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Impact of dopamine-mediated salivary secretion in the early and late phase of tick blood-feeding
The salivary glands of hard ticks consist of three types (type I, II, and III) of acini according to their functions and location. The type II and III acini play critical roles in tick salivation, which is likely controlled by a variety of neuropeptides or neurotransmitter via interaction with their receptor, G protein-coupled receptors (GPCRs). Orchestration of dopamine receptor (D1) and invertebrate specific D1-like dopamine receptor (InvD1L) located in type II and III acini precisely control tick salivary secretion via collection of primary saliva in the lumen and expulsion of collected saliva, respectively. The two dopamine receptors (D1 and InvD1L) in Haemaphysalis longicornis were identified as 1278 bp (426 aa) and 1362 bp (454 aa) in length, respectively. Both dopamine receptors were functionally analyzed through Ca2+ and cAMP assay using the heterologous expression system. The transcripts of D1 and InvD1L were profiled from synganglion and salivary glands of female ticks (unfed, 3/18/60/96 post blood meal and replete). D1 and InvD1L were significantly upregulated in the early phase of blood feeding from female H. longicornis. Salivary secretion induced by dopamine was significantly reduced by RNAi of D1 and InvD1L. Interestingly, RNAi of two dopamine receptors induced a significantly longer period of blood feeding in female ticks, which were significantly lighter after feeding than control. Taken together, it was suggested that D1 and InvD1L play critical roles in early and late phase of tick blood feeding for feeding capability.
