Engorgement of Rhipicephalus haemaphysaloides ticks blocked by silencing a protein inhibitor of apoptosis

Inhibitors of apoptosis (IAPs) are regulators of cell death and may play a role in the salivary glands of ticks during blood-feeding. We cloned the open reading frame (ORF) sequence of the IAP gene in Rhipicephalus haemaphysaloides (RhIAP). The RhIAP ORF of 1887 bp encodes a predicted protein of 607 amino acids, which contains three baculovirus IAP repeat domains and a RING finger motif. A real-time PCR assay showed that RhIAP mRNA was expressed in all the tick developmental stages (eggs, larvae, nymphs, and adults) and in all tissues examined (midgut, ovary, salivary glands, fat body, and hemolymph). Western blot showed that the protein level of RhIAP in salivary glands increased during tick blood-feeding and decreased towards the end of tick engorgement. RhIAP gene silencing in vitro experiments with salivary glands demonstrated that RhIAP could be effectively knocked down within 48 h after dsRNA treatment, and as a consequence, salivary glands displayed apoptotic morphology. RhIAP gene silencing also inhibited tick blood-feeding and decreased the engorgement rate. These data suggest that RhIAP might be a suitable RNAi target for tick control.

     

Detection of tick‐borne pathogens in ticks from migratory birds in the Baltic region of Russia

We report the finding of tick‐borne encephalitis (TBE)‐virus in indigenous Ixodes ricinus (L.), ‘Candidatus Neoehrlichia mikurensis’ in exotic Ixodes frontalis (Panzer) and Rickettsia aeshlimannii in exotic Hyalomma marginatum Koch subadult ticks detached from 18.5% (107/577) infested migratory birds in the Baltic region of Russia. This is the first record of human pathogenic ‘Candidatus N. mikurensis’ in I. frontalis ticks. Moreover, seven other pathogens were identified in I. ricinus ticks. Spotted Fever Group rickettsiae were the predominant pathogen group and were detected only in nymphs. Future investigations are warranted to further characterize the role of birds in the epizootiology of tick‐borne pathogens in this region.     

Functional Insights into Recombinant TROSPA Protein from Ixodes ricinus

Lyme disease (also called borreliosis) is a prevalent chronic disease transmitted by ticks and caused by Borrelia burgdorferi s. l. spirochete. At least one tick protein, namely TROSPA from I. scapularis, commonly occurring in the USA, was shown to be required for colonization of the vector by bacteria. Located in the tick gut, TROSPA interacts with the spirochete outer surface protein A (OspA) and initiates the tick colonization. Ixodes ricinus is a primary vector involved in B. burgdorferi s. l. transmission in most European countries. In this study, we characterized the capacities of recombinant TROSPA protein from I. ricinus to interact with OspA from different Borrelia species and to induce an immune response in animals. We also showed that the N-terminal part of TROSPA (a putative transmembrane domain) is not involved in the interaction with OspA and that reduction of the total negative charge on the TROSPA protein impaired TROSPA-OspA binding. In general, the data presented in this paper indicate that recombinant TROSPA protein retains the capacity to form a complex with OspA and induces a significant level of IgG in orally immunized rats. Thus, I. ricinus TROSPA may be considered a good candidate component for an animal vaccine against Borrelia.     

Ixodes ricinus and Its Endosymbiont Midichloria mitochondrii: A Comparative Proteomic Analysis of Salivary Glands and Ovaries

