Cellular and molecular characterization of an embryonic cell line (BME26) from the tick Rhipicephalus (Boophilus) microplus

PEPCK and glucose metabolism homeostasis in arthropods

The fat body is responsible for a variety of functions related to energy metabolism in arthropods, by controlling the processes of de novo glucose production (gluconeogenesis) and glycogen metabolism. The rate-limiting factor of gluconeogenesis is the enzyme phosphoenolpyruvate carboxykinase (PEPCK), generally considered to be the first committed step in this pathway. Although the study of PEPCK and gluconeogenesis has been for decades restricted to mammalian models, especially focusing on muscle and liver tissue, current research has demonstrated particularities about the regulation of this enzyme in arthropods, and described new functions. This review will focus on arthropod PEPCK, discuss different aspects to PEPCK regulation and function, its general role in the regulation of gluconeogenesis and other pathways. The text also presents our views on potentially important new directions for research involving this enzyme in a variety of metabolic adaptations (e.g. diapause), discussing enzyme isoforms, roles during arthropod embryogenesis, as well as involvement in vector-pathogen interactions, contributing to a better understanding of insect vectors of diseases and their control.

Phenotypic and Target-Directed Screening Yields New Acaricidal Alternatives for the Control of Ticks

Rhipicephalus microplus, the "common cattle tick", is the most important ectoparasite in livestock worldwide due to the economic and health losses it produces. This tick is a vector for pathogens of several tick-borne diseases. In Latin American countries, damages reach approximately USD 500 million annually due to tick infections, as well as tick-borne diseases. Currently, resistant populations for every chemical group of acaricides have been reported, posing a serious problem for tick control. This study aims to find new alternatives for controlling resistant ticks with compounds derived from small synthetic organic molecules and natural origins. Using BME26 embryonic cells, we performed phenotypic screening of 44 natural extracts from 10 Mexican plants used in traditional medicine, and 33 compounds selected from our chemical collection. We found 10 extracts and 13 compounds that inhibited cell growth by 50% at 50 µg/mL and 100 µM, respectively; the dose-response profile of two of them was characterized, and these compounds were assayed in vitro against different life stages of Rhipicephalus microplus. We also performed a target-directed screening of the activity of triosephosphate isomerase, using 86 compounds selected from our chemical collection. In this collection, we found the most potent and selective inhibitor of tick triosephosphate isomerase reported until now. Two other compounds had a potent acaricidal effect in vitro using adults and larvae when compared with other acaricides such as ivermectin and Amitraz. Those compounds were also selective to the ticks compared with the cytotoxicity in mammalian cells like macrophages or bovine spermatozoids. They also had a good toxicological profile, resulting in promising acaricidal compounds for tick control in cattle raising.

Pyrokinin receptor silencing in females of the southern cattle tick Rhipicephalus (Boophilus) microplus is associated with a reproductive fitness cost

Background

Rhipicephalusmicroplus is the vector of deadly cattle pathogens, especially Babesia spp., for which a recombinant vaccine is not available. Therefore, disease control depends on tick vector control. However, R.microplus populations worldwide have developed resistance to available acaricides, prompting the search for novel acaricide targets. G protein-coupled receptors (GPCRs) are involved in the regulation of many physiological processes and have been suggested as druggable targets for the control of arthropod vectors. Arthropod-specific signaling systems of small neuropeptides are being investigated for this purpose. The pyrokinin receptor (PKR) is a GPCR previously characterized in ticks. Myotropic activity of pyrokinins in feeding-related tissues of Rhipicephalussanguineus and Ixodesscapularis was recently reported.

Methods

The R.microplus pyrokinin receptor (Rhimi-PKR) was silenced through RNA interference (RNAi) in female ticks. To optimize RNAi, a dual-luciferase assay was applied to determine the silencing efficiency of two Rhimi-PKR double-stranded RNAs (dsRNA) prior to injecting dsRNA in ticks to be placed on cattle. Phenotypic variables of female ticks obtained at the endpoint of the RNAi experiment were compared to those of control female ticks (non-injected and beta-lactamase dsRNA-injected). Rhimi-PKR silencing was verified by quantitative reverse-transcriptase PCR in whole females and dissected tissues.

Results

The Rhimi-PKR transcript was expressed in all developmental stages. Rhimi-PKR silencing was confirmed in whole ticks 4 days after injection, and in the tick carcass, ovary and synganglion 6 days after injection. Rhimi-PKR silencing was associated with an increased mortality and decreased weight of both surviving females and egg masses (P < 0.05). Delays in repletion, pre-oviposition and incubation periods were observed (P < 0.05).

Conclusions

Rhimi-PKR silencing negatively affected female reproductive fitness. The PKR appears to be directly or indirectly associated with the regulation of female feeding and/or reproductive output in R.microplus. Antagonists of the pyrokinin signaling system could be explored for tick control.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05349-w.

REDOX IMBALANCE INDUCES REMODELING OF GLUCOSE METABOLISM IN RHIPICEPHALUS MICROPLUS EMBRYONIC CELL LINE

Carbohydrate metabolism not only functions in supplying cellular energy but also has an important role in maintaining physiological homeostasis and in preventing oxidative damage caused by reactive oxygen species. Previously, we showed that arthropod embryonic cell lines have high tolerance to H₂O₂ exposure. Here, we describe that Rhipicephalus microplus tick embryonic cell line (BME26) employs an adaptive glucose metabolism mechanism that confers tolerance to hydrogen peroxide at concentrations too high for other organisms. This adaptive mechanism sustained by glucose metabolism remodeling promotes cell survival and redox balance in BME26 cell line after millimolar H₂O₂ exposure. The present work shows that this tick cell line could tolerate high H₂O₂ concentrations by initiating a carbohydrate-related adaptive response. We demonstrate that gluconeogenesis was induced as a compensation strategy that involved, among other molecules, the metabolic enzymes NADP-ICDH, G6PDH, and PEPCK. We also found that this phenomenon was coupled to glycogen accumulation and glucose uptake, supporting the pentose phosphate pathway to sustain NADPH production and leading to cell survival and proliferation. Our findings suggest that the described response is not atypical, being also observed in cancer cells, which highlights the importance of this model to all proliferative cells. We propose that these results will be useful in generating basic biological information to support the development of new strategies for disease treatment and parasite control.

Three-Dimensional Culture of Rhipicephalus (Boophilus) microplus BmVIII-SCC Cells on Multiple Synthetic Scaffold Systems and in Rotating Bioreactors

Tick cell culture facilitates research on the biology of ticks and their role as vectors of pathogens that affect humans, domestic animals, and wildlife. Because two-dimensional cell culture doesn't promote the development of multicellular tissue-like composites, we hypothesized that culturing tick cells in a three-dimensional (3-D) configuration would form spheroids or tissue-like organoids. In this study, the cell line BmVIII-SCC obtained from the cattle fever tick, Rhipicephalus (Boophilus) microplus (Canestrini, 1888), was cultured in different synthetic scaffold systems. Growth of the tick cells on macrogelatinous beads in rotating continuous culture system bioreactors enabled cellular attachment, organization, and development into spheroid-like aggregates, with evidence of tight cellular junctions between adjacent cells and secretion of an extracellular matrix. At least three cell morphologies were identified within the aggregates: fibroblast-like cells, small endothelial-like cells, and larger cells exhibiting multiple cytoplasmic endosomes and granular vesicles. These observations suggest that BmVIII-SCC cells adapted to 3-D culture retain pluripotency. Additional studies involving genomic analyses are needed to determine if BmVIII-SCC cells in 3-D culture mimic tick organs. Applications of 3-D culture to cattle fever tick research are discussed.

