Ultrastructural changes of the midgut epithelial cells in feeding and moulting nymphs of the tick Haemaphysalis longicornis

A fluorescently-tagged tick kinin neuropeptide triggers peristalsis and labels tick midgut muscles

Ticks are blood-feeding arthropods that require heme for their successful reproduction. During feeding they also acquire pathogens that are subsequently transmitted to humans, wildlife and/or livestock. Understanding the regulation of tick midgut is important for blood meal digestion, heme and nutrient absorption processes and for aspects of pathogen biology in the host. We previously demonstrated the activity of tick kinins on the cognate G protein-coupled receptor. Herein we uncovered the physiological role of the kinin receptor in the tick midgut. A fluorescently-labeled kinin peptide with the endogenous kinin 8 sequence (TMR-RK8), identical in the ticks Rhipicephalus microplus and R. sanguineus, activated and labeled the recombinant R. microplus receptor expressed in CHO-K1 cells. When applied to the live midgut the TMR-RK8 labeled the kinin receptor in muscles while the labeled peptide with the scrambled-sequence of kinin 8 (TMR-Scrambled) did not. The unlabeled kinin 8 peptide competed TMR-RK8, decreasing confocal microscopy signal intensity, indicating TMR-RK8 specificity to muscles. TMR-RK8 was active, inducing significant midgut peristalsis that was video-recorded and evaluated with video tracking software. The TMR-Scrambled peptide used as a negative control did not elicit peristalsis. The myotropic function of kinins in eliciting tick midgut peristalsis was established.

Cytoarchitecture of ex vivo midgut cultures of unfed Ixodes scapularis infected with a tick-borne flavivirus

A bite from an infected tick is the primary means of transmission for tick-borne flaviviruses (TBFV). Ticks ingest the virus while feeding on infected blood. The traditional view is that the virus first replicates in and transits the tick midgut prior to dissemination to other organs, including salivary glands. Thus, understanding TBFV infection in the tick midgut is a key first step in identifying potential countermeasures against infection. Ex vivo midgut cultures prepared from unfed adult female Ixodes scapularis ticks were viable and remained morphologically intact for more than 8 days. The midgut consisted of two clearly defined cell layers separated by a basement membrane: an exterior network of smooth muscle cells and an internal epithelium composed of digestive generative cells. The smooth muscle cells were arranged in a stellate circumferential pattern spaced at regular intervals along the long axis of midgut diverticula. When the cultures were infected with the TBFV Langat virus (LGTV), virus production increased by two logs with a peak at 96 hours post-infection. Infected cells were readily identified by immunofluorescence staining for the viral envelope protein, nonstructural protein 3 (NS3) and dsRNA. Microscopy of the stained cultures suggested that generative cells were the primary target for virus infection in the midgut. Infected cells exhibited an expansion of membranes derived from the endoplasmic reticulum; a finding consistent with TBFV infected cell cultures. Electron microscopy of infected cultures revealed virus particles in the basolateral region between epithelial cells. These results demonstrated LGTV replication in midgut generative cells of artificially infected, ex vivo cultures of unfed adult female I. scapularis ticks.

Evaluation of cytotoxic effects of amitraz and fipronil on digestive, reproductive and neural processes of engorged Rhipicephalus microplus (Acari: Ixodidae) female

Fipronil and amitraz are potentially toxic compounds used for controlling ticks infesting pet and livestock. The use of fipronil on large animals was limited because of its high costs while amitraz is still persisting in the market since its introduction over four decades ago. Though resistance in ticks against these pesticides has been reported worldwide since 2000, the toxicity of these chemicals at cellular level in ticks is still poorly understood. The present study aimed to examine the gross and cellular impact of fipronil and amitraz on the gut, ovaries and synganglion of engorged Rhipicephalus microplus females. Fipronil and amitraz treated tick groups showed formation of a large number of vacuoles of different size throughout the cytoplasm of generative cells whereas sessile, residual and detached digestive cells were very low in numbers. The treatment of ticks resulted in the formation of vacuolations at periphery of all oocytes. Ultra-thin sections of the synganglion revealed severe rupture of neural lamella and perineurium with apoptosis of neural cells after fipronil treatment whereas in the amitraz treated ticks, severe destruction of neuropile region and extensive vacuolation of type I and II cells of cortical region as compared to the unexposed ticks were noted.

