Journal Article

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

Lohmeyer, Kimberly H., Pietrantonio, Patricia V., Xiong, Caixing, Schlechte, Kristie G., Temeyer, Kevin B., Tidwell, Jason P., Wulff, Juan P.

2022

Overview

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 have been suggested as druggable targets for the control of arthropod vectors. Arthropod-specific signaling systems of small neuropeptides are being investigated for this purpose. The pyrokinin receptor (PKR) is a GPCR previously characterized in ticks. Myotropic activity of pyrokinins in feeding-related tissues of Rhipicephalus sanguineus and Ixodes scapularis was recently reported. Methods The R. microplus pyrokinin receptor ( Rhimi-PKR ) was silenced through RNA interference (RNAi) in female ticks. 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 endpoint 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 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 4 days after injection, and in the tick carcass, ovary and synganglion 6 days after injection. Rhimi-PKR silencing was associated with an increased mortality and decreased weight of both surviving females and egg masses ( P  < 0.05). Delays in repletion, pre-oviposition and incubation periods were observed ( P  < 0.05). Conclusions Rhimi-PKR silencing negatively affected 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. Graphical abstract

• Publisher: BioMed Central,BioMed Central Ltd,Springer Nature B.V,BMC
• Subject: Acaricides / Acaricides - pharmacology / Amino acids / Animals / Antagonists / Arachnids / Babesia / beta-lactamase / Biomedical and Life Sciences / Biomedicine / Biosynthesis / Carcasses / Cattle / Cattle Diseases / Causes of / Cellular signal transduction / Cloning / Control / Developmental stages / Disease control / Diseases / Double-stranded RNA / eggs / Entomology / Experiments / Feeding / Female / Females / Fitness / G protein-coupled receptors / Gene expression / Genetic aspects / Genetic Fitness / GPCR / Incubation / Incubation period / Infectious Diseases / Injection / Insects / Ixodes scapularis / Laboratories / mortality / Neuropeptides / Nucleotide sequence / Ovaries / Oviposition / Parasitology / Pathogens / PCR / phenotype / Pheromones / Physiological aspects / Physiology / Proteins / pyrokinin / Pyrokinin/pheromone biosynthesis-activating neuropeptide/diapause hormone (PK/PBAN/DH) neuropeptide family / Pyrokinins / Receptors / recombinant vaccines / Recombinants / repletion / Reproductive fitness / reproductive performance / reverse transcriptase polymerase chain reaction / Rhipicephalus - physiology / Rhipicephalus microplus / Rhipicephalus sanguineus / RNA interference / RNA, Double-Stranded / RNA-mediated interference / Signalling systems / Survival / Tick CAPA gene / tick control / Tick fitness / Tick Infestations - veterinary / Tick survival / Tick-borne diseases / Ticks / Tissue / Tropical Medicine / Vaccines / vector control / Vectors / Veterinary Medicine/Veterinary Science / Virology / Zoological research / β Lactamase