Purification and partial characterization of vitellin from the black-legged tick, Ixodes scapularis

Insight into Hyalomma anatolicum biology by comparative genomics analyses

Hyalomma anatolicum is an obligatory blood-sucking ectoparasite and contributes to the transmission of Crimean-Congo haemorrhagic fever (CCHF) virus, Theileria spp. and Babesia spp. Progress in exploring the adaptive strategy of this ectoparasite and developing tools to fight it has been hindered by the lack of a complete genome. Herein, we assembled the genome using diverse sources of data from multiple sequencing platforms and annotated the 1.96 Gb genome of Hy. anatolicum. Comparative genome analyses and the predicted protein encoding genes reveal unique facets of this genome, including gene family expansion associated with blood feeding and digestion, multi-gene families involved in detoxification, a great number of neuropeptides and corresponding receptors regulating tick growth, development, and reproduction, and glutathione S-transferase genes playing roles in insecticide resistance and detoxification of multiple xenobiotic factors. This high quality reference genome provides fundamental data for obtaining insights into a variety of aspects of tick biology and developing novel strategies to fight notorious tick vectors of human and animal pathogens.

Egg protein profile and dynamics during embryogenesis in Haemaphysalis flava ticks

Tick eggs contain all essential proteins for embryogenesis, and egg proteins are a potential reservoir of tick-protective antigens. However, the protein profile and dynamics during embryonic development remain unknown. This study aimed to depict the protein profile and dynamics in tick embryogenesis, further providing protein candidates for targeted interventions. Eggs from Haemaphysalis flava ticks were incubated at 28 °C and 85% relative humidity. On days 0 (newly laid eggs without incubation), 7, 14 and 21, eggs were collected, dewaxed and subject to protein extraction. Extracted proteins were digested by filter-aided sample preparation and analyzed by liquid chromatography-tandem mass spectrometry (LC/MS-MS). MS data were searched against an in-house H. flava protein database for tick-derived protein identification. Abundances of 40 selected high-confidence proteins were further quantified by LC-parallel reaction monitoring (PRM)/MS analysis throughout egg incubation. A total of 93 high-confidence proteins were identified in eggs on 0-day incubation. Identified proteins belonged to seven functional categories: transporters, enzymes, proteinase inhibitors, immunity-related proteins, cytoskeletal proteins, heat shock proteins and uncharacterized proteins. The enzyme category contained the most types of proteins. Neutrophil elastase inhibitors represented the most abundant proteins in terms of intensity-based absolute-protein-quantification. LC-PRM/MS revealed that the abundances of 20 proteins increased including enolase, calreticulin, actin, GAPDH et cetera, and the abundances of 11 proteins decreased including vitellogenins, neutrophil elastase inhibitor, carboxypeptidase Q, et cetera from 0- to 21-day incubation. This study provides the most comprehensive egg protein profile and dynamics during tick embryogenesis. Further investigations are needed to test the tick-control efficacy by targeting the egg proteins.

Thymol and eugenol against Rhipicephalus sanguineus sensu lato engorged females: Biological, histopathological and bioinformatic analysis

The aim of this study was to evaluate the reproductive biology and histopathology of the ovaries of engorged females of Rhipicephalus sanguineus sensu lato exposed to combinations of thymol and eugenol, as well as to evaluate in silico the possible interactions of thymol and eugenol in tick cell membranes. To evaluate the tick reproductive biology, the adult immersion test (AIT) was performed, in which the engorged females were immersed in solutions of thymol and eugenol, combined or alone, at concentrations of 2.5 and 5.0 mg/mL. Two control groups (water and 3% DMSO) were also performed. The ticks were kept in a controlled chamber (B.O.D - 27 ± 1 °C and 80% ± 5% RH) to evaluate egg production and viability. To perform the ovaries histopathological evaluation, females were immersed in combination of thymol and eugenol (each at 2.5 and 5.0 mg/mL) and control (water and 3% DMSO) solutions. After immersion, the females were kept in B.O.D (27 ± 1 °C and RH of 80% ± 5%) for four days, they were dissected and the ovaries processed for histological analysis. In addition, an in silico analysis was performed using PASS online® software to predict probability activity (PA) of thymol and eugenol in cell membranes. The treatment with the combination of thymol and eugenol (each at 5.0 mg/mL) caused a reduction (p < 0.01) in oviposition, while the treatments with thymol (5.0 mg/mL) and combination of thymol and eugenol (5.0 mg/mL) reduced (p < 0.05) the egg viability. The treatment with combination of thymol and eugenol (5.0 mg/mL) resulted in a control percentage of 99.9%, while in the other treatments, control percentages below 56% were observed. Oocytes from the females exposed to the combinations of thymol and eugenol (each compound at 2.5 mg/mL) showed histopathological changes, except on oocyte V, while those treated with these compounds alone at 2.5 mg/mL, did not reveal any change. Changes in the shape of the oocyte, presence of vacuoles in the cytoplasm and germinal vesicle, reduction and fusion of yolk granules and rupture of some oocytes were observed. In silico analysis, showed that these compounds can act as membrane permeability inhibitors, membrane permeability agonists, membrane integrity antagonists and apoptosis agonists. We conclude that the combination of thymol and eugenol causes changes in the reproductive biology and morphophysiology of engorged females oocytes. The in silico analysis using thymol and eugenol revealed the possibility of disorganization in the cell membranes, a fact that may explain the histopathological alterations observed.

