Sialotranscriptomics of Rhipicephalus zambeziensis reveals intricate expression profiles of secretory proteins and suggests tight temporal transcriptional regulation during blood-feeding

Abstract

BackgroundTicks secrete a diverse mixture of secretory proteins into the host to evade its immune response and facilitate blood-feeding, making secretory proteins attractive targets for the production of recombinant anti-tick vaccines. The largely neglected tick species, Rhipicephalus zambeziensis, is an efficient vector of Theileria parva in southern Africa but its available sequence information is limited. Next generation sequencing has advanced sequence availability for ticks in recent years and has assisted the characterisation of secretory proteins. This study focused on the de novo assembly and annotation of the salivary gland transcriptome of R. zambeziensis and the temporal expression of secretory protein transcripts in female and male ticks, before the onset of feeding and during early and late feeding.ResultsThe sialotranscriptome of R. zambeziensis yielded 23,631 transcripts from which 13,584 non-redundant proteins were predicted. Eighty-six percent of these contained a predicted start and stop codon and were estimated to be putatively full-length proteins. A fifth (2569) of the predicted proteins were annotated as putative secretory proteins and explained 52% of the expression in the transcriptome. Expression analyses revealed that 2832 transcripts were differentially expressed among feeding time points and 1209 between the tick sexes. The expression analyses further indicated that 57% of the annotated secretory protein transcripts were differentially expressed. Dynamic expression profiles of secretory protein transcripts were observed during feeding of female ticks. Whereby a number of transcripts were upregulated during early feeding, presumably for feeding site establishment and then during late feeding, 52% of these were downregulated, indicating that transcripts were required at specific feeding stages. This suggested that secretory proteins are under stringent transcriptional regulation that fine-tunes their expression in salivary glands during feeding. No open reading frames were predicted for 7947 transcripts. This class represented 17% of the differentially expressed transcripts, suggesting a potential transcriptional regulatory function of long non-coding RNA in tick blood-feeding.ConclusionsThe assembled sialotranscriptome greatly expands the sequence availability of R. zambeziensis, assists in our understanding of the transcription of secretory proteins during blood-feeding and will be a valuable resource for future vaccine candidate selection.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-017-2312-4) contains supplementary material, which is available to authorized users.

Rhipicephalus bursa Sialotranscriptomic Response to Blood Feeding and Babesia ovis Infection: Identification of Candidate Protective Antigens

“…A strong transcriptional response was induced after tick feeding and during B. ovis infection, since a higher and more diverse number of transcripts were detected in the fed-uninfected sample, and even more diverse transcripts were detected in the fed-infected samples (Table 1 and Figure 1A ) in comparison with the unfed-uninfected SG samples. This type of response was previously described in other systems (Heekin et al, 2013 ; Tirloni et al, 2014 ; Ayllón et al, 2015 ; Villar et al, 2015 ; de Castro et al, 2016 , 2017 ; Kim et al, 2016 ; Perner et al, 2016 ; Valdés et al, 2016 ; Schroeder et al, 2017 ), thus indicating that different tick biological processes or statuses stimulate different gene expression regulatory strategies.…”

“…Few studies have focused on the sialotranscriptomic response to tick feeding (McNally et al, 2012 ; Kotsyfakis et al, 2015 ; Yu et al, 2015 ; de Castro et al, 2016 , 2017 ; Maruyama et al, 2017 ), but all demonstrated that transcription was highly affected in SG. Kotsyfakis et al ( 2015 ) showed that fed I. ricinus , SG exhibit 10 times more overexpression compared to the midgut.…”

Sialome diversity of ticks revealed by RNAseq of single tick salivary glands

“…As ticks feed, the tissue undergoes structural changes to facilitate secretion of bioactive components of saliva [ 42 ]. Previous studies revealed that feeding progression is linked with a timed regulation of gene expression in several tick species [ 5 , 43 , 44 ]. These studies clearly demonstrated that mRNA transcript repertoires differ substantially among groups of pooled salivary glands dissected at different time-points of feeding.…”

Ixonnexin from Tick Saliva Promotes Fibrinolysis by Interacting with Plasminogen and Tissue-Type Plasminogen Activator, and Prevents Arterial Thrombosis

“…Moreover, silencing of SALP14 in the salivary gland, which presumably also has pro-fibrinolytic activity given its conserved “basic tail”, is accompanied by reduced ability of ticks to feed resulting in a decline in engorgement weights 55 . Finally, Ixonnexin family is expanded in Amblyomma sp 56 , Hyalomma sp 57 , Rhipicephalus sp 58 , Antricola sp 59 and Ornithodorus sp ticks 28 . Altogether, these results highlight the importance of the “basic-tail” family of salivary proteins in tick biology.…”