Hard ticks are hematophagous arthropods that act as vectors of numerous pathogenic microorganisms of high relevance in human and veterinary medicine. Ixodes ricinus is one of the most important tick species in Europe, due to its role of vector of pathogenic bacteria such as Borrelia burgdorferi and Anaplasma phagocytophilum, of viruses such as tick borne encephalitis virus and of protozoans as Babesia spp. In addition to these pathogens, I. ricinus harbors a symbiotic bacterium, Midichloria mitochondrii. This is the dominant bacteria associated to I. ricinus, but its biological role is not yet understood. Most M. mitochondrii symbionts are localized in the tick ovaries, and they are transmitted to the progeny. M. mitochondrii bacteria have however also been detected in the salivary glands and saliva of I. ricinus, as well as in the blood of vertebrate hosts of the tick, prompting the hypothesis of an infectious role of this bacterium. To investigate, from a proteomic point of view, the tick I. ricinus and its symbiont, we generated the protein profile of the ovary tissue (OT) and of salivary glands (SG) of adult females of this tick species. To compare the OT and SG profiles, 2-DE profiling followed by LC-MS/MS protein identification were performed. We detected 21 spots showing significant differences in the relative abundance between the OT and SG, ten of which showed 4- to 18-fold increase/decrease in density. This work allowed to establish a method to characterize the proteome of I. ricinus, and to detect multiple proteins that exhibit a differential expression profile in OT and SG. Additionally, we were able to use an immunoproteomic approach to detect a protein from the symbiont. Finally, the method here developed will pave the way for future studies on the proteomics of I. ricinus, with the goals of better understanding the biology of this vector and of its symbiont M. mitochondrii.     

Investigating the relationship between environmental factors and tick abundance in a small,highly heterogeneous region

The tick Ixodes ricinus (L.) is the most important vector of tick‐borne zoonoses in Europe. Apart from factors related to human behavior, tick abundance is a major driver of the incidence of tick‐borne diseases in a given area and related data represent critical information for promoting effective public health policies. The present study analyzed the relationship between different environmental factors and tick abundance in order to improve the understanding of I. ricinus autecology and develop spatial predictive models that can be implemented in tick‐borne disease prevention strategies. Ticks were sampled in 27 sites over a four‐year period and different environmental variables were studied. Five simple models were developed that explain a large part of variation in tick abundance. Precipitation seems to play the most important role, followed by temperature, woodland coverage, and solar radiation. Model equations obtained in this study may enable the spatial interpolation and extension of tick abundance predicted values to sites of the same area, in order to build regional predictive maps. They could also be useful for the validation of large‐scale spatial predictive maps.     

A plant‐specific histone H3 lysine 4 demethylase represses the floral transition in Arabidopsis

Histone demethylation regulates chromatin structure and gene expression, and is catalyzed by various histone demethylases. Trimethylation of histone H3 at lysine 4 (H3K4) is coupled to active gene expression; trimethyl H3K4 is demethylated by Jumonj C (JmjC) domain‐containing demethylases in mammals. Here we report that a plant‐specific JmjC domain‐containing protein known as PKDM7B (At4g20400) demethylates trimethyl H3K4. PKDM7B mediates H3K4 demethylation in a key floral promoter, FLOWERING LOCUS T (FT), and an FT homolog, TWIN SISTER OF FT (TSF), and represses their expression to inhibit the floral transition in Arabidopsis. Our findings suggest that there are at least two distinct sub‐families of JmjC domain‐containing demethylases that demethylate the active trimethyl H3K4 mark in eukaryotic genes, and reveal a plant‐specific JmjC domain enzyme capable of H3K4 demethylation.     

The tomato I gene for Fusarium wilt resistance encodes an atypical leucine‐rich repeat receptor‐like protein whose function is nevertheless dependent on SOBIR1 and SERK3/BAK1

We have identified the tomato I gene for resistance to the Fusarium wilt fungus Fusarium oxysporum f. sp. lycopersici (Fol) and show that it encodes a membrane‐anchored leucine‐rich repeat receptor‐like protein (LRR‐RLP). Unlike most other LRR‐RLP genes involved in plant defence, the I gene is not a member of a gene cluster and contains introns in its coding sequence. The I gene encodes a loopout domain larger than those in most other LRR‐RLPs, with a distinct composition rich in serine and threonine residues. The I protein also lacks a basic cytosolic domain. Instead, this domain is rich in aromatic residues that could form a second transmembrane domain. The I protein recognises the Fol Avr1 effector protein, but, unlike many other LRR‐RLPs, recognition specificity is determined in the C‐terminal half of the protein by polymorphic amino acid residues in the LRRs just preceding the loopout domain and in the loopout domain itself. Despite these differences, we show that I/Avr1‐dependent necrosis in Nicotiana benthamiana depends on the LRR receptor‐like kinases (RLKs) SERK3/BAK1 and SOBIR1. Sequence comparisons revealed that the I protein and other LRR‐RLPs involved in plant defence all carry residues in their last LRR and C‐terminal LRR capping domain that are conserved with SERK3/BAK1‐interacting residues in the same relative positions in the LRR‐RLKs BRI1 and PSKR1. Tyrosine mutations of two of these conserved residues, Q922 and T925, abolished I/Avr1‐dependent necrosis in N. benthamiana, consistent with similar mutations in BRI1 and PSKR1 preventing their interaction with SERK3/BAK1.     