Protein profiling of hemolymph in Haemaphysalis flava ticks

Background

Tick hemolymph bathes internal organs, acts as an exchange medium for nutrients and cellular metabolites, and offers protection against pathogens. Hemolymph is abundant in proteins. However, there has been limited integrated protein analysis in tick hemolymph thus far. Moreover, there are difficulties in differentiating tick-derived proteins from the host source. The aim of this study was to profile the tick/host protein components in the hemolymph of Haemaphysalis flava.

Methods

Hemolymph from adult engorged H. flava females was collected by leg amputation from the Erinaceus europaeus host. Hemolymph proteins were extracted by a filter-aided sample preparation protocol, digested by trypsin, and assayed by liquid chromatography–tandem mass spectrometry (LC–MS/MS). MS raw data were searched against the UniProt Erinaceidae database and H. flava protein database for host- and tick-derived protein identification. Protein abundance was further quantified by intensity-based absolute quantification (iBAQ).

Results

Proteins extracted from hemolymph unevenly varied in size with intense bands between 100 and 130 kDa. In total, 312 proteins were identified in the present study. Therein 40 proteins were identified to be host-derived proteins, of which 18 were high-confidence proteins. Top 10 abundant host-derived proteins included hemoglobin subunit-α and subunit-β, albumin, serotransferrin-like, ubiquitin-like, haptoglobin, α-1-antitrypsin-like protein, histone H2B, apolipoprotein A-I, and C3-β. In contrast, 169 were high-confidence tick-derived proteins. These proteins were classified into six categories based on reported functions in ticks, i.e., enzymes, enzyme inhibitors, transporters, immune-related proteins, muscle proteins, and heat shock proteins. The abundance of Vg, microplusin and α-2-macroglobulin was the highest among tick-derived proteins as indicated by iBAQ.

Conclusions

Numerous tick- and host-derived proteins were identified in hemolymph. The protein profile of H. flava hemolymph revealed a sophisticated protein system in the physiological processes of anticoagulation, digestion of blood meal, and innate immunity. More investigations are needed to characterize tick-derived proteins in hemolymph.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05287-7.

Ovary Proteome Analysis Reveals RH36 Regulates Reproduction via Vitellin Uptake Mediated by HSP70 Protein in Hard Ticks

Ticks are blood-sucking vector arthropods, which play an important role in transmitting pathogens between humans and animals. RH36 is an immunomodulatory protein expressed in the salivary glands, but not other organs, of partially fed Rhipicephalus haemaphysaloides ticks, and it reaches its peak on the day of tick engorgement. RH36 gene silencing inhibited tick blood feeding and induced a significant decrease in tick oviposition, indicating that another function of immunosuppressor RH36 was regulating tick reproduction. Why did RH36 protein expressed uniquely in the salivary gland regulate tick reproduction? RH36 regulated positively the expression of vitellogenin in ovary, which indicated RH36 protein played an important role in the integration of nutrition and reproduction. According to proteomic analysis, heat shock protein 70 (HSP70) was significantly down-regulated in the immature ovary of post-engorged ticks. In addition, gene silencing of HSP70 not only inhibited tick blood-sucking and the expression of vitellogenin, but also increased tick death rate. These results suggested RH36 affected tick vitellogenin uptake and then regulated ovary cell maturation by modulating the expression of HSP70 protein, and finally controlled tick oviposition.

