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

Plant-derived artificial miRNA effectively reduced the proliferation of aphid (Aphidoidea) through spray-induced gene silencing

BACKGROUND

Aphids (Hemiptera: Aphididae) are notorious sap-sucking insects that rampantly threaten agricultural production worldwide. Current management against aphids in the field heavily relies on chemical pesticides, which makes economical and eco-friendly methods urgently needed. Spray-induced gene silencing (SIGS) offers a powerful and precise approach to pest management. However, the high costs and instability of double-stranded RNA (dsRNA) regulators applied for downstream RNA interference (RNAi) still limit this strategy. It remains uncertain if RNAi regulators applied in SIGS could extend to small RNA (sRNA), especially miRNA.

RESULTS

We chose two sRNA sequences, miR-9b and miR-VgR, whose corresponding targets ABCG4 and VgR are both essential for aphid growth and development. The efficacy of these sequences was initially verified by chemically synthetic single-stranded RNA (syn-ssRNA). Through spray treatment, we observed a significantly decreased survival number and increased abnormality rate of green peach aphids fed on the host under laboratory conditions. Based on our previous study, we generated transgenic plants expressing artificial miR-9b (amiR-9b) and miR-VgR (amiR-VgR). Remarkably, plant-derived amiRNA exerted potent and long-lasting inhibitory efficacy with merely one percent concentration of chemical synthetics. Notably, the simultaneous application of amiR-9b and amiR-VgR exhibited superior inhibitory efficacy.

CONCLUSION

We explored the potential use of sRNA-based biopesticide through SIGS while investigating the dosage requirements. To optimize this strategy, the utilization of plant-derived amiRNA was proposed. The results suggested that attributed to stability and durability, deploying amiRNA in pest management is a potential and promising solution for the field application. © 2024 Society of Chemical Industry.

The low-density lipoprotein receptor and apolipoprotein E associated with CCHFV particles mediate CCHFV entry into cells

The Crimean-Congo hemorrhagic fever virus (CCHFV) is an emerging pathogen of the Orthonairovirus genus that can cause severe and often lethal hemorrhagic diseases in humans. CCHFV has a broad tropism and can infect a variety of species and tissues. Here, by using gene silencing, blocking antibodies or soluble receptor fragments, we identify the low-density lipoprotein receptor (LDL-R) as a CCHFV entry factor. The LDL-R facilitates binding of CCHFV particles but does not allow entry of Hazara virus (HAZV), another member of the genus. In addition, we show that apolipoprotein E (apoE), an exchangeable protein that mediates LDL/LDL-R interaction, is incorporated on CCHFV particles, though not on HAZV particles, and enhances their specific infectivity by promoting an LDL-R dependent entry. Finally, we show that molecules that decrease LDL-R from the surface of target cells could inhibit CCHFV infection. Our study highlights that CCHFV takes advantage of a lipoprotein receptor and recruits its natural ligand to promote entry into cells.

Spatio-temporal patterns of ovarian development and VgR gene silencing reduced fecundity in parthenogenetic Artemia

The halophilic zooplankton brine shrimp Artemia has been used as an experimental animal in multidisciplinary studies. However, the reproductive patterns and its regulatory mechanisms in Artemia remain unclear. In this study, the ovarian development process of parthenogenetic Artemia (A. parthenogenetica) was divided into five stages, and oogenesis or egg formation was identified in six phases. The oogenesis mode was assumed to be polytrophic. We also traced the dynamic translocation of candidate germline stem cells (cGSCs) using EdU labelling and elucidated several key cytological events in oogenesis through haematoxylin and eosin staining and fluorescence imaging. Distinguished from the ovary structure of insects and crustaceans, Artemia germarium originated from ovariole buds and are located at the base of the ovarioles. RNA-seq based on five stages of ovarian development identified 2657 upregulated genes related to reproduction by pair-to-pair comparison. Gbb, Dpp, piwi, vasa, nanos, VgA and VgR genes associated with cGSCs recognition and reproductive development were screened and verified using qPCR. Silencing of the VgR gene in A. parthenogenetica (Ap-VgR) at ovarian development Stage II led to a low level of gene expression (less than 10%) within 5 days, which resulted in variations in oogenesis-related gene expression and significantly inhibited vitellogenesis, impeded oocyte maturation, and eventually decreased the number of offspring. In conclusion, we have illustrated the patterns of ovarian development, outlined the key spatio-temporal features of oogenesis and identified the negative impacts of VgR gene knockdown on oogenesis using A. parthenogenetica as an experimental animal. The findings of this study also lay a foundation for the further study of reproductive biology of invertebrates.

