Horizontal gene transfer of a vertebrate vasodilatory hormone into ticks

Similarities between Ixodes ricinus and Ixodes inopinatus genomes and horizontal gene transfer from their endosymbionts

The taxa Ixodes ricinus and Ixodes inopinatus are sympatric in Tunisia. The genetics underlying their morphological differences are unresolved. In this study, ticks collected in Jouza-Amdoun, Tunisia, were morphologically identified and sequenced using Oxford Nanopore Technologies. Three complete genome assemblies of I. inopinatus and three of I. ricinus with BUSCO scores of ∼98% were generated, including the reconstruction of mitochondrial genomes and separation of both alleles of the TRPA1, TROSPA and calreticulin genes. Deep sequencing allowed the first descriptions of complete bacterial genomes for "Candidatus Midichloria mitochondrii", Rickettsia helvetica and R. monacensis from North Africa, and the discovery of extensive integration of parts of the Spiroplasma ixodetis and "Ca. M. mitochondrii" into the nuclear genome of these ticks. Phylogenetic analyses of the mitochondrial genome, the nuclear genes, and symbionts showed differentiation between Tunisian and Dutch ticks, but high genetic similarities between Tunisian I. ricinus and I. inopinatus. Subtraction of the genome assemblies identified the presence of some unique sequences, which could not be confirmed when screening a larger batch of I. ricinus and I. inopinatus ticks using PCR. Our findings yield compelling evidence that I. inopinatus is genetically highly similar, if not identical, to sympatric I. ricinus. Defined morphological differences might be caused by extrinsic factors such as micro-climatic conditions or bloodmeal composition. Our findings support the existence of different lineages of I. ricinus as well of its symbionts/pathogens from geographically dispersed locations.

A tick C1q protein alters infectivity of the Lyme disease agent by modulating interferon γ

In North America, the Lyme disease agent, Borrelia burgdorferi, is commonly transmitted by the black-legged tick, Ixodes scapularis. Tick saliva facilitates blood feeding and enhances pathogen survival and transmission. Here, we demonstrate that I. scapularis complement C1q-like protein 3 (IsC1ql3), a tick salivary protein, directly interacts with B. burgdorferi and is important during the initial stage of spirochetal infection of mice. Mice fed upon by B. burgdorferi-infected IsC1ql3-silenced ticks, or IsC1ql3-immunized mice fed upon by B. burgdorferi-infected ticks, have a lower spirochete burden during the early phase of infection compared with control animals. Mechanically, IsC1ql3 interacts with the globular C1q receptor present on the surface of CD4+ and CD8+ T cells, resulting in decreased production of interferon γ. IsC1ql3 is a C1q-domain-containing protein identified in arthropod vectors and has an important role in B. burgdorferi infectivity as the spirochete transitions from the tick to vertebrate host.

Profiles of Microbial Community and Antibiotic Resistome in Wild Tick Species

Infections caused by antibiotic-resistant pathogens pose high risks to human and animal health worldwide. In recent years, the environment and wildlife as major sources and reservoirs of antibiotic resistance genes (ARGs) are being increasingly investigated. There have been many reports on bacterial community in ticks, but little is known about ARGs they carry, and the correlation between bacterial and ARGs in wild ticks also remains unknown. Here, the profiles of microbial community and antibiotic resistome in wild tick species were investigated using high-throughput 16S rRNA sequencing and smart chip-based high-throughput quantitative PCR approach (HT-qPCR), respectively. We found that bacterial composition in wild tick species is variable; the sequenced reads from all samples were assigned to 37 different phyla at the phylum level. The dominant phylum was Proteobacteria, which accounted for 75.60 ± 10.34%, followed by Bacteroidetes accounting for 13.78 ± 11.68% of the total bacterial community. In total, 100 different ARGs across 12 antibiotic classes and 20 mobile genetic elements (MGEs) were identified by HT-qPCR, and among them aminoglycosides, multidrug, macrolide-clinolamide-streptogramin B, and tetracycline resistance genes were the dominant ARG types. Co-occurrence patterns revealed by network analysis showed that eight bacterial genera may serve as the potential hosts for different ARGs. For the first time, this study provides comprehensive overview of the diversity and abundance of ARGs in wild ticks and highlights the possible role of wild ticks as ARG disseminators into the environment and vertebrate hosts, with implications for human and animal health.