A proteomics analysis of the ovarian development in females of Haemaphysalis longicornis

Haemaphysalis longicornis is an ixodid tick that can spread a wide variety of pathogens, affecting humans, livestock and wildlife health. The high reproductive capability of this species is initiated by the ingestion of a large amount of blood ingested by the engorged female tick. The degree of ovarian development is proportional to the number of eggs laid. Studying the regulatory mechanism of tick ovary development is relevant for the development of novel tick control methods. In this study, we used quantitative proteomics to study the dynamic changes in protein expression and protein phosphorylation during ovarian development of engorged female H. longicornis ticks. Synergistic action of many proteins (n = 3031) is required to achieve ovarian development and oocyte formation rapidly. Through bioinformatics analysis, changes in protein expressions and phosphorylation modifications in regulating the ovarian development of female ticks are described. Many proteins play an essential role during ovarian development. Also, protein phosphorylation appeared an important reproductive strategy to enable ticks to efficiently convert large amounts of blood in the ovaries into egg-producing components and ultimately produce many eggs.

Vitellogenesis in spiders: first analysis of protein changes in different reproductive stages of Polybetes pythagoricus

Vitellogenesis represents one of the most vital processes of oviparous species during which various proteins, carbohydrates, and lipids are synthesized and stored inside the developing oocytes. Through analyzing protein changes in the midgut diverticula, hemolymph, and ovaries of females throughout the different vitellogenic stages of the spider Polybetes pythagoricus, we determined the origin of the different proteins involved in the formation of lipovitellins (LVs) along with the existence of a linkage between the hemocyanin and this vital process. An increase in the total protein content of the midgut diverticula, hemolymph, and ovary occurred throughout vitellogenesis followed by a decrease in those levels after laying. The presence of hemocyanin in egg and in LV2, as well as its accumulation in the ovary throughout the vitellogenesis process, was determined. Considering that all biologic processes depend on the correct structure and function of proteins, this study establishes, for the first time for the Order Araneae, the coexistence of three different origins of vitellogenesis-related proteins: one predominantly ovarian involving peptides of 120, 75, 46, and 30 kDa; another extraovarian one originated from the midgut diverticula and represented by a 170 kDa peptide, and a third hemolymphatic one, represented by the 67 kDa peptide.

Acquisition of exogenous haem is essential for tick reproduction

Haem and iron homeostasis in most eukaryotic cells is based on a balanced flux between haem biosynthesis and haem oxygenase-mediated degradation. Unlike most eukaryotes, ticks possess an incomplete haem biosynthetic pathway and, together with other (non-haematophagous) mites, lack a gene encoding haem oxygenase. We demonstrated, by membrane feeding, that ticks do not acquire bioavailable iron from haemoglobin-derived haem. However, ticks require dietary haemoglobin as an exogenous source of haem since, feeding with haemoglobin-depleted serum led to aborted embryogenesis. Supplementation of serum with haemoglobin fully restored egg fertility. Surprisingly, haemoglobin could be completely substituted by serum proteins for the provision of amino-acids in vitellogenesis. Acquired haem is distributed by haemolymph carrier protein(s) and sequestered by vitellins in the developing oocytes. This work extends, substantially, current knowledge of haem auxotrophy in ticks and underscores the importance of haem and iron metabolism as rational targets for anti-tick interventions.

DOI:http://dx.doi.org/10.7554/eLife.12318.001

Ticks are small blood-feeding parasites that transmit a range of diseases through their bites, including Lyme disease and encephalitis in humans. Like other blood-feeders, ticks acquire essential nutrients from their host in order to develop and reproduce.

Iron and haem (the iron-containing part of haemoglobin) are essential for the metabolism of every breathing animal on Earth. Most organisms obtain iron by degrading haem and, reciprocally, most of the iron in cells is used to make haem. However, an initial search of existing genome databases revealed that ticks lack the genes required to make the proteins that make and degrade haem.