Mining gene expression data for rational identification of novel drug targets and vaccine candidates against the cattle tick, Rhipicephalus microplus

Control of complex parasites via vaccination remains challenging, with the current combination of vaccines and small drugs remaining the choice for an integrated control strategy. Studies conducted to date, are providing evidence that multicomponent vaccines will be needed for the development of protective vaccines against endo- and ectoparasites, though multicomponent vaccines require an in-depth understanding of parasite biology which remains insufficient for ticks. With the rapid development and spread of acaricide resistance in ticks, new targets for acaricide development also remains to be identified, along with novel targets that can be exploited for the design of lead compounds. In this study, we analysed the differential gene expression of Rhipicephalus microplus ticks that were fed on cattle vaccinated with a multi-component vaccine (Bm86 and 3 putative Bm86-binding proteins). The data was scrutinised for the identification of vaccine targets, small drug targets and novel pathways that can be evaluated in future studies. Limitations associated with targeting novel proteins for vaccine and/or drug design is also discussed and placed into the context of challenges arising when targeting large protein families and intracellular localised proteins. Lastly, this study provide insight into how Bm86-based vaccines may reduce successful uptake and digestion of the bloodmeal and overall tick fecundity.

Investigation of vertical and horizontal transmission of Spiroplasma in ticks under laboratory conditions

Many arthropods harbour bacterial symbionts, which are maintained by vertical and/or horizontal transmission. Spiroplasma is one of the most well-known symbionts of ticks and other arthropods. It is still unclear how Spiroplasma infections have spread in tick populations despite its high prevalence in some tick species. In this study, Ixodes ovatus, which has been reported to harbour Spiroplasma ixodetis at high frequencies, was examined for its vertical transmission potential under experimental conditions. Next, two isolates of tick-derived Spiroplasma, S. ixodetis and Spiroplasma mirum, were experimentally inoculated into Spiroplasma-free Haemaphysalis longicornis colonies and the presence of Spiroplasma in their eggs and larvae was tested. Our experimental data confirmed that S. ixodetis was transmitted to eggs and larvae in a vertical manner in the original host I. ovatus. In the second experiment, there was no significant difference in engorged weight, egg weight, and hatching rate between Spiroplasma-inoculated and control H. longicornis groups. This suggested that Spiroplasma infection does not affect tick reproduction. Spiroplasma DNA was only detected in the eggs and larvae derived from some individuals of S. ixodetis-inoculated groups. This has demonstrated the potential of horizontal transmission between different tick species. These findings may help understand the transmission dynamics of Spiroplasma in nature and its adaptation mechanism to host arthropod species.

Three-dimensional images reveal the impact of the endosymbiont Midichloria mitochondrii on the host mitochondria

The hard tick, Ixodes ricinus, a main Lyme disease vector, harbors an intracellular bacterial endosymbiont. Midichloria mitochondrii is maternally inherited and resides in the mitochondria of I. ricinus oocytes, but the consequences of this endosymbiosis are not well understood. Here, we provide 3D images of wild-type and aposymbiotic I. ricinus oocytes generated with focused ion beam-scanning electron microscopy. Quantitative image analyses of endosymbionts and oocyte mitochondria at different maturation stages show that the populations of both mitochondrion-associated bacteria and bacterium-hosting mitochondria increase upon vitellogenisation, and that mitochondria can host multiple bacteria in later stages. Three-dimensional reconstructions show symbiosis-dependent morphologies of mitochondria and demonstrate complete M. mitochondrii inclusion inside a mitochondrion. Cytoplasmic endosymbiont located close to mitochondria are not oriented towards the mitochondria, suggesting that bacterial recolonization is unlikely. We further demonstrate individual globular-shaped mitochondria in the wild type oocytes, while aposymbiotic oocytes only contain a mitochondrial network. In summary, our study suggests that M. mitochondrii modulates mitochondrial fragmentation in oogenesis possibly affecting organelle function and ensuring its presence over generations.

