Sequence and the developmental and tissue-specific regulation of the first complete vitellogenin messenger RNA from ticks responsible for heme sequestration

Vitellogenesis and Embryogenesis in Spiders: A Biochemical Perspective

This review compiles information on the biochemistry of spider reproduction, from vitellogenesis to postembryonic development. Despite the diversity of spiders, biochemical studies on their reproduction remain scarce. The structures, functions, and relationships of vitellogenins and lipovitellins across different groups are compared. Information on two vitellogenin-associated proteins (30 and 47 kDa) is presented and discussed. By analyzing females at different reproductive stages-previtellogenesis, early vitellogenesis, vitellogenesis, and postvitellogenesis-as well as males, we examined lipid and fatty acid synthesis, mobilization, and accumulation in the yolk. Lipid dynamics across vitellogenic organs, such as the intestinal diverticula, hemolymph, and ovaries, were established. Structural lipids, mainly phosphatidylcholine and phosphatidylethanolamine, were the predominant yolk components, followed by triacylglycerols. The gonadosomatic and hepatosomatic indices are described for the first time in spiders, providing a new tool for studying vitellogenesis. Hemocyanin was detected in early spider eggs, suggesting a role in organogenesis, with its concentration increasing in later embryonic stages. In contrast, lipovitellin consumption was observed throughout embryonic development until juvenile emergence. The data compiled in this review provide valuable insights into the molecular interactions underlying a key process for oviparous animals.

Morphological and histochemical characteristics of the foregut, midgut, and hindgut, and their alterations during ovarian development in female freshwater prawn, Macrobrachium rosenbergii

The anatomical, histological, and histochemical characteristics of the foregut (FG), midgut (MG), and hindgut (HG), as well as their alterations during the ovarian cycle in female prawns, Macrobrachium rosenbergii, were investigated. The esophagus (ESO), cardia (CD), and pylorus (PY) are the main components of the FG. An epithelium (Ep) with thick cuticle (Cu) layers lining the ESO, and the ESO is encircled by the ESO glands. The CD has a thick musculature, whereas the Ep of the PY are characterized by numerous villi and columnar Ep cells with a thinner layer of Cu. The inner longitudinal (LM) and the outer circular (CM) muscles were both present in the PY. The MG is lined by Ep cells which are connected to the basement membrane, and it lacks Cu. Microvilli, and subapical vacuoles are visible on the apical surface of Ep cells of the MG. The outermost layer is characterized by a dense strip of elastic fibers and a cluster of collagen fibers. The HG has the Ep cells with a thin Cu layer, and the HG glands form a rosette-like structure. The HG is surrounded by the CM and the LM fibers. The reactivities of Periodic Acid Schiff and Alcian Blue in these digestive organs altered throughout the ovarian cycle, and this was supported by the increased expression of mucin levels as ovarian maturation progressed. Our results offer novel and significant insights into the anatomical and histochemical structures of these digestive organs, and demonstrate a significant correlation between ovarian development and feeding in the female prawn, M. rosenbergii.

A multi-omics approach for understanding blood digestion dynamics in Ixodes scapularis and identification of anti-tick vaccine targets

Ixodes scapularis, the black-legged tick, is a major arthropod vector that transmits the causative agents of Lyme disease and several other pathogens of human significance. The tick midgut is the main tissue involved in blood acquisition and digestion and the first organ to have contact with pathogens ingested through the blood meal. Gene expression in the midgut before, during, and after a blood meal may vary in response to the physiological changes due to blood feeding. A systems biology approach based on RNA and protein sequencing was used to gain insight into the changes in tick midgut transcripts and proteins during blood ingestion (unfed and partially fed) and digestion (1-, 2-, 7-, and 14 days post detachment from the host) by the Ixodes scapularis female ticks. A total of 2,726 differentially expressed transcripts, and 449 proteins were identified across the time points. Genes involved in detoxification of xenobiotics, proteases, protease inhibitors, metabolism, and immunity were differentially expressed in response to blood feeding. Similarly, proteins corresponding to the same groups were also differentially expressed. Nine genes from major gene categories were chosen as potential vaccine candidates, and, using RNA interference, the effect of these gene knockdowns on tick biology was investigated. Knockdown of these genes had variable negative impacts on tick physiology, such as the inability to engorge fully and to produce eggs and increased mortality. These and additional gene targets provide opportunities to explore novel tick control strategies.

What are the main proteins in the hemolymph of Haemaphysalis flava ticks?

Background

Haemaphysalis flava is a notorious parasite for humans and animals worldwide. The organs of H. flava are bathed in hemolymph, which is a freely circulating fluid. Nutrients, immune factors, and waste can be transported to any part of the body via hemolymph. The main soluble components in hemolymph are proteins. However, knowledge of the H. flava proteome is limited.

Methods

The hemolymph was collected from fully engorged H. flava ticks by leg amputation. Hemolymph proteins were examined by both blue native polyacrylamide gel electrophoresis (BN-PAGE) and sodium dodecyl sulfate PAGE (SDS-PAGE). Proteins extracted from the gels were further identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Results

Two bands (380 and 520 kDa) were separated from tick hemolymph by BN-PAGE and were further separated into four bands (105, 120, 130, and 360 kDa) by SDS-PAGE. LC-MS/MS revealed that seven tick proteins and 13 host proteins were present in the four bands. These tick proteins mainly belonged to the vitellogenin (Vg) family and the α-macroglobulin family members. In silico structural analysis showed that these Vg family members all had common conserved domains, including the N-terminus lipid binding domain (LPD-N), the C-terminus von Willebrand type D domain (vWD), and the domain of unknown function (DUF). Additionally, two of the Vg family proteins were determined to belong to the carrier protein (CP) by analyzing the unique N-terminal amino acid sequences and the cleaving sites.

Conclusion

These findings suggest that the Vg family proteins and α-macroglobulin are the primary constituents of the hemolymph in the form of protein complexes. Our results provide a valuable resource for further functional investigations of H. flava hemolymph effectors and may be useful in tick management.

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.

More than Three Decades of Bm86: What We Know and Where to Go

Tick and tick-borne disease control have been a serious research focus for many decades. In a global climate of increasing acaricide resistance, host immunity against tick infestation has become a much-needed complementary strategy to common chemical control. From the earliest acquired resistance studies in small animal models to proof of concept in large production animals, it was the isolation, characterization, and final recombinant protein production of the midgut antigen Bm86 from the Australian cattle tick strain of Rhipicephalus (Boophilus) microplus (later reinstated as R. (B.) australis) that established tick subunit vaccines as a viable alternative in tick and tick-borne disease control. In the past 37 years, this antigen has spawned numerous tick subunit vaccines (either Bm86-based or novel), and though we are still describing its molecular structure and function, this antigen remains the gold standard for all tick vaccines. In this paper, advances in tick vaccine development over the past three decades are discussed alongside the development of biotechnology, where existing gaps and future directives in the field are highlighted.

