Molecular and functional characterization of the first tick CAP2b (periviscerokinin) receptor from Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

• CAP2b/PVK receptor cDNA was cloned from synganglia of female tick R. microplus.
• Receptor transcripts are in Malpighian tubules, salivary gland, synganglion and ovary.
• HA-tagged receptor was stably expressed in a CHO-K1 clonal cell line.
• Only tick CAP2b but not tick pyrokinins could activate the recombinant receptor.
• CAP2b peptides tested contain the canonical C-terminal Val for receptor activation.

The cDNA of the receptor for CAP2b/periviscerokinin (PVK) neuropeptides, designated Rhimi-CAP2b-R, was cloned from synganglia of tick Rhipicephalus (Boophilus) microplus. This receptor is the ortholog of the insect CAP2b/PVK receptor, as concluded from analyses of the predicted protein sequence, phylogenetics and functional expression. Expression analyses of synganglion, salivary gland, Malpighian tubule, and ovary revealed Rhimi-CAP2b-R transcripts. The expression in mammalian cells of the open reading frame of Rhimi-CAP2b-R cDNA fused with a hemagglutinin tag at the receptor N-terminus was confirmed by immunocytochemistry. In a calcium bioluminescence assay the recombinant receptor was activated by the tick Ixodes scapularis CAP2b/PVK and a PVK analog with EC50s of 64 nM and 249 nM, respectively. Tick pyrokinins were not active. This is the first report on the functional characterization of the CAP2b/PVK receptor from any tick species which will now permit the discovery of the physiological roles of these neuropeptides in ticks, as neurohormones, neuromodulators and/or neurotransmitters.

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