Pannier is a key regulator of embryogenesis, pupal development and female reproduction in the insect pest Bactrocera dorsalis

BACKGROUND

Most arthropods are famous for their large reproductive capacity, with the ovary playing a vital role in the process. The study of the regulatory mechanisms of ovarian development may have the potential for a reproduction-based pest management strategy. GATA-binding transcription factors (GATAs) as important regulatory factors mediate many physiological processes, including development, immunity, insecticide resistance and reproduction. The Pannier (pnr), a member of GATA family, was confirmed to be involved in ovarian development of Bactrocera dorsalis in our previous study. However, the direct evidence of pnr regulating the fly ovarian development is still lacking.

RESULTS

We used CRISPR/Cas9 to create Bdpnr loss-of-function mutations. Homozygous Bdpnr^-/- mutants were nonviable, with most individuals dying during embryogenesis, some surviving to the larval stages, and the remaining few dying during pupation. In contrast, heterozygous individuals reached the adult stage, but ovarian development was disrupted, with concomitant decreases in egg laying and hatching rates. We also found that two genes encoding vitellogenin proteins (BdVg1 and BdVg2) and the vitellogenin receptor (BdVgR) were significantly down-regulated in heterozygous mutants compared to wild-type controls.

CONCLUSION

These results indicate that Bdpnr is required for embryonic and post-embryonic development, including the formation of ovaries. Bdpnr could therefore be considered as a molecular target for tephritid fly pest control. © 2022 Society of Chemical Industry.

Vitellogenin receptor transports the 30K protein LP1 without cell-penetrating peptide, into the oocytes of the silkworm, Bombyx mori

Vitellogenin receptors (VgRs) transport vitellogenin (Vg) into oocytes, thereby promoting egg growth and embryonic development. VgRs recognize and transport multiple ligands in oviparous animals, but their role in insects is rarely reported. In this study, we investigated whether Bombyx mori VgR (BmVgR) binds and transports lipoprotein-1 (BmLP1) and lipoprotein-7 (BmLP7) of the 30 kDa lipoproteins (30 K proteins), which are essential for egg formation and embryonic development in B. mori. Protein sequence analysis showed BmLP7, similar to reported lipoprotein-3 (BmLP3), contains the cell-penetrating peptides and Cysteine position, while BmLP1 has not. Assays using Spodoptera frugiperda ovary cells (sf9) indicated the direct entry of BmLP7 into the cells, whereas BmLP1 failed to enter. However, co-immunoprecipitation (Co-IP) assays indicated that BmVgR could bind BmLP1. Western blotting and immunofluorescence assays further revealed that over-expressed BmVgR could transport BmLP1 into sf9 cells. Co-IP assays showed that SE11C (comprising LBD1+EGF1+OTC domains of BmVgR) or SE22C (comprising LBD2+EGF2+OTC domains of BmVgR) could bind BmLP1. Over-expressed SE11C or SE22C could also transport BmLP1 into sf9 cells. Western blotting revealed that the ability of SE11C to transport BmLP1 might be stronger than that of SE22C. In the vit mutant with BmVgR gene mutation (vit/vit), SDS-PAGE and western blotting showed the content of BmLP1 in the ovary, like BmVg, was lower than that in the normal silkworm. When transgenic with hsp70 promoter over-expressed BmVgR in the vit mutant, we found that the phenotype of the vit mutant was partly rescued after heat treatment. And contents of BmLP1 and BmVg in vit mutant over-expressed BmVgR were higher than in the vit mutant. We conclude that BmVgR and its two repeat domains could bind and transport BmLP1 into the oocytes of the silkworm, besides BmVg. These results will provide a reference for studying the molecular mechanism of VgR transporting ligands in insects.