Periviscerokinin (Cap2b; CAPA) receptor silencing in females of Rhipicephalus microplus reduces survival, weight and reproductive output

BACKGROUND

The cattle fever tick, Rhipicephalus (Boophilus) microplus, is a vector of pathogens causative of babesiosis and anaplasmosis, both highly lethal bovine diseases that affect cattle worldwide. In Ecdysozoa, neuropeptides and their G-protein-coupled receptors play a critical integrative role in the regulation of all physiological processes. However, the physiological activity of many neuropeptides is still unknown in ticks. Periviscerokinins (CAP2b/PVKs) are neuropeptides associated with myotropic and diuretic activities in insects. These peptides have been identified only in a few tick species, such as Ixodes ricinus, Ixodes scapularis and R. microplus, and their cognate receptor only characterized for the last two.

METHODS

Expression of the periviscerokinin receptor (Rhimi-CAP2bR) was investigated throughout the developmental stages of R. microplus and silenced by RNA interference (RNAi) in the females. In a first experiment, three double-stranded (ds) RNAs, named ds680-805, ds956-1109 and ds1102-1200, respectively, were tested in vivo. All three caused phenotypic effects, but only the last one was chosen for subsequent experiments. Resulting RNAi phenotypic variables were compared to those of negative controls, both non-injected and dsRNA beta-lactamase-injected ticks, and to positive controls injected with beta-actin dsRNA. Rhimi-CAP2bR silencing was verified by quantitative reverse-transcriptase PCR in whole females and dissected tissues.

RESULTS

Rhimi-CAP2bR transcript expression was detected throughout all developmental stages. Rhimi-CAP2bR silencing was associated with increased female mortality, decreased weight of surviving females and of egg masses, a delayed egg incubation period and decreased egg hatching (P < 0.05).

CONCLUSIONS

CAP2b/PVKs appear to be associated with the regulation of female feeding, reproduction and survival. Since the Rhimi-CAP2bR loss of function was detrimental to females, the discovery of antagonistic molecules of the CAP2b/PVK signaling system should cause similar effects. Our results point to this signaling system as a promising target for tick control.

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.

Molecular characterization, expression, and function of Vitellogenin genes in Phytoseiulus persimilis

Vitellogenin (Vg) is an important factor that impacts oocyte maturation, egg formation and embryonic development in Arthropoda. Two orthologs of Vg gene were obtained from the genome of Phytoseiulus persimilis and termed as PpVg1 and PpVg2. Both orthologs belong to the large lipid transfer protein superfamily. The expression of PpVg1 and PpVg2 was low in immatures and male adults, and increased rapidly in female adults after mating, and reached a peak before the first egg was laid (168×  and 20.5×  the level in virgin females, respectively). When PpVg1 and PpVg2 were interfered with dsRNA, the relative expression decreased by 81.0 and 30.9%, respectively, and 7.8 and 31.4% interfered individuals died within 24 h. Among surviving individuals, ca. 51.1 and 44.8% are infertile. Factors that might be related to expression of Vg genes are also discussed.

Cloning, expression, and function of ferritins in the tick Haemaphysalis flava

The full-length cDNA of two ferritins of Haemaphysalis flava were cloned after which recombinant Hf-FER1 and Hf-FER2 were expressed and their function was analyzed. In addition, RNA interference (RNAi) based on the injection of Hf-fer1 or Hf-fer2 dsRNA into fully engorged female ticks was performed. The cDNA encoding Hf-FER1 is 834 bp in length. It contains an iron-responsive element in the 5' untranslated region and encodes 174 amino acid residues. The full-length cDNA of Hf-FER2 contains 696 bp and encodes 199 amino acids, including a putative signal peptide sequence. Hf-FER1 and Hf-FER2 both have the ferroxidase iron center and the ferrihydrite nucleation center. The evolutionary relationship of Hf-FER1 and Hf-FER2 was established, and the predicted quaternary structures were assembled as typical spherical shells composed of 24 subunits which was demonstrated by nature PAGE. Real-time PCR showed that Hf-fer1 and Hf-fer2 were expressed in all developmental stages, with the highest expression in fully engorged females. The expression of Hf-fer1 and Hf-fer2 were relatively high in unfed larvae. Hf-fer1 was expressed in all tissues and was especially abundant in the salivary glands of fully engorged females. In contrast, the highest levels of Hf-fer2 were found in the midgut of fully engorged females, and no expression was found in the salivary glands of this life stage. Both recombinant Hf-FER1 and Hf-FER2 had iron-binding capabilities. Silencing of both Hf-fer1 and Hf-fer2 affected fecundity. Compared to the control, the percentage of ticks that laid eggs in the Hf-fer1 and Hf-fer2 RNAi groups was 73.3% and 66.7%, respectively. The silenced ticks that laid eggs had lower egg weight to body weight ratios, and the eggs had abnormal morphologies. The hatchability of eggs with normal morphology in the Hf-fer1 and Hf-fer2 silenced groups was 47.8% and 22.8%, respectively, which was significantly different from the control group (P < 0.005). These findings indicate that Hf-FER1 and Hf-FER2 play important roles in the iron storage of H. flava.

De novo transcriptome sequencing and comparative profiling of the ovary in partially engorged and fully engorged Haemaphysalis flava ticks

Haemaphysalis flava is the vector of several pathogens and has medical and veterinary importance. Transcriptome information of the ovary of H. flava is unavailable and limits understanding of its molecular basis of reproduction. We studied the ovary transcriptome of partially engorged and fully engorged H. flava using high-throughput RNA sequencing technology. A total of 53,025,360 and 57,942,890 clean reads were obtained with 7.95 GB and 8.69 GB clean bases in partially engorged ticks (PETs) and fully engorged ticks (FETs), respectively. The clean reads were assembled into 138,711 unigenes. A total of 72,043 unigenes (51.93%) were annotated and 66,668 unigenes (48.07%) were unknown. A total of 38,487 differentially expressed genes (DEGs) were found between PET and FET with 19,031 upregulated genes and 19,456 downregulated genes. The RNA-seq results were validated by qRT-PCR, including six upregulated genes and three downregulated genes. Some unigenes coding for nutrient transporters, proteases, and protease inhibitors were found and analyzed. This study was the first time to perform the transcriptome sequences of the ovary of partially engorged and fully engorged H. flava. The results can benefit the understanding of the molecular basis of ovary maturation and oogenesis of the H. flava and boost the development of the strategies for control of H. flava.

Development of a rapid scabies immunodiagnostic assay based on transcriptomic analysis of Sarcoptes scabiei var. nyctereutis

Scabies is a highly contagious skin disease caused by the mite Sarcoptes scabiei that affects many mammals. However, the sensitivity of traditional tests for scabies diagnosis in humans is less than 50%. To simplify the diagnosis of scabies, methods that are simple, sensitive, specific, and cost-effective are required. We developed an immunodiagnostic test based on S. scabiei var. nyctereutis RNA-seq data collected from Japanese raccoon dogs with sarcoptic mange. Three candidate antigens-a highly expressed hypothetical protein "QR98_0091190," another mite allergen known as "SMIPP-Cc," and an abundant "vitellogenin-like protein"-were evaluated by western-blot analysis. A lateral flow immunoassay, using specific antibodies against the vitellogenin-like protein, successfully detected scabies in the skin flakes of S. scabiei-infected raccoon dogs. This assay can potentially diagnose scabies more accurately in wildlife, as well as in humans.

