Next-Generation Sequencing Reveals Recent Horizontal Transfer of a DNA Transposon between Divergent Mosquitoes

Horizontal transfer of genetic material between complex organisms often involves transposable elements (TEs). For example, a DNA transposon mariner has been shown to undergo horizontal transfer between different orders of insects and between different phyla of animals. Here we report the discovery and characterization of an ITmD37D transposon, MJ1, in Anopheles sinensis. We show that some MJ1 elements in Aedes aegypti and An. sinensis contain intact open reading frames and share nearly 99% nucleotide identity over the entire transposon, which is unexpectedly high given that these two genera had diverged 145–200 million years ago. Chromosomal hybridization and TE-display showed that MJ1 copy number is low in An. sinensis. Among 24 mosquito species surveyed, MJ1 is only found in Ae. aegypti and the hyrcanus group of anopheline mosquitoes to which An. sinensis belongs. Phylogenetic analysis is consistent with horizontal transfer and provides the basis for inference of its timing and direction. Although report of horizontal transfer of DNA transposons between higher eukaryotes is accumulating, our analysis is one of a small number of cases in which horizontal transfer of nearly identical TEs among highly divergent species has been thoroughly investigated and strongly supported. Horizontal transfer involving mosquitoes is of particular interest because there are ongoing investigations of the possibility of spreading pathogen-resistant genes into mosquito populations to control malaria and other infectious diseases. The initial indication of horizontal transfer of MJ1 came from comparisons between a 0.4x coverage An. sinensis 454 sequence database and available TEs in mosquito genomes. Therefore we have shown that it is feasible to use low coverage sequencing to systematically uncover horizontal transfer events. Expanding such efforts across a wide range of species will generate novel insights into the relative frequency of horizontal transfer of different TEs and provide the evolutionary context of these lateral transfer events

Brown marmorated stink bug, Halyomorpha halys (Stål), genome: putative underpinnings of polyphagy, insecticide resistance potential and biology of a top worldwide pest

Background Halyomorpha halys (Stål), the brown marmorated stink bug, is a highly invasive insect species due in part to its exceptionally high levels of polyphagy. This species is also a nuisance due to overwintering in human-made structures. It has caused significant agricultural losses in recent years along the Atlantic seaboard of North America and in continental Europe. Genomic resources will assist with determining the molecular basis for this species’ feeding and habitat traits, defining potential targets for pest management strategies. Results Analysis of the 1.15-Gb draft genome assembly has identified a wide variety of genetic elements underpinning the biological characteristics of this formidable pest species, encompassing the roles of sensory functions, digestion, immunity, detoxification and development, all of which likely support H. halys’ capacity for invasiveness. Many of the genes identified herein have potential for biomolecular pesticide applications. Conclusions Availability of the H. halys genome sequence will be useful for the development of environmentally friendly biomolecular pesticides to be applied in concert with more traditional, synthetic chemical-based controls

Sequencing of Culex quinquefasciatus establishes a platform for mosquito comparative genomics

Culex quinquefasciatus (the southern house mosquito) is an important mosquito vector of viruses such as West Nile virus and St. Louis encephalitis virus, as well as of nematodes that cause lymphatic filariasis. C. quinquefasciatus is one species within the Culex pipiens species complex and can be found throughout tropical and temperate climates of the world. The ability of C. quinquefasciatus to take blood meals from birds, livestock, and humans contributes to its ability to vector pathogens between species. Here, we describe the genomic sequence of C. quinquefasciatus: Its repertoire of 18,883 protein-coding genes is 22% larger than that of Aedes aegypti and 52% larger than that of Anopheles gambiae with multiple gene-family expansions, including olfactory and gustatory receptors, salivary gland genes, and genes associated with xenobiotic detoxification

Multi-Platform Next-Generation Sequencing of the Domestic Turkey (Meleagris gallopavo): Genome Assembly and Analysis

The combined application of next-generation sequencing platforms has provided an economical approach to unlocking the potential of the turkey genome

