진드기는 박테리아, 바이러스, 원생동물 및 균류를 포함한 다양한 병원체를 전달할 수 있는 감염병매개체이다. 진드기는 불리한 환경조건에 서도 생존할 수 있는 능력이 있으며, 흡혈이 필수적인 절지동물의 진화적 산물로써 비흡혈 기간이 장기간 지속되는 경우에도 생존이 가능하다. 특 히, 높은 온도와 낮은 습도 환경에서도 견딜 수 있는 수분 조절 메커니즘과 내열성의 생리적 특징은 진드기가 전 세계적으로 분포하도록 한 중요한 요인이다. 진드기의 침샘, 말피기관, 후장 그리고 뇌를 포함하는 여러 기관이 관여하는 물과 이온의 획득 및 배출은 복합적인 메커니즘에 의해 조절 된다. 진드기가 수분을 확보하는 주요 경로는 흡혈과정 또는 공기 중 수증기를 직접 포집하는 방식이며, 이와 더불어 진드기가 자연조건에서 맺힌 물방울을 직접 마시며 수분을 보충한다는 것이 최근 본 연구진의 연구를 통해 밝혀졌다. 물방울에서 획득된 수분은 진드기 침샘의 포도상 부위(유형 I) 또는 중장을 통해 체내로 흡수된다는 것이 형광물질 추적을 통해 확인되었다. 이 연구 결과는 진드기 방제 및 병원체 전파 억제를 위한 전략 개발에 새로운 방향을 제시하였다. 본 종설에서는 진드기 방제를 위한 잠재적 표적인 진드기의 수분조절 및 표피 배설의 생리적 메커니즘을 종합적으로 다 룬다.

Ticks are obligatory hematophagous ectoparasites, which can transmit various pathogens including bacteria, protozoa, and viruses via salivary secretion during feeding. Understanding salivation in ticks is crucial for the development of novel methods to prevent tick-borne disease transmission. The central nervous system (synganglion) of ticks controls salivary glands via several neuropeptidergic innervation: myoinhibitory peptide (MIP), SIFamide, and elevenin. These neuropeptides are thought to be modulators of dopamine’s action controlling the salivary glands including inward fluid transport into the lumen of salivary glands acini and emptying lumen solute into salivary duct by pumping and gating. These actions are via two distinct dopamine receptors, dopamine receptor (D1) and invertebrate D1-like dopamine receptor (InvD1L), respectively.

Temperature as a major environmental factor affects on organisms on various levels including molecular, physiological, behavioral and ecological levels. Transient receptor potential channels (TRPs) are a cation channel family. Among them, thermo-TRPs are known as a thermosensor. The potential role of thermo-TRPs have been identified in the fruit fly, Drosophila melanogaster, in thermotaxis and in thermal acclimation. With RNA interference (RNAi) technique, the role of thermo-TRPs in the red flour beetle, Tribolium castaneum, was identified by measuring thermal avoidance behavior in a behavioral assay. RNAi of trpA1 reduced high temperature avoidance, 39 and 42 °C. Moreover, the effects of RNAi of thermo-TRPs on the heat-induced knockout and the death after short exposure to high temperature was measured after one minute exposure at 52 °C, either with or without a 42 °C 10-minute thermal acclimation period. Even though it was relatively short time exposure to high temperature, it was enough to induce high temperature thermal acclimation. RNAi of trpA1 made faster knockout at 52 °C. With RNAi of painless, the recovery rates from heat-induced knockout after thermal acclimation. RNAi of pyrexia reduced long-term total survivorship without thermal acclimation.

Ticks are obligatory ectoparasites of many vertebrates and transmit pathogens causing diseases such as Heartland virus and Ehrlichiosis. The lone star tick, Ambloyomma americanum L., is the primary vector of Ehrlichia chaffeensis, which causes human monocytic Ehrlichiosis. We aimed to investigate the genomic levels of gene regulation in the processes of acquiring the pathogen and of immune to pathogen. We designed six experimental groups: E. chaffeensis positive and negative groups of males and females, and pathogen free male and female ticks. Illumine HiSeq 2500 sequenced six libraries with 100-cycle single direction. Raw sequence reads (more than 209 million) were trimmed and filtered based on minimum quality score (Q-value >30) and size (> 40nt) for de novo assembly. Assembly using Trinity pipeline produced 140,574 contigs from trimmed and filtered sequence reads (about 117 million reads, 56% of raw data). For quality control of the de novo assembly of transcripts, we filtered out the sequences for mitochondrial, E. chaffeensis, and transposable elements sequences, and tested for contig redundancy and gap separations of the assembled sequences. RSEM and edgeR analyses of 61,802 contigs for identifying differentially expressed genes were followed by Blast2GO analyses for annotations of contigs and enriched-gene ontology (GO) term analyses in pairwise comparisons of the libraries. Further investigation of major groups of genes induced by pathogen would provide better understanding of pathogen-vector interaction, which will allow us to prevent of pathogen transmission by interrupting interaction between pathogen and ticks.