Recovery of Partially Engorged Haemaphysalis longicornis (Acari: Ixodidae) Ticks from Active Surveillance

The invasive Asian longhorned tick, Haemaphysalis longicornis, has rapidly spread across the northeastern United States and is associated with pathogens of public health and veterinary concern. Despite its importance in pathogen dynamics, H. longicornis blood-feeding behavior in nature, specifically the likelihood of interrupted feeding, remains poorly documented. Here, we report the recovery of partially engorged, questing H. longicornis from active tick surveillance in Pennsylvania. Significantly more engorged H. longicornis nymphs (1.54%) and adults (3.07%) were recovered compared to Ixodes scapularis nymphs (0.22%) and adults (zero). Mean Scutal Index difference between unengorged and engorged nymph specimens was 0.65 and 0.42 for I. scapularis and H. longicornis, respectively, suggesting the questing, engorged H. longicornis also engorged to a comparatively lesser extent. These data are among the first to document recovery of engorged, host-seeking H. longicornis ticks and provide initial evidence for interrupted feeding and repeated successful questing events bearing implications for pathogen transmission and warranting consideration in vector dynamics models.

Exposure of Rhipicephalus sanguineus sensu lato Latreille, 1806 (Acari: Ixodidae) to hexane extract of Acmella oleracea (Jambu): semi-engorged and engorged ticks

The present study analyzed the efficacy of hexane extract of Acmella oleracea against Rhipicephalus sanguineus sensu lato. After exposure of R. sanguineus s. l. female ticks to 14 different concentrations of the hexane extract of A. oleracea, the LC₅₀ was established as 18.135 mg/mL (limits: 16.251-22.675). The effects of the extract were more significant in the ovary of the semi-engorged females, that presented damages in most oocytes. Since such changes would not be repaired, the oocytes could not advance to further stages of development (I-V), thereby causing the inhibition of ovary development, interruption of vitellogenesis, oocyte death and, consequently, infertility. The semi-engorged females also presented extensive damages in the midgut cells, which would prevent (totally or partially) these cells from functioning properly (blood intake and release of nutrients), impairing the ectoparasite nutrition and the viability of the individual. Thus, the hexane extract of A. oleracea can be considered as a promising alternative to chemical control of pests of medical and veterinary importance, due to its efficient acaricidal activity and lesser environmental impact, when used against female ticks in the middle feeding stage.

Pictorial dissection guide and internal anatomy of the cattle tick, Rhipicephalus (Boophilus) microplus (Canestrini)

Ticks are pests and vectors of diseases that are of public health and veterinary importance. The cattle tick, Rhipicephalus microplus (Canestrini, 1888), is one of the most studied tick species because of its impact on livestock health and production in the tropical and subtropical parts of the world, costing the cattle industry billions annually. Control methods have evolved throughout the years but so has R. microplus. Reliance upon chemical control has created a consistent need to develop new technologies to overcome the pesticide resistance that occurs as the ticks adapt. In order to utilize the more advanced tools such as RNAi or Crispr/Cas9 systems, tick tissues need to be isolated and manipulated. Unfortunately, there are a limited number of dissection guides available providing a detailed view of tick internal anatomy. This manual includes photomicrographs to guide the dissection of R. microplus adults, male and female. Topography and anatomical differences between the internal organs of unfed and gravid adult females are described. We were able to locate the crucial tissues for cattle tick physiology and lay out spatial and temporal guidelines for their identification and dissection. Examples of how this information can be used at the nexus between organismal and molecular research to innovate tick control technologies is discussed.

Cytotoxic Effects of Extract of Acmella oleracea in the Ovaries and Midgut of Rhipicephalus sanguineus Latreille, 1806 (Acari: Ixodidae) Female Ticks

The present study investigated the effects of different concentrations of Acmella oleracea extract on the germinative cells and digestive processes of semi-engorged Rhipicephalus sanguineus females. For this experiment, 150 ticks were divided into five groups (30 individuals each). The animals were immersed for 5 min in different concentrations of the extract, distilled water, or ethanol 50%/DMSO 1%, dried, and kept in biological oxygen demand incubator for 7 days. The alterations were associated with the size of germinative cells and yolk granules; presence, size, and location of vacuoles in the cytoplasm of germinative cells; nuclear modifications in the germinative cells; damages to the nucleus and cytoplasm of the midgut generative cells; size of digestive cells; number of captured blood elements; accumulated digestive residues and digestive vacuoles in the digestive cells cytoplasm; and the number and distribution of proteins and polysaccharides in all the cells of both organs. The concentrations used in this study prevented an efficient and complete blood digestion by the midgut epithelial cells of the treated animals, resulting in the absence of the necessary nutrients to maintain the physiological events in the ectoparasites. In advanced stages, This can lead the ectoparasite to death. The germinative cells were highly impaired and probably not able to advance developmental stages (I–V) or complete vitellogenesis to be released during ovulation, which would prevent the females from originating a new individual. Thus, it can be concluded that the effects of A. oleracea are similar to those caused by chemical products widely recognized as effective to control ticks.