Cell Line Platforms Support Research into Arthropod Immunity

Simple Summary

Many insect and tick species are serious pests, because insects damage crop plants and, along with ticks, transmit a wide range of human and animal diseases. One way of controlling these pests is by impairing their immune system, which protects them from bacterial, fungal, and viral infections. An important tool for studying immunity is using long-lasting cell cultures, known as cell lines. These lines can be frozen and thawed at will to be used in automated tests, and they provide consistent results over years. Questions that can be asked using cell lines include: How do insects or ticks recognize when they have been infected and by what organism? What kinds of defensive strategies do they use to contain or kill infectious agents? This article reviews research with insect or tick cell lines to answer these questions, as well as other questions relating to immunity. This review also discusses future research strategies for working with cell lines.

Abstract

Innate immune responses are essential to maintaining insect and tick health and are the primary defense against pathogenic viruses, bacteria, and fungi. Cell line research is a powerful method for understanding how invertebrates mount defenses against pathogenic organisms and testing hypotheses on how these responses occur. In particular, immortal arthropod cell lines are valuable tools, providing a tractable, high-throughput, cost-effective, and consistent platform to investigate the mechanisms underpinning insect and tick immune responses. The research results inform the controls of medically and agriculturally important insects and ticks. This review presents several examples of how cell lines have facilitated research into multiple aspects of the invertebrate immune response to pathogens and other foreign agents, as well as comments on possible future research directions in these robust systems.

Establishment and characterization of a cell line (RBME-6) of Rhipicephalus (Boophilus) microplus from Brazil

Tick cell lines have already proved to be a useful tool for obtaining more information about possible vector species and the factors governing their ability to transmit a pathogen. Here, we established and characterized a cell line (RBME-6) derived from embryos of Rhipicephalus microplus from Brazil. Primary tick cell cultures were prepared in L-15B medium supplemented with 20% fetal bovine serum and 10% tryptose phosphate broth. The cell monolayers were subcultured when they reached a density of approximately 8 × 10 ⁵ cells/mL (95% viability). Only after the sixth subculture were cells thawed from storage in liquid nitrogen successfully. Cytological analyses were performed using live phase contrast microscopy and cytocentrifuge smears stained with Giemsa, while periodic acid-Schiff and bromophenol blue staining techniques were used to detect total polysaccharides and total protein, respectively . No DNA from Anaplasma spp., Anaplasma marginale, Babesia spp., Bartonella spp., Coxiella spp., Ehrlichia canis, Rickettsia spp. or Mycoplasma spp. was detected in the cells through PCR assays. In addition, we performed chromosomal characterization of the tick cell line and confirmed the R. microplus origin of the cell line through conventional PCR and sequencing of a fragment of the mitochondrial 16S rRNA gene. In conclusion, we established and characterized a new cell line from a Brazilian population of R. microplus, which may form a useful tool for studying several aspects of ticks and tick-borne pathogens.

The intracellular bacterium Rickettsia rickettsii exerts an inhibitory effect on the apoptosis of tick cells

BACKGROUND

Rickettsia rickettsii is a tick-borne obligate intracellular bacterium that causes Rocky Mountain spotted fever, a life-threatening illness. To obtain an insight into the vector-pathogen interactions, we assessed the effects of infection with R. rickettsii on the proteome cells of the tick embryonic cell line BME26.

METHODS

The proteome of BME26 cells was determined by label-free high-performance liquid chromatography coupled with tandem mass spectrometry analysis. Also evaluated were the effects of infection on the activity of caspase-3, assessed by the hydrolysis of a synthetic fluorogenic substrate in enzymatic assays, and on the exposition of phosphatidyserine, evaluated by live-cell fluorescence microscopy after labeling with annexin-V. Finally, the effects of activation or inhibition of caspase-3 activity on the growth of R. rickettsii in BME26 cells was determined.

RESULTS

Tick proteins of different functional classes were modulated in a time-dependent manner by R. rickettsii infection. Regarding proteins involved in apoptosis, certain negative regulators were downregulated at the initial phase of the infection (6 h) but upregulated in the middle of the exponential phase of the bacterial growth (48 h). Microorganisms are known to be able to inhibit apoptosis of the host cell to ensure their survival and proliferation. We therefore evaluated the effects of infection on classic features of apoptotic cells and observed DNA fragmentation exclusively in noninfected cells. Moreover, both caspase-3 activity and phosphatidylserine exposition were lower in infected than in noninfected cells. Importantly, while the activation of caspase-3 exerted a detrimental effect on rickettsial proliferation, its inhibition increased bacterial growth.

CONCLUSIONS

Taken together, these results show that R. rickettsii modulates the proteome and exerts an inhibitory effect on apoptosis in tick cellsthat seems to be important to ensure cell colonization.

Tick Cell Lines in Research on Tick Control

Ticks and the diseases they transmit are of huge veterinary, medical and economic importance worldwide. Control of ticks attacking livestock and companion animals is achieved primarily by application of chemical or plant-based acaricides. However, ticks can rapidly develop resistance to any new product brought onto the market, necessitating an ongoing search for novel active compounds and alternative approaches to tick control. Many aspects of tick and tick-borne pathogen research have been facilitated by the application of continuous cell lines derived from some of the most economically important tick species. These include cell lines derived from acaricide-susceptible and resistant ticks, cell sub-lines with in vitro-generated acaricide resistance, and genetically modified tick cells. Although not a replacement for the whole organism, tick cell lines enable studies at the cellular and molecular level and provide a more accessible, more ethical and less expensive in vitro alternative to in vivo tick feeding experiments. Here we review the role played by tick cell lines in studies on acaricide resistance, mode-of-action of acaricides, identification of potential novel control targets through better understanding of tick metabolism, and anti-tick vaccine development, that may lead to new approaches to control ticks and tick-borne diseases.

The identification of tick autophagy-related genes in Ixodes scapularis responding to amino acid starvation

Ticks are obligate hematophagous arthropods and must tolerate starvation during off-host periods. Macroautophagy (hereafter autophagy) is a well-conserved self-eating mechanism of cell survival and is essential for recycling cellular contents during periods of starvation, stress, and injury in organisms. Although the genome sequence of Ixodes scapularis (Say) is available, the characteristics and functions of autophagy-related gene families remain largely unknown. To advance our understanding of autophagy in I. scapularis, we used comprehensive genomic approaches to identify Atg genes. Homologues of 14 Atg genes were identified, and their protein motif compositions were predicted. Phylogenetic analysis indicated that ATGs in I. scapularis were evolutionarily closely related to their homologues in Haemaphysalis longicornis and Rhipicephalus microplus ticks. Expression patterns of Atg genes differed across tick developmental stages. Immunofluorescence results by monodansylcadaverine (MDC) staining indicated that autophagy was activated after amino acid starvation treatments in I. scapularis embryo-derived cell lines ISE6 and IDE8. Subsequently, the expression of key Atg genes involved in autophagy pathway in both cell lines were examined. In ISE6 cells, the expression levels of three Atg genes (Atg4B, Atg6 and Atg8A) increased significantly after amino acid starvation; similarly, four Atg genes (Atg4A, Atg4B, Atg6 and Atg8B) were upregulated in IDE8 cells in response to starvation. In parallel, the MDC and lysotracker staining results indicated that autophagy was triggered after amino acid starvation treatments in R. microplus embryo-derived cell line BME26. Our observations showed that Atg family genes are highly conserved in ticks and function in autophagy pathway induced by amino acid starvation. These results also provide valuable insight for further autophagy-related research as a new strategy for blocking the transmission of tick-borne pathogens.