Tick infestation of small mammals in an English woodland

Tick infestations on small mammals were studied from April to November, 2010, in deciduous woodland in southern England in order to determine whether co‐infestations with tick stages occurred on small mammals, a key requirement for endemic transmission of tick‐borne encephalitis virus (TBEV). A total of 217 small mammals was trapped over 1,760 trap nights. Yellow‐necked mice (Apodemus flavicollis) made up the majority (52.5%) of animals, followed by wood mice (A. sylvaticus) 35.5% and bank voles (Myodes glareolus) 12%. A total of 970 ticks was collected from 169 infested animals; 96% of ticks were Ixodes ricinus and 3% I. trianguliceps. Over 98% of ticks were larval stages. Mean infestation intensities of I. ricinus were significantly higher on A. flavicollis (6.53 ± 0.67) than on A. sylvaticus (4.96 ± 0.92) and M. glareolus (3.25 ± 0.53). Infestations with I. ricinus were significantly higher in August than in any other month. Co‐infestations with I. ricinus nymphs and larvae were observed on six (3.6%) infested individuals, and fifteen small mammals (8.9%) supported I. ricinus – I. trianguliceps co‐infestations. This work contributes further to our understanding of European small mammal hosts that maintain tick populations and their associated pathogens, and indicates that co‐infestation of larvae and nymph ticks does occur in lowland UK. The possible implications for transmission of tick‐borne encephalitis virus between UK ticks and small mammals are discussed.     

Characterization of a novel salivary immunosuppressive protein from Ixodes ricinus ticks.

In tick salivary glands, several genes are induced during the feeding process, leading to the expression of new proteins. These proteins are typically secreted in tick saliva and are potentially involved in the modulation of the host immune and hemostatic responses. In a previous study, the construction and the analysis of a subtractive library led to the identification of Ixodes ricinus immunosuppressor (Iris), a novel protein, differentially expressed in I. ricinus salivary glands during the blood meal. In the present study, the data strongly suggest that this protein is secreted by tick salivary glands into the saliva. In addition, Iris is also found to modulate T lymphocyte and macrophage responsiveness by inducing a Th2 type response and by inhibiting the production of pro-inflammatory cytokines. In conclusion, these results suggest that Iris is an immunosuppressor, which might play an important role in the modulation of host immune response.     

Infestation of urban populations of the Northern white‐breasted hedgehog,Erinaceus roumanicus,by Ixodes spp. ticks in Poland

Infestation by the nest‐dwelling Ixodes hexagonus Leach and the exophilic Ixodes ricinus (Linnaeus) (Ixodida: Ixodidae) on the Northern white‐breasted hedgehog, Erinaceus roumanicus (Erinaceomorpha: Erinaceidae), was investigated during a 4‐year study in residential areas of the city of Poznań, west‐central Poland. Of 341 hedgehogs, 303 (88.9%) hosted 10 061 Ixodes spp. ticks encompassing all parasitic life stages (larvae, nymphs, females). Ixodes hexagonus accounted for 73% and I. ricinus for 27% of the collected ticks. Male hedgehogs carried significantly higher tick burdens than females. Analyses of seasonal prevalence and abundance of I. hexagonus revealed relatively stable levels of infestation of all parasitic stages, with a modest summer peak in tick abundance noted only on male hosts. By contrast, I. ricinus females and nymphs peaked in spring and declined steadily thereafter in summer and autumn, whereas the less abundant larvae peaked in summer. This is the first longterm study to evaluate the seasonal dynamics of both tick species on populations of wild hedgehogs inhabiting urban residential areas.