Comparative transcriptome analysis reveals key candidate genes mediating ovarian development in Spodoptera frugiperda fed on two host plants

The fall armyworm (FAW), Spodoptera frugiperda, is a highly polyphagous lepidopteran pest, with its growth and adaptation affected by different host plants. However, little is known about the effects of host plants on ovarian development in this species. Thus, we evaluated the effects of feeding on corn (Zea mays L.) and goosegrass (Eleusine indica), on the ovarian development of S. frugiperda. Using various stages of S. frugiperda, we also evaluated the larval and pupal weights, number of eggs, and differentiation of ovarioles over time. Results showed that females fed on goosegrass had shorter ovarioles and laid less eggs than those fed on corn. Transcriptome analysis identified 3,213 genes involved in ovarian development in the fall armyworm. Of these, 881 genes were differentially expressed when fed on corn and goosegrass. The analysis also indicated that the hormone biosynthetic pathways may be involved in the reproductive system. In relation to the reproductive function, nine juvenile hormone (JH) biosynthetic genes, four 20-hydroxyecdysone (20E) biosynthetic genes, and four ovary-relevant functional genes were identified. The time course of the expression profiles of these hormone- and ovary development-related genes was measured by quantitative real-time PCR (qRT-PCR). In total, six of them showed a decreasing trend in the ovary of the FAW fed on goosegrass, while two genes showed an increasing trend. Our results showed that significant changes in the reproductive activity/ovary development in the FAW occurred in response to different diets. These results serve as bases for evaluating how optimal host plants and feeding preference affect ovarian development in the FAW.

Vitellogenin-2 Accumulation in the Fat Body and Hemolymph of Babesia-Infected Haemaphysalis longicornis Ticks

The protozoan parasite Babesia spp. invades into tick oocytes and remains in the offspring. The transovarial transmission phenomenon of Babesia in ticks has been demonstrated experimentally, but the molecular mechanisms remain unclear. Babesia invasion into oocytes occurs along with the progression of oogenesis. In the present study, to find the key tick factor(s) for Babesia transmission, we focused on molecules involved in yolk protein precursor (vitellogenin, Vg) synthesis and Vg uptake, which are crucial events in tick oogenesis. With a Haemaphysalis longicornis tick–Babesia ovata experimental model, the expression profiles of Akt, target of rapamycin, S6K, GATA, and Vg, Vg synthesis-related genes, and Vg receptor (VgR) and autophagy-related gene 6 (ATG6), Vg uptake-related genes, were analyzed using real-time PCR using tissues collected during the preovipositional period in Babesia-infected ticks. The expression levels of H. longicornis Vg-2 (HlVg-2) and HlVg-3 decreased in the fat body of Babesia-infected ticks 1 day after engorgement. In the ovary, HlVg-2 mRNA expression was significantly higher in Babesia-infected ticks than in uninfected ticks 1 and 2 days after engorgement and decreased 3 days after engorgement. HlVgR expression was significantly lower in Babesia-infected ticks than in uninfected ticks 2 and 4 days after engorgement. HlATG6 had a lower gene expression in Babesia-infected ticks compared to uninfected ticks 2 days after engorgement. Additionally, western blot analysis using protein extracts from each collected tissue revealed that H. longicornis Vg-2 (HlVg-2) accumulate in the fat body and hemolymph of Babesia-infected ticks. These results suggest that Vg uptake from the hemolymph to the ovary was suppressed in the presence of B. ovata. Moreover, HlVg-2 knockdown ticks had a lower detection rate of B. ovata DNA in the ovary and a significant reduction of B. ovata DNA in the hemolymph compared with control ticks. Taken together, our results suggest that accumulated HlVg-2 is associated with Babesia infection or transmission in the tick body. These findings, besides previous reports on VgR, provide important information to elucidate the transovarial transmission mechanisms of pathogens in tick vectors.

Independent somatic distribution of heme and iron in ticks

Ticks are blood-feeding ectoparasites with distinct genomic reductions, inevitably linking them to a parasitic lifestyle. Ticks have lost the genomic coding and, thus, biochemical capacity to synthesize heme, an essential metabolic cofactor, de novo. Instead, they are equipped with acquisition and distribution pathways for reuse of host heme. Unlike insects or mammals, ticks and mites cannot cleave the porphyrin ring of heme to release iron. Bioavailable iron is thus acquired by ticks from the host serum transferrin. Somatic trafficking of iron, however, is independent of heme and is mediated by a secretory type of ferritin. Heme and iron systemic homeostasis in ticks represents, therefore, key adaptive traits enabling successful feeding and reproduction.

