Pyrokinin receptor silencing in females of the southern cattle tick Rhipicephalus (Boophilus) microplus is associated with a reproductive fitness cost

Authors: WULFF, JUAN - Texas A&M University; Temeyer, Kevin; Tidwell, Jason; Schlechte, Kristie; Lohmeyer, Kimberly - Kim; PIETRANTONIO, PATRICIA - Texas A&M University

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2022
Publication Date: 7/11/2022
Citation: Wulff, J.P., Temeyer, K.B., Tidwell, J.P., Schlechte, K.G., Lohmeyer, K.H., Pietrantonio, P.V. 2022. Pyrokinin receptor silencing in females of the southern cattle tick Rhipicephalus (Boophilus) microplus is associated with a reproductive fitness cost. Parasites & Vectors. https://doi.org/10.1186/s13071-022-05349-w.
DOI: https://doi.org/10.1186/s13071-022-05349-w

Interpretive Summary: Cattle fever ticks transmit at least two potentially fatal diseases to cattle and are a worldwide threat to cattle producers. Tick control is dependent on chemical acaricides, however, ticks have developed resistance to nearly all acaricides, emphasizing the need for development of new tick control technologies. Cooperative research between scientists from Texas A&M University and U.S. Department of Agriculture reports that silencing of a hormone-like receptor in ticks results in decreased survival and reproduction of the ticks, suggesting that the tick hormone receptor may be a valuable target for development of new chemical acaricides.

Technical Abstract: Background: Rhipicephalus microplus is the vector of deadly cattle pathogens, especially Babesia spp., for which a recombinant vaccine is not available. Therefore, disease control depends on tick vector control. However, R. microplus populations worldwide have developed resistance to available acaricides, prompting the search for novel acaricide targets. G protein-coupled receptors (GPCRs) are involved in the regulation of many physiological processes and were suggested as druggable targets for the control of arthropod vectors. Arthropod-specific signaling systems of small neuropeptides are investigated for such purpose. The pyrokinin receptor (PKR) is a GPCR previously characterized in ticks. Pyrokinins myotropic activity in feeding tissues of Rhipicephalus sanguineus and Ixodes scapularis was recently reported. Methods: The Rhimi-PKR was silenced through RNA interference (RNAi) in females. To optimize RNAi, a dual-luciferase assay was applied to determine the silencing efficiency of two Rhimi-PKR-double stranded RNAs (dsRNA) prior to injecting dsRNA in ticks to be placed on cattle. Phenotypic variables of female ticks obtained at the end- point of the RNAi experiment were compared to those of control female ticks (non-injected and beta-lactamase dsRNA-injected). Rhimi-PKR silencing was verified by quantitative reverse-transcriptase PCR (qRT-PCR) in whole females and dissected tissues. Results: The Rhimi-PKR transcript was expressed in all developmental stages. Rhimi-PKR silencing was confirmed in whole ticks 3-day after injection, and in tick carcass, ovary and synganglion after 5 days of injection. Rhimi-PKR silencing was associated with increased mortality and decreased weight of surviving females and of egg masses (P < 0.05). Delays in repletion, pre-oviposition and incubation periods were observed (P < 0.05). Conclusions: Rhimi-PKR silencing negatively affected the female reproductive fitness. The PKR appears to be directly or indirectly associated with the regulation of female feeding and/or reproductive output in R. microplus. Antagonists of the pyrokinin signaling system could be explored for tick control.