IMPORTANCE The emergence of antibiotic-resistant bacteria poses serious threat to the public health around the world. Ticks are obligate hematophagous ectoparasites, surviving via feeding on the blood of various animal hosts. Although some previous studies have confirmed wild ticks carried various bacterial community, the role of wild ticks in the antibiotic resistance remains unknown. Here, identification of microbial community and antibiotic resistome in wild tick species revealed that wild ticks are the reservoir, postulated potential spreaders of antibiotic resistance. Our findings highlight the contribution of wild ticks to the maintenance and dissemination of ARGs, and the associated health risks.

Aedes aegypti sialokinin facilitates mosquito blood feeding and modulates host immunity and vascular biology

Saliva from mosquitoes contains vasodilators that antagonize vasoconstrictors produced at the bite site. Sialokinin is a vasodilator present in the saliva of Aedes aegypti. Here, we investigate its function and describe its mechanism of action during blood feeding. Sialokinin induces nitric oxide release similar to substance P. Sialokinin-KO mosquitoes produce lower blood perfusion than parental mosquitoes at the bite site during probing and have significantly longer probing times, which result in lower blood feeding success. In contrast, there is no difference in feeding between KO and parental mosquitoes when using artificial membrane feeders or mice that are treated with a substance P receptor antagonist, confirming that sialokinin interferes with host hemostasis via NK1R signaling. While sialokinin-KO saliva does not affect virus infection in vitro, it stimulates macrophages and inhibits leukocyte recruitment in vivo. This work highlights the biological functionality of salivary proteins in blood feeding.

Transcriptomic Analysis of Salivary Glands of Ornithodoros brasiliensis Aragão, 1923, the Agent of a Neotropical Tick-Toxicosis Syndrome in Humans

Tick salivary glands produce and secrete a variety of compounds that modulate host responses and ensure a successful blood meal. Despite great progress made in the identification of ticks salivary compounds in recent years, there is still a paucity of information concerning salivary molecules of Neotropical argasid ticks. Among this group of ticks, considering the number of human cases of parasitism, including severe syndromes and hospitalization, Ornithodoros brasiliensis can be considered one of the major Neotropical argasid species with impact in public health. Here, we describe the transcriptome analysis of O. brasiliensis salivary glands (ObSG). The transcriptome yielded ~14,957 putative contigs. A total of 368 contigs were attributed to secreted proteins (SP), which represent approximately 2.5% of transcripts but ~53% expression coverage transcripts per million. Lipocalins are the major protein family among the most expressed SP, accounting for ~16% of the secretory transcripts and 51% of secretory protein abundance. The most expressed transcript is an ortholog of TSGP4 (tick salivary gland protein 4), a lipocalin first identified in Ornithodoros kalahariensis that functions as a leukotriene C₄ scavenger. A total of 55 lipocalin transcripts were identified in ObSG. Other transcripts potentially involved in tick-host interaction included as: basic/acid tail secretory proteins (second most abundant expressed group), serine protease inhibitors (including Kunitz inhibitors), 5' nucleotidases (tick apyrases), phospholipase A₂, 7 disulfide bond domain, cystatins, and tick antimicrobial peptides. Another abundant group of proteins in ObSG is metalloproteases. Analysis of these major protein groups suggests that several duplication events after speciation were responsible for the abundance of redundant compounds in tick salivary glands. A full mitochondrial genome could be assembled from the transcriptome data and confirmed the close genetic identity of the tick strain sampled in the current study, to a tick strain previously implicated in tick toxicoses. This study provides novel information on the molecular composition of ObSG, a Brazilian endemic tick associated with several human cases of parasitism. These results could be helpful in the understanding of clinical findings observed in bitten patients, and also, could provide more information on the evolution of Neotropical argasids.

The structures of two salivary proteins from the West Nile vector Culex quinquefasciatus reveal a beta-trefoil fold with putative sugar binding properties