The importance of vitellogenin receptors in the oviposition of the pond wolf spider, Pardosa pseudoannulata

Vitellogenin receptor (VgR) is crucial for vitellogenin (Vg) uptake by oocytes. VgR is less known in Arachnida, especially in spiders. Different from only one VgR in an arthropod species, two VgRs, VgR-1 and VgR-2, were found in the pond wolf spider, Pardosa pseudoannulata. Both VgRs had the typical domains of the low-density lipoprotein receptor family except for the absence of the ligand-binding domain 1 in VgR-2. Spatiotemporal expression profiles showed that two VgR genes were consistently highly expressed in females and their ovaries, but VgR-1 was 48-fold that of VgR-2 in ovaries. The transcriptional level of VgR-1 was significantly downregulated by RNAi, but it did not work for VgR-2 although several trials were performed. Vg-1 and Vg-2 might be the ligands of VgR-1 because their expressions were also decreased in the dsVgR-1-treated females. Silencing VgR-1 prolonged the pre-oviposition period by 56 h. The expression of VgRs and Vgs were upregulated by juvenile hormones (JHs), which suggested that JHs were the essential factors to vitellogenesis in the spider. The present study revealed the importance of VgR-1 in the spider oviposition, which will improve the understanding on VgR physiological functions in spiders.

Insights into gene manipulation techniques for Acari functional genomics

Functional genomics is an essential tool for elucidating the structure and function of genes in any living organism. Here, we review the use of different gene manipulation techniques in functional genomics of Acari (mites and ticks). Some of these Acari species inflict severe economic losses to managed crops and health problems to humans, wild and domestic animals, but many also provide important ecosystem services worldwide. Currently, RNA interference (RNAi) is the leading gene expression manipulation tool followed by gene editing via the bacterial type II Clustered Regularly Interspaced Short Palindromic Repeats and associated protein 9 system (CRISPR-Cas9). Whilst RNAi, via siRNA, does not always lead to expected outcomes, the exploitations of the CRISPR systems in Acari are still in their infancy and are limited only to CRISP/Cas9 to date. In this review, we discuss the advantages and disadvantages of RNAi and CRISPR-Cas9 and the technical challenges associated with their exploitations. We also compare the biochemical machinery of RNAi and CRISPR-Cas9 technologies. We highlight some potential solutions for experimental optimization of each mechanism in gene function studies. The potential benefits of adopting various CRISPR-Cas9 systems for expanding on functional genomics experiments in Acari are also discussed.

Disruption of egg-specific protein causes female sterility in Bombyx mori

Yolk proteins are the main source of nutrients during embryonic and early larval development in oviparous animals. Therefore, vitellogenesis is crucial for reproduction. The silkworm, Bombyx mori, is a model lepidopteran insect in which there are three yolk proteins: vitellin, 30-kDa protein, and egg-specific protein (Esp). In this study, we explored the gene function of Esp through transgenic clustered regularly interspaced palindromic repeats (CRISPR) / CRISPR-associated protein 9 technology-mediated mutations in the silkworm. We found that Esp mutation resulted in female sterility but had no effect on male fertility. Female mutants could lay eggs after mating, but the eggs were smaller and lighter colored than those laid by wild-type females. The most important finding is that the eggs laid by female mutants did not hatch. Furthermore, we observed stable inheritance of female sterility caused by Esp mutation through successive generations. Thus, Esp encodes a yolk protein that is crucial for female reproductive success and is a potential target for pest control.

Screening and Identification of Transcription Factors Potentially Regulating Foxl2 Expression in Chlamys farreri Ovary

Foxl2 is an evolutionarily conserved female sex gene, which is specifically expressed in the ovary and mainly involved in oogenesis and ovarian function maintenance. However, little is known about the mechanism that regulates Foxl2 specific expression during the ovary development. In the present study, we constructed the gonadal yeast one-hybrid (Y1H) library of Chlamysfarreri with ovaries and testes at different developmental stages using the Gateway technology. The library capacity was more than 1.36 × 10⁷ CFU, and the length of the inserted fragment was 0.75 Kb~2 Kb, which fully met the demand of yeast library screening. The highly transcriptional activity promoter sequence of C. farreri Foxl2 (Cf-Foxl2) was determined at -1000~-616 bp by dual-luciferase reporter (DLR) assay and was used as bait to screen possible transcription factors from the Y1H library. Eleven candidate factors, including five unannotated factors, were selected based on Y1H as well as their expressional differences between ovaries and testes and were verified for the first time to be involved in the transcriptional regulation of Cf-Foxl2 by RT-qPCR and DLR. Our findings provided valuable data for further studying the specific regulation mechanism of Foxl2 in the ovary.

