviour/human splicing (DBHS) gene family, is the potential primary signal for sex determination in the human filariasis vector mosquito, Ar. subalbatus. Our results show that AsuMf satisfies two fundamental requirements of an M factor: male-specific expression and early embryonic expression. Ablations of AsuMf result in a shift from male- to female-specific splicing of doublesex and fruitless, leading to feminization of males both in morphology and general transcription profile. These data support the conclusion that AsuMf is essential for male development in Ar. subalbatus and reveal a male-determining factor that is derived from duplication and subsequent neofunctionalization of a member of the conserved DBHS family.

Masculinizer is not post-transcriptionally regulated by female-specific piRNAs during sex determination in the Asian corn borer, Ostrinia furnacalis

Lepidopteran insects are heterogametic in females, although most insect species are heterogametic in males. In a lepidopteran model species, the silkworm Bombyx mori (Bombycoidea), the uppermost sex determinant Feminizer (Fem) has been identified on the female-specific W chromosome. Fem is a precursor of PIWI-interacting small RNA (piRNA). Fem piRNA forms a complex with Siwi, one of the two B. mori PIWI-clade Argonaute proteins. In female embryos, Fem piRNA-Siwi complex cleaves the mRNA of the male-determining gene Masculinizer (Masc), directing the female-determining pathway. In male embryos, Masc activates the male-determining pathway in the absence of Fem piRNA. Recently, W chromosome-derived piRNAs complementary to Masc mRNA have also been identified in the diamondback moth Plutella xylostella (Yponomeutoidea), indicating the convergent evolution of piRNA-dependent sex determination in Lepidoptera. Here, we show that this is not the case in the Asian corn borer, Ostrinia furnacalis (Pyraloidea). Although our previous studies demonstrated that O. furnacalis Masc (OfMasc) has a masculinizing function in the embryonic stage, the expression level of OfMasc was indistinguishable between the sexes at the timing of sex determination. Deep sequencing analysis identified no female-specific small RNAs mapped onto OfMasc mRNA. Embryonic knockdown of two PIWI genes did not affect the expression level of OfMasc in either sex. These results demonstrated that piRNA-dependent reduction of Masc mRNA in female embryos is not a common strategy of sex determination, which suggests the possibility of divergent evolution of sex determinants across the order Lepidoptera.

CRISPR/Cas advancements for genome editing, diagnosis, therapeutics, and vaccine development for Plasmodium parasites, and genetic engineering of Anopheles mosquito vector

Malaria as vector-borne disease remains important health concern with over 200 million cases globally. Novel antimalarial medicines and more effective vaccines must be developed to eliminate and eradicate malaria. Appraisal of preceding genome editing approaches confirmed the CRISPR/Cas nuclease system as a novel proficient genome editing system and a tool for species-specific diagnosis, and drug resistance researches for Plasmodium species, and gene drive to control Anopheles population. CRISPR/Cas technology, as a handy tool for genome editing can be justified for the production of transgenic malaria parasites like Plasmodium transgenic lines expressing Cas9, chimeric Plasmodium transgenic lines, knockdown and knockout transgenic parasites, and transgenic parasites expressing alternative alleles, and also mutant strains of Anopheles such as only male mosquito populations, generation of wingless mosquitoes, and creation of knock-out/ knock-in mutants. Though, the incorporation of traditional methods and novel molecular techniques could noticeably enhance the quality of results. The striking development of a CRISPR/Cas-based diagnostic kit that can specifically diagnose the Plasmodium species or drug resistance markers is highly required in malaria settings with affordable cost and high-speed detection. Furthermore, the advancement of genome modifications by CRISPR/Cas technologies resolves contemporary restrictions to culturing, maintaining, and analyzing these parasites, and the aptitude to investigate parasite genome functions opens up new vistas in the better understanding of pathogenesis.

CRISPR Cas9 mediated knockout of sex determination pathway genes in Aedes aegypti

The vector role of Aedes aegypti for viral diseases including dengue and dengue hemorrhagic fever makes it imperative for its proper control. Despite various adopted control strategies, genetic control measures have been recently focused against this vector. CRISPR Cas9 system is a recent and most efficient gene editing tool to target the sex determination pathway genes in Ae. aegypti. In the present study, CRISPR Cas9 system was used to knockout Ae. aegypti doublesex (Aaedsx) and Ae. aegypti sexlethal (AaeSxl) genes in Ae. aegypti embryos. The injection mixes with Cas9 protein (333 ng ul^-1) and gRNAs (each at 100 ng ul^-1) were injected into eggs. Injected eggs were allowed to hatch at 26 ± 1°C, 60 ± 10% RH. The survival and mortality rate was recorded in knockout Aaedsx and AaeSxl. The results revealed that knockout produced low survival and high mortality. A significant percentage of eggs (38.33%) did not hatch as compared to control groups (P value 0.00). Highest larval mortality (11.66%) was found in the knockout of Aaedsx female isoform, whereas, the emergence of only male adults also showed that the knockout of Aaedsx (female isoform) does not produce male lethality. The survival (3.33%) of knockout for AaeSxl eggs to the normal adults suggested further study to investigate AaeSxl as an efficient upstream of Aaedsx to target for sex transformation in Ae. aegypti mosquitoes.

