Transcriptome response of female Culicoides sonorensis biting midges (Diptera: Ceratopogonidae) to early infection with epizootic hemorrhagic disease virus (EHDV-2)

Authors: Nayduch, Dana; SHANKAR, VIJAY - Clemson University; MILLS, MARY - University Of South Carolina; ROBL, TANNER - University Of Kansas Medical School; Drolet, Barbara; RUDER, MARK - University Of Georgia; Scully, Erin; SASKI, CHRISTOPHER - Clemson University

Submitted to: Viruses
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2019
Publication Date: 5/24/2019
Citation: Nayduch, D., Shankar, V., Mills, M., Robl, T., Drolet, B.S., Ruder, M., Scully, E.D., Saski, C. 2019. Transcriptome response of female Culicoides sonorensis biting midges (Diptera: Ceratopogonidae) to early infection with epizootic hemorrhagic disease virus (EHDV-2). Viruses. 11:473. https://doi.org/10.3390/v11050473.
DOI: https://doi.org/10.3390/v11050473

Interpretive Summary: Female Culicoides sonorensis biting midges are vectors of viral agents such as epizootic hemorrhagic disease virus (EHDV) that cause illness and death in in wild and domesticated ruminants. When midges ingest viruses in the animal's blood, the virus enters the gut and infects those tissues, eventually disseminating to the rest of the body. Successful dissemination to the midge's salivary glands can result in transmission of the virus to the next host upon which the midge feeds. As the virus infects the various tissues within the midge's body, the midge responds by altering the expression (i.e. up and down regulation) of gene expression. Changes in gene expression can be captured by sequencing the expressed genes (e.g. messenger RNA) from midges (called a 'transcriptome'), and comparing those sequence counts across conditions in a process called RNAseq. The aims in this study were to identify key changes in female midge transcriptome profiles occurring during early infection with EHDV-2. Midges were fed either negative control bloodmeals or bloodmeals containing EHDV-2 and transcriptomes were acquired at 36 h after ingestion. The transcriptome consisted of of 18,467 assembled unigenes . Overall, there were 2,401 differentially expressed unigenes and ~60% were downregulated in response to virus (953 up; 1,448 down). In order to understand the effects of these changes in gene expression on the biology of the midge, a process called Gene Ontology enrichment along with KEGG pathway mapping, and other manual analyses were used to identify the effect of virus ingestion at both the gene and biological pathway levels. Downregulated unigenes were predominantly assigned to pathways related to cell/tissue structure and integrity (actin cytoskeleton, adherens junction, focal adhesion, hippo signaling), calcium signaling, eye morphogenesis and axon guidance. Unigenes attributed to sensory functions (especially vision), behavior, learning and memory were largely downregulated. These results suggest that viruses may be escaping the midge gut and disseminating to other tissues, including those of the nervous system, brain, eye and other sensory organs as soon as 36 h after ingestion. Upregulated unigenes included those coding for innate immune processes, olfaction and photoreceptor pigments. These results suggest that the midge mounts an immune response to virus infection and that other sensory functions may try to compensate for the loss of function due to the downregulated genes. The potential for EHDV-2 to modify the behavior of the midge (e.g. its vision and brain function) will be addressed in follow up studies.

Technical Abstract: Female Culicoides sonorensis biting midges are vectors of epizootic hemorrhagic disease virus (EHDV), which causes morbidity and mortality in wild and domesticated ruminants. The aims in this study were to identify key changes in female midge transcriptome profiles occurring during early infection with EHDV-2. Midges were fed either negative control bloodmeals or bloodmeals containing EHDV-2 and transcriptomes were acquired at 36 h through deep sequencing. Reads were de novo assembled into a transcriptome comprised of 18,467 unigenes. Overall, there were 2,401 differentially expressed unigenes and ~60% were downregulated in response to virus (953 up; 1,448 down). Downstream Gene Ontology enrichment, KEGG pathway mapping, and manual analyses were used to identify the effect of virus ingestion at both the gene and pathway levels. Downregulated unigenes were predominantly assigned to pathways related to cell/tissue structure and integrity (actin cytoskeleton, adherens junction, focal adhesion, hippo signaling), calcium signaling, eye morphogenesis and axon guidance. Unigenes attributed to sensory functions (especially vision), behavior, learning and memory were largely downregulated. Upregulated unigenes included those coding for innate immune processes, olfaction and photoreceptor pigments. Our results suggest that midges respond to disseminated infection as soon as 36 h post-ingestion, and that EHDV-2 may have a significant phenotypic effect on sensory and neural tissues.