Transport pathways of hydrocarbon and free fatty acids to the cuticle in arthropods and hypothetical models in spiders

Cuticular lipids in terrestrial arthropods are not only essential for desiccation resistance; they also play an important role as chemical signals for intra- and interspecific communication (pheromones and kairomones, respectively). Most of the studies on cuticular lipid research was dedicated to one class of arthropods, the insects. This type of research on the class arachnids is poorly developed, and the majority of studies has listed the compounds present in cuticular extracts, and, in some cases, compared the lipid profiles of different life stages (juveniles, adults). Consequently, we reviewed in relation to lipids description, biosynthesis, and transport of spiders. To illustrate a novel concept of lipid transportation, a scheme is now presented to show the hypothetical transport pathways of hydrocarbon and free fatty acids to cuticle in spiders. These concepts are taken from the knowledge of different arachnids to obtain a general illustration on the biosynthesis and transport of hemolymphatic lipids to the cuticle in spider.

De novo assembly and analysis of the transcriptome of the Dermacentor marginatus genes differentially expressed after blood-feeding and long-term starvation

Background

The ixodid tick Dermacentor marginatus is a vector of many pathogens wide spread in Eurasia. Studies of gene sequence on many tick species have greatly increased the information on tick protective antigen which might have the potential to function as effective vaccine candidates or drug targets for eco-friendly acaricide development. In the current study, RNA-seq was applied to identify D. marginatus sequences and analyze differentially expressed unigenes.

Methods

To obtain a broader picture of gene sequences and changes in expression level, RNA-seq was performed to obtain the whole-body transcriptome data of D. marginatus adult female ticks after engorgement and long-term starvation. Subsequently, the real-time quantitative PCR (RT-qPCR) was applied to validate the RNA-seq data.

Results

RNA-seq produced 30,251 unigenes, of which 32% were annotated. Gene expression was compared among groups that differed by status as newly molted, starved and engorged female adult ticks. Nearly one third of the unigenes in each group were differentially expressed compared to the other two groups, and the most numerous were genes encoding proteins involved in catalytic and binding activities and apoptosis. Selected up-regulated differentially expressed genes in each group were associated to protein, lipids, carbohydrate and chitin metabolism. Blood-feeding and long-term starvation also caused genes differentially expressed in the defense response and antioxidant response. RT-qPCR results indicated 6 differentially expressed transcripts showed similar trends in expression changes with RNA-seq results confirming that the gene expression profiles in transcriptome data is in consistent with RT-qPCR validation.

Conclusions

Obtaining the sequence information of D. marginatus and characterizing the expression pattern of the genes involved in blood-feeding and during starvation would be helpful in understanding molecular physiology of D. marginatus and provides data for anti-tick vaccine and drug development for controlling the tick.

Proteomic Analysis of Exosome-Like Vesicles Isolated From Saliva of the Tick Haemaphysalis longicornis

Extracellular vesicles (EVs), are considered as vehicles of cellular communication. Parasites usually release EVs in their excretory-secretory products to modulate host environment. However, little is known about the secretion of EVs by ticks. In this study, we show for the first time that the tick Haemaphysalis longicornis secretes EVs in saliva that resembles exosomes. EVs were purified from pilocarpine induced saliva of partially engorged H. longicornis ticks. Electron microscopy analysis revealed the presence of exosome-like vesicles with a size of 100 nm. Proteomic analysis by LC-MS/MS identified a total of 356 proteins in tick-derived EVs. Proteome data of tick-derived EVs was validated by Western blot analysis. Immunodetection of Hsp70 and GAPDH proteins indicated that the proteomics data of tick-derived EVs were highly reliable. Bioinformatics analysis (Gene Ontology) indicated association of certain biological and molecular functions with proteins which may be helpful during tick development. Likewise, KEGG database revealed involvement of vesicular proteins in proton transport, detoxification, ECM-receptor interaction, ribosome, RNA transport, ABC transporters, and oxidative phosphorylation. The results of this study provide evidence that EVs are being secreted in tick saliva and suggest that tick saliva-derived EVs could play important roles in host-parasite relationships. Moreover, EVs could be a useful tool in development of vaccines or therapeutics against ticks.

A survey of proteins in midgut contents of the tick, Haemaphysalis flava, by proteome and transcriptome analysis

Tick blood meals are stored and digested in their midguts. Blood digestion is complex, and many proteins are involved. Study of the tick-derived proteins in the midgut content may aid in the discovery of active molecules that would be useful for anti-tick vaccines. We analyzed the midgut content proteomes of partially engorged female Haemaphysalis flava, fully engorged female H. flava, and hedgehog serum using liquid chromatography tandem-mass spectrometry and label-free quantitation. In this study, high-confidence protein profiling of tick midgut content was determined. Based on the search against our in-house transcriptome database, the 28 high-confidence proteins were identified. Of these, 17 were identified as tick-derived, and the rest were of unspecified origin (proteins that could not be differentiated as host-derived or tick-derived proteins). The function of these midgut content proteins identified here may involve nutrient transportation, anti-coagulation, erythrocyte lysis, detoxification, lipid metabolism, and immunization. The presence of hemoglobin suggested that the red blood cells were lysed in the gut lumen. The midgut contents contain a large amount of fibrinogen and it has the ability to clot immediately. The midgut contained mostly host-derived proteins, and these host proteins provide rich nutrients for tick development and reproduction. However, some intracellular proteins were also identified, suggesting the possibility of shedding of the midgut epithelium and ingestion of saliva during feeding. This finding advances our understanding of the digestive mechanism and will be useful in the screening of vaccine antigens.

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.

Ovarian Transcriptomic Analyses in the Urban Human Health Pest, the Western Black Widow Spider

Due to their abundance and ability to invade diverse environments, many arthropods have become pests of economic and health concern, especially in urban areas. Transcriptomic analyses of arthropod ovaries have provided insight into life history variation and fecundity, yet there are few studies in spiders despite their diversity within arthropods. Here, we generated a de novo ovarian transcriptome from 10 individuals of the western black widow spider (Latrodectus hesperus), a human health pest of high abundance in urban areas, to conduct comparative ovarian transcriptomic analyses. Biological processes enriched for metabolism—specifically purine, and thiamine metabolic pathways linked to oocyte development—were significantly abundant in L. hesperus. Functional and pathway annotations revealed overlap among diverse arachnid ovarian transcriptomes for highly-conserved genes and those linked to fecundity, such as oocyte maturation in vitellogenin and vitelline membrane outer layer proteins, hormones, and hormone receptors required for ovary development, and regulation of fertility-related genes. Comparative studies across arachnids are greatly needed to understand the evolutionary similarities of the spider ovary, and here, the identification of ovarian proteins in L. hesperus provides potential for understanding how increased fecundity is linked to the success of this urban pest.

