De novo assembly and annotation of the salivary gland transcriptome of Rhipicephalus appendiculatus male and female ticks during blood feeding

Abstract

Tick secretory proteins modulate haemostasis, inflammation and immune responses of the host and are attractive recombinant anti-tick vaccine candidates. Yet, many of the proteins have not been characterised due to the limited sequence availability for ticks and other arthropods for homology-based annotation. To address this limitation, we sequenced the salivary glands of the economically important adult male and female Rhipicephalus appendiculatus ticks during feeding. The quality filtered Illumina sequencing reads were de novo assembled to generate a R. appendiculatus sialotranscriptome of 21 410 transcripts. A non-redundant set of 12 761 R. appendiculatus proteins was predicted from the transcripts, including 2134 putative secretory and 8237 putative housekeeping proteins. Secretory proteins accounted for most of the expression in the salivary gland transcriptome (63%). Of the secretory protein class, the Glycine rich superfamily contributed 66% and the Lipocalin family 12% of the transcriptome expression. Differential expression analysis identified 1758 female and 2346 male up regulated transcripts, suggesting varying blood-feeding mechanisms employed between female and male ticks. The sialotranscriptome assembled in this work, greatly improves on the sequence information available for R. appendiculatus and is a valuable resource for potential future vaccine candidate selection.

A repertoire of protease inhibitor families in Amblyomma americanum and other tick species: inter-species comparative analyses

“…Based on these results, we predict many more tick PIs are as yet undiscovered, primarily from one of the big three families: I2, I4 and I8. Though limited by the fact that transcripts in this study may not have been found due to technical and not biological reasons, our analysis of A. americium transcriptomes showed all PI families were always present, (with the exception of I35), but also supported previous in silico , semi-quantitiative and quantitative RT-PCR data showing differential expression of specific PIs within families [49, 51–59], between the sexes, tissues, and throughout feeding. It is not possible to study all 1,595 tick PIs in a reasonable time frame, therefore this study provides a prioritization template for selecting suitable anti-tick vaccine and/or pharmacologically relevant targets.…”

“…We found and analyzed 1,595 non-redundant putative PI sequences across 26 ixodid tick species. In A. americanum we found evidence to support previous findings of a time-dependent PI expression in salivary glands [49, 51] coined as “sialome switch” [52], however our analyses provide evidence of time-dependent PI expression throughout tick tissues. Additionally, our global analysis differentiated tick PI families that are likely redundant or non-redundant, as well as PIs that are conserved across tick species and that may regulate pathways essential in all ticks.…”

“…Evidence in other in silico transcriptome analyses show evidence of sex-based differences in transcript levels during feeding in R. appendiculatus [51], and temporal and sex-based differences in transcript repertoires across feeding time points in R. pulchellus [49]. Additionally, studies using qRT-PCR analysis have validated spatio-temporal variance of PI expression in ticks [54–56] as well as semi-quantitative RT-PCR analyses showing spatio-temporal differences in PI expression patterns [57–59].…”

Gut transcriptome analysis on females of Ornithodoros mimon (Acari: Argasidae) and phylogenetic inference of ticks

“…Thus, knowledge about the vital molecular constituents of ticks, such as genes and/or proteins, have become the target of several studies (CASTRO et al, 2016;CHMELAŘ et al, 2016;DÍAZ-MARTÍN et al, 2015;HEEKIN et al, 2013;KOTSYFAKIS et al, 2015;PERNER et al, 2016;RIBEIRO et al, 2017;XU et al, 2016). These studies have sought to ascertain and understand the roles of the molecules involved in the tick-host or tick-pathogen relationship.…”

“…DNA sequencing technologies, together with bioinformatics tools, allow a broad view of the probable protein constituents of a tissue, by isolating the messenger RNA repertoire and sequencing of the cDNA (complementary DNA), leading to an increasing knowledge of the putative molecules expressed by a tissue, such as, salivary gland and midgut, from different species (CASTRO et al, 2016;CHMELAŘ et al, 2016;KOTSYFAKIS et al, 2015;PERNER et al, 2016;RIBEIRO et al 2017;SCHWARZ et al, 2014;VALENZUELA, 2004;XU et al, 2016).…”