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Title: Targeted silencing of the aquaporin 2 gene of rhipicephalus (Boophilus) microplus reduces tick fitness

Author
item HUSSEIN, HALA - Cairo University
item Scoles, Glen
item Ueti, Massaro
item Suarez, Carlos
item ADHAM, FATMA - Cairo University
item Guerrero, Felicito
item BASTOS, REGINALDO - Washington State University

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2015
Publication Date: 12/2/2015
Publication URL: http://handle.nal.usda.gov/10113/61820
Citation: Hussein, H.E., Scoles, G.A., Ueti, M.W., Suarez, C.E., Adham, F.K., Guerrero, F., Bastos, R.G. 2015. Targeted silencing of the aquaporin 2 gene of rhipicephalus (Boophilus) microplus reduces tick fitness. Parasites & Vectors. doi: 10.1186/s13071-015-1226-2.

Interpretive Summary: We demonstrate in this study the pattern of expression of aquaporin 2, a newly identified gene of R. microplus tick. The transcripts were present in unfed larvae, engorged nymphs, and salivary glands and guts of partially fed female ticks. Among several distinct tissues and tick life stages, the newly identified protein was only found in salivary glands of partially engorged females. We demonstrated in vivo that silencing of this gene decreased tick fitness. The effect of gene silencing on tick fitness was even more pronounced in females fed on a Babesia bovis-infected calf and none of their larval progeny survived. We conclude that Aquaporin is involved in osmoregulation during tick feeding and is a potential target for the development of novel strategies to control the biological vector of bovine babesiosis.

Technical Abstract: Ticks are blood-feeding arthropods that can affect human and animal health both directly by up taking blood and indirectly by transmitting pathogens. The cattle tick Rhipicephalus (Boophilus) microplus is one of the most economically important ectoparasites of bovines 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 RT-qPCR. 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. Interestingly, among all tick tissues and stages examined, RmAQP2 protein was only found expressed in salivary glands of partially engorged females. RmAQP2 silencing significantly reduced tick fitness. The effect of RmAQP2 silencing on fitness was even more pronounced in females fed on a B. bovis-infected calf and none of their larval progeny survived. Collectively, considering the gene expression and tick fitness data, we conclude that RmAQP2 is important for tick blood feeding and could be a suitable candidate target for the development of novel strategies to control R. microplus and tick-borne parasites.