Perner et al. wanted to find out if ticks can steal haem from the host and use it for their own development. To achieve this, Perner et al. exploited a method of tick membrane feeding that simulates natural feeding on a host by using a silicone imitation of a skin and cow smell extracts (“l´odeur de vache”). Ticks were fed either a haemoglobin-rich (whole blood) or a haemoglobin-poor (serum) diet. This experiment revealed that ticks can develop normally without haemoglobin, but female ticks fed a haemoglobin-poor diet lay sterile eggs out of which no offspring can hatch.

Further investigation showed that haemoglobin is vitally important as a source of haem but not as a source of the amino acids needed to produce the vitellin proteins that nourish embryos. As ticks are not armed with the ability to degrade haem, they do not acquire iron from the host haem but rather from a serum transferrin, a major iron transporter protein found in mammalian blood. Further experiments revealed that ticks have evolved proteins that can transport and store haem and so make the obtained haem available across the whole tick body.

Overall, Perner et al.’s findings suggest that targeting the mechanisms by which ticks metabolise haem and iron could lead to the design of new “anti-tick” strategies.

DOI:http://dx.doi.org/10.7554/eLife.12318.002

Purification of vitellin and dynamics of vitellogenesis in the parthenogenetic tick Haemaphysalis longicornis (Acari: Ixodidae)

Vitellin (Vt) was purified from eggs of parthenogenetic bush tick Haemaphysalis longicornis by gel filtration and ion exchange chromatography. Our results revealed that only one single Vt existed in parthenogenetic bush tick, and the purified Vt was proved to be a hemoglycolipoprotein consisting of nine polypeptides with molecular weights of 203, 147, 126, 82, 74, 70, 61, 47 and 31 kDa, respectively. Polyclonal antibody and monoclonal antibody against Vt were produced using the purified Vt. The change in vitellogenin (Vg) and Vt levels over time of the parthenogenetic H. longicornis was established, and the Vg content in haemolymph and Vt in ovary at different feeding or engorgement statuses was also determined using a double antibody sandwich enzyme-linked immunosorbent assay. The Vg level in haemolymph was distinctly increased on the day of engorgement (1.785 mg/mL) and continued to increase until 2nd day post-engorgement (5.611 mg/mL). There was a slight decrease in Vg level after 4 days of engorgement, and a second peak was observed on day 2 post-oviposition (10.774 mg/mL). Subsequently, Vg content continuously decreased and reached a low level on the 10th day post-oviposition. The Vt content in ovary continuously increased once the female reached its critical weight (0.024 mg per female), and reached the maximum level on day 2 post-oviposition (1.942 mg per female). Afterwards, Vt content rapidly decreased.

Energy sources from the eggs of the wolf spider Schizocosa malitiosa: isolation and characterization of lipovitellins

In oviparous species, proteins and lipids found in the vitellus form the lipoproteins called lipovitellins that are the major source of energy for the development, growth, and survival of the embryo. The energy resources provided by the lipovitellins have not yet been investigated in the Order Araneae. Using the wolf spider Schizocosa malitiosa (Lycosidae) as an experimental model, we identified and characterized the lipovitellins present in the cytosol, focusing on the energetic contribution of those lipoprotein particles in the vitellus. Two lipovitellins (LV) named SmLV1 and SmLV2 were isolated. SmLV1 is a high-density lipoprotein with 67% lipid and 3.6% carbohydrate, and SmLV2 is a very high-density lipoprotein with 9% lipid and 8.8% carbohydrate. Through electrophoresis in native conditions we observed that SmLV1 has a molecular mass of 559 kDa composed of three apolipoproteins of 116, 87, and 42 kDa, respectively. SmLV2 comprised several proteins composed of different proportions of the same subunits (135, 126, 109, and 70 kDa). The principal lipids of these lipovitellins are sphingomyelin + lysophosphatidylcholine, esterified sterols, and phosphatidylcholine. Lipovitellin-free cytosol contains abundant phospatidylcholine and triacylglyceride related to the yolk nuclei (the vitellus organizing center). The principal fatty acids of SmLV1 and SmLV2 are 18:2 n-6, 18:1 n-9, and 16:0. Spectrophotometry detected no pigments in either the lipovitellins or the cytosol. The egg caloric content was 92 cal/g, at proportions of 59.8% protein, 20.1% carbohydrate, and 19.9% lipid. SmLV1 and SmLV2 provided 19.5% and 17.1% of the calories, respectively. Both lipovitellins contribute mainly with proteins (15.8-18%), with the input of carbohydrates and lipids being lower than 1.3%.