Overview of Aedes aegypti and Use in Laboratory Studies

The yellow fever mosquito Aedes aegypti is a prolific disease vector. This mosquito has been the subject of scientific investigation for more than a century. Continued research into Aedes aegypti biology is crucial for understanding how to halt the suite of major arthropod-borne viral diseases this mosquito transmits. Here, we provide an introductory overview of Aedes aegypti life cycle; evolutionary history, biology, and ecology; genetics and sex differences; vector competence; and laboratory colonization and considerations for rearing this robust mosquito species for use in laboratory research.

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.

Theme and variation in the evolution of insect sex determination

The development of dimorphic adult sexes is a critical process for most animals, one that is subject to intense selection. Work in vertebrate and insect model species has revealed that sex determination mechanisms vary widely among animal groups. However, this variation is not uniform, with a limited number of conserved factors. Therefore, sex determination offers an excellent context to consider themes and variations in gene network evolution. Here we review the literature describing sex determination in diverse insects. We have screened public genomic sequence databases for orthologs and duplicates of 25 genes involved in insect sex determination, identifying patterns of presence and absence. These genes and a 3.5 reference set of 43 others were used to infer phylogenies and compared to accepted organismal relationships to examine patterns of congruence and divergence. The function of candidate genes for roles in sex determination (virilizer, female-lethal-2-d, transformer-2) and sex chromosome dosage compensation (male specific lethal-1, msl-2, msl-3) were tested using RNA interference in the milkweed bug, Oncopeltus fasciatus. None of these candidate genes exhibited conserved roles in these processes. Amidst this variation we wish to highlight the following themes for the evolution of sex determination: (1) Unique features within taxa influence network evolution. (2) Their position in the network influences a component's evolution. Our analyses also suggest an inverse association of protein sequence conservation with functional conservation.

Juvenile hormone acts on male accessory gland function via regulating l-asparaginase expression and triacylglycerol mobilization in Aedes aegypti

Hormones control the reproductive development of Aedes aegypti mosquitoes. The adult male reproductive process and mating behavior require adequate nutrients and energy. Understanding the molecular mechanism linking hormones, energy metabolism, and reproduction in male mosquitoes is important. In this study, we found that the size of the male accessory gland, an essential part of the male reproductive system, gradually increased after eclosion. However, it was significantly reduced in male mosquitoes deficient in methoprene-tolerant (Met), the receptor of juvenile hormone. Likewise, egg hatchability of females that mated with Met-depleted males showed the same downward trend. The mRNA level of the gene encoding accessory gland protein, l-asparaginase (ASNase), was reduced in Met dsRNA-treated males. Electrophoretic mobility shift assay and quantitative reverse transcription-PCR results revealed that Met was capable of binding directly to the promoter of ASNase and activated its transcription. RNA interference of ASNase in males resulted in the reduction of egg hatchability of the females with which they mated. These results showed that Met influenced the fecundity of male mosquitoes by directly upregulating the expression of the ASNase gene. Moreover, the levels of triacylglycerol and the sizes of lipid droplets were decreased by 72-78 h after eclosion in the fat body cells, whereas both of them increased in Met-depleted male mosquitoes, indicating that Met knockdown reduced lipid catabolism. These data demonstrate that Met might influence the egg hatchability of females by regulating lipid metabolism and the development of the male accessory gland in male mosquitoes.

Descriptive versus causal morphology: gynandromorphism and intersexuality

In animal species with separate sexes, abnormal individuals with a mix of phenotypically male and phenotypically female body parts are generally indicated as gynandromorphs, whereas individuals with intermediate sexual phenotypic traits are generally indicated as intersexes. However, this distinction, clear as it may seem, is neither universally agreed upon, nor free of critical issues. In consideration of the role of sex anomalies in understanding normal development, we reassess these phenomena of abnormal sexual development, taking into consideration the more recent advances in the study of sex determination and sexual differentiation. We argue that a distinction between gynandromorphism and intersexuality, although useful for descriptive purposes, is not always possible or sensible. We discuss the conceptual and terminological intricacies of the literature on this subject and provide reasons for largely, although not strictly, preferring a terminology based on descriptive rather than causal morphology, that is, on the observed phenotypic patterns rather on the causal process behind them.

