Transmission of arboviruses such as Dengue Virus by Aedes aegypti causes debilitating disease across the globe. Disease in humans can include severe acute symptoms such as hemorrhagic fever and organ failure, but mosquitoes tolerate high titers of virus in a persistent infection. The mechanisms responsible for this viral tolerance are unclear. Recent publications highlighted the integration of genetic material from non-retroviral RNA viruses into the genome of the host during infection that relies upon endogenous retro-transcriptase activity from transposons. These endogenous viral elements (EVEs) found in the genome are predicted to be ancient, and at least some EVEs are under…
Transmission of arboviruses such as Dengue and Zika viruses by Aedes aegypti causes widespread and debilitating disease across the globe. Disease in humans can include severe acute symptoms such as hemorrhagic fever, organ failure, and encephalitis; and yet, mosquitoes tolerate high titers of virus in a persistent infection. The mechanisms responsible for tolerance to viral infection in mosquitoes are still unclear. Recent publications have highlighted the integration of genetic material from non-retroviral RNA viruses into the genome of the host during infection that relies upon endogenous retro-transcriptase activity from transposons. These endogenous viral elements (EVEs) found in the genome are…
Aedes aegypti is a tropical and subtropical mosquito vector for Zika, yellow fever, dengue fever, chikungunya, and other diseases. The outbreak of Zika in the Americas, which can cause microcephaly in the fetus of infected women, adds urgency to the need for a high-quality reference genome in order to better understand the organism’s biology and its role in transmitting human disease. We describe the first diploid assembly of an insect genome, using SMRT sequencing and the open-source assembler FALCON-Unzip. This assembly has high contiguity (contig N50 1.3 Mb), is more complete than previous assemblies (Length 1.45 Gb with 87% BUSCO…
Aedes aegypti is a tropical and subtropical mosquito vector for Zika, yellow fever, dengue fever, and chikungunya. We describe the first diploid assembly of an insect genome, using SMRT Sequencing and the open-source assembler FALCON-Unzip. This assembly has high contiguity (contig N50 1.3 Mb), is more complete than previous assemblies (Length 1.45 Gb with 87% BUSCO genes complete), and is high quality (mean base >QV30 after polishing). Long-range haplotype structure, in some cases encompassing more than 4 Mb of extremely divergent homologous sequence with dramatic differences in coding sequence content, is resolved using a combination of the FALCON-Unzip assembler, genome…
In this PAG 2017 presentation, Ben Matthews describes a new genome assembly for Aedes aegypti, the mosquito responsible for spreading Zika virus, yellow fever, and other infectious diseases. By using PacBio long-read sequencing, scientists produced an assembly that is much more complete and contiguous than a previous assembly; 7,500 transcripts map to the new contigs but not to the old assembly. The genome is important for designing guide RNAs for CRISPR, understanding resistance to mosquito repellants, and much more.
PacBio Sequencing is characterized by very long sequence reads (averaging > 10,000 bases), lack of GC-bias, and high consensus accuracy. These features have allowed the method to provide a new gold standard in de novo genome assemblies, producing highly contiguous (contig N50 > 1 Mb) and accurate (> QV 50) genome assemblies. We will briefly describe the technology and then highlight the full workflow, from sample preparation through sequencing to data analysis, on examples of insect genome assemblies, and illustrate the difference these high-quality genomes represent with regard to biological insights, compared to fragmented draft assemblies generated by short-read sequencing.
At AGBT 2017, the Broad Institute’s Daniel Neafsey reported a large collaborative effort to sequence the mosquito that carries Zika virus. The team is using long-read PacBio sequencing to produce a high-quality genome assembly, which Neafsey expects will replace the 10-year-old Sanger assembly for Aedes aegypti. The new assembly reduces the number of contigs by at least 10-fold, boosts the contig N50 to nearly 2 Mb, and features more complete gene content.
In the wake of constant improvements in sequencing technologies, numerous insect genomes have been sequenced. Currently, 1219 insect genome-sequencing projects have been registered with the National Center for Biotechnology Information, including 401 that have genome assemblies and 155 with an official gene set of annotated protein-coding genes. Comparative genomics analysis showed that the expansion or contraction of gene families was associated with well-studied physiological traits such as immune system, metabolic detoxification, parasitism and polyphagy in insects. Here, we summarize the progress of insect genome sequencing, with an emphasis on how this impacts research on pest control. We begin with a…
Wolbachia, an alpha-proteobacterium closely related to Rickettsia, is a maternally transmitted, intracellular symbiont of arthropods and nematodes. Aedes albopictus mosquitoes are naturally infected with Wolbachia strains wAlbA and wAlbB. Cell line Aa23 established from Ae. albopictus embryos retains only wAlbB and is a key model to study host-endosymbiont interactions. We have assembled the complete circular genome of wAlbB from the Aa23 cell line using long-read PacBio sequencing at 500× median coverage. The assembled circular chromosome is 1.48 megabases in size, an increase of more than 300 kb over the published draft wAlbB genome. The annotation of the genome identified 1,205…
The codling moth Cydia pomonella, a major invasive pest of pome fruit, has spread around the globe in the last half century. We generated a chromosome-level scaffold assembly including the Z chromosome and a portion of the W chromosome. This assembly reveals the duplication of an olfactory receptor gene (OR3), which we demonstrate enhances the ability of C. pomonella to exploit kairomones and pheromones in locating both host plants and mates. Genome-wide association studies contrasting insecticide-resistant and susceptible strains identify hundreds of single nucleotide polymorphisms (SNPs) potentially associated with insecticide resistance, including three SNPs found in the promoter of CYP6B2.…