Institute of Parasitology, Biology Centre of the Czech Academy of Sciences, Branišovská 31, 370 05, České Budějovice, Czech Republic; Faculty of Science, University of South Bohemia, Branišovská 31, 370 05, České Budějovice, Czech Republic.
Institute of Entomology, Biology Centre of the Czech Academy of Sciences, Branišovská 31, 370 05, České Budějovice, Czech Republic.
Ticks Tick Borne Dis. 2021 Jul;12(4):101694. doi: 10.1016/j.ttbdis.2021.101694. Epub 2021 Feb 25.
Ticks are blood-feeding arachnids transmitting a variety of pathogens to humans and animals. A unique trait in tick physiology is their ability to engorge and digest large amounts of host blood, ensuring their high reproductive potential. Activation of the blood digestive machinery in the tick gut, as well as processes controlling maturation of ovaries, are triggered upon blood meal uptake by still largely unknown mechanisms. Sensing of the nutritional status in metazoan organisms is facilitated by the evolutionarily conserved Insulin Signaling Pathway (ISP) and the interlinked Target of Rapamycin (TOR) pathway. Recently, we have identified three components of these pathways in the hard tick Ixodes ricinus midgut transcriptome, namely a putative insulin receptor (InR), and the downstream intracellular serine/threonine kinases AKT and TOR. In this study, we primarily focus on the molecular and functional characterization of the I. ricinus insulin receptor (IrInR), the first InR characterized in Chelicerates. A phylogenetic analysis across the major Arthropod lineages demonstrated that ticks possess only one gene encoding an InR-related molecule. Tissue expression profiling by quantitative PCR in semi-engorged I. ricinus females revealed that the IrInR, as well as AKT (IrAKT) and TOR (IrTOR) are expressed in various organs, with the highest expression being detected in ovaries. We have further evaluated the impact of RNAi-mediated knock-down (KD) of IrInR, IrAKT, and IrTOR on tick blood-feeding and reproductive capacity. Weights of engorged IrInR KD females and laid egg clutches were reduced compared to the control group, and these quantitative parameters clearly correlated with the efficiency of RNAi-KD achieved in individual ticks. The most striking phenotype was observed for IrAKT KD that impaired tick feeding and completely aborted egg production. A recombinant extracellular fragment of the IrInR α-subunit was used to produce antibodies in experimental rabbits to assess its potential as a protective antigen against tick feeding and reproduction. Our data clearly indicate the functionality of the ISP in ticks and demonstrate the need for further investigation of specific roles played by the endogenous insulin-like peptides in tick physiological processes.
蜱是吸血的蛛形纲动物，可将多种病原体传播给人类和动物。蜱在生理学上的一个独特特征是它们能够大量饱食和消化宿主血液，从而确保其高繁殖潜力。蜱肠道中血液消化机制的激活以及控制卵巢成熟的过程，在很大程度上是由尚未完全了解的机制触发的。在多细胞生物中，营养状况的感知是通过进化上保守的胰岛素信号通路（ISP）和相互关联的雷帕霉素靶蛋白（TOR）途径来实现的。最近，我们在硬蜱 Ixodes ricinus 中肠转录组中鉴定出了这两个途径的三个成分，即一个假定的胰岛素受体（InR），以及下游的细胞内丝氨酸/苏氨酸激酶 AKT 和 TOR。在这项研究中，我们主要关注 I. ricinus 胰岛素受体（IrInR）的分子和功能特征，这是在螯肢动物中首次鉴定出的 InR。通过对主要节肢动物谱系的系统发育分析表明，蜱只拥有一个编码与 InR 相关分子的基因。在半饱食的 I. ricinus 雌性中通过定量 PCR 进行的组织表达谱分析表明，IrInR 以及 AKT（IrAKT）和 TOR（IrTOR）在各种器官中表达，在卵巢中表达最高。我们进一步评估了 RNAi 介导的 IrInR、IrAKT 和 IrTOR 敲低（KD）对蜱吸血和生殖能力的影响。与对照组相比，IrInR KD 雌性的饱食体重和产卵量减少，这些定量参数与个体蜱的 RNAi-KD 效率明显相关。IrAKT KD 观察到的最显著表型是阻止了蜱的吸血并完全终止了产卵。使用 IrInR α 亚基的重组细胞外片段在实验兔中产生抗体，以评估其作为抗蜱吸血和繁殖的保护性抗原的潜力。我们的数据清楚地表明了 ISP 在蜱中的功能，并表明需要进一步研究内源性胰岛素样肽在蜱生理过程中的特定作用。