Dinotefuran-induced morphophysiological changes in semi-engorged females Rhipicephalus sanguineus Latreille, 1806 (Acari: Ixodidae) ticks: Ultra-structural evaluation

The present study demonstrated the effects of dinotefuran (active ingredient of the acaricide Protetor Pet^®) on the ovary and midgut cells of semi engorged R. sanguineus females exposed to different concentrations of this chemical. For this, 120 semi-engorged females were divided into four treatment groups with 30 individuals each: group I or control (distilled water), group II (5000ppm), groups III (6250ppm) and group IV (8334ppm of dinotefuran). All the ticks were immersed in the different concentrations of dinotefuran or in distilled water for 5min and then dried and kept in BOD incubator for 7days. The results showed alterations mainly regarding the damaged cell structures, such as yolk granules, organelles and the plasma membrane of the germ cells. In addition, structures related with defense mechanisms were found, such as vacuoles, cytoskeletal filaments, and myelin figures in the germ cells. Damages in the generative cells of the midgut, alterations in the size of digestive cells, the number of endosomes, digestive vacuoles, digestive residues, lipid drops and organelles in the cytoplasm of the digestive cells and the presence of microvilli in the plasma membrane of these cells also demonstrate the progressive damages caused by the action of dinotefuran in the midgut and germ cells of R. sanguineus semi-engorged females. The concentrations applied partially impaired the digestive processes; and, without proper nutrition, all the ectoparasite's physiologic events are prevented from occurring, leading the individual to death. The germ cells were also damaged, and probably would not be able to advance in their development (I-V) and complete the vitellogenesis, which would affect the fertility of the female and consequently impede the formation of a new individual.

Dinotefuran-induced morphophysiological changes in the ovaries and midgut of semi-engorged females Rhipicephalus sanguineus Latreille, 1806 (Acari: Ixodidae) ticks

The present study demonstrated the effects of dinotefuran (active compound of the Protetor Pet® acaricide) in germ cells and the digestive processes of semi-engorged females of R. sanguineus exposed to different concentrations of the chemical. For this purpose, 120 semi-engorged females were divided into four treatment groups with 30 individuals each: group I or control (distilled water), group II (5000 ppm), group III (6250 ppm), and group IV (8334 ppm of dinotefuran). All ticks were immersed in different concentrations of dinotefuran or in distilled water for 5 min and then were dried and stored in biological oxygen demand (BOD) incubator for 7 days. The results show the action of this compound, exhibiting morphohistologic and histochemical changes in the oocytes and the midgut cells of individuals of different groups, which were compared with those of group I (control). The alterations occurred mainly in relation to the size of the germ cells and yolk granules; presence, quantity, size, and location of vacuoles found in the cytoplasm of these germ cells; the damage occurred in the generative cells of the midgut; the size of the digestive cells; the quantity of blood elements captured, accumulated digestive wastes and digestive vacuoles found in the cytoplasm of the digestive cells of the midgut, as well as the amount and distribution of proteins, polysaccharides, lipids of all cells in both organs. So, it has demonstrated the effectiveness of dinotefuran in the reduction of fertility and digestive processes of semi-engorged females of R. sanguineus, data that points the possibility of employing this chemical to control these ectoparasites.

Fluazuron-induced morphological changes in Rhipicephalus sanguineus Latreille, 1806 (Acari: Ixodidae) nymphs: An ultra-structural evaluation of the cuticle formation and digestive processes