CRISPR mediated transactivation in the human disease vector Aedes aegypti

As a major insect vector of multiple arboviruses, Aedes aegypti poses a significant global health and economic burden. A number of genetic engineering tools have been exploited to understand its biology with the goal of reducing its impact. For example, current tools have focused on knocking-down RNA transcripts, inducing loss-of-function mutations, or expressing exogenous DNA. However, methods for transactivating endogenous genes have not been developed. To fill this void, here we developed a CRISPR activation (CRISPRa) system in Ae. aegypti to transactivate target gene expression. Gene expression is activated through pairing a catalytically-inactive ('dead') Cas9 (dCas9) with a highly-active tripartite activator, VP64-p65-Rta (VPR) and synthetic guide RNA (sgRNA) complementary to a user defined target-gene promoter region. As a proof of concept, we demonstrate that engineered Ae. aegypti mosquitoes harboring a binary CRISPRa system can be used to effectively overexpress two developmental genes, even-skipped (eve) and hedgehog (hh), resulting in observable morphological phenotypes. We also used this system to overexpress the positive transcriptional regulator of the Toll immune pathway known as AaRel1, which resulted in a significant suppression of dengue virus serotype 2 (DENV2) titers in the mosquito. This system provides a versatile tool for research pathways not previously possible in Ae. aegypti, such as programmed overexpression of endogenous genes, and may aid in gene characterization studies and the development of innovative vector control tools.

A history of the genetic and molecular identification of genes and their functions controlling insect sex determination

The genetics of the sex determination regulatory cascade in Drosophila melanogaster has a fascinating history, interlinked with the foundation of the Genetics discipline itself. The discovery that alternative splicing rather than differential transcription is the molecular mechanism underlying the upstream control of sex differences in the Drosophila model system was surprising. This notion is now fully integrated into the scientific canon, appearing in many genetics textbooks and online education resources. In the last three decades, it was a key reference point for starting evolutionary studies in other insect species by using homology-based approaches. This review will introduce a very brief history of Drosophila genetics. It will describe the genetic and molecular approaches applied for the identifying and cloning key genes involved in sex determination in Drosophila and in many other insect species. These comparative analyses led to supporting the idea that sex-determining pathways have evolved mainly by recruiting different upstream signals/genes while maintaining widely conserved intermediate and downstream regulatory genes. The review also provides examples of the link between technological advances and research achievements, to stimulate reflections on how science is produced. It aims to hopefully strengthen the related historical and conceptual knowledge of general readers of other disciplines and of younger geneticists, often focused on the latest technical-molecular approaches.

Marker-assisted mapping enables forward genetic analysis in Aedes aegypti, an arboviral vector with vast recombination deserts

Aedes aegypti is a major vector of arboviruses that cause dengue, chikungunya, yellow fever, and Zika. Although recent success in reverse genetics has facilitated rapid progress in basic and applied research, integration of forward genetics with modern technologies remains challenging in this important species, as up to 47% of its chromosome is refractory to genetic mapping due to extremely low rate of recombination. Here, we report the development of a marker-assisted mapping strategy to readily screen for and genotype only the rare but informative recombinants, drastically increasing both the resolution and signal-to-noise ratio. Using marker-assisted mapping, we mapped a transgene that was inserted in a >100-Mb recombination desert and a sex-linked spontaneous red-eye (re) mutation just outside the region. We subsequently determined, by CRISPR/Cas9-mediated knockout, that cardinal is the causal gene of re, which is the first forward genetic identification of a causal gene in Ae. aegypti. The identification of the causal gene of the sex-linked re mutation provides the molecular foundation for using gene editing to develop versatile and stable genetic sexing methods. To facilitate genome-wide forward genetics in Ae. aegypti, we generated and compiled a number of lines with markers throughout the genome. Thus, by overcoming the challenges presented by the vast recombination deserts and the scarcity of markers, we have shown that effective forward genetic analysis is increasingly feasible in this important arboviral vector species.

Phillips GC, Greene KK, Poletto M, Sperry BD, Warner SA, Rose NR, Frandsen GK, Verza NC, Gorman KJ, Matzen KJ. New self-sexing Aedes aegypti strain eliminates barriers to scalable and sustainable vector control for governments and communities in dengue-prone environments