TOR as a Regulatory Target in Rhipicephalus microplus Embryogenesis

Embryogenesis is a metabolically intensive process carried out under tightly controlled conditions. The insulin signaling pathway regulates glucose homeostasis and is essential for reproduction in metazoan model species. Three key targets are part of this signaling pathway: protein kinase B (PKB, or AKT), glycogen synthase kinase 3 (GSK-3), and target of rapamycin (TOR). While the role of AKT and GSK-3 has been investigated during tick embryonic development, the role of TOR remains unknown. In this study, TOR and two other downstream effectors, namely S6 kinase (S6K) and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1), were investigated in in vitro studies using the tick embryonic cell line BME26. First, we show that exogenous insulin can stimulate TOR transcription. Second, TOR chemical inhibition led to a decrease in BME26 cell viability, loss of membrane integrity, and downregulation of S6K and 4E-BP1 transcription. Conversely, treating BME26 cells with chemical inhibitors of AKT or GSK-3 did not affect S6K and 4E-BP1 transcription, showing that TOR is specifically required to activate its downstream targets. To address the role of TOR in tick reproduction, in vivo studies were performed. Analysis of relative transcription during different stages of tick embryonic development showed different levels of transcription for TOR, and a maternal deposition of S6K and 4E-BP1 transcripts. Injection of TOR double-stranded RNA (dsRNA) into partially fed females led to a slight delay in oviposition, an atypical egg external morphology, decreased vitellin content in eggs, and decreased larval hatching. Taken together, our data show that the TOR signaling pathway is important for tick reproduction, that TOR acts as a regulatory target in Rhipicephalus microplus embryogenesis and represents a promising target for the development of compounds for tick control.

Inhibition of energy metabolism by 3-bromopyruvate in the hard tick Rhipicephalus microplus

The cattle tick R. microplus is the biggest obstacle to livestock rearing in tropical countries. It is responsible for billions of dollars in losses every year, affecting meat and milk production, beef and dairy cattle, and the leather industry. The lack of knowledge and strategies to combat the tick only increases the losses, it leads to successive and uncontrolled applications of acaricides, favouring the selection of strains resistant to commercially available chemical treatments. In this paper, we tested 3‑bromopyruvate (3‑BrPA), an alkylating agent with a high affinity for cysteine residues, on the R. microplus metabolism. We found that 3-BrPA was able to induce cell death in an assay using BME26 strain cell cultures derived from embryos, it was also able to reduce cellular respiration in developing embryos. 3-BrPA is a nonspecific inhibitor, affecting enzymes of different metabolic pathways in R. microplus. In our experiments, we demonstrated that 3-BrPA was able to affect the glycolytic enzyme hexokinase, reducing its activity by approximately 50%; and it strongly inhibited triose phosphate isomerase, which is an enzyme involved in both glycolysis and gluconeogenesis. Also, the mitochondrial respiratory chain was affected, NADH cytochrome c reductase (complex I-III) and succinate cytochrome c reductase (complex II-III) were strongly inhibited by 3-BrPA. Glutamate dehydrogenase was also affected by 3-BrPA, showing a gradual inhibition of activity in all the 3-BrPA concentrations tested. Altogether, these results show that 3-BrPA is a harmful compound to the tick organism.

Carbohydrate Metabolic Compensation Coupled to High Tolerance to Oxidative Stress in Ticks

Reactive oxygen species (ROS) are natural byproducts of metabolism that have toxic effects well documented in mammals. In hematophagous arthropods, however, these processes are not largely understood. Here, we describe that Rhipicephalus microplus ticks and embryonic cell line (BME26) employ an adaptive metabolic compensation mechanism that confers tolerance to hydrogen peroxide (H2O2) at concentrations too high for others organisms. Tick survival and reproduction are not affected by H2O2 exposure, while BME26 cells morphology was only mildly altered by the treatment. Furthermore, H2O2-tolerant BME26 cells maintained their proliferative capacity unchanged. We evaluated several genes involved in gluconeogenesis, glycolysis, and pentose phosphate pathway, major pathways for carbohydrate catabolism and anabolism, describing a metabolic mechanism that explains such tolerance. Genetic and catalytic control of the genes and enzymes associated with these pathways are modulated by glucose uptake and energy resource availability. Transient increase in ROS levels, oxygen consumption, and ROS-scavenger enzymes, as well as decreased mitochondrial superoxide levels, were indicative of cell adaptation to high H2O2 exposure, and suggested a tolerance strategy developed by BME26 cells to cope with oxidative stress. Moreover, NADPH levels increased upon H2O2 challenge, and this phenomenon was sustained mainly by G6PDH activity. Interestingly, G6PDH knockdown in BME26 cells did not impair H2O2 tolerance, but generated an increase in NADP-ICDH transcription. In agreement with the hypothesis of a compensatory NADPH production in these cells, NADP-ICDH knockdown increased G6PDH relative transcript level. The present study unveils the first metabolic evidence of an adaptive mechanism to cope with high H2O2 exposure and maintain redox balance in ticks.

Viral diversity of Rhipicephalus microplus parasitizing cattle in southern Brazil

Ticks are ectoparasites spread worldwide and are well known as vectors of many viruses of great importance to human and animal health. However, the viral diversity in ticks is still poorly understood, particularly in South America. Here we characterized the viral diversity present in Rhipicephalus microplus parasitizing cattle in the southern region of Brazil using metagenomics. Our study revealed the presence of viruses that had not been previously described in the region, including lihan tick virus (Phenuiviridae family) and wuhan tick virus 2 (Chuviridae family), as well as expands the biogeography of jingmen tick virus (Flaviviridae family) in Brazil. Also, we described three novel tymoviruses (Tymovirales order), named guarapuava tymovirus-like 1 to 3. We described the genomic and phylogenetic characterization of these viruses. Our study sheds light on the viral diversity of Rhipicephalus microplus in South America, and also expands the biogeography of tick viruses that were previously described only in Asia.

Transcriptional activities of two newly identified Haemaphysalis longicornis tick-derived promoter regions in the Ixodes scapularis tick cell line (ISE6)

Ticks are obligate haematophagous ectoparasites considered to be second to mosquitoes as vectors of human diseases and the most important vector for animals. Despite efforts to control tick infestations, they remain a serious health problem. Gene manipulation has been established in mosquitoes and led to the control of mosquito populations and of mosquito-borne pathogens. Therefore, gene manipulation could be useful for controlling ticks and tick-borne pathogens. To investigate effective gene expression vectors for ticks, the promoter activities of commercial plasmids were evaluated in a tick cell line (ISE6). Dual luciferase assays revealed that pmirGLO, the human phosphoglycerate kinase promoter contained plasmid vector, showed the highest activity in ISE6 cells amongst the tested plasmids. Moreover, we identified the promoter regions of the Haemaphysalis longicornis actin (HlAct) and the intracellular ferritin (HlFer1) genes. To construct a more effective expression vector for ticks, these promoter regions were inserted into pmirGLO (pmirGLO-HlAct pro and pmirGLO-HlFer1 pro). The pmirGLO-HlAct pro vector showed significantly higher promoter activity than pmirGLO, whereas the pmirGLO-HlFer1 pro vector demonstrated significantly lower promoter activity than pmirGLO in ISE6 cells. The HlAct promoter region may have high promoter activity in ISE6 cells. The results of the present study provide useful information for the development of a genetic modification system in ticks.