Characterization of a Vitellogenin Gene Fragment in Boophilus microplus Ticks

The objective of this study was to isolate, clone, and characterize a fragment of the vitellogenin (Vg) gene from a B. microplus tick strain from Mexico. Using cDNA and specific primers, an 1800-bp fragment was amplified, cloned, and transformed in into E. coli, and then sequenced. Comparative analysis with a previously reported sequence showed 99% identity at both the nucleotide and amino acid level. The predicted amino acid sequence of the Mexican Vg has 6 positive mutations. There is an insertion of an aspartic acid on position 26 and a deletion on position 552 with respect to the reported sequence. There were 11 predicted glycosylation sites conserved in both strains. It is concluded that there is a high sequence homology of Vg in both strains.

A cysteine endopeptidase from tick (Rhipicephalus (Boophilus) microplus) larvae with vitellin digestion activity

The hard tick Rhipicephalus (Boophilus) microplus is a blood-sucking ectoparasite. R. microplus free-living stage comprises egg development, hatching, and subsequent larval development until encountering a host. In order to complete the embryological development, this tick relies on yolk reserve substances, mainly vitellin (Vt), which is still present in the larval stage. The present study demonstrates presence and digestion of Vt in unfed R. microplus larvae. An increasing proteolytic activity is observed in larval development, as well as a decrease in total protein and in Vt content. Partial purification and characterization of a R. microplus larval cysteine endopeptidase (RmLCE) with Vt-degrading activity is also described. RmLCE has optimal activity at 37 degrees C at pH 5.0, being unstable at pH > or =7.5. This enzyme is active upon fluorogenic peptide substrates and is able to degrade Vt, its putative natural substrate. These results indicate that RmLCE has a role in supporting the nutritional needs of unfed R. microplus larva through Vt proteolysis, allowing survival until the first blood meal.

Hormonal control of tick development and reproduction

Ecdysteroids (moulting hormones), juvenoids and neuropeptides in ticks are reviewed but, by far, the emphasis is on the former since this class of hormones has been the subject of most investigations. In immature stages of ticks, ecdysteroids have been shown to regulate moulting and to terminate larval diapause. Although there is a paucity of information on the molecular action of ecdysteroids in ticks, their action appears to be via a heterodimeric ecdysone/ultraspiracle receptor, as in insects. The role of ecdysteroids in sperm maturation in adult males is considered. In females, ecdysteroids function in the regulation of salivary glands, of production of sex pheromones and of oogenesis and oviposition. There is evidence for ecdysteroid production in the integument and pathways of hormone inactivation are similar to those in insects. Ecdysteroids also function in embryogenesis. Although evidence for the occurrence and functioning of juvenile hormones in ticks has been contradictory, in recent thorough work it has not been possible to detect known juvenile hormones in ticks, nor to demonstrate effects of extracts on insects. Factors (neuropeptides) from the synganglion affect physiological processes and limited immunocytochemical studies are reviewed. Sigificantly, a G-protein-coupled receptor has been cloned, expressed, and specifically responds to myokinins.

Quantification of vitellogenesis and its control by 20-hydroxyecdysone in the ixodid tick, Amblyomma hebraeum

Ovaries of the ixodid tick, Amblyomma hebraeum Koch, grew rapidly after engorgment as a result of yolk uptake. At 26 degrees C, oviposition began by day 10 post-engorgement, plateaued on days 16-18, and ended by day 38. Vitellin (Vt) was partially purified from ovaries of day 10 engorged ticks by gel filtration and ion exchange chromatography. This Vt comprises seven major and several minor polypeptides. Two polypeptides (211 and 148 kD) from haemolymph of engorged female ticks corresponded to minor polypeptides of similar molecular weight in the ovary. The haemolymph titre of the 211 and 148 kD polypeptides increased up to the onset of oviposition. These polypeptides were absent in males and non-vitellogenic females (day 0 engorged or day 10 partially-fed females), and were thus designated as vitellogenin (Vg). Antibodies raised against haemolymph Vg211 and 148 recognized these polypeptides in partially purified Vt, as well as six of the seven major polypeptides. Using these antibodies we developed an indirect, competitive ELISA to quantify Vg. Rise in haemolymph Vg-concentration lagged slightly behind the rise in haemolymph ecdysteroid (ES)-concentration, and Vg-synthesis was stimulated by injections of 20E into non-vitellogenic females. These observations indicate that an ES is the vitellogenic hormone in A. hebraeum.