Female mosquitoes require blood meals for egg development. The saliva of blood feeding arthropods contains biochemically active molecules, whose anti-hemostatic and anti-inflammatory properties facilitate blood feeding on vertebrate hosts. While transcriptomics has presented new opportunities to investigate the diversity of salivary proteins from hematophagous arthropods, many of these proteins remain functionally undescribed. Previous transcriptomic analysis of female salivary glands from Culex quinquefasciatus, an important vector of parasitic and viral infections, uncovered a 12-member family of putatively secreted proteins of unknown function, named the Cysteine and Tryptophan-Rich (CWRC) proteins. Here, we present advances in the characterization of two C. quinquefasciatus CWRC family members, CqDVP-2 and CqDVP-4, including their enrichment in female salivary glands, their specific localization within salivary gland tissues, evidence that these proteins are secreted into the saliva, and their native crystal structures, at 2.3 ​Å and 1.87 ​Å, respectively. The β-trefoil fold common to CqDVP-2 and CqDVP-4 is similar to carbohydrate-binding proteins, including the B subunit of the AB toxin, ricin, from the castor bean Ricinus communis. Further, we used a glycan array approach, which identifies carbohydrate ligands associated with inflammatory processes and signal transduction. Glycan array 300 testing identified 100 carbohydrate moieties with positive binding to CqDVP-2, and 77 glycans with positive binding to CqDVP-4. The glycan with the highest relative fluorescence intensities, which exhibited binding to both CqDVP-2 and CqDVP-4, was used for molecular docking experiments. We hypothesize that these proteins bind to carbohydrates on the surface of cells important to host immunology. Given that saliva is deposited into the skin during a mosquito bite, and acts as the vehicle for arbovirus inoculation, understanding the role of these proteins in pathogen transmission is of critical importance. This work presents the first solved crystal structures of C. quinquefasciatus salivary proteins with unknown function. These two molecules are the second and third structures reported from salivary proteins from C. quinquefasciatus, an important, yet understudied disease vector.

Molecular Mechanisms of Class B GPCR Activation: Insights from Adrenomedullin Receptors

Adrenomedullin (AM) is a 52 amino acid peptide that plays a regulatory role in the vasculature. Receptors for AM comprise the class B G protein-coupled receptor, the calcitonin-like receptor (CLR), in complex with one of three receptor activity-modifying proteins (RAMPs). The C-terminus of AM is involved in binding to the extracellular domain of the receptor, while the N-terminus is proposed to interact with the juxtamembranous portion of the receptor to activate signaling. There is currently limited information on the molecular determinants involved in AM signaling, thus we set out to define the importance of the AM N-terminus through five signaling pathways (cAMP production, ERK phosphorylation, CREB phosphorylation, Akt phosphorylation, and IP1 production). We characterized the three CLR:RAMP complexes through the five pathways, finding that each had a distinct repertoire of intracellular signaling pathways that it is able to regulate. We then performed an alanine scan of AM from residues 15-31 and found that most residues could be substituted with only small effects on signaling, and that most substitutions affected signaling through all receptors and pathways in a similar manner. We identify F18, T20, L26, and I30 as being critical for AM function, while also identifying an analogue (AM15-52 G19A) which has unique signaling properties relative to the unmodified AM. We interpret our findings in the context of new structural information, highlighting the complementary nature of structural biology and functional assays.

Chemical Equilibrium at the Tick-Host Feeding Interface:A Critical Examination of Biological Relevance in Hematophagous Behavior

Ticks secrete hundreds to thousands of proteins into the feeding site, that presumably all play important functions in the modulation of host defense mechanisms. The current review considers the assumption that tick proteins have functional relevance during feeding. The feeding site may be described as a closed system and could be treated as an ideal equilibrium system, thereby allowing modeling of tick-host interactions in an equilibrium state. In this equilibrium state, the concentration of host and tick proteins and their affinities will determine functional relevance at the tick-host interface. Using this approach, many characterized tick proteins may have functional relevant concentrations and affinities at the feeding site. Conversely, the feeding site is not an ideal closed system, but is dynamic and changing, leading to possible overestimation of tick protein concentration at the feeding site and consequently an overestimation of functional relevance. Ticks have evolved different possible strategies to deal with this dynamic environment and overcome the barrier that equilibrium kinetics poses to tick feeding. Even so, cognisance of the limitations that equilibrium binding place on deductions of functional relevance should serve as an important incentive to determine both the concentration and affinity of tick proteins proposed to be functional at the feeding site.

Deep sequencing revealed molecular signature of horizontal gene transfer of plant like transcripts in the mosquito Anopheles culicifacies: an evolutionary puzzle

In prokaryotes, horizontal gene transfer (HGT) has been regarded as an important evolutionary drive to acquire and retain beneficial genes for their survival in diverse ecologies. However, in eukaryotes, the functional role of HGTs remains questionable, although current genomic tools are providing increased evidence of acquisition of novel traits within non-mating metazoan species. Here, we provide another transcriptomic evidence for the acquisition of massive plant genes in the mosquito, Anopheles culicifacies. Our multiple experimental validations including genomic PCR, RT-PCR, real-time PCR, immuno-blotting and immuno-florescence microscopy, confirmed that plant like transcripts (PLTs) are of mosquito origin and may encode functional proteins. A comprehensive molecular analysis of the PLTs and ongoing metagenomic analysis of salivary microbiome provide initial clues that mosquitoes may have survival benefits through the acquisition of nuclear as well as chloroplast encoded plant genes. Our findings of PLTs further support the similar questionable observation of HGTs in other higher organisms, which is still a controversial and debatable issue in the community of evolutionists. We believe future understanding of the underlying mechanism of the feeding associated molecular responses may shed new insights in the functional role of PLTs in the mosquito.