Novel and Selective Rhipicephalus microplus Triosephosphate Isomerase Inhibitors with Acaricidal Activity

The cattle tick Rhipicephalus microplus is one of the most important ectoparasites causing significant economic losses for the cattle industry. The major tool of control is reducing the number of ticks, applying acaricides in cattle. However, overuse has led to selection of resistant populations of R. microplus to most of these products, some even to more than one active principle. Thus, exploration for new molecules with acaricidal activity in R. microplus has become necessary. Triosephosphate isomerase (TIM) is an essential enzyme in R. microplus metabolism and could be an interesting target for the development of new methods for tick control. In this work, we screened 227 compounds, from our in-house chemo-library, against TIM from R. microplus. Four compounds (50, 98, 14, and 161) selectively inhibited this enzyme with IC₅₀ values between 25 and 50 μM. They were also able to diminish cellular viability of BME26 embryonic cells by more than 50% at 50 μM. A molecular docking study showed that the compounds bind in different regions of the protein; compound 14 interacts with the dimer interface. Furthermore, compound 14 affected the survival of partially engorged females, fed artificially, using the capillary technique. This molecule is simple, easy to produce, and important biological data—including toxicological information—are available for it. Our results imply a promising role for compound 14 as a prototype for development of a new acaricidal involving selective TIM inhibition.

The Tick Cell Biobank: A global resource for in vitro research on ticks, other arthropods and the pathogens they transmit

Tick cell lines are increasingly used in many fields of tick and tick-borne disease research. The Tick Cell Biobank was established in 2009 to facilitate the development and uptake of these unique and valuable resources. As well as serving as a repository for existing and new ixodid and argasid tick cell lines, the Tick Cell Biobank supplies cell lines and training in their maintenance to scientists worldwide and generates novel cultures from tick species not already represented in the collection. Now part of the Institute of Infection and Global Health at the University of Liverpool, the Tick Cell Biobank has embarked on a new phase of activity particularly targeted at research on problems caused by ticks, other arthropods and the diseases they transmit in less-developed, lower- and middle-income countries. We are carrying out genotypic and phenotypic characterisation of selected cell lines derived from tropical tick species. We continue to expand the culture collection, currently comprising 63 cell lines derived from 18 ixodid and argasid tick species and one each from the sand fly Lutzomyia longipalpis and the biting midge Culicoides sonorensis, and are actively engaging with collaborators to obtain starting material for primary cell cultures from other midge species, mites, tsetse flies and bees. Outposts of the Tick Cell Biobank will be set up in Malaysia, Kenya and Brazil to facilitate uptake and exploitation of cell lines and associated training by scientists in these and neighbouring countries. Thus the Tick Cell Biobank will continue to underpin many areas of global research into biology and control of ticks, other arthropods and vector-borne viral, bacterial and protozoan pathogens.

Antimicrobial Metallopeptides

Antimicrobial peptides are short amphipathic peptides that are produced by the innate immune system in order to protect a host from pathogens. They have been shown to have broad-spectrum antimicrobial activity toward Gram-positive and Gram-negative bacteria, as well as antifungal, antiprotozoan, and antiviral activity. These peptides are able to exert their activity through a variety of mechanisms that include inhibiting DNA and RNA replication, inhibiting protein synthesis, permeabilizing the cell membrane, disrupting proton and ion transmembrane gradients, and inhibiting cell wall biosynthesis. Certain antimicrobial peptides are able to utilize metals to modulate their activity through structural changes upon metal binding, metal sequestration, and redox chemistry. This work aims to provide a review of the current literature regarding the influence of metals on the activity of antimicrobial metallopeptides and their uses in drug delivery and the treatment of implant-associated infections.

Immune-related redox metabolism of embryonic cells of the tick Rhipicephalus microplus (BME26) in response to infection with Anaplasma marginale

Background

It is well known that reactive oxygen species (ROS) and reactive nitrogen species (RNS) are involved in the control of pathogens and microbiota in insects. However, the knowledge of the role of ROS and RNS in tick-pathogen and tick-microbiota interactions is limited. Here, we evaluated the immune-related redox metabolism of the embryonic cell line BME26 from the cattle tick Rhipicephalus microplus in response to Anaplasma marginale infection.

Methods

A high-throughput qPCR approach was used to determine the expression profile of 16 genes encoding proteins involved in either production or detoxification of ROS and RNS in response to different microbial challenges. In addition, the effect of RNAi-mediated gene silencing of catalase, glutathione peroxidase, thioredoxin and protein oxidation resistance 1 in the control of infection with A. marginale was evaluated.

Results

Infection with A. marginale resulted in downregulation of the genes encoding ROS-generating enzymes dual oxidase and endoplasmic reticulum oxidase. In contrast, the genes encoding the antioxidant enzymes superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, thioredoxin, thioredoxin reductase and peroxiredoxin were upregulated. The gene expression pattern in response to infection with Rickettsia rickettsii and exposure to heat-killed microorganisms, Micrococcus luteus, Enterobacter cloacae or S. cerevisiae was the opposite of that triggered by A. marginale challenge. The simultaneous silencing of three genes, catalase, glutathione peroxidase, and thioredoxin as well as the oxidation resistance 1 gene by RNAi apparently favoured the colonization of BME26 cells by A. marginale, suggesting that the antioxidant response might play a role in the control of infection.

Conclusions

Taken together, our results suggest that a general response of tick cells upon microbial stimuli is to increase ROS/RNS production. In contrast, A. marginale infection triggers an opposite profile, suggesting that this pathogen might manipulate the tick redox metabolism to evade the deleterious effect of the oxidant-based innate immune response.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2575-9) contains supplementary material, which is available to authorized users.

Relative transcription of autophagy-related genes in Amblyomma sculptum and Rhipicephalus microplus ticks

Ticks endure stressful off-host periods and perform as vectors of a diversity of infectious agents, thus engaging pathways that expectedly demand for autophagy. Little is known of ticks' autophagy, a conserved eukaryotic machinery assisting in homeostasis processes that also participates in tissue-dependent metabolic functions. Here, the autophagy-related ATG4 (autophagin-1), ATG6 (beclin-1) and ATG8 (LC3) mRNAs from the human diseases vector Amblyomma sculptum and the cattle-tick Rhipicephalus microplus were identified. Comparative qPCR quantifications evidenced different transcriptional status for the ATG genes in the salivary glands (SG), ovaries and intestines of actively feeding ticks. These ATGs had increased relative transcription under nutrient-deprivation, as determined by validation tests with R. microplus embryo-derivative cells BME26 and A. sculptum SG explants incubations in HBSS. Starvation lead to 4-31.8× and ~ 60-500× increments on the ATGs mRNA loads in BME26 and A. sculptum SG explants, respectively. PI3K inhibitor 3MA treatment also affected ATGs expression in BME26. Some ATGs were more transcribed in the SGs than in the ovaries of cattle-ticks. Amblyomma sculptum/R. microplus interspecific comparisons showed that ATG4 and ATG6 were 0.18× less expressed in A. sculptum SGs, but ~ 10-100× more expressed in their ovaries when compared to R. microplus organs. ATG4 and ATG8a transcript loads were ~ 120× and ~ 40× higher, respectively, in A. sculptum intestines when compared to cattle-ticks of similar weight category. ATGs expression in A. sculptum intestines increased with tick weight, indicating Atgs contribution to intracellular blood digestion. Possible roles of the autophagy machinery and their organ-specific expression profile on vector biology are discussed.