Rhipicephalus sanguineus is a species of tick which is widely distributed in America, Africa and Australia and is probably the most prevalent among all the other ixodid tick species. The present study demonstrated the effects of the arthropod growth regulator fluazuron (Acatak(®)), in the formation of the integument and the digestive processes of R. sanguineus nymphs fed on rabbits treated with different doses of this chemical acaricide. For this, three different doses of fluazuron (20mg/kg, 40mg/kg and 80mg/kg) were applied "pour on" to the hosts divided into three different treated-groups (II, III, IV) of three animals each. A fourth group (I) of rabbits (n=3) was given distilled water as control. On the first day after treatment (24h), the hosts were artificially infested with R. sanguineus nymphs. After full engorgement (7 days), the nymphs were removed and placed on labeled Petri dishes and kept in BOD incubator for 7 days. The engorged nymphs were then taken to ultra-structural analysis. Results revealed the following main ultra-structural changes in the nymphs integument and midgut of the different treated groups (II, III, IV): cuticle disorganization and the absence of subdivisions, damages in the integument epithelial cells, size of digestive cells, amount of endosomes, autophagic and digestive vacuoles, accumulated digestive residues, lipid droplets and organelles found in the digestive cells' cytoplasm, as well as the presence of microvilli in their plasma membranes. It is concluded that fluazuron may act on the integument and midgut cells of R. sanguineus engorged nymphs by impairing the synthesis of the new cuticle and the digestive processes (absorption of the blood ingested from the host, digestion - hemolysis, formation of digestive residues and release of nutrients to be converted into lipid, as well as for the synthesis of structural protein), which interfere in the development of nymphs, being able to prevent the emergence of adults after periodical ecdysis. These data indicate the possibility to use this arthropod growth regulator (AGR) in the control of R. sanguineus, at least in the nymphal stage of its biological cycle.

A hemocyte-derived Kunitz-BPTI-type chymotrypsin inhibitor, HlChI, from the ixodid tick Haemaphysalis longicornis, plays regulatory functions in tick blood-feeding processes

Inhibitors of proteases play key roles in the biological processes of vertebrate and invertebrate animals, including arthropod parasites. Here, we describe a cDNA that encodes a functionally active chymotrypsin inhibitor of the BPTI/Kunitz family of serine protease inhibitors from the hemocytes of the ixodid tick, Haemaphysalis longicornis, herein called HlChI. HlChI sequence is evolutionarily conserved and contains six cysteine residues and three disulfide bonds with a calculated molecular weight of 9.1 kDa. HlChI-specific mRNA was expressed in all developmental stages of ticks and the expression was up-regulated by host's blood-feeding processes. Endogenous HlChI was localized mainly in the hemocytes. HlChI potently inhibited bovine pancreatic α-chymotrypsin for hydrolyzing the fluorogenic substrate (IC(50) 8.32 nM, K(d) 5.35 ± 1.01 nM) and bovine casein digestion. However, HlChI weakly inhibited bovine pancreatic trypsin and could not affect the porcine elastase activity, suggesting its narrow specificity to chymotrypsin. HlChI was stable over the pH range 2-11 and heating up to 70 °C at pH 8. HlChI was highly stable to 8 M urea and 2% SDS at pH 8.0, when treated for 24 h at 37 °C. However, 0.2 M 2-mercaptoethanol caused complete but reversible inactivation of HlChI. Knockdown of HlChI gene by RNA interference (RNAi) caused death of the feeding ticks, failure of ticks to engorge and significantly reduced body weight gain. RNAi also resulted in significantly decreased egg conversion ratio and fecundity. These results suggest that HlChI is a chymotrypsin-specific inhibitor with high stability and may play regulatory functions in host's blood-feeding processes and tick reproduction.

Morphology of the midgut of Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) adult ticks in different feeding stages

The intestinal epithelial cells of ticks are fundamental for their full feeding and reproductive success, besides being considered important sites for the development of pathogens. Rhipicephalus sanguineus ticks are known for their great medical and veterinary importance, and for this reason, the knowledge of their intestinal morphology may provide relevant subsidies for the control of these animals, either by direct acaricidal action over these cells or by the production of vaccines. Therefore, this study aimed to describe the midgut morphology of male and female R. sanguineus ticks in different feeding stages, by means of histological analysis. Significant differences were observed between the genders, and such alterations may refer mainly to the distinct demands for nutrients, much higher in females, which need to develop and carry out the egg-laying process. In general, the midgut is coated by a thin muscle layer and presents a pseudostratified epithelium, in which two basic types of cells can be observed, connected to a basal membrane-generative or stem and digestive cells. The latter was classified as follows: residual, deriving from the phase anterior to ecdysis; pinocytic, with vesicles containing liquid or pre-digested components of blood; phagocytic, with entire cells or remnants of nuclear material inside cytoplasmic vesicles; and mature, free in the lumen. Digestion is presumably intracellular and asynchronous and corresponds to a process which starts with the differentiation of generative cells into pinocytic digestive cells, which subsequently start to phagocytize intact blood cells and finally detach from the epithelium, being eliminated with feces.