For more than 60 years, efforts to develop mating-based mosquito control technologies have largely failed to produce solutions that are both effective and scalable, keeping them out of reach of most governments and communities in disease-impacted regions globally. High pest suppression levels in trials have yet to fully translate into broad and effective Aedes aegypti control solutions. Two primary challenges to date-the need for complex sex-sorting to prevent female releases, and cumbersome processes for rearing and releasing male adult mosquitoes-present significant barriers for existing methods. As the host range of Aedes aegypti continues to advance into new geographies due to increasing globalisation and climate change, traditional chemical-based approaches are under mounting pressure from both more stringent regulatory processes and the ongoing development of insecticide resistance. It is no exaggeration to state that new tools, which are equal parts effective and scalable, are needed now more than ever. This paper describes the development and field evaluation of a new self-sexing strain of Aedes aegypti that has been designed to combine targeted vector suppression, operational simplicity, and cost-effectiveness for use in disease-prone regions. This conditional, self-limiting trait uses the sex-determination gene doublesex linked to the tetracycline-off genetic switch to cause complete female lethality in early larval development. With no female progeny survival, sex sorting is no longer required, eliminating the need for large-scale mosquito production facilities or physical sex-separation. In deployment operations, this translates to the ability to generate multiple generations of suppression for each mosquito released, while being entirely self-limiting. To evaluate these potential benefits, a field trial was carried out in densely-populated urban, dengue-prone neighbourhoods in Brazil, wherein the strain was able to suppress wild mosquito populations by up to 96%, demonstrating the utility of this self-sexing approach for biological vector control. In doing so, it has shown that such strains offer the critical components necessary to make these tools highly accessible, and thus they harbour the potential to transition mating-based approaches to effective and sustainable vector control tools that are within reach of governments and at-risk communities who may have only limited resources.

A perspective on the expansion of the genetic technologies to support the control of neglected vector-borne diseases and conservation

Genetic-based technologies are emerging as promising tools to support vector population control. Vectors of human malaria and dengue have been the main focus of these development efforts, but in recent years these technologies have become more flexible and adaptable and may therefore have more wide-ranging applications. Culex quinquefasciatus, for example, is the primary vector of avian malaria in Hawaii and other tropical islands. Avian malaria has led to the extinction of numerous native bird species and many native bird species continue to be threatened as climate change is expanding the range of this mosquito. Genetic-based technologies would be ideal to support avian malaria control as they would offer alternatives to interventions that are difficult to implement in natural areas, such as larval source reduction, and limit the need for chemical insecticides, which can harm beneficial species in these natural areas. This mosquito is also an important vector of human diseases, such as West Nile and Saint Louis encephalitis viruses, so genetic-based control efforts for this species could also have a direct impact on human health. This commentary will discuss the current state of development and future needs for genetic-based technologies in lesser studied, but important disease vectors, such as C. quinquefasciatus, and make comparisons to technologies available in more studied vectors. While most current genetic control focuses on human disease, we will address the impact that these technologies could have on both disease and conservation focused vector control efforts and what is needed to prepare these technologies for evaluation in the field. The versatility of genetic-based technologies may result in the development of many important tools to control a variety of vectors that impact human, animal, and ecosystem health.

Aedes albopictus Sterile Male Production: Influence of Strains, Larval Diet and Mechanical Sexing Tools

The sterile insect technique (SIT) is a biologically based method of pest control, which relies on the mass production, sterilization, and release of sterile males of the target species. Since females can transmit viruses, it is important to develop a mass rearing system to produce a large number of males with a low presence of females. We evaluated the effects of different strains, larval diets and sexing tools on male productivity and residual female presence for the application of SIT against Aedes albopictus. Strains coming from Italy, Germany, Greece, and Montenegro, with different levels of colonization, were reared with three larval diets: IAEA-BY, BLP-B and SLP-BY. Developed pupae were sexed using two different mechanical methods: sieve or Fay-Morlan separator. The results proved that adoption of the Fay-Morlan separator increased the productivity and limited the female presence. The IAEA-BY diet showed the lowest female contamination. Strains with a high number of breeding generations showed a decreased productivity and an increased female presence. Increased female presence was found only in extensively reared strains and only when the sorting operation was conducted with sieves. We hypothesize that extensive colonization may determine a size reduction which limits the sexing tool efficiency itself.

CRISPR/Cas9-Mediated Knockout Reveals the Involvement of CYP304F1 in β-Cypermethrin and Chlorpyrifos Resistance in Spodoptera litura

Functions of insect CYP2 clan P450s in insecticide resistance are relatively less reported. In Spodoptera litura, a gene from the CYP2 clan (CYP304F1) was validated to be up-regulated significantly in a pyrethroid- and organophosphate-resistant population (QJ) than a susceptible population by RNA-Seq and qRT-PCR. Spatial-temporal expression indicated the high expression of CYP304F1 in the fourth, fifth, and sixth instar larvae and the metabolism-related tissue fat body and malpighian tubules. CYP304F1 was knocked out by CRISPR/Cas9, and a homozygous population (QJ-CYP304F1) with a G-base deletion at exon 2 was obtained after selection. Bioassay results showed that the LD₅₀ values to β-cypermethrin and chlorpyrifos in the QJ-CYP304F1 population decreased significantly, and the resistance ratio was both 1.81-fold in the QJ population compared with that in the QJ-CYP304F1 population. The toxicity of fenvalerate, cyhalothrin, or phoxim showed no significant change. These results suggested that CYP304F1 is involved in β-cypermethrin and chlorpyrifos resistance in S. litura.