Tick salivary secretion during blood-feeding is crucial for successful tick feeding. Control of salivary secretion involves dopamine, which is the most potent inducer of tick salivation. Dopamine activates salivation by orchestrating two different physiological responses through two distinct dopamine receptors. In addition, the study demonstrated that two different types of cells in the salivary gland acini are responsible for each of the diverging physiological pathways: epithelial cells for inward fluid transport and myoepithelial cells for expelling fluid out through the acinar ducts. We were further interested in the downstream physiology of the dopamine receptors. A candidate gene (Na/K-ATPase), which is highly expressed in the salivary glands, was investigated. Immunoreactivity revealed that Na/K-ATPase is expressed in epithelial cells of acini. Ouabain, a Na/K-ATPase blocker, significantly suppressed both dopamine induced inward fluid transport and dopamine induced salivation in a dose-dependent manner. We measured the salivary contents to determine Na, K, and Cl ion, and protein concentrations. Treatment of ouabain at the low dose produced hyperosmolar saliva, but with same amount of protein as the control saliva. The results suggest that ouabain-sensitive Na/K-ATPase is the main downstream pathway for dopamine response in the epithelial cells of salivary gland for water transport, but not for protein secretion.

Insect science has been experiencing the power of genomics and new developing technologies in the last decade. Currently, more than 29 species of arthropod genome sequencing projects have been completed or in progress. The number of species being sequenced will be rapidly increased in the near future by taking advantage of reduced sequencing cost and developing new sequencing technologies. At the same time, other technologies in bioscience have also been undergone rapid development. Among many, the most noticeable techniques that have been applied in the studies of insect science are proteomics, insect transgenesis, and RNA interference (RNAi). Like other important transitional points in biology aided by technological revolution, breaking the technical limitations is expected to lead to innovations in biological concepts.

Phospholipase A2 (PLA2) is the committed catalytic step of eicosanoid biosynthesis, which has been a common molecular target of several entomopathogens to induce insect immunosuppression. Despite critical importance of PLA2 in insect immunity, its gene structure was not known. This study identified insect PLA2 gene associated with immune reactions in the red flour beetle, Tribolium castaneum. Based on a previous study that an immune-associated PLA2 in insect is secretory type of PLA2 (sPLA2), five highly matched cDNA sequences were obtained from T. castaneum genome database using an sPLA2 sequence probe encoded in Drosophila melanogaster. The expressions of these five putative PLA2 were confirmed by reverse transcriptase-polymerase chain reaction. Out of five genes, one PLA2 gene called TcPLA2B was chosen because it showed specific expression in hemocyte and fat body. TcPLA2B was cloned and expressed in Escherichia coli and its protein was purified. The purified TcPLA2B showed PLA2enzyme activity, which was specifically inhibited by bromophenacyl bromide (a specific sPLA2inhibitor) and dithiothreitol (reducing agent of disulfide bond). It was sensitive to pH (optimum at pH 6.0) and reaction temperature (optimum at 10-30°C), and calcium dependency. An immunofluorescence assay indicated that TcPLA2B was localized near to cellular membrane of the cytosol in the hemocytes of T. castaneum at immune chanlenge. Double-stranded RNA (dsRNA) of TcPLA2B-treated larvae showed knockdown of its mRNA expression and did not form hemocyte nodule formation, while control larvae could exhibit time- and bacterial dose-dependent nodule formation in response to bacterial challenge. Addition of arachidonic acid (the catalytic product of PLA2) to the dsRNA-treated larvae rescued the inhibition of nodule formation. These results suggest that TcPLA2B gene is associated with insect immune reaction.