Deciphering Babesia-Vector Interactions

Understanding host-pathogen-tick interactions remains a vitally important issue that might be better understood by basic research focused on each of the dyad interplays. Pathogens gain access to either the vector or host during tick feeding when ticks are confronted with strong hemostatic, inflammatory and immune responses. A prominent example of this is the Babesia spp.—tick—vertebrate host relationship. Babesia spp. are intraerythrocytic apicomplexan organisms spread worldwide, with a complex life cycle. The presence of transovarial transmission in almost all the Babesia species is the main difference between their life cycle and that of other piroplasmida. With more than 100 species described so far, Babesia are the second most commonly found blood parasite of mammals after trypanosomes. The prevalence of Babesia spp. infection is increasing worldwide and is currently classified as an emerging zoonosis. Babesia microti and Babesia divergens are the most frequent etiological agents associated with human babesiosis in North America and Europe, respectively. Although the Babesia-tick system has been extensively researched, the currently available prophylactic and control methods are not efficient, and chemotherapeutic treatment is limited. Studying the molecular changes induced by the presence of Babesia in the vector will not only elucidate the strategies used by the protozoa to overcome mechanical and immune barriers, but will also contribute toward the discovery of important tick molecules that have a role in vector capacity. This review provides an overview of the identified molecules involved in Babesia-tick interactions, with an emphasis on the fundamentally important ones for pathogen acquisition and transmission.

Exploring the immune signalling pathway-related genes of the cattle tick Rhipicephalus microplus: From molecular characterization to transcriptional profile upon microbial challenge

In dipteran insects, invading pathogens are selectively recognized by four major pathways, namely Toll, IMD, JNK, and JAK/STAT, and trigger the activation of several immune effectors. Although substantial advances have been made in understanding the immunity of model insects such as Drosophila melanogaster, knowledge on the activation of immune responses in other arthropods such as ticks remains limited. Herein, we have deepened our understanding of the intracellular signalling pathways likely to be involved in tick immunity by combining a large-scale in silico approach with high-throughput gene expression analysis. Data from in silico analysis revealed that although both the Toll and JAK/STAT signalling pathways are evolutionarily conserved across arthropods, ticks lack central components of the D. melanogaster IMD pathway. Moreover, we show that tick immune signalling-associated genes are constitutively transcribed in BME26 cells (a cell lineage derived from embryos of the cattle tick Rhipicephalus microplus) and exhibit different transcriptional patterns in response to microbial challenge. Interestingly, Anaplasma marginale, a pathogen that is naturally transmitted by R. microplus, causes downregulation of immune-related genes, suggesting that this pathogen may manipulate the tick immune system, favouring its survival and vector colonization.

Discovery, adaptation and transcriptional activity of two tick promoters: Construction of a dual luciferase reporter system for optimization of RNA interference in rhipicephalus (boophilus) microplus cell lines

Dual luciferase reporter systems are valuable tools for functional genomic studies, but have not previously been developed for use in tick cell culture. We evaluated expression of available luciferase constructs in tick cell cultures derived from Rhipicephalus (Boophilus) microplus, an important vector of bovine babesiosis and anaplasmosis. Commercial promoters were evaluated for transcriptional activity driving luciferase expression in the tick cell lines. The human phosphoglycerate kinase (PGK) promoter resulted in detectable firefly luciferase activity within 2 days post-transfection of the R. microplus cell line BME26, with maximal activity at 5 days post-transfection. Several other promoters were weaker or inactive in the tick cells, prompting identification and assessment of transcriptional activity of the homologous ribosomal protein L4 (rpL4, GenBank accession no.: KM516205) and elongation factor 1α (EF-1α, GenBank accession no.: KM516204) promoters cloned from R. microplus. Evaluation of luciferase expression driven by various promoters in tick cell culture resulted in selection of the R. microplus rpL4 promoter and the human PGK promoter driving transcription of sequences encoding modified firefly and NanoLuc® luciferases for construction of a dual luciferase reporter system for use in tick cell culture.

An Ixodes scapularis cell line with a predominantly neuron-like phenotype

The Ixodes scapularis embryo-derived cell line ISE6 is the most widely utilized tick-derived cell line due to its susceptibility to a wide variety of tick- and non-tick-vectored pathogens. Little is known about its tissue origin or biological background. Protein expression of ISE6 cells was compared with that of another I. scapularis-derived cell line, IDE12, and dissected tick synganglia. Results demonstrated the presence of a neuronal marker protein, type 3 β-tubulin, in all three samples, as well as other shared and unique neuronal and immune response-associated proteins. Of neuronal proteins shared between the two cell lines, ISE6 expressed several in significantly greater quantities than IDE12. Stimulation of ISE6 cells by in vivo exposure to the hemocoel environment in unfed larval and molting nymphal ticks, but not unfed nymphal ticks, resulted in the development of neuron-like morphologic characteristics in the implanted cells.

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.

Non-classical gluconeogenesis-dependent glucose metabolism in Rhipicephalus microplus embryonic cell line BME26

In this work we evaluated several genes involved in gluconeogenesis, glycolysis and glycogen metabolism, the major pathways for carbohydrate catabolism and anabolism, in the BME26 Rhipicephalus microplus embryonic cell line. Genetic and catalytic control of the genes and enzymes associated with these pathways are modulated by alterations in energy resource availability (primarily glucose). BME26 cells in media were investigated using three different glucose concentrations, and changes in the transcription levels of target genes in response to carbohydrate utilization were assessed. The results indicate that several genes, such as glycogen synthase (GS), glycogen synthase kinase 3 (GSK3), phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6 phosphatase (GP) displayed mutual regulation in response to glucose treatment. Surprisingly, the transcription of gluconeogenic enzymes was found to increase alongside that of glycolytic enzymes, especially pyruvate kinase, with high glucose treatment. In addition, RNAi data from this study revealed that the transcription of gluconeogenic genes in BME26 cells is controlled by GSK-3. Collectively, these results improve our understanding of how glucose metabolism is regulated at the genetic level in tick cells.

In vitro establishment of ivermectin-resistant Rhipicephalus microplus cell line and the contribution of ABC transporters on the resistance mechanism

The cattle tick Rhipicephalus microplus is one of the most economically damaging livestock ectoparasites, and its widespread resistance to acaricides is a considerable challenge to its control. In this scenario, the establishment of resistant cell lines is a useful approach to understand the mechanisms involved in the development of acaricide resistance, to identify drug resistance markers, and to develop new acaricides. This study describes the establishment of an ivermectin (IVM)-resistant R. microplus embryonic cell line, BME26-IVM. The resistant cells were obtained after the exposure of IVM-sensitive BME26 cells to increasing doses of IVM in a step-wise manner, starting from an initial non-toxic concentration of 0.5 μg/mL IVM, and reaching 6 μg/mL IVM after a 46-week period. BME26-IVM cell line was 4.5 times more resistant to IVM than the parental BME26 cell line (lethal concentration 50 (LC50) 15.1 ± 1.6 μg/mL and 3.35 ± 0.09 μg/mL, respectively). As an effort to determine the molecular mechanisms governing resistance, the contribution of ATP-binding cassette (ABC) transporter was investigated. Increased expression levels of ABC transporter genes were found in IVM-treated cells, and resistance to IVM was significantly reduced by co-incubation with 5 μM cyclosporine A (CsA), an ABC transporter inhibitor, suggesting the involvement of these proteins in IVM-resistance. These results are similar to those already described in IVM-resistant tick populations, and suggest that similar resistance mechanisms are involved in vitro and in vivo. They reinforce the hypothesis that ABC transporters are involved in IVM resistance and support the use of BME26-IVM as an in vitro approach to study acaricide resistance mechanisms.

