Ixodes ricinus Transcriptome or Gene expression

Tick salivary gland (SG) proteins possess powerful immunomodulatory and pharmacological properties that facilitate tick feeding. We present here a high-throughput analysis of the SG transcriptome (sialome) of Ixodes ricinus using next generation sequencing. For the first time in any sialome study, we consider in our study different tick life stages (including tick co-feeding) and various animal models during tick feeding for the entire tick feeding period. Four cDNA libraries were constructed discriminating the tick salivary transcript repertoire of early feeding nymphs (EN) and female adults (EA) from late feeding nymphs (LN) and adults (LA). A total of 441,381 pyrosequencing and 67,703,183 Illumina reads were sequenced from all libraries. Their combined de novo assembly revealed a total of 272,220 contigs from which 34,560 coding sequences were annotated. Overall, 13% of the annotated contigs were secreted proteins that were mainly identified as protease inhibitors, enzymes, lipocalins, Ixodes specific and as uncharacterized tick proteins. Significant differences in the transcript frequency (from 10 to 15,000 fold frequency) between the four SG libraries and high numbers of library specific transcripts were detected. Furthermore, our large EST dataset allowed us to perform a detailed phylogenetic reconstruction of abundant I. ricinus protein families considering also the different transcript abundance in different tick developmental stages as tick feeding progresses. The herein disclosed sequences contribute to our better understanding of the molecular evolution of hematophagy in arachnids and they can improve the annotation of tick genomes as well as might pioneer future high throughput studies of this important disease vector.