Fluazuron-induced morphophysiological changes in the cuticle formation and midgut of Rhipicephalus sanguineus Latreille, 1806 (Acari: Ixodidae) nymphs

The present study demonstrated the effects of the arthropod growth regulator, fluazuron (Acatak®), in the formation of the integument and digestive processes of Rhipicephalus sanguineus nymphs fed on rabbits treated with different doses of this chemical acaricide. For this, three different doses of fluazuron (20, 40, or 80 mg/kg) were applied "pour on" to the hosts (groups II, III, and IV), as well as distilled water to the control group. On the first day after treatment (24 h), the hosts were artificially infested with R. sanguineus nymphs. After full engorgement (7 days), the nymphs were removed, placed on labeled Petri dishes, and kept in biochemical oxygen demand incubator for 7 days. The engorged nymphs were then taken for morphological, histochemical, and histological analyses. The results showed the occurrence of cytological, morphohistological, and histochemical alterations in the integument and midgut of nymphs from all the different treated groups. These alterations occurred at cuticular level in the subdivisions of the cuticle, related to the size of the digestive cells, amount of accumulated blood elements, and digestive residues, as well as the presence of vacuoles in the cytoplasm of the digestive cells. Thus, this study demonstrated that fluazuron acts on the integument and midgut cells of R. sanguineus nymphs fed on treated rabbits and pointed out the possibility of the use of this chemical-which is more specific, less toxic, and less harmful to the environment and nontarget organisms-in the control of R. sanguineus, at least in the nymphal stage of its biological cycle.

RNAi of the translation inhibition gene 4E-BP identified from the hard tick, Haemaphysalis longicornis, affects lipid storage during the off-host starvation period of ticks

4E-BP, an eIF4E-binding protein, is well known as a cap-dependent translation inhibitor. Here, the 4E-BP homolog, Hl4E-BP, was isolated and identified from the hard tick Haemaphysalis longicornis. Hl4E-BP transcripts were ubiquitously expressed in the active stages, including the larvae, nymphs, and female adults, and the transcription levels were found to be higher in unfed than engorged ticks. In contrast, the expression levels of non-phosphorylated Hl4E-BP, which is a 13.4-kDa protein detected by the anti-recombinant Hl4E-BP antibody, were the highest in engorged ticks and significantly decreased progressively during the unfed starvation period of ticks. The functional role of Hl4E-BP as a metabolic brake was verified by histochemical observations on the lipid storage in midguts and fat bodies during the starvation period using ticks injected with dsHl4E-BP. The results indicate that Hl4E-BP is highly relevant to the lipid storage of ticks during the non-feeding starvation period. Our results suggest, for the first time, that Hl4E-BP may have a crucial role in the starvation resistance of ticks in an off-host condition via lipid metabolism control, although it was unclear whether Hl4E-BP might be involved in lipid synthesis regulation and/or lipid consumption inhibition.

Boophilus microplus cathepsin L-like (BmCL1) cysteine protease: specificity study using a peptide phage display library

The tick Rhipicephalus (Boophilus) microplus is one of the most important bovine ectoparasites, a disease vector responsible for losses in meat and milk productions. A cysteine protease similar to cathepsin L, named BmCL1, was previously identified in R. microplus gut, suggesting a role of the enzyme in meal digestion. In this work, BmCL1 was successfully expressed in Pichia pastoris system, yielding 54.8 mg/L of culture and its activity was analyzed by synthetic substrates and against a R. microplus cysteine protease inhibitor, Bmcystatin. After rBmCl1 biochemical characterization it was used in a selection of a peptide phage library to determine rBmCL1 substrate preference. Obtained sequenced clones showed that rBmCL1 has preference for Leu or Arg at P(1) position. The preference for Leu at position P(1) and the activation of BmCL1 after a Leu amino acid residue suggest possible self activation.

Developmental stage- and organ-specific expression profiles of asparaginyl endopeptidases/legumains in the ixodid tick Haemaphysalis longicornis

We previously identified two cDNAs from the midgut of adult Haemaphysalis longicornis that encode asparaginyl endopeptidases/legumains, HlLgm and HlLgm2. Functionally, both recombinant HlLgm and HlLgm2 efficiently digested blood proteins, haemoglobin and bovine serum albumin. Here, we investigated the expression profiles of legumain genes in the developmental stages in the life cycle of H. longicornis and in different tissues of adult ticks. Both HlLgm and HlLgm2 were well expressed in larvae, nymphs and adults. Legumain transcripts were expressed specifically in the midgut and were localized in some digestive vacuoles of gut epithelial cells. Furthermore, expression of either transcript was up-regulated by blood feeding in larvae and nymphs, suggesting the important roles of legumains in blood feeding and blood-meal digestion in ticks.