Identification of Halloween Genes and RNA Interference-Mediated Functional Characterization of a Halloween Gene shadow in Plutella xylostella

Ecdysteroids play an essential role in controlling insect development and reproduction. Their pathway is regulated by a group of enzymes called Halloween gene proteins. The relationship between the Halloween genes and ecdysteroid synthesis has yet to be clearly understood in diamondback moth, Plutella xylostella (L.), a worldwide Lepidoptera pest attacking cruciferous crops and wild plants. In this study, complete sequences for six Halloween genes, neverland (nvd), shroud (sro), spook (spo), phantom (phm), disembodied (dib), shadow (sad), and shade (shd), were identified. Phylogenetic analysis revealed a strong conservation in insects, including Halloween genes of P. xylostella that was clustered with all other Lepidoptera species. Three Halloween genes, dib, sad, and shd were highly expressed in the adult stage, while nvd and spo were highly expressed in the egg and pupal stages, respectively. Five Halloween genes were highly expressed specifically in the prothorax, which is the major site of ecdysone production. However, shd was expressed predominantly in the fat body to convert ecdysone into 20-hydroxyecdysone. RNAi-based knockdown of sad, which is involved in the last step of ecdysone biosynthesis, significantly reduced the 20E titer and resulted in a longer developmental duration and lower pupation of fourth-instar larvae, as well as caused shorter ovarioles and fewer fully developed eggs of P. xylostella. Furthermore, after the knockdown of sad, the expression levels of Vg and VgR genes were significantly decreased by 77.1 and 53.0%. Meanwhile, the number of eggs laid after 3 days was significantly reduced in sad knockdown females. These results suggest that Halloween genes may play a critical role in the biosynthesis of ecdysteroids and be involved in the development and reproduction of P. xylostella. Our work provides a solid basis for understanding the functional importance of these genes, which will help to screening potential genes for pest management of P. xylostella.

Vitellogenin Receptor as a Target for Tick Control: A Mini-Review

While much effort has been put into understanding vitellogenesis in insects and other organisms, much less is known of this process in ticks. There are several steps that facilitate yolk formation in developing oocytes of which the vitellogenin receptor (VgR) is a key component. The tick VgR binds vitellogenin (Vg) circulating in the hemolymph to initiate receptor-mediated endocytosis and its transformation into vitellin (Vn). The conversion of Vg into Vn, the final form of the yolk protein, occurs inside oocytes of the female tick ovary. Vn is critical to tick embryos since it serves as the nutritional source for their development, survival, and reproduction. Recent studies also suggest that pathogenic microbes, i.e., Babesia spp., that rely on ticks for propagation and dissemination likely "hitchhike" onto Vg molecules as they enter developing oocytes through the VgR. Suppressing VgR messenger RNA synthesis via RNA interference (RNAi) completely blocked Babesia spp. transmission into developing tick oocytes, thereby inhibiting vertical transmission of these pathogenic microbes from female to eggs. To date, VgRs from only four tick species, Dermacentor variabilis, Rhipicephalus microplus, Amblyomma hebraeum, and Haemaphysalis longicornis, have been fully sequenced and characterized. In contrast, many more VgRs have been described in various insect species. VgR is a critical component in egg formation and maturation that can serve as a precise target for tick control. However, additional research will help identify unique residues within the receptor that are specific to ticks or other arthropod disease vectors while avoiding cross-reactivity with non-target species. Detailed knowledge of the molecular structure and functional role of tick VgRs will enable development of novel vaccines to control ticks and tick-borne diseases.

Intracellular localization of vitellogenin receptor mRNA and protein during oogenesis of a parthenogenetic tick, Haemaphysalis longicornis

BACKGROUND

Vitellogenin (Vg), a key molecule for oocyte development synthesized in the fat body during blood-feeding, is released into the hemolymph and then taken into the oocytes via Vg receptor (VgR) in ticks. Previously, we showed that VgR mRNA is expressed in the ovary at the adult stage of parthenogenetic Haemaphysalis longicornis ticks and its expression increases after blood-feeding. However, intracellular localization of VgR mRNA and protein at each developmental stage of oocytes during oogenesis remains largely unclear.

METHODS

mRNA and protein expression profiles of H. longicornis VgR (HlVgR) in the oocytes from the unfed to oviposition periods were analyzed by real-time PCR, in situ hybridization, and immunostaining. To elucidate the timing of the onset of Vg uptake, RNA interference (RNAi)-mediated gene silencing of HlVgR was performed.

RESULTS

In situ hybridization revealed that HlVgR mRNA was detected in the cytoplasm of stage I-III oocytes, and weaker positive signals for HlVgR mRNA were found in the cell periphery of stage IV and V oocytes. Likewise, HlVgR protein was detected by immunostaining in the cytoplasm of stage I-III oocytes and in the cell periphery of stage IV and V oocytes. Each developmental stage of the oocytes showed distinct patterns of mRNA and protein expression of HlVgR. Moreover, RNAi of HlVgR caused delayed or arrested development in the oocytes. The ovaries of control ticks showed all developmental stages of oocytes, whereas stage I-III oocytes were found in the ovaries of HlVgR-RNAi ticks at 5 days after engorgement.

CONCLUSIONS

These results suggest that active uptake of Vg is required for development from stage III to stage IV during oogenesis. Our data clearly revealed an apparent shift in the intracellular localization of VgR for both mRNA and protein level in oocytes during oogenesis.

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.

Transcriptome and Proteome Response of Rhipicephalus annulatus Tick Vector to Babesia bigemina Infection

A system biology approach was used to gain insight into tick biology and interactions between vector and pathogen. Rhipicephalus annulatus is one of the main vectors of Babesia bigemina which has a massive impact on animal health. It is vital to obtain more information about this relationship, to better understand tick and pathogen biology, pathogen transmission dynamics, and new potential control approaches. In ticks, salivary glands (SGs) play a key role during pathogen infection and transmission. RNA sequencing obtained from uninfected and B. bigemina infected SGs obtained from fed female ticks resulted in 6823 and 6475 unigenes, respectively. From these, 360 unigenes were found to be differentially expressed (p < 0.05). Reversed phase liquid chromatography-mass spectrometry identified a total of 3679 tick proteins. Among them 406 were differently represented in response to Babesia infection. The omics data obtained suggested that Babesia infection lead to a reduction in the levels of mRNA and proteins (n = 237 transcripts, n = 212 proteins) when compared to uninfected controls. Integrated transcriptomics and proteomics datasets suggested a key role for stress response and apoptosis pathways in response to infection. Thus, six genes coding for GP80, death-associated protein kinase (DAPK-1), bax inhibitor-1 related (BI-1), heat shock protein (HSP), heat shock transcription factor (PHSTF), and queuine trna-ribosyltransferase (QtRibosyl) were selected and RNA interference (RNAi) performed. Gene silencing was obtained for all genes except phstf. Knockdown of gp80, dapk-1, and bi-1 led to a significant increase in Babesia infection levels while hsp and QtRibosyl knockdown resulted in a non-significant decrease of infection levels when compared to the respective controls. Gene knockdown did not affect tick survival, but engorged female weight and egg production were affected in the gp80, dapk-1, and QtRibosyl-silenced groups in comparison to controls. These results advanced our understanding of tick-Babesia molecular interactions, and suggested new tick antigens as putative targets for vaccination to control tick infestations and pathogen infection/transmission.