Hemolymph proteins in ticks

In comparison to insects and Crustacea, our knowledge of the predominant hemolymph proteins in ticks is minimal. The hemolymph protein most studied in ticks has been vitellogenin (Vg). Vg is synthesized by the tick fat body after female adults obtain a blood meal, is released into the hemolymph and is absorbed by developing oocytes as vitellin (Vn). Much of what we know about Vg is from studies of Vn. In general, the carbohydrate, lipid and amino acid composition is similar to insects except that in the tick, Vg contains heme, most likely from the digestion of host hemoglobin. In the American dog tick, Dermacentor variabilis, Vg is comprised of two native proteins and seven subunits on SDS-PAGE. Vg has been characterized in five tick species but the amino acid sequence is not yet available. Another predominant hemolymph protein, apparently a carrier protein (CP), has recently been studied in two tick species. This protein is found in the hemolymph of both male and females adults, in adult tissues outside of the hemolymph in some tick species, in coxal fluid of soft ticks and in whole body homogenates from eggs, larvae and nymphs. CP from the hard tick, D. variabilis, contains cholesterol, phospholipids, monoacylglycerides, triacylglycerides, free fatty acids, carbohydrate and heme. Under identical assay conditions, the analogous protein in the soft tick, Ornithodoros parkeri, did not contain heme. CP in the American dog tick consists of two subunits, one of which has 61% identity to the biliprotein, artemocyanin, from the fairy shrimp. CP is identical to a heme-lipoprotein (HeLp) from Boophilus microplus. The exact roles of CP and HeLp have not yet been fully determined, but they apparently are important in heme sequestration and as a storage depot for protein and lipid. Macroglobulin, lectin, antimicrobial, JH binding, JH esterase, and other tick hemolymph proteins are also discussed.

Tissue distribution and characterization of predominant hemolymph carrier proteins from Dermacentor variabilis and Ornithodoros parkeri

The tissue distribution of the predominant hemolymph protein found throughout tick development was examined in the hard tick, Dermacentor variabilis, and in the soft tick, Ornithodoros parkeri. In D. variabilis, the predominant (purified) hemolymph protein was a lipoglycoheme-carrier protein (DvCP) with a molecular weight of 200K. A protein with a similar mobility on native-PAGE was found in fat body, salivary gland, muscle and ovary from partially fed females which was most abundant in the plasma and salivary gland. DvCP from plasma, salivary gland and fat body of partially fed females consisted of two subunits on SDS-PAGE (98 and 92K). In replete females, only salivary gland exhibited protein subunits equivalent to hemolymph CP. CP in salivary gland and fat body stained positive for lipids. The concentration of CP in tissues varied between partially fed and replete females, indicating a difference in the expression and/or sequestration of CP during adult development. The predominant hemolymph carrier protein from O. parkeri (OpCP) was purified to homogeneity for the first time and is presumed to have similar functions to CP from D. variabilis. Purified OpCP exhibited a molecular weight of 668K by native-PAGE. Unlike CP from D. variabilis, OpCP was not detected in fat body or salivary gland tissues but occurred abundantly in coxal fluid. By SDS-PAGE, purified hemolymph OpCP consisted of two major subunits (114 and 93K) and a less abundant protein with an apparent molecular weight of 48K. Purified native OpCP was a lipoprotein like DvCP. A spectral analysis of purified OpCP failed to demonstrate the presence of heme like that found for CP from D. variabilis, purified by the same methods. However, plasma from O. parkeri contained heme with a lambda(max) of 410nm.