Selective targeting of biting females to control mosquito-borne infectious diseases

Mosquitoes are vectors for a number of infectious diseases. Only females feed on blood to provision for their embryos and, in doing so, transmit pathogens to the associated vertebrate hosts. Therefore, sex is an important phenotype in the context of genetic control programs, both for sex separation in the rearing facilities to avoid releasing biting females and for ways to distort the sex ratio towards nonbiting males. We review recent progress in the fundamental knowledge of sex determination and sex chromosomes in mosquitoes and discuss new methods to achieve sex separation and sex ratio distortion to help control mosquito-borne infectious diseases. We conclude by suggesting a few critical areas for future research.

CRISPR/Cas9-mediated Serine protease 2 disruption induces male sterility in Spodoptera litura

Male fertility is essential for reproduction and population growth in animals. Many factors affect male fertility, such as courtship behavior, sperm quantity, and sperm motility, among others. Seminal Fluid Proteins (SFPs) are vital components of seminal fluid in the male ejaculate, which affect male fertility, sperm activation, and female ovulation. However, the knowledge of SFPs is insufficient; the function of many SFPs remains unknown, and most described functions were mainly characterized in Drosophila or other laboratory models. Here, we focus on the Serine protease 2 (Ser2) gene in the lepidopteran pest Spodoptera litura. The Ser2 gene was specifically expressed in male adults. Disruption of the Ser2 gene mediated by CRISPR/Cas9 induced male sterility but females remained fertile. PCR-based detection of the next-generation mutants showed that male sterility was stably inherited. The qRT-PCR analysis of SlSer2 mutants showed that motor protein family genes and structural protein family genes were down-regulated, while protein modification family genes were up-regulated, suggesting that SlSer2 may be involved in sperm movement and activity. These results demonstrate that Ser2 is an important component of SFPs in seminal fluid and was identified for a useful sterile gene for pest control that may lead to new control strategies for lepidopteran insect pests such as S. litura.

Partial masculinization of Aedes aegypti females by conditional expression of Nix

Background

Aedes aegypti, the main vector of dengue, yellow fever, and other arboviruses thrives in tropical and subtropical areas around the globe putting half of the world’s population at risk. Despite aggressive efforts to control the transmission of those viruses, an unacceptable number of cases occur every year, emphasizing the need to develop new control strategies. Proposals for vector control focused on population suppression could offer a feasible alternative method to reduce disease transmission. The induction of extreme male-biased sex ratios has been hypothesized to be able to suppress or collapse a population, with previous experiments showing that stable expression of the male determining factor Nix in A. aegypti is sufficient to convert females into fertile males.

Methodology/Principal findings

Here, we report on the conditional expression of Nix in transgenic A. aegypti under the control of the tetracycline-dependent (Tet-off) system, with the goal of establishing repressible sex distortion. A masculinization phenotype was observed in three of the seven transgenic lines with females exhibiting male-like long maxillary palps and most importantly, the masculinized females were unable to blood feed. Doxycycline treatment of the transgenic lines only partially restored the normal phenotype from the masculinized transgenic lines, while RT-qPCR analysis of early embryos or adults showed no correlation between the level of masculinization and ectopic Nix expression.

Conclusions/Significance

While the conditional expression of Nix produced intersex phenotypes, the level of expression was insufficient to program full conversion. Modifications that increase both the level of activation (no tet) and the level of repression (with tet) will be necessary, as such this study represents one step forward in the development of genetic strategies to control vector-borne diseases via sex ratio distortion.

Natural and Engineered Sex Ratio Distortion in Insects

Insects have evolved highly diverse genetic sex-determination mechanisms and a relatively balanced male to female sex ratio is generally expected. However, selection may shift the optimal sex ratio while meiotic drive and endosymbiont manipulation can result in sex ratio distortion (SRD). Recent advances in sex chromosome genomics and CRISPR/Cas9-mediated genome editing brought significant insights into the molecular regulators of sex determination in an increasing number of insects and provided new ways to engineer SRD. We review these advances and discuss both naturally occurring and engineered SRD in the context of the Anthropocene. We emphasize SRD-mediated biological control of insects to help improve One Health, sustain agriculture, and conserve endangered species.