Vitellogenins in the spider Parasteatoda tepidariorum - expression profile and putative hormonal regulation of vitellogenesis

BACKGROUND

Knowledge about vitellogenesis in spiders is rudimentary. Therefore, the aim of study was to check the vitellogenin (Vg) presence in various tissues of the female spider Parasteatoda tepidariorum, determine when and where vitellogenesis starts and takes place, and the putative role of selected hormones in the vitellogenesis.

RESULTS

Here we show two genes encoding Vg (PtVg4 and PtVg6) in the genome of the spider P. tepidariorum. One gene PtVg4 and three subunits of Vg (250 kDa, 47 kDa and 30 kDa) are expressed in the midgut glands, ovaries and hemolymph. Heterosynthesis of the Vg in the midgut glands and autosynthesis in the ovaries were observed. Vitellogenesis begins in the last nymphal stage in the midgut glands (heterosynthesis). However, after sexual maturity is reached, Vg is also synthesized in the ovaries (autosynthesis). Changes in the PtVg4 expression level and in the Vg concentration after treatment with 20-hydroxyecdysone, a juvenile hormone analog (fenoxycarb) and an antijuvenoid compound (precocene I) were observed. Therefore, we propose a hypothetical model for the hormonal regulation of vitellogenesis in P. tepidariorum.

CONCLUSIONS

Our results are the first comprehensive study on spider vitellogenesis. In our opinion, this work will open discussion on the evolutionary context of possible similarities in the hormonal control of vitellogenesis between P. tepidariorum and other arthropods as well as their consequences.

Silencing expression of the Rhipicephalus microplus vitellogenin receptor gene blocks Babesia bovis transmission and interferes with oocyte maturation

Background

Rhipicephalus microplus is an efficient biological vector of Babesia bovis, a causative agent of bovine babesiosis. Babesia bovis is passed transovarially to the next generation of ticks, which then transmit the parasite to naïve animals. Due to the importance of the R. microplus ovary for tick reproduction and transmission of B. bovis, we investigated the hypothesis that silencing vitellogenin receptor gene expression in the ovary during tick feeding on B. bovis-infected cattle would affect parasite transmission to the next generation of ticks.

Results

Silencing expression of the vitellogenin receptor in the ovary by RNA interference, resulted in reduced tick fertility. We observed reduced egg production (i.e. reduced weight of eggs), a lower rate of embryonic development, and a reduction in hatching. Analysis of individual larvae by PCR confirmed that RNAi mediated downregulation of the R. microplus vitellogenin receptor and also interfered with transovarial transmission of B. bovis. None of the larvae (0/58) from the RmVgR dsRNA-injected group were PCR-positive, whereas 12% (7/58) and 17% (10/58) of larvae from the non-injected and buffer-injected control groups, respectively, were infected with B. bovis.

Conclusions

The combined effects of reduced fecundity and reduced infection in surviving larvae resulting from silencing indicate that vitellogenin receptor is essential for tick reproduction and may play a vital role in B. bovis transmission.

Rhipicephalus bursa Sialotranscriptomic Response to Blood Feeding and Babesia ovis Infection: Identification of Candidate Protective Antigens

Ticks are among the most prevalent blood-feeding arthropods, and they act as vectors and reservoirs for numerous pathogens. Sialotranscriptomic characterizations of tick responses to blood feeding and pathogen infections can offer new insights into the molecular interplay occurring at the tick-host-pathogen interface. In the present study, we aimed to identify and characterize Rhipicephalus bursa salivary gland (SG) genes that were differentially expressed in response to blood feeding and Babesia ovis infection. Our experimental approach consisted of RNA sequencing of SG from three different tick samples, fed-infected, fed-uninfected, and unfed-uninfected, for characterization and inter-comparison. Overall, 7,272 expressed sequence tags (ESTs) were constructed from unfed-uninfected, 13,819 ESTs from fed-uninfected, and 15,292 ESTs from fed-infected ticks. Two catalogs of transcripts that were differentially expressed in response to blood feeding and B. ovis infection were produced. Four genes coding for a putative vitellogenin-3, lachesin, a glycine rich protein, and a secreted cement protein were selected for RNA interference functional studies. A reduction of 92, 65, and 51% was observed in vitellogenin-3, secreted cement, and lachesin mRNA levels in SG, respectively. The vitellogenin-3 knockdown led to increased tick mortality, with 77% of ticks dying post-infestation. The reduction of the secreted cement protein-mRNA levels resulted in 46% of ticks being incapable of correctly attaching to the host and significantly lower female weights post-feeding in comparison to the control group. The lachesin knockdown resulted in a 70% reduction of the levels associated with B. ovis infection in R. bursa SG and 70% mortality. These results improved our understanding of the role of tick SG genes in Babesia infection/proliferation and tick feeding. Moreover, lachesin, vitellogenin-3, and secreted cement proteins were validated as candidate protective antigens for the development of novel tick and tick-borne disease control measures.

Bactericera cockerelli vitellogenin-6 like, a vitellogenin without a direct reproductive function?

Vitellogenin-like proteins are members of the large lipid transfer proteins, a family of proteins involved in reproduction, lipid circulation and immune defences. In this study, we identified a new Bactericera cockerelli vitellogenin-like (Vg-like) transcript, and named it BcVg6-like based on its similarity to Acyrthosiphon pisum Vg6. In silico analyses predicted different conserved domains in BcVg6-like compared with the conventional Ba. cockerelli vitellogenin, BcVg1-like, previously described by our research group. Phylogenetic analyses determined that BcVg6-like clustered with Vg-like-B proteins and not the conventional vitellogenins involved in vitellogenesis. Also, the expression analyses showed differences in BcVg6-like transcript expression between 7-day-old males and 3- and 7-day-old females. BcVg6-like was not upregulated after exogenous application of juvenile hormone III, but its relative expression increased significantly in alimentary canals of adult females exposed to tomato plants infected by the bacterial plant pathogen 'Candidatus Liberibacter solanacearum'. Our results suggest that in Ba. cockerelli, both vitellogenin genes may have different functions: BcVg1-like is a conventional vitellogenin that conserved its ancestral function as an egg yolk precursor whereas BcVg6-like might have acquired a function in lipid and/or other molecule transport, and could potentially play a role in immune defence.

A proteomic insight into vitellogenesis during tick ovary maturation

Ticks are arthropod ectoparasites of importance for public and veterinary health. The understanding of tick oogenesis and embryogenesis could contribute to the development of novel control methods. However, to date, studies on the temporal dynamics of proteins during ovary development were not reported. In the present study we followed protein profile during ovary maturation. Proteomic analysis of ovary extracts was performed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) using shotgun strategy, in addition to dimethyl labelling-based protein quantification. A total of 3,756 proteins were identified, which were functionally annotated into 30 categories. Circa 80% of the annotated proteins belong to categories related to basal metabolism, such as protein synthesis and modification machineries, nuclear regulation, cytoskeleton, proteasome machinery, transcriptional machinery, energetic metabolism, extracellular matrix/cell adhesion, immunity, oxidation/detoxification metabolism, signal transduction, and storage. The abundance of selected proteins involved in yolk uptake and degradation, as well as vitellin accumulation during ovary maturation, was assessed using dimethyl-labelling quantification. In conclusion, proteins identified in this study provide a framework for future studies to elucidate tick development and validate candidate targets for novel control methods.