Reduced oviposition of Boophilus microplus feeding on sheep vaccinated with vitellin

The most abundant protein present in Boophilus microplus eggs, vitellin, was isolated and purified as a non-covalent complex of six glyco-polypeptides of Mr 44-107kDa. The protein complex bound haem. Immuno-blots demonstrated that antibodies raised to vitellin recognised a 200kDa polypeptide in the haemolymph of adult female ticks. This is consistent with the general proposal that in arthropods vitellin is derived by proteolytic processing from a large precursor protein, vitellogenin. In parallel with this study, an 80kDa glycoprotein (GP80) was independently purified from larvae of B. microplus using efficacy in vaccination trials as an assay. Antibodies to GP80 also recognised a 200kDa protein in the haemolymph of ticks and a major 87kDa polypeptide present in the vitellin complex. Conversely, antibodies to purified vitellin recognised GP80. The amino-terminal amino acid sequences of the 87kDa vitellin polypeptide and GP80 were identical for at least the first 11 residues and internal peptide sequences from both polypeptides were co-located in a single but incomplete deduced amino sequence of B. microplus vitellogenin. Thus, GP80 is a processed product from vitellogenin and highly related to but not completely identical with the 87kDa vitellin polypeptide. Vaccination trials in the model host sheep were performed with purified vitellin and GP80. Sheep vaccinated with either purified vitellin or GP80 returned significantly reduced numbers of engorged female ticks with decreased weights and reduced oviposition. In contrast, sheep vaccinated with recombinant hexahis-GP80, which was incorrectly folded and not glycosylated showed no significant effects on ticks. It was concluded that vitellin and GP80 could induce immune responses that partially protect sheep from the tick, B. microplus. However, critical protective epitopes are associated with the folding of the protein and/or the oligosaccharides attached to it.

Developmental profile, isolation, and biochemical characterization of a novel lipoglycoheme-carrier protein from the American dog tick, Dermacentor variabilis (Acari: Ixodidae) and observations on a similar protein in the soft tick, Ornithodoros parkeri (Acari: Argasidae)

A novel lipoglycoheme-carrier protein (CP) in the American dog tick, Dermacentor variabilis (Say) has been purified and characterized. CP was purified by native-PAGE from partially fed virgin females. CP has a density of 1.25 g/ml with a molecular weight of 200 K by native-PAGE and 340 K by gel filtration chromatography. CP is comprised of two majour subunits, 98 K and 92 K in molecular weight by SDS-PAGE. Separate amino acid composition of the two subunits indicated high contents of As(x), Gl(x) and leucine. However, the N-terminal amino acid sequence of the two subunits was only 13% identical. The lower molecular weight subunit showed 61% identity to artemocyanin (biliprotein) in fairy shrimps, 46% identity to minor vitellogenin in chickens and 13% identity to vitellin of the black-legged tick. No similarity match was found for the other subunit. CP is a lipoglycoheme-protein as indicated by selective staining of native-PAGE gel for lipids, carbohydrates and heme. Lipid analysis by thin layer chromatography revealed the presence of cholesterol, phospholipids, monoacylglycerides, triacylglycerides and free fatty acids. Heme associated with purified CP demonstrated a lambda(max) of 397.5 nm while the lambda(max) of crude hemolymph plasma was 402.5 nm. The presence of CP in whole body homogenates of eggs, unfed and fed larvae and fed nymphs as well as in the plasma of unfed and fed adults including vitellogenic females was demonstrated by native-PAGE. Although a protein of analogous size was not found in the soft tick, Ornithodoros parkeri Cooley, a high molecular weight protein (500 K) is the predominant plasma protein in both unfed and fed male and female adults of that species as determined by native-PAGE. Also, CP appears to function as a biliprotein which sequesters heme.

Role of juvenile hormone in the synthesis and sequestration of vitellogenins in the red cotton stainer, Dysdercus koenigii (Heteroptera: Pyrrhocoridae)

Investigations were carried out to determine the role of juvenile hormone (JH) and 20-hydroxy ecdysone in the synthesis and uptake of vitellogenins, which were earlier identified, purified and characterised, in Dysdercus koenigii. The concentration(s) of vitellogenin(s) in fat body, haemolymph and that of vitellin(s) in ovary were significantly lower after chemical allatectomy at eclosion. In addition, at 70 h after emergence, chemical allatectomy reduced ovarian vitellin concentration, but vitellogenin levels remained normal in the fat body and haemolymph. The haemolymph vitellogenins were not incorporated into oocytes in such insects. Administration of JH-III at 20 h after allatectomy restored vitellogenin levels in the fat body and haemolymph, but the ovary failed to incorporate the available vitellogenins from haemolymph in such insects. However, when JH-III was administered twice, one at 20 h and then at 70 h after allatectomy, vitellogenin concentrations in fat body and haemolymph and also vitellin concentrations in ovary approached control levels. It is suggested that JH has two separate roles, one in vitellogenin synthesis and the other in uptake. 20-hydroxy ecdysone had no apparent role in either vitellogenin synthesis or uptake in D. koenigii.