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Functional analysis of the promoter of an early zygotic gene KLC2 in Aedes aegypti

Abstract Background Aedes aegypti is an important mosquito vector that transmits arboviruses that cause devastating diseases including Zika, dengue fever, yellow fever and chikungunya. Improved understanding of gene regulation in the early development of Ae. aegypti will facilitate genetic studies and help the development of novel control strategies of this important disease vector. Results In this study, we demonstrated through transgenic assays that the promoter of an endogenous early zygotic gene KLC2 could drive gene expression in the syncytial blastoderm and early cellular blastoderm, which is a stage that the developing germline and the rest of embryo are accessible to genetic manipulation. An unexpected expression of the reporter gene in transgenic male testes was also observed. Further analysis confirmed the expression of the endogenous KLC2 in the testes, which was not detected in the previous RNA sequencing data. Conclusions Our finding provided a new promoter element that can be used in future genetic studies and applications in Ae. aegypti. Moreover, our transgenic reporter assays showed that cautions are needed when interpreting RNA sequencing data as transient or tissue-specific transcription may go undetected by RNAseq

Pure early zygotic genes in the Asian malaria mosquito Anopheles stephensi

Abstract Background The Asian malaria mosquito, Anopheles stephensi, is a major urban malaria vector in the Middle East and on the Indian subcontinent. Early zygotic transcription, which marks the maternal-to-zygotic transition, has not been systematically studied in An. stephensi or any other Anopheles mosquitoes. Improved understanding of early embryonic gene expression in An. stephensi will facilitate genetic and evolutionary studies and help with the development of novel control strategies for this important disease vector. Results We obtained RNA-seq data in biological triplicates from four early An. stephensi embryonic time points. Using these data, we identified 70 and 153 pure early zygotic genes (pEZGs) under stringent and relaxed conditions, respectively. We show that these pEZGs are enriched in functional groups related to DNA-binding transcription regulators, cell cycle modulators, proteases, transport, and cellular metabolism. On average these pEZGs are shorter and have less introns than other An. stephensi genes. Some of the pEZGs may arise de novo while others have clear non-pEZG paralogs. There is no or very limited overlap between An. stephensi pEZGs and Drosophila melanogaster or Aedes aegypti pEZGs. Interestingly, the upstream region of An. stephensi pEZGs lack significant enrichment of a previously reported TAGteam/VBRGGTA motif found in the regulatory region of pEZGs in D. melanogaster and Ae. aegypti. However, a GT-rich motif was found in An. stephensi pEZGs instead. Conclusions We have identified a number of pEZGs whose predicted functions and structures are consistent with their collective roles in the degradation of maternally deposited components, activation of the zygotic genome, cell division, and metabolism. The pEZGs appear to rapidly turn over within the Dipteran order and even within the Culicidae family. These pEZGs, and the shared regulatory motif, could provide the promoter or regulatory sequences to drive gene expression in the syncytial or early cellular blastoderm, a period when the developing embryo is accessible to genetic manipulation. In addition, these molecular resources may be used to achieve sex separation of mosquitoes for sterile insect technique

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

Genome sequence of Aedes aegypti, a major arbovirus vector

We present a draft sequence of the genome of Aedes aegypti, the primary vector for yellow fever and dengue fever, which at approximately 1376 million base pairs is about 5 times the size of the genome of the malaria vector Anopheles gambiae. Nearly 50% of the Ae. aegypti genome consists of transposable elements. These contribute to a factor of approximately 4 to 6 increase in average gene length and in sizes of intergenic regions relative to An. gambiae and Drosophila melanogaster. Nonetheless, chromosomal synteny is generally maintained among all three insects, although conservation of orthologous gene order is higher (by a factor of approximately 2) between the mosquito species than between either of them and the fruit fly. An increase in genes encoding odorant binding, cytochrome P450, and cuticle domains relative to An. gambiae suggests that members of these protein families underpin some of the biological differences between the two mosquito species.6 page(s