Analysis of the Salivary Gland Transcriptome of Unfed and Partially Fed Amblyomma sculptum Ticks and Descriptive Proteome of the Saliva

Ticks are obligate blood feeding ectoparasites that transmit a wide variety of pathogenic microorganisms to their vertebrate hosts. Amblyomma sculptum is vector of Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever (RMSF), the most lethal rickettsiosis that affects humans. It is known that the transmission of pathogens by ticks is mainly associated with the physiology of the feeding process. Pathogens that are acquired with the blood meal must first colonize the tick gut and later the salivary glands (SG) in order to be transmitted during a subsequent blood feeding via saliva. Tick saliva contains a complex mixture of bioactive molecules with anticlotting, antiplatelet aggregation, vasodilatory, anti-inflammatory, and immunomodulatory properties to counteract both the hemostasis and defense mechanisms of the host. Besides facilitating tick feeding, the properties of saliva may also benefits survival and establishment of pathogens in the host. In the current study, we compared the sialotranscriptome of unfed A. sculptum ticks and those fed for 72 h on rabbits using next generation RNA sequencing (RNA-seq). The total of reads obtained were assembled in 9,560 coding sequences (CDSs) distributed in different functional classes. CDSs encoding secreted proteins, including lipocalins, mucins, protease inhibitors, glycine-rich proteins, metalloproteases, 8.9 kDa superfamily members, and immunity-related proteins were mostly upregulated by blood feeding. Selected CDSs were analyzed by real-time quantitative polymerase chain reaction preceded by reverse transcription (RT-qPCR), corroborating the transcriptional profile obtained by RNA-seq. Finally, high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis revealed 124 proteins in saliva of ticks fed for 96–120 h. The corresponding CDSs of 59 of these proteins were upregulated in SG of fed ticks. To the best of our knowledge, this is the first report on the proteome of A. sculptum saliva. The functional characterization of the identified proteins might reveal potential targets to develop vaccines for tick control and/or blocking of R. rickettsii transmission as well as pharmacological bioproducts with antihemostatic, anti-inflammatory and antibacterial activities.

Identification and expression analyses of vitellogenin in Bactericera cockerelli (Šulc)

The potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae), is a phloem-feeding insect with preference for Solanaceae. This insect species is vector of the pathogenic bacteria 'Candidatus Liberibacter solanacearum' the causative agent of zebra chip, an important disease of commercial potatoes in several countries worldwide. The recent classification of psyllids among the most dangerous vectors has promoted their study, but still many biological processes such as reproduction and vitellogenesis need to be investigated. As a first step towards the elucidation of vitellogenesis in B. cockerelli, one candidate vitellogenin transcript (6622 bases long) was identified and the expression of the transcript and the protein were analyzed in virgin and mated females between 1 and 7days old. In virgin females, Vg expression increased up to 5days old; while mating significantly up-regulated Vg expression in 5- and 7-day-old females. To determine the role of juvenile hormone in B. cockerelli Vg expression, topical applications of juvenile hormone III were performed on virgin females, resulting in an up-regulation of Vg expression and an increase in the number of mature oocytes present in female reproductive organs. Overall, this study represents the first step to understand vitellogenesis of B. cockerelli and it highlights the role of JH III in the hormonal regulation of Vg expression and oocyte development.

Physiological and molecular mechanisms underlying photoperiodism in the spider mite: comparisons with insects

Photoperiodism is an adaptive, seasonal timing system that enables organisms to coordinate their development and physiology to annual changes in the environment using day length (photoperiod) as a cue. This review summarizes our knowledge of the physiological mechanisms underlying photoperiodism in spider mites. In particular, the two-spotted spider mite Tetranychus urticae is focussed, which has long been used as a model species for studying photoperiodism. Photoperiodism is established by several physiological modules, such as the photoreceptor, photoperiodic time measurement system, counter system, and endocrine effector. It is now clear that retinal photoreception through the ocelli is indispensable for the function of photoperiodism, at least in T. urticae. Visual pigment, which comprised opsin protein and a vitamin A-based pigment, is involved in photoreception. The physiological basis of the photoperiodic time measurement system is still under debate, and we have controversial evidence for the hourglass-based time measurement and the oscillator-based time measurement. Less attention has been centred on the counter system in insects and mites. Mite reproduction is possibly regulated by the ecdysteroid, ponasterone A. Prior physiological knowledge has laid the foundation for the next steps essential for the elucidation of the molecular mechanisms driving photoperiodism.

Mevalonate-Farnesal Biosynthesis in Ticks: Comparative Synganglion Transcriptomics and a New Perspective

Juvenile hormone (JH) controls the growth, development, metamorphosis, and reproduction of insects. For many years, the general assumption has been that JH regulates tick and other acarine development and reproduction the same as in insects. Although researchers have not been able to find the common insect JHs in hard and soft tick species and JH applications appear to have no effect on tick development, it is difficult to prove the negative or to determine whether precursors to JH are made in ticks. The tick synganglion contains regions which are homologous to the corpora allata, the biosynthetic source for JH in insects. Next-gen sequencing of the tick synganglion transcriptome was conducted separately in adults of the American dog tick, Dermacentor variabilis, the deer tick, Ixodes scapularis, and the relapsing fever tick, Ornithodoros turicata as a new approach to determine whether ticks can make JH or a JH precursor. All of the enzymes that make up the mevalonate pathway from acetyl-CoA to farnesyl diphosphate (acetoacetyl-CoA thiolase, HMG-S, HMG-R, mevalonate kinase, phosphomevalonate kinase, diphosphomevalonate decarboxylase, and farnesyl diphosphate synthase) were found in at least one of the ticks studied but most were found in all three species. Sequence analysis of the last enzyme in the mevalonate pathway, farnesyl diphosphate synthase, demonstrated conservation of the seven prenyltransferase regions and the aspartate rich motifs within those regions typical of this enzyme. In the JH branch from farnesyl diphosphate to JH III, we found a putative farnesol oxidase used for the conversion of farnesol to farnesal in the synganglion transcriptome of I. scapularis and D. variabilis. Methyltransferases (MTs) that add a methyl group to farnesoic acid to make methyl farnesoate were present in all of the ticks studied with similarities as high as 36% at the amino acid level to insect JH acid methyltransferase (JHAMT). However, when the tick MTs were compared to the known insect JHAMTs from several insect species at the amino acid level, the former lacked the farnesoic acid binding motif typical in insects. The P450s shown in insects to add the C10,11 epoxide to methyl farnesoate, are in the CYP15 family; this family was absent in our tick transcriptomes and in the I. scapularis genome, the only tick genome available. These data suggest that ticks do not synthesize JH III but have the mevalonate pathway and may produce a JH III precursor.

Identification and evaluation of vaccine candidate antigens from the poultry red mite (Dermanyssus gallinae)

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Ten poultry red mite vaccine candidate antigens were identified and recombinant versions produced.

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Mite mortality was monitored after feeding on the blood from vaccinated hens.

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A ⩾1.6-fold increased risk of mite death was observed with four of the vaccine candidates (P < 0.001).