A set of serine proteinase paralogs are required for blood-digestion in the ixodid tick Haemaphysalis longicornis

We present evidence demonstrating that genes encoding enzymes essential for successful blood-feeding are differentially induced in the midgut of the hard tick Haemaphysalis longicornis. Three serine proteinase genes (HlSP, HlSP2 and HlSP3) isolated from H. longicornis midgut exhibit protein sequence similarity with other trypsin-like serine proteinases reported from arthropods and vertebrate animal species. The endogenous enzymes were mainly detected in the midgut epithelial cells and in the lumen of an adult tick. The recombinant enzymes expressed in Escherichia coli efficiently hydrolyzed synthetic substrates specific for serine proteinases over a broad range of pH and temperature values. Notably, the transcript levels of HlSP2 and HlSP3 were detected to significantly increase at 96 h post infestation, while the transcript of HlSP was induced in the earlier stage of blood-feeding. Further, silencing of HlSP, HlSP2 and HlSP3 genes by RNA interference led to a significant reductions in the engorged tick body weight, suggesting synergetic roles of these serine proteinases in blood-feeding and digestion.

A cysteine protease is critical for Babesia spp. transmission in Haemaphysalis ticks

Vector ticks possess a unique system that enables them to digest large amounts of host blood and to transmit various animal and human pathogens, suggesting the existence of evolutionally acquired proteolytic mechanisms. We report here the molecular and reverse genetic characterization of a multifunctional cysteine protease, longipain, from the babesial parasite vector tick Haemaphysalis longicornis. Longipain shares structural similarity with papain-family cysteine proteases obtained from invertebrates and vertebrates. Endogenous longipain was mainly expressed in the midgut epithelium and was specifically localized at lysosomal vacuoles and possibly released into the lumen. Its expression was up-regulated by host blood feeding. Enzymatic functional assays using in vitro and in vivo substrates revealed that longipain hydrolysis occurs over a broad range of pH and temperature. Haemoparasiticidal assays showed that longipain dose-dependently killed tick-borne Babesia parasites, and its babesiacidal effect occurred via specific adherence to the parasite membranes. Disruption of endogenous longipain by RNA interference revealed that longipain is involved in the digestion of the host blood meal. In addition, the knockdown ticks contained an increased number of parasites, suggesting that longipain exerts a killing effect against the midgut-stage Babesia parasites in ticks. Our results suggest that longipain is essential for tick survival, and may have a role in controlling the transmission of tick-transmittable Babesia parasites.

Ticks are important ectoparasites among the blood-feeding arthropods and serve as vectors of many deadly diseases of humans and animals. Of tick-transmitted pathogens, Babesia, an intracellular haemoprotozoan parasite causing a malaria-like disease, called babesiosis, gain increasing interest due to its zoonotic significance. When vector ticks acquire the protozoa via blood-meals, they invade midgut and undergo several developmental stages prior to exit through salivary glands. It has long been conceived that midguts of these ticks evolve diverse innate immune mechanisms and perform blood digestion critical for tick survival. A cysteine proteinase, longipain, was identified from the three-host tick Haemaphysalis longicornis, which shows potent parasiticidal activity. Longipain is localized in midgut epithelium and its expression is induced by blood feeding. This protein is passively secreted into midgut lumen where it exerts enzymatic degradation of blood-meals. A series of experiments unveil that longipain-knockdown ticks when fed on Babesia-infected dog, exhibited a significantly increased numbers of parasites compared with controls. Longipain has shown to interact on the surface of Babesia parasites in vitro and in vivo, and is thought to mediate direct killing of the parasites, suggesting that longipain may be a potential chemotherapeutic target against babesiosis and ticks themselves.

HlLgm2, a member of asparaginyl endopeptidases/legumains in the midgut of the ixodid tick Haemaphysalis longicornis, is involved in blood-meal digestion

Here we describe a cDNA encoding the second asparaginyl endopeptidase/legumain (HlLgm2) from the midgut of the ixodid tick Haemaphysalis longicornis. Endogenous HlLgm2 was expressed in all the developmental stages of the tick, localized mainly in the midgut epithelium and was up-regulated by the host blood-feeding process, as demonstrated by immunoblotting and immunohistochemistry. RT-PCR and real-time PCR showed that the HlLgm2 gene was expressed at a lower level during all phases of blood-feeding than our previously characterized legumain (HlLgm) gene from the same tick. More strikingly, there was no expression of HlLgm2 mRNA beyond 96 h of blood-feeding, while HlLgm mRNA expression continued until full engorgement. Escherichia coli-expressed recombinant HlLgm2 (rHlLgm2) efficiently hydrolysed the legumain-specific synthetic substrate. rHlLgm2 activity was inhibited by iodoacetamide and N-ethylmaleimide and also by Fe(2+), Cu(2+), Co(2+) and Ni(2+). rHlLgm2 digested bovine haemoglobin and exhibited strict specificity for the asparaginyl bonds on the carboxy-terminal side of a peptide, as demonstrated by internal amino acid sequence analysis of the cleaved bovine serum albumin products. Our results suggest that HlLgm2, together with HlLgm, plays a pivotal role in host blood-meal digestion process.

