Hussein Hala E, Scoles Glen A, Ueti Massaro W, Suarez Carlos E, Adham Fatma K, Guerrero Felix D, Bastos Reginaldo G
Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA, 99164, USA.
Department of Entomology, Faculty of Science, Cairo University, Giza, 12613, Egypt.
Parasit Vectors. 2015 Dec 2;8:618. doi: 10.1186/s13071-015-1226-2.
Ticks are blood-feeding arthropods that can affect human and animal health both directly by blood-feeding and indirectly by transmitting pathogens. The cattle tick Rhipicephalus (Boophilus) microplus is one of the most economically important ectoparasites of bovines worldwide and it is responsible for the transmission of the protozoan Babesia bovis, the etiological agent of bovine babesiosis. Aquaporins (AQPs) are water channel proteins implicated in physiological mechanisms of osmoregulation. Members of the AQP family are critical for blood-feeding arthropods considering the extreme osmoregulatory changes that occur during their feeding. We investigated the pattern of expression of a newly identified AQP2 gene of R. microplus (RmAQP2) in different tick tissues and stages. We also examined in vivo the biological implications of silencing expression of RmAQP2 silencing during tick feeding on either uninfected or B. bovis-infected cattle.
In silico gene analyses were performed by multiple alignments of amino acid sequences and topology prediction. Levels of RmAQP2 transcripts in different tick tissues and stages were analyzed by reverse transcriptase quantitative PCR. Patterns of expression of RmAQP2 protein were investigated by immunoblots. Gene silencing was performed by RNA interference and in vivo functional analyses carried out by feeding ticks on either uninfected or B. bovis-infected cattle.
RmAQP2 transcripts were found in unfed larvae, engorged nymphs, and salivary glands and guts of partially engorged females; however, of all tick tissues and stages examined, RmAQP2 protein was found only in salivary glands of partially engorged females. RmAQP2 silencing significantly reduced tick fitness and completely abrogated protein expression. The effect of RmAQP2 silencing on fitness was more pronounced in females fed on a B. bovis-infected calf than in ticks fed on an uninfected calf and none of their larval progeny survived.
Collectively, considering the gene expression and tick fitness data, we conclude that RmAQP2 is critical for tick blood feeding and may be a suitable candidate target for the development of novel strategies to control R. microplus and tick-borne parasites.
蜱是吸血节肢动物，可通过吸血直接影响人类和动物健康，并通过传播病原体间接影响。牛蜱微小牛蜱（Rhipicephalus (Boophilus) microplus）是全球牛最重要的经济外寄生虫之一，它负责传播原生动物牛巴贝斯虫（Babesia bovis），即牛巴贝斯虫病的病原体。水通道蛋白（AQPs）是参与渗透调节生理机制的水通道蛋白。考虑到吸血节肢动物在进食过程中发生的极端渗透调节变化，AQP家族成员对它们至关重要。我们研究了新鉴定的微小牛蜱AQP2基因（RmAQP2）在不同蜱组织和发育阶段的表达模式。我们还在体内研究了在未感染或感染牛巴贝斯虫的牛身上蜱进食期间沉默RmAQP2表达的生物学意义。
通过氨基酸序列的多重比对和拓扑预测进行计算机基因分析。通过逆转录定量PCR分析不同蜱组织和发育阶段的RmAQP2转录本水平。通过免疫印迹研究RmAQP2蛋白的表达模式。通过RNA干扰进行基因沉默，并通过让蜱吸食未感染或感染牛巴贝斯虫的牛进行体内功能分析。
在未进食的幼虫、饱血若虫以及部分饱血雌蜱的唾液腺和肠道中发现了RmAQP2转录本；然而，在所有检查的蜱组织和发育阶段中，仅在部分饱血雌蜱的唾液腺中发现了RmAQP2蛋白。RmAQP2沉默显著降低了蜱的适应性并完全消除了蛋白表达。RmAQP2沉默对适应性的影响在吸食感染牛巴贝斯虫小牛的雌蜱中比在吸食未感染小牛的蜱中更明显，并且它们的幼虫后代均未存活。
总体而言，考虑到基因表达和蜱适应性数据，我们得出结论，RmAQP2对蜱吸血至关重要，可能是开发控制微小牛蜱和蜱传寄生虫新策略的合适候选靶点。
