The transcriptome of the salivary glands of the female western black-legged tick Ixodes pacificus (Acari: Ixodidae)

Abstract

SummarySequencing of an Ixodes pacificus salivary gland cDNA library yielded 1068 sequences with an average undetermined nucleotide of 1.9% and an average length of 487 base pairs. Assembly of the expressed sequence tags yielded 557 contigs, 138 of which appear to code for secreted peptides or proteins based on translation of a putative signal peptide. Based on the BLASTX similarity of these contigs to 66 matches of Ixodes scapularis peptide sequences, only 58% sequence identity was found, indicating a rapid divergence of salivary proteins as observed previously for mosquito and triatomine bug salivary proteins. Here we report 106 mostly full-length sequences that clustered in 16 different families: Basic-tail proteins rich in lysine in the carboxy-terminal, Kunitz-containing proteins (monolaris, ixolaris and penthalaris families), proline-rich peptides, 5-kDa.-, 9.4 kDa.-, and 18.7 kDa.-proteins of unknown functions, in addition to metalloproteases (class PIII-like) similar to reprolysins. We also have found a family of disintegrins, named ixodegrins that display homology to variabilin, a GPIIb/IIIa antagonist from the tick Dermacentor variabilis. In addition, we describe peptides (here named ixostatins) that display remarkable similarities to the cysteine-rich domain of ADAMST-4 (aggrecanase). Many molecules were assigned in the lipocalin family (histaminebinding proteins); others appear to be involved in oxidant metabolism, and still others were similar to ixodid proteins such as the anticomplement ISAC. We also identified for the first time a neuropeptide-like protein (nlp-31) with GGY repeats that may have antimicrobial activity. In addition, 16 novel proteins without significant similarities to other tick proteins and 37 housekeeping proteins that may be useful for phylogenetic studies are described. Some of these proteins may be useful for studying vascular biology or the immune system, for vaccine development, or as immunoreagents to detect prior exposure to ticks. Electronic version of the manuscript can be found at http://www.ncbi.nlm.nih.gov/projects/omes/.

Ancestral reconstruction of tick lineages

“…These include platelet aggregation inhibitors from prostriate and metastriate ticks, that targets integrin α IIb β 3 , but do not belong to the Kunitz-BPTI fold, but a fold termed the ixodegrins (Francischetti et al 2005;Tang et al 2015;Wang et al 1996). Prostriates possess complement C3 inhibitors that belong to the Isac family and fXa inhibitors that belong to the basic tail secretory family (Narasimhan et al 2002;Valenzuela et al 2000).…”

“…However, the complexity of salivary glands became apparent with the advent of conventional transcriptomics, when numbers of secretory proteins detected in the salivary glands jumped to hundreds (Francischetti et al 2008a(Francischetti et al , 2005Ribeiro et al 2006;Valenzuela et al 2002). The introduction of next-generation sequencing technologies caused a jump to hundreds of genes for each major protein family (Karim et al 2011).…”

An insight into the sialome of the soft tick, Ornithodorus parkeri

“…Multiple Kunitz domains may occur in a single protein, thus providing for inhibition in multiple protease amplification cascades such as occur with the vertebrate tissue-factor pathway inhibitor (TFPI) of the extrinsic blood coagulation cascade (Bajaj et al, 2001). Tick salivary proteins containing this domain are known in both hard and soft ticks, and were found abundantly expressed in hard tick sialotranscriptomes (AlarconChaidez et al, 2007;Francischetti et al, 2005;Nene et al, 2004a;Ribeiro et al, 2006). Some of the hard proteins have been characterized functionally and have both expected and unexpected functions.…”

“…Salivary transcriptomes (sialotranscriptomes) of several hard tick species have been characterized to date (Alarcon-Chaidez et al, 2007;Francischetti et al, 2005;Lambson et al, 2005;Nene et al, 2004b;Ribeiro et al, 2006;Santos et al, 2004). These databases indicate a large expansion of genes coding for several protein families, including metalloproteases, cysteine-rich proteins similar to metalloprotease domains (the ixostatins and ixodegrins), lipocalins, Kunitz-domain containing proteins, RGD containing peptides, defensins, and many novel protein families that may include antimicrobial proteins.…”

Ixodes scapularistick saliva proteins sequentially secreted every 24h during blood feeding

“…With the advent of next-generation sequencing (NGS) technologies, tick salivary gland transcriptomes have been described [23,[30][31][32][33][34][35][36][37][38][39]. However, the major limitation to these data is that it does not inform on which transcripts that encode for proteins are secreted in tick saliva.…”