The AalNix3&4 isoform is required and sufficient to convert Aedes albopictus females into males

Aedes albopictus is one of the most invasive insect species in the world and an effective vector for many important arboviruses. We reported previously that Ae. albopictus Nix (AalNix) is the male-determining factor of this species. However, whether AalNix alone is sufficient to initiate male development is unknown. Transgenic lines that express each of the three AalNix isoforms from the native promoter were obtained using piggyBac transformation. We verified the stable expression of AalNix isoforms in the transgenic lines and confirm that one isoform, AalNix3&4, is sufficient to convert females into fertile males (pseudo-males) that are indistinguishable from wild-type males. We also established a stable sex-converted female mosquito strain, AalNix3&4-♂4-pseudo-male. The pseudo-male mosquitoes can fly and mate normally with wild-type female, although their mating competitiveness is lower than wild-type. This work further clarifies the role of AalNix in the sex determination pathway and will facilitate the development of Ae. albopictus control strategies that rely on male-only releases such as SIT and sex-ratio distortion.

Early embryonic transcriptomes of Zeugodacus tau provide insight into sex determination and differentiation genes

Zeugodacus tau (Walker) is an invasive pest. The sterile insect technique is an environment-friendly method for pest control. Understanding the mechanism of sex determination will contribute to improving efficiency of this technique. In this study, we identified the transformer (tra) gene in Z. tau. One female-specific and two male-specific isoforms of tra were found in Z. tau, and the male-specific splicing pattern of tra was found to occur 5 h after egg laying. We performed transcriptome sequencing at 1 h (E1), 5 h (E5), and 9 h (E9) after egg laying and obtained high-quality transcriptome libraries of early embryo development. We identified 13 297 and 11 713 differentially expressed genes (DEGs) from E5 versus E1 and E9 versus E1 comparisons, respectively. To explore the potential functions of the DEGs during embryonic development, Gene Ontology, Clusters of Orthologous Groups of proteins, and Kyoto Encyclopedia of Genes and Genomes analyses were performed. Twenty-six genes potentially involved in sex determination or differentiation, including Maleness-on-the-Y (MoY), were identified in Z. tau. To verify the transcriptome results, 15 genes were selected for quantitative real-time PCR validation. The results were consistent with the transcriptome sequencing results. Moreover, U2 small nuclear riboprotein auxiliary factor (U2AF-50), female lethal d (fl(2)d), and virilizer (vir) were highly expressed at E5, indicating that they may be related to the sex-specific splicing of tra. Further functional analysis is needed to confirm this speculation. Our data provide an insight into the mechanism underlying sex determination and differentiation in tephritid species.

Novel molecular approaches to combat vectors and vector-borne viruses: Special focus on RNA interference (RNAi) mechanisms

Vector-borne diseases, such as dengue, chikungunya, zika, yellow fever etc pose significant burden among the infectious diseases globally, especially in tropical and sub-tropical regions. Globalization, deforestation, urbanization, climate change, uncontrolled population growth, inadequate waste management and poor vector-management infrastructure have all contributed to the expansion of vector habitats and subsequent increase in vector-borne diseases throughout the world. Conventional vector control methods, such as use of insecticides, have significant negative environmental repercussions in addition to developing resistance in vectors. Till date, a very few vaccines or antiviral therapies have been approved for the treatment of vector borne diseases. In this review, we have discussed emerging molecular approaches like CRISPR (clustered regularly interspaced short palindromic repeats)/Cas-9, sterile insect technique (SIT), release of insects carrying a dominant lethal (RIDL), Wolbachia (virus transmission blocking) and RNA interference (RNAi) to combat vector and vector-borne viruses. Due to the extensive advancements in RNAi research, a special focus has been given on its types, biogenesis, mechanism of action, delivery and experimental studies evaluating their application as anti-mosquito and anti-viral agent. These technologies appear to be highly promising in terms of contributing to vector control and antiviral drug development, and hence can be used to reduce global vector and vector-borne disease burden.

Interspecific mating bias may drive Aedes albopictus displacement of Aedes aegypti during its range expansion

Aedes albopictus is the most invasive mosquito in the world and often displaces Ae. aegypti in regions where their populations overlap. Interspecific mating has been proposed as a possible cause for this displacement, but whether this applies across the range of their sympatry remains unclear. Aedes albopictus and Ae. aegypti collected from allopatric and sympatric areas in China were allowed to interact in cage experiments with different crosses and sex-choices. The results confirm that asymmetric interspecific mating occurs in these populations with matings between allopatric Ae. albopictus males and Ae. aegypti females being significantly higher (55.2%) than those between Ae. aegypti males and Ae. albopictus females (27.0%), and sympatric mosquitoes showed a similar but lower frequency bias, 25.7% versus 6.2%, respectively. The cross-mated females can mate second time (remate) with the respective conspecific males and the 66.7% remating success of female Ae. albopictus was significantly higher than the 9.3% of Ae. aegypti females. Furthermore, 17.8% of the matings of Ae. albopictus males exposed to mixed pools of Ae. albopictus and Ae. aegypti females and 9.3% of the matings of Ae. aegypti males with mixed Ae. aegypti and Ae. albopictus females were interspecific. The difference in the length of clasper between male Ae. albopictus (0.524 mm) and Ae. aegypti (0.409 mm) may be correlated with corresponding mates. We conclude that stronger Ae. albopictus male interspecific mating and more avid female intraspecific remating result in a satyr effect and contribute to competitive displacement of Ae. aegypti as allopatric Ae. albopictus invade during range expansion.