Knockdown of the Rhipicephalus microplus cytochrome c oxidase subunit III gene is associated with a failure of Anaplasma marginale transmission

Rhipicephalus microplus is an obligate hematophagous ectoparasite of cattle and an important biological vector of Anaplasma marginale in tropical and subtropical regions. The primary determinants for A. marginale transmission are infection of the tick gut, followed by infection of salivary glands. Transmission of A. marginale to cattle occurs via infected saliva delivered during tick feeding. Interference in colonization of either the tick gut or salivary glands can affect transmission of A. marginale to naïve animals. In this study, we used the tick embryonic cell line BME26 to identify genes that are modulated in response to A. marginale infection. Suppression-subtractive hybridization libraries (SSH) were constructed, and five up-regulated genes {glutathione S-transferase (GST), cytochrome c oxidase sub III (COXIII), dynein (DYN), synaptobrevin (SYN) and phosphatidylinositol-3,4,5-triphosphate 3-phosphatase (PHOS)} were selected as targets for functional in vivo genomic analysis. RNA interference (RNAi) was used to determine the effect of tick gene knockdown on A. marginale acquisition and transmission. Although RNAi consistently knocked down all individually examined tick genes in infected tick guts and salivary glands, only the group of ticks injected with dsCOXIII failed to transmit A. marginale to naïve calves. To our knowledge, this is the first report demonstrating that RNAi of a tick gene is associated with a failure of A. marginale transmission.

Multiple lines of evidence on the genetic relatedness of the parthenogenetic and bisexual Haemaphysalis longicornis (Acari: Ixodidae)

As an obligate hematophagous ectoparasite, the hard tick Haemaphysalis longicornis exhibits two reproductive strategies, bisexual reproduction, and obligate parthenogenesis, which have attracted a widespread attention. However, the speciation of parthenogenetic population remained ambiguous due to its similarity in morphology but the remarkable differences in cytogenetics as compared with those of the bisexual ones. In the present study, we explored several new lines of genetic evidence to resolve this controversial issue. The number of the chromosomes in two lineages was checked by classical methods and their total DNA levels were determined utilizing flowcytometry. In addition, the sequences of 12S rDNA, 16S rDNA, cytochrome c oxidase I and II (COI, COII) and internal transcribed spacer-2 (ITS-2) genes were used to assess their phylogenetic relationship. We observed that the chromosome ploidy of bisexual and parthenogenetic H. longicornis collected by our laboratory was diploid and triploid, respectively. Flowcytometry analysis indicated a ratio close to 2:3 in the DNA contents of bisexual to parthenogenetic H. longicornis. Although the chromosome ploidy is different, their gene sequences are extremely similar. Analogous to the intra-species genetic difference of other invertebrates, sequence differences of all loci examined are below 2%. Phylogenetic trees constructed from 12S rDNA, 16S rDNA, COI, and ITS-2 genes revealed that they were all in the same monophyletic clade instead of splitting independently into evolutional branches. Moreover, according to 4× Rule, the K/θ ratio of two reproductive populations calculated based on COI was much smaller than four, strongly supporting that they belong to the same species. Therefore, we conclude that the evolutionary process just disturbs the chromosome ploidy and the sexual determination of parthenogenetic population and that it would be better to consider parthenogenetic H. longicornis as a metapopulation rather than a cryptic species.

Identification and structural-functional analysis of cyclin-dependent kinases of the cattle tick Rhipicephalus (Boophilus) microplus

Cyclin-dependent kinases (CDKs) are a family of serine/threonine kinases essential for cell cycle progression. Herein, we describe the participation of CDKs in the physiology of Rhipicephalus microplus, the southern cattle tick and an important disease vector. Firstly, amino acid sequences homologous with CDKs of other organisms were identified from a R. microplus transcriptome database in silico. The analysis of the deduced amino acid sequences of CDK1 and CDK10 from R. microplus showed that both have caspase-3/7 cleavage motifs despite their differences in motif position and length of encoded proteins. CDK1 has two motifs (DKRGD and SAKDA) located opposite to the ATP binding site while CDK10 has only one motif (SLLDN) for caspase 3–7 near the ATP binding site. Roscovitine (Rosco), a purine derivative that inhibits CDK/cyclin complexes by binding to the catalytic domain of the CDK molecule at the ATP binding site, which prevents the transfer of ATP's γphosphoryl group to the substrate. To determine the effect of Rosco on tick CDKs, BME26 cells derived from R. microplus embryo cells were utilized in vitro inhibition assays. Cell viability decreased in the Rosco-treated groups after 24 hours of incubation in a concentration-dependent manner and this was observed up to 48 hours following incubation. To our knowledge, this is the first report on characterization of a cell cycle protein in arachnids, and the sensitivity of BME26 tick cell line to Rosco treatment suggests that CDKs are potential targets for novel drug design to control tick infestation.

The conserved role of the AKT/GSK3 axis in cell survival and glycogen metabolism in Rhipicephalus (Boophilus) microplus embryo tick cell line BME26

BACKGROUND

Tick embryogenesis is a metabolically intensive process developed under tightly controlled conditions and whose components are poorly understood.

METHODS

In order to characterize the role of AKT (protein kinase B) in glycogen metabolism and cell viability, glycogen determination, identification and cloning of an AKT from Rhipicephalus microplus were carried out, in parallel with experiments using RNA interference (RNAi) and chemical inhibition.

RESULTS

A decrease in glycogen content was observed when AKT was chemically inhibited by 10-DEBC treatment, while GSK3 inhibition by alsterpaullone had an opposing effect. RmAKT ORF is 1584-bp long and encodes a polypeptide chain of 60.1 kDa. Phylogenetic and sequence analyses showed significant differences between vertebrate and tick AKTs. Either AKT or GSK3 knocked down cells showed a 70% reduction in target transcript levels, but decrease in AKT also reduced glycogen content, cell viability and altered cell membrane permeability. However, the GSK3 reduction promoted an increase in glycogen content. Additionally, either GSK3 inhibition or gene silencing had a protective effect on BME26 viability after exposure to ultraviolet radiation. R. microplus AKT and GSK3 were widely expressed during embryo development. Taken together, our data support an antagonistic role for AKT and GSK3, and strongly suggest that such a signaling axis is conserved in tick embryos, with AKT located upstream of GSK3.

GENERAL SIGNIFICANCE

The AKT/GSK3 axis is conserved in tick in a way that integrates glycogen metabolism and cell survival, and exhibits phylogenic differences that could be important for the development of novel control methods.

Inhibition of enzyme activity of Rhipicephalus (Boophilus) microplus triosephosphate isomerase and BME26 cell growth by monoclonal antibodies

In the present work, we produced two monoclonal antibodies (BrBm37 and BrBm38) and tested their action against the triosephosphate isomerase of Rhipicephalus (Boophilus) microplus (RmTIM). These antibodies recognize epitopes on both the native and recombinant forms of the protein. rRmTIM inhibition by BrBm37 was up to 85% whereas that of BrBrm38 was 98%, depending on the antibody-enzyme ratio. RmTIM activity was lower in ovarian, gut, and fat body tissue extracts treated with BrBm37 or BrBm38 mAbs. The proliferation of the embryonic tick cell line (BME26) was inhibited by BrBm37 and BrBm38 mAbs. In summary, the results reveal that it is possible to interfere with the RmTIM function using antibodies, even in intact cells.