Deep Sequencing Analysis of the Ixodes ricinus Haemocytome

BACKGROUND

Ixodes ricinus is the main tick vector of the microbes that cause Lyme disease and tick-borne encephalitis in Europe. Pathogens transmitted by ticks have to overcome innate immunity barriers present in tick tissues, including midgut, salivary glands epithelia and the hemocoel. Molecularly, invertebrate immunity is initiated when pathogen recognition molecules trigger serum or cellular signalling cascades leading to the production of antimicrobials, pathogen opsonization and phagocytosis. We presently aimed at identifying hemocyte transcripts from semi-engorged female I. ricinus ticks by mass sequencing a hemocyte cDNA library and annotating immune-related transcripts based on their hemocyte abundance as well as their ubiquitous distribution.

METHODOLOGY/PRINCIPAL FINDINGS

De novo assembly of 926,596 pyrosequence reads plus 49,328,982 Illumina reads (148 nt length) from a hemocyte library, together with over 189 million Illumina reads from salivary gland and midgut libraries, generated 15,716 extracted coding sequences (CDS); these are displayed in an annotated hyperlinked spreadsheet format. Read mapping allowed the identification and annotation of tissue-enriched transcripts. A total of 327 transcripts were found significantly over expressed in the hemocyte libraries, including those coding for scavenger receptors, antimicrobial peptides, pathogen recognition proteins, proteases and protease inhibitors. Vitellogenin and lipid metabolism transcription enrichment suggests fat body components. We additionally annotated ubiquitously distributed transcripts associated with immune function, including immune-associated signal transduction proteins and transcription factors, including the STAT transcription factor.

CONCLUSIONS/SIGNIFICANCE

This is the first systems biology approach to describe the genes expressed in the haemocytes of this neglected disease vector. A total of 2,860 coding sequences were deposited to GenBank, increasing to 27,547 the number so far deposited by our previous transcriptome studies that serves as a discovery platform for studies with I. ricinus biochemistry and physiology.

The sialotranscriptome of Amblyomma triste, Amblyomma parvum and Amblyomma cajennense ticks, uncovered by 454-based RNA-seq

Background

Tick salivary constituents antagonize inflammatory, immune and hemostatic host responses, favoring tick blood feeding and the establishment of tick-borne pathogens in hosts during hematophagy. Amblyomma triste, A. cajennense and A. parvum ticks are very important in veterinary and human health because they are vectors of the etiological agents for several diseases. Insights into the tick salivary components involved in blood feeding are essential to understanding vector-pathogen-host interactions, and transcriptional profiling of salivary glands is a powerful tool to do so. Here, we functionally annotated the sialotranscriptomes of these three Amblyomma species, which allowed comparisons between these and other hematophagous arthropod species.

Methods

mRNA from the salivary glands of A. triste, A. cajennense and A. parvum ticks fed on different host species were pyrosequenced on a 454-Roche platform to generate four A. triste (nymphs fed on guinea pigs and females fed on dogs) libraries, one A. cajennense (females fed on rabbits) library and one was A. parvum (females fed on dogs) library. Bioinformatic analyses used in-house programs with a customized pipeline employing standard assembly and alignment algorithms, protein databases and protein servers.

Results

Each library yielded an average of 100,000 reads, which were assembled to obtain contigs of coding sequences (CDSs). The sialotranscriptome analyses of A. triste, A. cajennense and A. parvum ticks produced 11,240, 4,604 and 3,796 CDSs, respectively. These CDSs were classified into over 100 distinct protein families with a wide range of putative functions involved in physiological and blood feeding processes and were catalogued in annotated, hyperlinked spreadsheets. We highlighted the putative transcripts encoding saliva components with critical roles during parasitism, such as anticoagulants, immunosuppressants and anti-inflammatory molecules. The salivary content underwent changes in the abundance and repertoire of many transcripts, which depended on the tick and host species.

Conclusions

The annotated sialotranscriptomes described herein richly expand the biological knowledge of these three Amblyomma species. These comprehensive databases will be useful for the characterization of salivary proteins and can be applied to control ticks and tick-borne diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-3305-7-430) contains supplementary material, which is available to authorized users.