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Best candidates include: a serpin, vitellogenin, hemelipoglycoprotein and a novel protein.

An aqueous extract of the haematophagous poultry ectoparasite, Dermanyssus gallinae, was subfractionated using anion exchange chromatography. Six of these subfractions were used to immunise hens and the blood from these hens was fed, in vitro, to poultry red mites. Mite mortality following these feeds was indicative of protective antigens in two of the subfractions, with the risks of mites dying being 3.1 and 3.7 times higher than in the control group (P < 0.001). A combination of two-dimensional immunoblotting and immunoaffinity chromatography, using IgY from hens immunised with these subfractions, was used in concert with proteomic analyses to identify the strongest immunogenic proteins in each of these subfractions. Ten of the immunoreactive proteins were selected for assessment as vaccine candidates using the following criteria: intensity of immune recognition; likelihood of exposure of the antigen to the antibodies in a blood meal; proposed function and known vaccine potential of orthologous molecules. Recombinant versions of each of these 10 proteins were produced in Escherichia coli and were used to immunise hens. Subsequent in vitro feeding of mites on blood from these birds indicated that immunisation with Deg-SRP-1 (serpin), Deg-VIT-1 (vitellogenin), Deg-HGP-1 (hemelipoglycoprotein) or Deg-PUF-1 (a protein of unknown function) resulted in significantly increased risk of mite death (1.7–2.8 times higher than in mites fed blood from control hens immunised with adjuvant only, P < 0.001). The potential for using these antigens in a recombinant vaccine is discussed.

Molecular characterization of vitellogenin and its receptor genes from citrus red mite, Panonychus citri (McGregor)

The production and uptake of yolk protein play an important role in the reproduction of all oviparous organisms. Vitellogenin (Vg) is the precursor of vitellin (Vn), which is the major egg storage protein, and vitellogenin receptor (VgR) is a necessary protein for the uptake of Vg into developing oocytes. In this paper, we characterize the full-length Vg and VgR, PcVg1 and PcVgR, respectively, of the citrus red mite Panonychus citri (McGregor). The PcVg1 cDNA is 5748 nucleotides (nt) with a 5553-nt open reading frame (ORF) coding for 1851 amino acids (aa), and the PcVgR is 6090 nt, containing an intact ORF of 5673 nt coding an expected protein of 1891 aa. The PcVg1 aa sequence shows a typical GLCG domain and several K/RXXR cleavage sites, and PcVgR comprises two ligand-binding domains, two epidermal growth factor (EGF)-like regions containing YWTD motifs, a transmembrane domain, and a cytoplasmic domain. An analysis of the aa sequences and phylogenetics implied that both genes were genetically distinct from those of ticks and insects. The transcriptional profiles determined by real-time quantitative PCR in different developmental stages showed that both genes present the same expressional tendencies in eggs, larvae, nymphs, and adults. This suggested that the biosynthesis and uptake of PcVg occurs coordinately. The strong reproductive capacity of P. citri has been hypothesized as an important factor in its resistance; consequently, understanding the molecular mechanisms regulating Vg and VgR are fundamental for mite control.

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.

Variable induction of vitellogenin genes in the varroa mite, Varroa destructor (Anderson & Trueman), by the honeybee, Apis mellifera L, host and its environment

Transcript levels of vitellogenins (Vgs) in the varroa mite, Varroa destructor (Anderson & Trueman), were variably induced by interactions between the developing honeybee, Apis mellifera L, as a food source and the capped honeybee cell environment. Transcripts for two Vgs of varroa mites were sequenced and putative Vg protein products characterized. Sequence analysis of VdVg1 and VdVg2 proteins showed that each had greater similarity with Vg1 and Vg2 proteins from ticks, respectively, than between themselves and were grouped separately by phylogenetic analyses. This suggests there was a duplication of the ancestral acarine Vg gene prior to the divergence of the mites and ticks. Low levels of transcript were detected in immature mites, males and phoretic females. Following cell invasion by phoretic females, VdVg1 and VdVg2 transcript levels were up-regulated after cell capping to a maximum at the time of partial cocoon formation by the honeybee. During oviposition the two transcripts were differentially expressed with higher levels of VdVg2 being observed. A bioassay based on assessing the transcript levels was established. Increases in VdVg1 and VdVg2 transcripts were induced experimentally in phoretic females when they were placed inside a cell containing an early metamorphosing last instar bee but not when exposed to the metamorphosing bee alone. The variable response of Vg expression to the food source as well as environmental cues within the capped cell demonstrates that perturbation of host-parasite interactions may provide avenues to disrupt the reproductive cycle of the varroa mites and prevent varroasis.

One ring to rule them all: trafficking of heme and heme synthesis intermediates in the metazoans

The appearance of heme, an organic ring surrounding an iron atom, in evolution forever changed the efficiency with which organisms were able to generate energy, utilize gasses and catalyze numerous reactions. Because of this, heme has become a near ubiquitous compound among living organisms. In this review we have attempted to assess the current state of heme synthesis and trafficking with a goal of identifying crucial missing information, and propose hypotheses related to trafficking that may generate discussion and research. The possibilities of spatially organized supramolecular enzyme complexes and organelle structures that facilitate efficient heme synthesis and subsequent trafficking are discussed and evaluated. Recently identified players in heme transport and trafficking are reviewed and placed in an organismal context. Additionally, older, well established data are reexamined in light of more recent studies on cellular organization and data available from newer model organisms. This article is part of a Special Issue entitled: Cell Biology of Metals.

Gene silencing in parasites: current status and future prospects

Parasitic diseases cause important losses in public and veterinary health worldwide. Novel drugs, more reliable diagnostic techniques and vaccine candidates are urgently needed. Due to the complexity of parasites and the intricate relationship with their hosts, development of successful tools to fight parasites has been very limited to date. The growing information on individual parasite genomes is now allowing the use of a broader range of potential strategies to gain deeper insights into the host-parasite relationship and has increased the possibilities to develop molecular-based tools in the field of parasitology. Nevertheless, functional studies of respective genes are still scarce. The RNA interference phenomenon resulting in the regulation of protein expression through the specific degradation of defined mRNAs, and more specifically the possibility of artificially induce it, has shown to be a powerful tool for the investigation of proteins function in many organisms. Recent advances in the design and delivery of targeting molecules allow efficient and highly specific gene silencing in different types of parasites, pointing out this technology as a powerful tool for the identification of novel vaccine candidates or drug targets at the high-throughput level in the near future, and could enable researchers to functionally annotate parasite genomes. The aim of this review is to provide a comprehensive overview on the current advances and pitfalls in gene silencing mechanisms, techniques, applications and prospects in animal parasites.