Expression patterns of Anaplasma marginale Msp2 variants change in response to growth in cattle, and tick cells versus mammalian cells

Antigenic variation of major surface proteins is considered an immune-evasive maneuver used by pathogens as divergent as bacteria and protozoa. Likewise, major surface protein 2 (Msp2) of the tick-borne pathogen, Anaplasma marginale, is thought to be involved in antigenic variation to evade the mammalian host immune response. However, this dynamic process also works in the tick vector in the absence of immune selection pressure. We examined Msp2 variants expressed during infection of four tick and two mammalian cell-lines to determine if the presence of certain variants correlated with specific host cell types. Anaplasma marginale colonies differed in their development and appearance in each of the cell lines (P<0.001). Using Western blots probed with two Msp2-monospecific and one Msp2-monoclonal antibodies, we detected expression of variants with differences in molecular weight. Immunofluorescence-assay revealed that specific antibodies bound from 25 to 60% of colonies, depending on the host cell-line (P<0.001). Molecular analysis of cloned variant-encoding genes demonstrated expression of different predominant variants in tick (V1) and mammalian (V2) cell-lines. Analysis of the putative secondary structure of the variants revealed a change in structure when A. marginale was transferred from one cell-type to another, suggesting that the expression of particular Msp2 variants depended on the cell-type (tick or mammalian) in which A. marginale developed. Similarly, analysis of the putative secondary structure of over 200 Msp2 variants from ticks, blood samples, and other mammalian cells available in GenBank showed the predominance of a specific structure during infection of a host type (tick versus blood sample), demonstrating that selection of a possible structure also occurred in vivo. The selection of a specific structure in surface proteins may indicate that Msp2 fulfils an important role in infection and adaptation to diverse host systems. Supplemental Abstract in Spanish (File S1) is provided.

The expression pattern of scygonadin during the ontogenesis of Scylla paramamosain predicting its potential role in reproductive immunity

The antimicrobial peptide scygonadin (Scy) was first isolated from the gonad of Scylla serrata and its gene is predominantly expressed in the ejaculatory duct of adult males. Thus, its function was predicted to be associated with reproductive immunity, but this is still unclear and needs further investigation. In our study, the expression pattern of Scy at different developmental stages of both male and female S. paramamosain was investigated, so that the potential function of this peptide could be examined. Using real-time quantitative PCR, Scy mRNA transcripts were demonstrated obviously in the vulnerable embryos and larvae-zoea I but very weakly detected in the larvae-zoea III, megalops and juveniles. The gene expression pattern showed a decreasing trend during the early developmental stages. The Scy gene had low expression in the ejaculatory duct of small and medium crabs (100g and 200g in weight) whose gonads were underdeveloped. However, the level of Scy expression was significantly increased in large crabs (300g in weight), which had normally become sexually mature at this size. It was further observed that the numbers of Scy mRNA transcripts in sexually mature crabs were significantly more abundant than in immature ones. In addition, the Scy gene was significantly expressed in the ejaculatory duct of mature male crabs during the mating period (April and May) and reached their highest expression in May. Using immunohistochemistry, the Scy protein was strongly detected in the testis and seminal vesicle of small crabs. However, in large crabs, Scy protein was intensively present in more tissues than in small crabs, including the ejaculatory duct, posterior ejaculatory duct, gill and muscle of males, and also in the spermatheca, gill and muscle of females. It is also interesting to note that Scy mRNA transcripts were detected in other crab species and showed similar expression pattern to those in S. paramamosain. This study extended our knowledge concerning the antimicrobial peptide scygonadin, which has its function principally in the ejaculatory duct of males but which may also play a role at different developmental stages of S. paramamosain from embryogenesis to maturation, and is also widely distributed in other crabs.

Expression of Heat Shock and Other Stress Response Proteins in Ticks and Cultured Tick Cells in Response to Anaplasma spp. Infection and Heat Shock

Ticks are ectoparasites of animals and humans that serve as vectors of Anaplasma and other pathogens that affect humans and animals worldwide. Ticks and the pathogens that they transmit have coevolved molecular interactions involving genetic traits of both the tick and the pathogen that mediate their development and survival. In this paper, the expression of heat shock proteins (HSPs) and other stress response proteins (SRPs) was characterized in ticks and cultured tick cells by proteomics and transcriptomics analyses in response to Anaplasma spp. infection and heat shock. The results of these studies demonstrated that the stress response was activated in ticks and cultured tick cells after Anaplasma spp. infection and heat shock. However, in the natural vector-pathogen relationship, HSPs and other SRPs were not strongly activated, which likely resulted from tick-pathogen coevolution. These results also demonstrated pathogen- and tick-specific differences in the expression of HSPs and other SRPs in ticks and cultured tick cells infected with Anaplasma spp. and suggested the existence of post-transcriptional mechanisms induced by Anaplasma spp. to control tick response to infection. These results illustrated the complexity of the stress response in ticks and suggested a function for the HSPs and other SRPs during Anaplasma spp. infection.

Structure and mode of action of microplusin, a copper II-chelating antimicrobial peptide from the cattle tick Rhipicephalus (Boophilus) microplus

Microplusin, a Rhipicephalus (Boophilus) microplus antimicrobial peptide (AMP) is the first fully characterized member of a new family of cysteine-rich AMPs with histidine-rich regions at the N and C termini. In the tick, microplusin belongs to the arsenal of innate defense molecules active against bacteria and fungi. Here we describe the NMR solution structure of microplusin and demonstrate that the protein binds copper II and iron II. Structured as a single alpha-helical globular domain, microplusin consists of five alpha-helices: alpha1 (residues Gly-9 to Arg-21), alpha2 (residues Glu-27 to Asn-40), alpha3 (residues Arg-44 to Thr-54), alpha4 (residues Leu-57 to Tyr-64), and alpha5 (residues Asn-67 to Cys-80). The N and C termini are disordered. This structure is unlike any other AMP structures described to date. We also used NMR spectroscopy to map the copper binding region on microplusin. Finally, using the Gram-positive bacteria Micrococcus luteus as a model, we studied of mode of action of microplusin. Microplusin has a bacteriostatic effect and does not permeabilize the bacterial membrane. Because microplusin binds metals, we tested whether this was related to its antimicrobial activity. We found that the bacteriostatic effect of microplusin was fully reversed by supplementation of culture media with copper II but not iron II. We also demonstrated that microplusin affects M. luteus respiration, a copper-dependent process. Thus, we conclude that the antibacterial effect of microplusin is due to its ability to bind and sequester copper II.

Functional genomics and evolution of tick-Anaplasma interactions and vaccine development

The genus Anaplasma (Rickettsiales: Anaplasmataceae) includes several tick-transmitted pathogens that impact veterinary and human health. Tick-borne pathogens cycle between tick vectors and vertebrate hosts and their interaction is mediated by molecular mechanisms at the tick-pathogen interface. These mechanisms have evolved characteristics that involve traits from both the tick vector and the pathogen to insure their mutual survival. Herein, we review the information obtained from functional genomics and genetic studies to characterize the tick-Anaplasma interface and evolution of A. marginale and A. phagocytophilum. Anaplasma and tick genes and proteins involved in tick-pathogen interactions were characterized. The results of these studies demonstrated that common and Anaplasma species-specific molecular mechanism occur by which pathogen and tick cell gene expression mediates or limits Anaplasma developmental cycle and trafficking through ticks. These results have advanced our understanding of the biology of tick-Anaplasma interactions and have opened new avenues for the development of improved methods for the control of tick infestations and the transmission of tick-borne pathogens.

