Targeted silencing of the Aquaporin 2 gene of Rhipicephalus (Boophilus) microplus reduces tick fitness

Abstract

BackgroundTicks 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.MethodsIn 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.ResultsRmAQP2 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.ConclusionsCollectively, 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-015-1226-2) contains supplementary material, which is available to authorized users.

Strategies for new and improved vaccines against ticks and tick‐borne diseases

“…We are entering an era where our understanding of how ticks evade vaccination and immune responses with their highly repetitive genomes, and how to formulate our vaccines to ensure that protective epitopes remain accessible is vital. To date, only two examples of promising combinatorial vaccines are known that of BM86 and subolesin and the peptide vaccine derived from a RV approach (Table ) . Although not fully understood, the functions of BM86 and Subolesin are most likely to be different based on the phenotypes observed after vaccination with individual antigens and the subcellular localization of the antigens.…”

Anti-tick vaccines in the omics era

“…Larger scale proteomic approaches have been used to identify proteins in R. microplus ovaries (68) and gut (69) of engorged females in response to infection with Babesia bovis. Out of these proteomic studies, several anti-tick vaccine antigens were identified and tested in vitro and in vivo (33,70). As the relationship between transcript and protein abundance is not direct and cannot reliably be predicted, proteomic and transcriptomic provide complementary information and are not redundant.…”

“…In addition, there can be physiological issues (99) responsible for the variable efficacy of the vaccines based on Bm86 antigen. Other concealed antigens that have been evaluated for efficacy against the cattle tick are the ribosomal protein P0, showing 96 % efficacy in pen trial (100), Subolesin, showing efficacy from 0-86 % (4), and 68 and 75 % with aquaporin (33,101). The antibodyantigen recognition process is poorly understood in the tick gut, hemolymph, and the intracellular space where tick digestion occurs.…”

Ferritin 1 silencing effect in Rhipicephalus sanguineus sensu lato (Acari: Ixodidae) during experimental infection with Ehrlichia canis

“…Thirty adult females were injected with 0.2 L ferritin 1 dsRNA (9.74 × 10 11 molecules of dsRNA) between the coxa and trochanter I using a nanoinjector (Nanoject, Drummond Scientific, Broomall, PA, USA). The control group was injected with the same volume of elution buffer, similar to what has been described in other studies (Duscher et al, 2014;Hussein et al, 2015). Whilst the use of unrelated dsRNA is now a well-established control in species with full genome annotation, the R. sanguineus genome is poorly annotated, meaning inoculation with unconfirmed unrelated sequences can increase the off target effects in silencing experiments with this species.…”