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Title: The reference transcriptome of the adult female biting midge (Culicoides sonorensis) and differential gene expression profiling during teneral, blood, and sucrose feeding conditions

Author
item Nayduch, Dana
item Lee, Matthew
item SASKI, CHRISTOPHER - Clemson University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2014
Publication Date: 5/27/2014
Citation: Nayduch, D., Lee, M.B., Saski, C.A. 2014. The reference transcriptome of the adult female biting midge (Culicoides sonorensis) and differential gene expression profiling during teneral, blood, and sucrose feeding conditions. PLoS One. 9(5):e98123. DOI: 10.1371/journal.pone.0098123.

Interpretive Summary: Culicoides biting midges transmit a large number of arboviruses and other pathogens that cause disease in humans, livestock and wildlife. Compared to other important insect vectors such as mosquitoes or sand flies, genetic and genomic tools for Culicoides biting midges are lacking. In North America, female Culicoides sonorensis midges are important vectors of bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV), which are orbiviruses that impact animals such as sheep, cattle and deer. Libraries of midge tissue-specific genes that are activated in response to feeding and oral orbivirus challenge in C. sonorensis have previously been reported by this unit at USDA-ARS. However, extensive genome-wide gene expression profiling in midges has not been explored. Here, we successfully used modern sequencing technologies to construct the first adult female C. sonorensis reference transcriptome, or database of expressed (activated) genes for this vector. We also compared the expression profiles of these genes in response to blood and sucrose feeding over time in order to get a glimpse into how midges function on a molecular level. We produced a catalog of 19,041 genes, and described the molecular processes behind blood feeding, blood and sugar digestion and other important events such as egg production. This is the first extensive transcriptome for this genus, which will serve as a platform for developing new or novel mitigation strategies, as well as provide a rich dataset that can contribute to the ongoing Culicoides sonorensis genome project. Moreover, this study will serve as a foundation for subsequent studies that aim to understand the molecular basis of vector competence, including genetic components that impact the ability of midges to harbor and transmit pathogens.

Technical Abstract: Unlike other important vectors such as mosquitoes and sandflies, genetic and genomic tools for Culicoides biting midges are lacking, despite the fact that they vector a large number of arboviruses and other pathogens impacting humans and domestic animals world-wide. In North America, female Culicoides sonorensis midges are important vectors of bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV), orbiviruses that cause significant disease in livestock and wildlife. Libraries of tissue-specific transcripts expressed in response to feeding and oral orbivirus challenge in C. sonorensis have previously been reported, but extensive genome-wide expression profiling in the midge has not. Here, we successfully used deep sequencing technologies to construct the first adult female C. sonorensis reference transcriptome, and utilized genome-wide expression profiling to elucidate the genetic response to blood and sucrose feeding over time. The adult female midge unigene consists of 19,041 genes, of which less than 7% are differentially expressed during the course of a sucrose meal, while up to 52% of the genes respond significantly in blood-fed midges, indicating hematophagy induces complex physiological processes. Many genes that were differentially expressed during blood feeding were associated with digestion (e.g. proteases, lipases), hematophagy (e.g., salivary proteins), and vitellogenesis, revealing many major metabolic and biological factors underlying these critical processes. Additionally, key genes in the vitellogenesis pathway were identified, which provides the first glimpse into the molecular basis of anautogeny for C. sonorensis. This is the first extensive transcriptome for this genus, which will serve as a framework for future expression studies, RNAi, and provide a rich dataset contributing to the ultimate goal of informing a reference genome assembly and annotation. Moreover, this study will serve as a foundation for subsequent studies of genome-wide expression analyses during early orbivirus infection and dissecting the molecular mechanisms behind vector competence in midges.