CRISPR/Cas9 mediated sex-ratio distortion by sex specific gene editing in Aedes aegypti

Aedes aegypti is a principal vector for several viruses including dengue virus, chikungunya virus and zika virus. Economic burden of mosquito-borne diseases, relative failure of traditional control strategies and the resistance development against insecticides enforces towards genetic manipulation of Ae. aegypti. Hence, a key gene doublesex (Aedsx) which regulate sex differentiation and alternatively splices to form male and female specific transcripts (AedsxM and AedsxF ). CRISPR/Cas9 technique was employed to sex specifically disrupt the female-specific isoforms, AedsxF1 and AedsxF2 , both of which were shown to be expressed only in female mosquitoes. Targeting of dsxF at the developmental stage has resulted in various phenotypic anomalies of adult females. The rate of adult mutation phenotype was recorded between 29 and 37% along with anomalies of wing size, proboscis length and reduction in the sizes of pre-blood-meal and after blood-meal ovaries in dsxF1 and dsxF2 microinjected groups, respectively. These findings can be correlated with reduced fecundity rate of Go female, where AedsxF1 and AedsxF2 groups showed reduction rate in range of 23-31%. Furthermore, hatching inhibition rate of 28 to 36% was also observed in G1 generation when compared to the wildtype. Overall, these results demonstrated that AedsxF disruption has resulted in multiple female traits disruption including decreased fertility of the female that could directly or indirectly associated with reproduction and its disease transmitting abilities. All these findings suggesting that CRISPR works to alter the developmental pathways as predicted, and therefore this method potentially gives us the basis for the sex-ratio distortion system as genetic control approach for the management of this vector.

Sexual diversification of splicing regulation during embryonic development in honeybees (Apis mellifera), A haplodiploid system

The honeybee is a haplodiploid organism in which sexual development is determined by the complementary sex determiner (csd) gene and realized by sex-specific splicing processes involving the feminizer (fem) gene. We used high throughput transcriptome sequencing (RNA-Seq) to characterize the transcriptional differences between the sexes caused by the fertilization and sex determination processes in honeybee (Apis mellifera) embryos. We identified 758, 372 and 43 differentially expressed genes (DEGs) and 58, 176 and 233 differentially spliced genes (DSGs) in 10-15-h-old, 25-40-h-old and 55-70-h-old female and male embryos, respectively. The early difference in male and female embryos in response to the fertilization and non-fertilization processes resulted mainly in differential expression of genes (758 DEGs vs. 58 DSGs). In the latest sampled embryonic stage, the transcriptional differences between the sexes were dominated by alternative splicing of transcripts (43 DEGs vs. 233 DSGs). Interestingly, differentially spliced transcripts that encode RNA-binding properties were overrepresented in 55-70-h-old embryos, indicating a more diverse regulation via alternative splicing than previous work on the sex determination pathway suggested. These stage- and sex-specific transcriptome data from honeybee embryos provide a comprehensive resource for examining the roles of fertilization and sex determination in developmental programming in a haplodiploid system.

Transgenic expression of Nix converts genetic females into males and allows automated sex sorting in Aedes albopictus

Aedes albopictus is a major vector of arboviruses. Better understanding of its sex determination is crucial for developing mosquito control tools, especially genetic sexing strains. In Aedes aegypti, Nix is the primary gene responsible for masculinization and Nix-expressing genetic females develop into fertile, albeit flightless, males. In Ae. albopictus, Nix has also been implicated in masculinization but its role remains to be further characterized. In this work, we establish Ae. albopictus transgenic lines ectopically expressing Nix. Several are composed exclusively of genetic females, with transgenic individuals being phenotypic and functional males due to the expression of the Nix transgene. Their reproductive fitness is marginally impaired, while their flight performance is similar to controls. Overall, our results show that Nix is sufficient for full masculinization in Ae. albopictus. Moreover, the transgene construct contains a fluorescence marker allowing efficient automated sex sorting. Consequently, such strains constitute valuable sexing strains for genetic control.

Nix expression with a fluorescent marker in genetically female Ae. albopictus causes masculinization with minimal effects to reproductive fitness and flight performance.

