Identification, functional characterization and expression patterns of a water-specific aquaporin in the brown dog tick, Rhipicephalus sanguineus

Much is known about the physiology of tick salivation, but nothing is known about the movement of water through the cell membranes of salivary glands, a phenomenon usually associated with water channels or aquaporins (AQPs). An AQP, RsAQP1, was identified in a salivary gland cDNA library of Rhipicephalus sanguineus. In the first functional characterization of an acarine AQP, Xenopus oocytes expressing RsAQP1 became water permeable, whereas RsAQP1 did not transport glycerol or urea. RsAQP1 was inhibited by Hg2+ but not by triethylammonium. Treatment with a protein kinase A activator (cAMP) had no effect on RsAQP1 transport, whereas treatment with a protein kinase C activator (phorbol 12,13-dibutyrate) reduced water flux by 60%. RsAQP1 transcript was present in unfed larvae, nymphs and adult R. sanguineus, but absent in embryos. Partially fed female R. sanguineus expressed RsAQP1 in gut, Malpighian tubules and was particularly abundant in salivary gland tissue, but absent in ovary and synganglion tissues. Because of the importance of water management in tick biology for both the off-host and on-host phases of the life cycle, our findings on tick AQP1 represent a major advancement in our understanding of tick osmoregulation that could potentially be exploited in tick control.