Tick Immunobiology and Extracellular Traps: An Integrative Vision to Control of Vectors

Ticks are hematophagous ectoparasites that infest a diverse number of vertebrate hosts. The tick immunobiology plays a significant role in establishing and transmitting many pathogens to their hosts. To control tick infestations, the acaricide application is a commonly used method with severe environmental consequences and the selection of tick-resistant populations. With these drawbacks, new tick control methods need to be developed, and the immune system of ticks contains a plethora of potential candidates for vaccine design. Additionally, tick immunity is based on an orchestrated action of humoral and cellular immune responses. Therefore, the actors of these responses are the object of our study in this review since they are new targets in anti-tick vaccine design. We present their role in the immune response that positions them as feasible targets that can be blocked, inhibited, interfered with, and overexpressed, and then elucidate a new method to control tick infestations through the development of vaccines. We also propose Extracellular Traps Formation (ETosis) in ticks as a process to eliminate their natural enemies and those pathogens they transmit (vectorial capacity), which results attractive since they are a source of acting molecules with potential use as vaccines.

The vitellogenin receptor functionality of the migratory locust depends on its phosphorylation by juvenile hormone

Vitellogenin receptor (VgR) plays a pivotal role in ovarian vitellogenin (Vg) uptake and vertical transmission of pathogenic microbes and Wolbachia symbionts. However, the regulatory mechanisms of VgR action as an endocytic receptor and translocation from oocyte cytoplasm to the membrane remain poorly understood. Here, by using the migratory locust Locusta migratoria as a model system, we report that juvenile hormone (JH) promotes VgR phosphorylation at Ser¹³⁶¹ in the second EGF-precursor homology domain. A signaling cascade including GPCR, PLC, extracellular calcium, and PKC-ι is involved in JH-stimulated VgR phosphorylation. This posttranslational regulation is a prerequisite for VgR binding to Vg on the external surface of the oocyte membrane and subsequent VgR/Vg endocytosis. Acidification, a condition in endosomes, induces VgR dephosphorylation along with the dissociation of Vg from VgR. Phosphorylation modification is also required for VgR recycling from oocyte cytoplasm to the membrane. Additionally, VgR phosphorylation and its requirement for Vg uptake and VgR recycling are evolutionarily conserved in other representative insects including the cockroach Periplaneta americana and the cotton bollworm Helicoverpa armigera This study fills an important knowledge gap of low-density lipoprotein receptors in posttranslational regulation, endocytosis, and intracellular recycling.

Modulation of the PGE2-Mediated Pathway in the Eclosion Blocking Effect of Flumethrin and Terpenoid Subfraction Isolated from Artemesia nilagirica in Rhipicephalus annulatus

Prostaglandins are a group of important cell-signaling molecules involved in the regulation of ovarian maturation, oocyte development, egg laying and associated behaviors in invertebrates. However, the presence of prostaglandin E₂ (PGE₂), the key enzymes for PGE₂ biosynthesis and its interference by drugs were not investigated previously in the ovary of ticks. The present study was undertaken to assess the modulation of the PGE₂-mediated pathway in the eclosion blocking effect of flumethrin and terpenoid subfraction isolated from Artemisia nilagirica in Rhipicephalus annulatus ticks. The acaricidal activities and chemical profiling of the terpenoid subfraction were performed. The localization of the cyclooxygenase1 (COX1) and prostaglandin E synthase (PGES) enzymes and the quantification of PGE₂ in the ovaries of the ticks treated with methanol (control), flumethrin and terpenoid subfraction were also undertaken. In addition, the vitellogenin concentration in hemolymph was also assayed. Both flumethrin and the terpenoid subfraction of A. nilagirica elicited a concentration-dependent inhibition of fecundity and blocking of hatching of the eggs. The COX1 could not be detected in the ovaries of treated and control ticks, while there was no significant difference observed in the concentration of vitellogenin (Vg) in them. The presence of PGES in the oocytes of control ticks was confirmed while the immunoreactivities against PGES were absent in the vitellogenic oocytes of ticks treated with flumethrin and terpenoid subfraction. The levels of PGE₂ were below the detection limit in the ovaries of the flumethrin-treated ticks, while it was significantly lower in the ovaries of the terpenoid subfraction-treated ticks. Hence, the prostaglandin E synthase and PGE₂ were identified as very important mediators for the signaling pathway for ovarian maturation and oviposition in ticks. In addition, the key enzyme for prostaglandin biosynthesis, PGES and the receptors for PGE₂ can be exploited as potential drug targets for tick control. The detection of PGES by immunohistochemistry and quantification of PGE₂ by LC-MSMS can be employed as valuable tools for screening newer compounds for their eclosion blocking acaricidal effects.

