Valosin-containing protein from the hard tick Haemaphysalis longicornis: effects of dsRNA-mediated HlVCP gene silencing

Proteomic profiling of the midgut contents of Haemaphysalis flava

Scant information is available regarding the proteins involved in blood meal processing in ticks. Here, we aimed to highlight the midgut proteins involved in preventing blood meal coagulation, and in facilitating intracellular digestion in the tick Haemaphysalis flava. Proteins were extracted from the midgut contents of fully engorged and partially engorged ticks. We used liquid chromatography tandem-mass spectrometry (LC-MS/MS) analysis to identify 131 unique peptides, and 102 proteins. Of these, 15 proteins, each with at least two unique peptides, were recognized with high confidence. We also retrieved 18 unigenes from our previous published transcriptomic libraries of the midguts and salivary glands of H. flava, and inferred the primary structures of nine proteins and fragments of five proteins. There were 23 and 21 unique proteins in the midgut contents of fully engorged and partially engorged ticks, respectively. We detected 58 shared proteins in the midgut contents of both fully engorged and partially engorged ticks. Of these, seven were significantly differentially expressed between fully engorged and partially engorged ticks: actin, calmodulin, elongation factor-1α, hsp90, multifunctional chaperone, tubulin α, and tubulin β. Our results demonstrated that the proteome of the midgut contents, combined with the transcriptome of the midgut, was a viable method for the reinforcement of protein identification. This method will facilitate further study of blood meal processing by ticks, as well as the identification of clues for tick infestation control. The existence of numerous proteins detected in the midgut contents also highlight the complexity of blood digestion in ticks; this area is in need of further investigation.

Transmission-Blocking Vaccines: Focus on Anti-Vector Vaccines against Tick-Borne Diseases

Tick-borne diseases are a potential threat that account for significant morbidity and mortality in human population worldwide. Vaccines are not available to treat several of the tick-borne diseases. With the emergence and resurgence of several tick-borne diseases, emphasis on the development of transmission-blocking vaccines remains increasing. In this review, we provide a snap shot on some of the potential candidates for the development of anti-vector vaccines (a form of transmission-blocking vaccines) against wide range of hard and soft ticks that include Ixodes, Haemaphysalis, Dermacentor, Amblyomma, Rhipicephalus and Ornithodoros species.

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.

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.

GATA transcription, translation and regulation in Haemaphysalis longicornis tick: analysis of the cDNA and an essential role for vitellogenesis

Blood feeding tightly regulates the reproductive cycles of ticks. Vitellogenesis and nutritional signaling are key events in the tick reproductive cycle. Here we report the identification of a GATA factor that is synthesized after a blood meal and acts as a transcriptional activator of vitellogenin (Vg), and the identification of an S6 kinase that is a transcription regulator of the amino acid signaling pathway. Tick GATA mRNA accumulated in the midgut prior to blood feeding. However, translation of GATA was activated by blood feeding because the GATA protein dramatically increased in the fat body of engorged females. RNA interference-mediated knockdown of S6 kinase and GATA factor revealed the involvements of S6 kinase in GATA activation and resulted in a significant inhibition of the major yolk protein vitellogenin in engorged ticks and effectively disrupting egg development after a blood meal. These results indicate that the GATA factor, a specific transcriptional activator of Vg gene, represents an important molecule for the regulation of tick vitellogenesis and reproduction.

Tick vitellogenin receptor reveals critical role in oocyte development and transovarial transmission of Babesia parasite

A cDNA encoding the vitellogenin receptor of the ixodid tick, Haemaphysalis longicornis Neumann (HlVgR) was cloned and characterized. The full-length cDNA is 5631 bp, including an intact ORF encoding an expected protein with 1782 amino acids. The deduced amino acid sequence of the HlVgR cDNA revealed two ligand-binding domains with four class A cysteine-rich repeats in the first domain and eight in the second domain similar to those of insect VgRs. The immunoblot analysis detected approximately 197 kDa protein in both tick ovary and egg. The developmental expression profile demonstrated that HlVgR mRNA exists throughout the ovarian development, and the transcriptional level is especially high in the previtellogenic period. Immuno electron microscopy analysis demonstrated that the localization of HlVgR is detected on the external surface of oocyte plasma membrane. RNAi showed that eggs of HlVgR dsRNA-injected adult ticks had not developed into fully mature oocytes and laid abnormal eggs. The Babesia parasite DNA was not detected in the eggs of HlVgR dsRNA-injected tick that fed on Babesia gibsoni infected dog, whereas it was detected in the eggs of PBS-injected ticks and noninjected ticks. Expression of HlVgR was increased by the vitellogenic hormone 20-hydroxyecdysone. These results indicate that HlVgR, which is produced by the developing oocytes, is essential for Vg uptake, egg development in the H. longicornis tick, and transovarial transmission of Babesia parasites.