Identification and characterization of antimicrobial peptide, defensin, in the taiga tick, Ixodes persulcatus

Ixodes persulcatus is the primary vector for human tick-borne diseases in Japan. A cDNA library was constructed from whole body homogenates of fed nymphs of I. persulcatus. From this library, one cDNA encoding defensin-like antimicrobial peptide was identified. The amino-acid sequence showed high similarity to those of the defensins of other ticks and arthropods. I. persulcatus defensin mRNA transcripts were detected at all life cycle stages of fed ticks and found to be predominantly expressed in the midguts of adult female ticks, but not in the salivary glands, a finding corroborated by Western blotting analysis. To investigate the function of I. persulcatus defensin, we examined its antibacterial activity by evaluation of growth of several bacterial strains in the presence of the synthetic peptide. The defensin from I. persulcatus markedly inhibited the growth of Gram-positive bacteria including Staphylococcus aureus, Bacillus subtilis and Corynebacterium renale, but not Gram-negative bacteria except Escherichia coli O157. In conclusion, these results suggest that I. persulcatus defensin may be playing a significant role in the defence against microbes from bloodmeals.

Antimicrobial activity in the tick Rhipicephalus (Boophilus) microplus eggs: Cellular localization and temporal expression of microplusin during oogenesis and embryogenesis

Arthropods display different mechanisms to protect themselves against infections, among which antimicrobial peptides (AMPs) play an important role, acting directly against invader pathogens. We have detected several factors with inhibitory activity against Candida albicans and Micrococcus luteus on the surface and in homogenate of eggs of the tick Rhipicephalus (Boophilus) microplus. One of the anti-M. luteus factors of the egg homogenate was isolated to homogeneity. Analysis by electrospray mass spectrometry (ESI-MS) revealed that it corresponds to microplusin, an AMP previously isolated from the cell-free hemolymph of R. (B.) microplus. Reverse transcription (RT) quantitative polymerase chain reactions (qPCR) showed that the levels of microplusin mRNA gradually increase along ovary development, reaching an impressive highest value three days after the adult females have dropped from the calf and start oviposition. Interestingly, the level of microplusin mRNA is very low in recently laid eggs. An enhance of microplusin gene expression in eggs is observed only nine days after the onset of oviposition, achieving the highest level just before the larva hatching, when the level of expression decreases once again. Fluorescence microscopy analysis using an anti-microplusin serum revealed that microplusin is present among yolk granules of oocytes as well as in the connecting tube of ovaries. These results, together to our previous data, suggest that microplusin may be involved not only in protection of adult female hemocele, but also in protection of the female reproductive tract and embryos, what points this AMP as a considerable target for development of new methods to control R. (B.) microplus as well as the vector-borne pathogens.

Evidence of a tick RNAi pathway by comparative genomics and reverse genetics screen of targets with known loss-of-function phenotypes in Drosophila

Background

The Arthropods are a diverse group of organisms including Chelicerata (ticks, mites, spiders), Crustacea (crabs, shrimps), and Insecta (flies, mosquitoes, beetles, silkworm). The cattle tick, Rhipicephalus (Boophilus) microplus, is an economically significant ectoparasite of cattle affecting cattle industries world wide. With the availability of sequence reads from the first Chelicerate genome project (the Ixodes scapularis tick) and extensive R. microplus ESTs, we investigated evidence for putative RNAi proteins and studied RNA interference in tick cell cultures and adult female ticks targeting Drosophila homologues with known cell viability phenotype.

Results

We screened 13,643 R. microplus ESTs and I. scapularis genome reads to identify RNAi related proteins in ticks. Our analysis identified 31 RNAi proteins including a putative tick Dicer, RISC associated (Ago-2 and FMRp), RNA dependent RNA polymerase (EGO-1) and 23 homologues implicated in dsRNA uptake and processing. We selected 10 R. microplus ESTs with >80% similarity to D. melanogaster proteins associated with cell viability for RNAi functional screens in both BME26 R. microplus embryonic cells and female ticks in vivo. Only genes associated with proteasomes had an effect on cell viability in vitro. In vivo RNAi showed that 9 genes had significant effects either causing lethality or impairing egg laying.

Conclusion

We have identified key RNAi-related proteins in ticks and along with our loss-of-function studies support a functional RNAi pathway in R. microplus. Our preliminary studies indicate that tick RNAi pathways may differ from that of other Arthropods such as insects.

Exogenous insulin stimulates glycogen accumulation in Rhipicephalus (Boophilus) microplus embryo cell line BME26 via PI3K/AKT pathway

Ticks are obligatory blood-feeding arthropods and important vectors of both human and animal disease agents. Besides its metabolic role, insulin signaling pathway (ISP) is widely described as crucial for vertebrate and invertebrate embryogenesis, development and cell survival. In such cascade, Phosphatidylinositol 3-OH Kinase (PI3K) is hierarchically located upstream Protein Kinase B (PKB). To study the insulin-triggered pathway and its possible roles during embryogenesis we used a culture of embryonic Rhipicephalus microplus cells (BME26). Exogenous insulin elevated cell glycogen content in the absence of fetal calf serum (FCS) when compared to cells without treatment. Moreover, in the presence of PI3K inhibitors (Wortmannin or LY294002) these effects were blocked. We observed an increase in the relative expression level of PI3K's regulatory subunit (p85), as determined by qRT-PCR. In the presence of PI3K inhibitors these effects on transcription were also reversed. Additionally, treatment with Wortmannin increased the expression level of the insulin-regulated downstream target glycogen synthase kinase 3 beta (GSK3beta). The p85 subunit showed elevated transcription levels in ovaries from fully engorged females, but was differentially expressed during tick embryogenesis. These results strongly suggest the presence of an insulin responsive machinery in BME26 cells, and its correlation with carbohydrate/glycogen metabolism also during embryogenesis.

Propagation of a Brazilian isolate of Anaplasma marginale with appendage in a tick cell line (BME26) derived from Rhipicephalus (Boophilus) microplus

Anaplasma marginale is a tick-borne pathogen of cattle responsible for the disease anaplasmosis. Data suggest that Rhipicephalus (Boophilus) microplus and R. annulatus may be the major tick vectors of A. marginale in tropical and subtropical regions of the world. In this work we demonstrated the first infection and propagation of a Brazilian isolate of A. marginale (UFMG1) in the BME26 cell line derived originally from embryos of R. (Boophilus) microplus. The establishment of A. marginale infection in a cell line derived from R. (Boophilus) microplus is relevant for studying the A. marginale/tick interface.

Transgene expression and silencing in a tick cell line: A model system for functional tick genomics

The genome project of the black legged tick, Ixodes scapularis, provides sequence data for testing gene function and regulation in this important pathogen vector. We tested Sleeping Beauty (SB), a Tc1/mariner group transposable element, and cationic lipid-based transfection reagents for delivery and genomic integration of transgenes into I. scapularis cell line ISE6. Plasmid DNA and dsRNA were effectively transfected into ISE6 cells and they were successfully transformed to express a red fluorescent protein (DsRed2) and a selectable marker, neomycin phosphotransferase (NEO). Frequency of transformation was estimated as 1 transformant per 5000-10,000 cells and cultures were incubated for 2-3 months in medium containing the neomycin analog G418 in order to isolate transformants. Genomic integration of the DsRed2 transgene was confirmed by inverse PCR and sequencing that demonstrated a TA nucleotide pair inserted between SB inverted/direct repeat sequences and tick genomic sequences, indicating that insertion of the DsRed2 gene into the tick cell genome occurred through the activity of SB transposase. RNAi using dsRNA transcribed from the DsRed2 gene silenced expression of red fluorescent protein in transformed ISE6 cells. SB transposition in cell line ISE6 provides an effective means to explore the functional genomics of I. scapularis.