Resistance to Ticks and the Path to Anti-Tick and Transmission Blocking Vaccines

The medical and veterinary public health importance of ticks and tick-borne pathogens is increasing due to the expansion of the geographic ranges of both ticks and pathogens, increasing tick populations, growing incidence of tick-borne diseases, emerging tick transmitted pathogens, and continued challenges of achieving effective and sustained tick control. The past decades show an increasing interest in the immune-mediated control of tick infestations and pathogen transmission through the use of vaccines. Bovine tick resistance induced by repeated infestations was reported over a century ago. This review addresses the phenomena and immunological underpinning of resistance to tick infestation by livestock and laboratory animals; the scope of tick countermeasures to host immune defenses; and the impact of genomics, functional genomics, and proteomics on dissecting complex tick-host-pathogen interactions. From early studies utilizing tick tissue extracts to salivary gland derived molecules and components of physiologically important pathways in tick gut and other tissues, an increased understanding of these relationships, over time, impacted the evolution of anti-tick vaccine antigen selection. Novel antigens continue to emerge, including increased interest in the tick microbiome. Anti-tick and transmission blocking vaccines targeting pathogen reservoirs have the potential to disrupt enzootic cycles and reduce human, companion, domestic animal, and wildlife exposure to infected ticks.

Tick Ecdysteroid Hormone, Global Microbiota/Rickettsia Signaling in the Ovary versus Carcass during Vitellogenesis in Part-Fed (Virgin) American Dog Ticks, Dermacentor variabilis

The transovarial transmission of tick-borne bacterial pathogens is an important mechanism for their maintenance in natural populations and transmission, causing disease in humans and animals. The mechanism for this transmission and the possible role of tick hormones facilitating this process have never been studied. Injections of physiological levels of the tick hormone, 20-hydroxyecdysone (20E), into part-fed (virgin) adult females of the American dog tick, Dermacentor variabilis, attached to the host caused a reduction in density of Rickettsia montanensis in the carcass and an increase in the ovaries compared to buffer-injected controls. This injection initiates yolk protein synthesis and uptake by the eggs but has no effect on blood feeding. Francisella sp. and R. montanensis were the predominant bacteria based on the proportionality in the carcass and ovary. The total bacteria load increased in the carcass and ovaries, and bacteria in the genus Pseudomonas increased in the carcass after the 20E injection. The mechanism of how the Rickettsia species respond to changes in tick hormonal regulation needs further investigation. Multiple possible mechanisms for the proliferation of R. montanensis in the ovaries are proposed.

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.

Antibodies against EGF-like domains in Ixodes scapularis BM86 orthologs impact tick feeding and survival of Borrelia burgdorferi

Ixodes scapularis ticks transmit multiple pathogens, including Borrelia burgdorferi sensu stricto, and encode many proteins harboring epidermal growth factor (EGF)-like domains. We show that I. scapularis produces multiple orthologs for Bm86, a widely studied tick gut protein considered as a target of an anti-tick vaccine, herein termed as Is86. We show that Is86 antigens feature at least three identifiable regions harboring EGF-like domains (termed as EGF-1, EGF-2, and EGF-3) and are differentially upregulated during B. burgdorferi infection. Although the RNA interference-mediated knockdown of Is86 genes did not show any influences on tick engorgement or B. burgdorferi sensu stricto persistence, the immunization of murine hosts with specific recombinant EGF antigens marginally reduced spirochete loads in the skin, in addition to affecting tick blood meal engorgement and molting. However, given the borderline impact of EGF immunization on tick engorgement and pathogen survival in the vector, it is unlikely that these antigens, at least in their current forms, could be developed as potential vaccines. Further investigations of the biological significance of Is86 (and other tick antigens) would enrich our knowledge of the intricate biology of ticks, including their interactions with resident pathogens, and contribute to the development of anti-tick measures to combat tick-borne illnesses.