Characterization of asparaginyl endopeptidase, legumain induced by blood feeding in the ixodid tick Haemaphysalis longicornis

We characterize here a cDNA from the ixodid tick Haemaphysalis longicornis, which encodes an asparaginyl endopeptidase, legumain (HlLgm), that was present as a functional molecule in the midgut of this tick. Endogenous HlLgm was detected as a 38-kDa antigen in H. longicornis extracts and was seen throughout all developmental stages. Endogenous HlLgm was mainly localized in the midgut epithelium by immunohistochemistry, and was shown to be up-regulated by the host blood-feeding process. Recombinant HlLgm (rHlLgm) produced in Escherichia coli was shown to hydrolyze the synthetic substrate Z-Ala-Ala-Asn-MCA at the rate of 6.42x10(-4)mumol/min/mg protein. Its activity was inhibited by the thiol blocking reagents iodoacetamide and N-ethylmaleimide. The enzyme was shown to possess a unique feature of having an autocatalyzed cleavage at asparagines(364-365) at the C-terminus of both endogenous HlLgm and rHlLgm. rHlLgm degraded bovine hemoglobin and bovine serum albumin (BSA) showing its strict specificity for hydrolysis of the peptide on the carboxyl side of the asparagines, as demonstrated by internal amino acid sequence analysis of proteolytic product of BSA cleavage. These results suggest that HlLgm plays an important role in host blood-meal digestion and may be critical for the final process of digestion of blood components.

Molecular and reverse genetic characterization of serine proteinase-induced hemolysis in the midgut of the ixodid tick Haemaphysalis longicornis

Enzyme-induced hemolysis has been shown to occur in the midgut of ticks; however, little is known about the molecular basis for hemolytic activity. We report here the molecular and reverse genetic characterization of a hemolytic midgut serine proteinase, HlSP, recently identified from the ixodid tick Haemaphysalis longicornis. Endogenous HlSP was found in the midgut lumen and its contents, indicating that HlSP is extracellularly secreted. Recombinant H. longicornis serine proteinase (rHlSP) expressed in Escherichia coli showed dose-dependent hemolytic activity towards rabbit erythrocytes, with a maximum hemolysis of 94.5% within 1 h in vitro. Tests of pH dependency showed that rHlSP displayed optimal activity at pH 6.0. In binding assays, rHlSP showed high affinity to band 3, which shares the major erythrocyte membrane proteins. Disruption of HlSP-specific mRNA by RNA interference resulted in inhibition of the degradation of host erythrocyte membranes by endogenous HlSP in the knock-down ticks, indicating that HlSP plays a crucial role in the hemolysis in the midgut of haematophagous ticks. Our results suggest that HlSP may be essential for initiating the proteolytic cascade for the degradation of the host blood-meal.

RNA interference of cytosolic leucine aminopeptidase reduces fecundity in the hard tick, Haemaphysalis longicornis

Ticks are effective vectors of pathogens because of their blood feeding and high fecundity. This high fecundity is related to the size of the blood meal. Therefore, knowledge of how blood proteins are degraded and converted to proteins, including yolk protein, is important for the development of ways to inhibit the utilization of blood proteins by ticks. RNA interference (RNAi) is becoming a powerful post-transcriptional gene silencing technique that provides insight into gene function. We constructed a double-stranded RNA (dsRNA) based on a previously cloned Haemaphysalis longicornis leucine aminopeptidase (HlLAP) gene to reevaluate the biological role in tick blood digestion. Gene specific transcriptional, translational, and functional disruptions were achieved by the introduction of dsRNA into the ticks. Significantly delayed onset of egg-laying and reduced egg oviposition resulted from the RNAi for the HlLAP gene. These results suggest that HlLAP actually works as a blood digestive enzyme and affects tick fecundity via unknown mechanisms. The reduction of egg oviposition may be caused by a decrease in nutrients, especially free amino acids generated by HlLAP, from the blood meal. This is the first report of an impact on tick reproduction caused by gene silencing of a blood digestion-related molecule.