Cellular diversity and gene expression profiles in the male and female brain of Aedes aegypti

BACKGROUND

Aedes aegypti is a medically-important mosquito vector that transmits arboviruses including yellow fever, dengue, chikungunya, and Zika viruses to humans. The mosquito exhibits typical sexually dimorphic behaviors such as courtship, mating, host seeking, bloodfeeding, and oviposition. All these behaviors are mainly regulated by the brain; however, little is known about the function and neuron composition of the mosquito brain. In this study, we generated an initial atlas of the adult male and female brain of Ae. aegypti using 10xGenomics based single-nucleus RNA sequencing.

RESULTS

We identified 35 brain cell clusters in male and female brains, and 15 of those clusters were assigned to known cell types. Identified cell types include glia (astrocytes), Kenyon cells, (ventral) projection neurons, monoaminergic neurons, medulla neurons, and proximal medulla neurons. In addition, the cell type compositions of male and female brains were compared to each other showing that they were quantitatively distinct, as 17 out of 35 cell clusters varied significantly in their cell type proportions. Overall, the transcriptomes from each cell cluster looked very similar between the male and female brain as only up to 25 genes were differentially expressed in these clusters. The sex determination factor Nix was highly expressed in neurons and glia of the male brain, whereas doublesex (dsx) was expressed in all neuron and glia cell clusters of the male and female brain.

CONCLUSIONS

An initial cell atlas of the brain of the mosquito Ae. aegypti has been generated showing that the cellular compositions of the male and female brains of this hematophagous insect differ significantly from each other. Although some of the rare brain cell types have not been detected in our single biological replicate, this study provides an important basis for the further development of a complete brain cell atlas as well as a better understanding of the neurobiology of the brains of male and female mosquitoes and their sexually dimorphic behaviors.

Introgression of the Aedes aegypti Red-Eye Genetic Sexing Strains Into Different Genomic Backgrounds for Sterile Insect Technique Applications

Aedes aegypti is an invasive mosquito species and major vector of human arboviruses. A wide variety of control methods have been employed to combat mosquito populations. One of them is the sterile insect technique (SIT) that has recently attracted considerable research efforts due to its proven record of success and the absence of harmful environmental footprints. The efficiency and cost-effectiveness of SIT is significantly enhanced by male-only releases. For mosquito SIT, male-only releases are ideally needed since females bite, blood-feed and transmit the pathogens. Ae. aegypti genetic sexing strains (GSS) have recently become available and are based on eye colour mutations that were chosen as selectable markers. These genetic sexing strains were developed through classical genetics and it was shown to be subjected to genetic recombination, a phenomenon that is not suppressed in males as is the case in many Diptera. The genetic stability of these GSS was strengthened by the induction and isolation of radiation-induced inversions. In this study, we used the red eye mutation and the inversion Inv35 line of the Ae. aegypti red-eye GSS s and introgressed them in six different genomic backgrounds to develop GSS with the respective local genomic backgrounds. Our goal was to assess whether the recombination frequencies in the strains with and without the inversion are affected by the different genomic backgrounds. In all cases the recombination events were suppressed in all Inv35 GSS strains, thus indicating that the genomic background does not negatively affect the inversion result. Absence of any effect that could be ascribed to genetic differences, enables the introgression of the key elements of the GSS into the local genomic background prior to release to the target areas. Maintaining the local background increases the chances for successful matings between released males and wild females and addresses potential regulatory concerns regarding biosafety and biosecurity.

A novel non-invasive identification of genome editing mutants from insect exuviae

With the wide application of genome editing in insects, a simple and efficient identification method is urgently needed to meet the increasing demand for mutation detection. Here, taking migratory locusts as a model system, we developed a non-invasive method to accurately identify genome-edited mutants by using DNA from insect exuviae. We compared the quantity and quality of genomic DNA from exuviae in five instar hoppers and found that the 1st instar exuviae had the highest DNA yield and content, while the 3rd instar exuviae had the best quality. Consensus genotypes were identified from genomic DNA of hoppers at different developmental stages in the same individuals. Moreover, we demonstrated that the amplification products from DNA extracted from locust exuviae are the consensus sequences with those from the hemolymph and foreleg pre-tarsus. Therefore, non-invasive samples provide the same genotyping results as minimally invasive and invasive samples of the same individuals. Furthermore, this identification method that uses genomic DNA from exuviae can be used for early screening of positive genome-edited individuals in each generation for adult crossing. In our study, the non-invasive identification method was not only simpler and provided results earlier than existing methods, but also had a better reproducibility and accuracy. This non-invasive identification approach using genomic DNA from exuviae can be adapted to meet the growing demand for genetic analysis and will find wide application in insect genome editing research.