Vitellins and vitellogenins of Dysdercus koenigii (Heteroptera: Pyrrhocoridae)--identification, purification and temporal pattern

Two vitellins, VtA and VtB, were purified from the eggs of Dysdercus koenigii by gel filtration and ion exchange chromatography. VtA and VtB have molecular weights of 290 and 260 kDa, respectively. Both Vts are glycolipoproteinaceous in nature. VtA is composed of three polypeptides of M(r) 116, 92 and 62 kDa while VtB contained an additional subunit of M(r) 40 kDa. All subunits except the 116-kDa subunit are glycolipopolypeptides. Polyclonal antibody raised against VtA (anti-VtA antibody) cross-reacted with VtB and also with vitellogenic haemolymph and ovaries and pre-vitellogenic fat bodies, but not with haemolymph from either adult male, fifth instar female, or pre-vitellogenic females demonstrating sex and stage specificity of the Vts. Immunoblots in the presence of anti-VtA revealed two proteins (of 290 and 260 kDa) in both vitellogenic haemolymph and pre-vitellogenic fat bodies that are recognised as D. koenigii Vgs. In newly emerged females, Vgs appeared on day 1 in fat bodies and on day 3 in haemolymph and ovaries. Vg concentration was maximum on day 2 in fat body, day 4 in haemolymph and day 7 in ovary. Although the biochemical and temporal characteristics of these proteins show similarity to some hemipterans, they are strikingly dissimilar with those of a very closely related species.

Effect of methoprene and 20-hydroxyecdysone on vitellogenin production in cultured fat bodies and backless explants from unfed female Dermacentor variabilis

The effect of 20-hydroxyecdysone (20HE) and the juvenile hormone analogue methoprene (JHA) on vitellogenin (Vg) production in fat body organ cultures and backless explants of unfed female Dermacentor variabilis was measured. An indirect double antibody enzyme linked immunosorbent assay (ELISA) was developed using a monoclonal antibody that recognized a 98 kDa subunit of Vg and a Vg specific polyclonal antibody made against vitellin (Vn). Peak Vg titers in culture medium from fat body cultures treated with 0.1 &mgr;M 20HE or 1 &mgr;M 20HE were 24 ng/ml and 20 ng/ml respectively. In culture medium from backless explants treated with 0.1 &mgr;M 20HE or 1 &mgr;M 20HE, peak Vg titers were 36 ng/ml and 26 ng/ml, respectively. JHA produced only a slight increase in Vg titers that was statistically different from Vg titers produced by 20HE but was not statistically different from hormone-free controls. These results support the conclusion that Vg production in fat body trophocytes of D. variabilis is regulated by 20HE.

Purification and characterization of beta-N-acetylhexosaminidase from bovine tick Boophilus microplus (Ixodide) larvae

beta-N-Acetylhexosaminidase (HEX, E.C. 3.2.1.52) from larvae of the ixodid tick Boophilus microplus was purified to capillary zone electrophoresis homogeneity, and characterized. Enzyme purification was carried out by sequential liquid chromatography on Sephadex G-200, p-aminobenzyl-N-acetyl-beta-D-thioglucosamine affinity, and Mono-Q FPLC columns. Purification was about 1600-fold, with a yield of 10%, as determined with p-nitrophenyl-N-acetylglucosaminide as substrate. The enzyme presented optimum pH 4.7, and optimum temperature 65 degrees C. The molecular weight of non-denatured enzyme was estimated as 127,000 by gel filtration chromatography, and 60,000 in SDS-PAGE. The tick hexosaminidase presented glycosyl residues, as evidenced by binding to Concanavalin-A. Among several p-nitrophenyl glycosides tested as substrate, HEX was active only on p-nitrophenyl-N-acetylglucosaminide and p-nitrophenyl-N-acetylgalactosaminide. The purified enzyme presented immunogenicity in rabbit, and the correspondent antibodies inhibited about 90% of its original, in vitro activity.