Identification and characterisation of a leucine aminopeptidase from the hard tick Haemaphysalis longicornis

Aminopeptidases responsible for blood digestion have yet to be identified in haematophagous ticks. We report here the cloning and molecular characterisation of a cDNA encoding leucine aminopeptidase, a member of the M17 cytosolic aminopeptidase family, from the hard tick Haemaphysalis longicornis (HlLAP). Endogenous HlLAP was detected in the soluble fraction of adult tick extracts by immunoblotting. Immunohistochemical studies demonstrated that endogenous HlLAP expression mainly took place in the cytosol of midgut epithelial cells. Furthermore, expression of HlLAP was induced by a blood-feeding process. A functional recombinant HlLAP expressed in Escherichia coli efficiently hydrolyses synthetic substrates for aminopeptidase, a leucyl (with the Km value 0.19 +/- 0.011 mM and Vmax value 157.2 +/- 3.17 nmol/min/mgprotein) and a methionyl substrate (with the Km value 0.12+/-0.0052 mM and Vmax value 171.9 +/- 2.31 nmol/min/mgprotein). Enzyme activity was found to be optimum at pH 8 and 35 degrees C. The recombinant HlLAP enzyme activity was strongly dependent on metal divalent cations, Mn2+, and was inhibited by bestatin. These results indicate that HlLAP play an important role for host's blood digestion process.

Tracing heme in a living cell: hemoglobin degradation and heme traffic in digest cells of the cattle tick Boophilus microplus

Heme is present in all cells, acting as a cofactor in essential metabolic pathways such as respiration and photosynthesis. Moreover, both heme and its degradation products, CO, iron and biliverdin, have been ascribed important signaling roles. However, limited knowledge is available on the intracellular pathways involved in the flux of heme between different cell compartments. The cattle tick Boophilus microplus ingests 100 times its own mass in blood. The digest cells of the midgut endocytose blood components and huge amounts of heme are released during hemoglobin digestion. Most of this heme is detoxified by accumulation into a specialized organelle, the hemosome. We followed the fate of hemoglobin and albumin in primary cultures of digest cells by incubation with hemoglobin and albumin labeled with rhodamine. Uptake of hemoglobin by digest cells was inhibited by unlabeled globin, suggesting the presence of receptor-mediated endocytosis. After endocytosis, hemoglobin was observed inside large digestive vesicles. Albumin was exclusively associated with a population of small acidic vesicles, and an excess of unlabeled albumin did not inhibit its uptake. The intracellular pathway of the heme moiety of hemoglobin was specifically monitored using Palladium-mesoporphyrin IX (Pd-mP) as a fluorescent heme analog. When pulse and chase experiments were performed using digest cells incubated with Pd-mP bound to globin (Pd-mP-globin), strong yellow fluorescence was found in large digestive vesicles 4 h after the pulse. By 8 h, the emission of Pd-mP was red-shifted and more evident in the cytoplasm, and at 12 h most of the fluorescence was concentrated inside the hemosomes and had turned green. After 48 h, the Pd-mP signal was exclusively found in hemosomes. In methanol, Pd-mP showed maximal emission at 550 nm, exhibiting a red-shift to 665 nm when bound to proteins in vitro. The red emission in the cytosol and at the boundary of hemosomes suggests the presence of heme-binding proteins, probably involved in transport of heme to the hemosome. The existence of an intracellular heme shuttle from the digestive vesicle to the hemosome acting as a detoxification mechanism should be regarded as a major adaptation of ticks to a blood-feeding way of life. To our knowledge, this is the first direct observation of intracellular transport of heme in a living eukaryotic cell. A similar approach, using Pd-mP fluorescence, could be applied to study heme intracellular metabolism in other cell types.

Studies on the morphological changes in the midguts of two ixodid tick species Boophilus microplus and Rhipicephalus appendiculatus during digestion of the blood meal

Light and electron microscopy were used to study the morphological changes which accompanied feeding and digestion of the blood meal in the midgut epithelium of two ixodid tick species Boophilus microplus and Rhipicephalus appendiculatus. In unfed ticks of both species, the midgut epithelium was lined by stem cells and empty digest cells in which haematin accumulated with starvation. On attachment to its hosts, differentiation of the stem cells and the loss of haematin from the midgut epithelium, seemed to be synchronous. Digestive activity with the appearance of the digest cell series started in the anterior end of the midgut when it came in contact with the blood meal. Although various stages can be distinguished, it would appear that these are in reality phases of activity of a single cell type--the digest cell. No additional evidence was obtained on other cell types.