Synganglion transcriptome and developmental global gene expression in adult females of the American dog tick, Dermacentor variabilis (Acari: Ixodidae)

454 Pyrosequencing was used to characterize the expressed genes from the synganglion and associated neurosecretory organs of unfed and partially fed virgin and mated replete females of the American dog tick, Dermacentor variabilis. A total of 14,881 contiguous sequences (contigs) was assembled, with an average size of 229 bp. Gene ontology terms for Level 2 biological processes were assigned to 4366 contigs. Seven acetylcholinesterases, a muscarinic acetylcholine (ACh) receptor, two nicotinic ACh receptor β-subunits, two ACh unc-18 regulators, two dopamine receptors, two gamma aminobutyric acid (GABA) receptors, two GABA transporters, two norepinephrine transporters and an octopamine receptor are described. Microarrays were conducted to examine global gene expression and quantitative real-time polymerase chain reaction was used to verify expression of selected neuropeptides. Hierarchical clustering of all differentially expressed transcripts grouped part-fed and replete ticks as being more similar in terms of differentially expressed genes with unfed ticks as the outgroup. Nine putative neuropeptides (allatostatin, bursicon-β, preprocorazonin, glycoprotein hormone α, insulin-like peptide, three orcokinins, preprosulphakinin) and a gonadotropin releasing hormone receptor were differentially expressed, and their developmental expression and role in reproduction was investigated. The presence of eclosion hormone, corazonin and bursicon in the synganglion, which in insects regulate behaviour and cuticle development associated with moulting, suggest that this system may be used in ticks to regulate blood feeding, cuticle expansion and development related to female reproduction; adult ticks do not moult.

Full-length sequence, regulation and developmental studies of a second vitellogenin gene from the American dog tick, Dermacentor variabilis

Vitellogenin (Vg) is the precursor of vitellin (Vn) which is the major yolk protein in eggs. In a previous report, we isolated and characterized the first Vg message from the American dog tick Dermacentor variabilis. In the current study, we describe a second Vg gene from the same tick. The Vg2 cDNA is 5956 nucleotides with a 5775 nt open reading frame coding for 1925 amino acids. The conceptual amino acid translation contains a 16-residues putative signal peptide, N-terminal lipid binding domain and C-terminal von Willebrand factor type D domain present in all known Vgs. Moreover, the amino acid sequence shows a typical GLCG domain and several RXXR cleavage sites present in most isolated Vgs. Tryptic digest-mass fingerprinting of Vg and Vn recognized 11 fragments that exist in the amino acid translation of DvVg2 cDNA. Injection of virgin females with 20 hydroxyecdysone induced DvVg2 expression, vitellogenesis and oviposition. Using RT-PCR, DvVg2 expression was detected only in tick females after mating and feeding to repletion. Northern blot analysis showed that DvVg2 is expressed in fat body and gut cells of vitellogenic females but not in the ovary. DvVg2 expression was not detected in adult fed or unfed males. The characteristics that distinguish Vg from other similar tick storage proteins like the carrier protein, CP (another hemelipoglycoprotein) are discussed.

New approach for the study of mite reproduction: The first transcriptome analysis of a mite, Phytoseiulus persimilis (Acari: Phytoseiidae)

Many species of mites and ticks are of agricultural and medical importance. Much can be learned from the study of transcriptomes of acarines which can generate DNA-sequence information of potential target genes for the control of acarine pests. High throughput transcriptome sequencing can also yield sequences of genes critical during physiological processes poorly understood in acarines, i.e., the regulation of female reproduction in mites. The predatory mite, Phytoseiulus persimilis, was selected to conduct a transcriptome analysis using 454 pyrosequencing. The objective of this project was to obtain DNA-sequence information of expressed genes from P. persimilis with special interest in sequences corresponding to vitellogenin (Vg) and the vitellogenin receptor (VgR). These genes are critical to the understanding of vitellogenesis, and they will facilitate the study of the regulation of mite female reproduction. A total of 12,556 contiguous sequences (contigs) were assembled with an average size of 935bp. From these sequences, the putative translated peptides of 11 contigs were similar in amino acid sequences to other arthropod Vgs, while 6 were similar to VgRs. We selected some of these sequences to conduct stage-specific expression studies to further determine their function.

Multiple vitellogenins from the Haemaphysalis longicornis tick are crucial for ovarian development

Ovarian development and egg maturation are crucial processes for the success of reproduction in ticks. Three full-length cDNAs encoding the precursor of major yolk protein, vitellogenin, were obtained from cDNA libraries of the Haemaphysalis longicornis tick and designated as HlVg-1, HlVg-2 and HlVg-3. The HlVg mRNAs were found in fed females with major expression sites in the midgut, fat body and ovary. Native PAGE and Western blot demonstrated that HlVgs in the hemolymph, fat body and ovary of fed females consisted of four major polypeptides. RNAi results showed that HlVg dsRNA-injected ticks obtained lower body weight, egg weight and showed higher mortality of engorged females after blood sucking than control groups. Our results indicate that all HlVgs are essential for egg development and oviposition.

Characterization of a vitellogenin gene reveals two phase regulation of vitellogenesis by engorgement and mating in the soft tick Ornithodoros moubata (Acari: Argasidae)

Synthesis of the precursor yolk protein vitellogenin (Vg) occurs after engorgement in haematophagous arthropods. We identified the Vg cDNA of the soft tick Ornithodoros moubata (OmVg) and compared its expression in mated and virgin females. Both mated and virgin females showed increases in OmVg expression after engorgement but expression was higher in mated females than virgin females particularly as time advanced. Delayed mating in virgin females induced an increase in OmVg expression. OmVg expression was observed in the midgut and fat body by whole mount in situ hybridization, but enlarged fat body with high expression occurred in only mated females during the late phase of vitellogenesis. Therefore, engorgement initially induces OmVg expression but mating is necessary for continued Vg expression to produce mature eggs.

Comparative microarray analysis of Rhipicephalus (Boophilus) microplus expression profiles of larvae pre-attachment and feeding adult female stages on Bos indicus and Bos taurus cattle

Background

Rhipicephalus (Boophilus) microplus is an obligate blood feeder which is host specific to cattle. Existing knowledge pertaining to the host or host breed effects on tick transcript expression profiles during the tick - host interaction is poor.

Results

Global analysis of gene expression changes in whole R. microplus ticks during larval, pre-attachment and early adult stages feeding on Bos indicus and Bos taurus cattle were compared using gene expression microarray analysis. Among the 13,601 R. microplus transcripts from BmiGI Version 2 we identified 297 high and 17 low expressed transcripts that were significantly differentially expressed between R. microplus feeding on tick resistant cattle [Bos indicus (Brahman)] compared to R. microplus feeding on tick susceptible cattle [Bos taurus (Holstein-Friesian)] (p ≤ 0.001). These include genes encoding enzymes involved in primary metabolism, and genes related to stress, defence, cell wall modification, cellular signaling, receptor, and cuticle formation. Microarrays were validated by qRT-PCR analysis of selected transcripts using three housekeeping genes as normalization controls.

Conclusion

The analysis of all tick stages under survey suggested a coordinated regulation of defence proteins, proteases and protease inhibitors to achieve successful attachment and survival of R. microplus on different host breeds, particularly Bos indicus cattle. R. microplus ticks demonstrate different transcript expression patterns when they encounter tick resistant and susceptible breeds of cattle. In this study we provide the first transcriptome evidence demonstrating the influence of tick resistant and susceptible cattle breeds on transcript expression patterns and the molecular physiology of ticks during host attachment and feeding.

The microarray data used in this analysis have been submitted to NCBI GEO database under accession number GSE20605 http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE20605.