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

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

Regulatory Mechanisms of Vitellogenesis in Insects

Vitellogenesis is pre-requisite to insect egg production and embryonic development after oviposition. During insect vitellogenesis, the yolk protein precursor vitellogenin (Vg) is mainly synthesized in the fat body, transported by the hemolymph through the intercellular spaces (known as patency) in the follicular epithelium to reach the membrane of maturing oocytes, and sequestered into the maturing oocytes via receptor-mediated endocytosis. Insect vitellogenesis is governed by two critical hormones, the sesquiterpenoid juvenile hormone (JH) and the ecdysteriod 20-hydroxyecdysone (20E). JH acts as the principal gonadotropic hormone to stimulate vitellogenesis in basal hemimetabolous and most holometabolous insects. 20E is critical for vitellogenesis in some hymenopterans, lepidopterans and dipterans. Furthermore, microRNA (miRNA) and nutritional (amino acid/Target of Rapamycin and insulin) pathways interplay with JH and 20E signaling cascades to control insect vitellogenesis. Revealing the regulatory mechanisms underlying insect vitellogenesis is critical for understanding insect reproduction and helpful for developing new strategies of insect pest control. Here, we outline the recent research progress in the molecular action of gonadotropic JH and 20E along with the role of miRNA and nutritional sensor in regulating insect vitellogenesis. We highlight the advancements in the regulatory mechanisms of insect vitellogenesis by the coordination of hormone, miRNA and nutritional signaling pathways.

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.

Molecular characterization, expression pattern and RNAi-mediated silencing of vitellogenin receptor gene in almond moth, Cadra cautella

The almond moth is an important pest of date fruits worldwide. The females produce several eggs; however, role of vitellogenin receptor (VgR) in oocyte development by mediating endocytosis of major yolk protein precursor Vg remains yet unexplored. To investigate the role of vitellogenin receptor (VgR) in reproduction, Cadra cautella vitellogenin receptor (CcVgR) transcript was obtained using rapid amplification of cDNA ends-polymerase chain reaction. Expression analysis of CcVgR was performed using reverse transcriptase and quantitative polymerase chain reaction (qPCR) in different developmental stages. RNA interference was performed by injecting CcVgR-based double-stranded (ds)RNA at different exposure times. The results revealed that CcVgR is 5421 bp long, encoded 1807 amino acid, belongs to low-density lipoprotein receptor superfamily and contains all conserved domains. Expression analysis confirmed that CcVgR is sex-specific and starts to express in female larvae on day 19. Additionally, RNA interference (RNAi) of CcVgR-based dsRNA inhibited CcVgR expression up to 83% after 72 h, reduced fecundity and hatchability, and confirmed involvement of CcVgR in C. cautella reproduction. This report provides a basis for gene silencing in this species, and proposes RNAi technology potential for pest management.

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.

Molecular characterization and functional analysis of the vitellogenin receptor in the rice stem borer, Chilo suppressalis

As a member of the low-density lipoprotein receptor (LDLR) superfamily, vitellogenin (Vg) receptor (VgR) is responsible for the uptake of Vg into developing oocytes and is a potential target for pest control. Here, a full-length VgR complementary DNA (named as CsVgR) was isolated and characterized in the rice stem borer, Chilo suppressalis. The composite CsVgR gene contained an open reading frame of 5,484 bp encoding a protein of 1,827 amino acid residues. Structural analysis revealed that CsVgR contained two ligand-binding domains (LBDs) with four Class A (LDLR_A ) repeats in LBD1 and seven in LBD2, which was structurally different from most non-Lepidopteran insect VgRs having five repeats in LBD1 and eight in LBD2. The developmental expression analysis showed that CsVgR messenger RNA expression was first detectable in 3-day-old pupae, sharply increased in newly emerged female adults, and reached a peak in 2-day-old female adults. Consistent with most other insects VgRs, CsVgR was exclusively expressed in the ovary. Notably, injection of dsCsVgR into late pupae resulted in fewer follicles in the ovarioles as well as reduced fecundity, suggesting a critical role of CsVgR in female reproduction. These results may contribute to the development of RNA interference-mediated disruption of reproduction as a control strategy of C. suppressalis.