Salivary gland RNA-seq from arbovirus-infected Aedes aegypti and Aedes albopictus provides insights into virus transmission

Yellow fever mosquitoes (Aedes aegypti) and Asian tiger mosquitoes (Aedes albopictus) are the primary vectors of dengue virus (DENV), Zika virus (ZIKV) and chikungunya virus (CHIKV). These viruses are transmitted to humans through mosquito saliva, making the vector salivary gland (SG) a critical tissue to identify transmission-blocking targets. We examined gene expression in infected SGs for both vector species and for three different virus infections. Aedes aegypti SGs were infected separately with DENV, ZIKV and CHIKV, and Ae. albopictus with CHIKV. RNA-sequencing identified differentially expressed coding and long non-coding RNAs (lncRNAs). Differentially expressed genes determined from genome annotations were greater in number and functional diversity in comparison to differentially expressed transcripts from de novo transcriptome assemblies. Salivary protein transcripts were the most abundant, but were downregulated in all three virus infections. Commonly upregulated genes were associated with apoptosis, cytoskeletal proteins, replication/transcription/translation, redox/stress and immunity. An enrichment of upregulated genes related to apoptosis were observed in CHIKV infection in comparison to DENV and ZIKV infections. Upregulation of serine proteases and other genes associated with immunity and cellular stress responses (cytochrome P450 genes) varied between vectors. There were also immune response commonalities between vectors, for instance RNA-interference was observed to be a non-specific antiviral defense. The number of lncRNA transcripts differentially expressed were few and none were common to all infections, likely having minor roles, unlike the lncRNA antiviral effects proposed for mosquito midgut. Determining common infection patterns for different viruses and vectors has applications in refractory vector engineering.