Myoinhibitory peptide and pigment dispersing factor peptidergic inervation of the salivary glands of the blacklegged tick (Ixodes scapularis Say)

Peptidergic signal system is an ancient cell-cell communication mechanism and involved in numerous behavioral and physiology events of multicellular organisms. We have been interested in exploring neuropeptidergic system in the blacklegged tick (Ixodes scapularis Say) that transmits Lyme disease. We focused to the neuropeptides that are involved in the control of salivary glands. Salivary secretion in the tick is an essential process allowing the long-term blood feeding. Immunohistochemistry using a total of 15 different antibodies, originally raised against various insect neuropeptides, were performed to identify immunoreactive cells and neural projections. Specific staining patterns in the immunohistochemitry indicated that the tick nervous system is a rich source of diverse neuropeptides which are related to those identified in insects and in other arthropods. Particularly, we found the immunoreactivities for myoinhibitory peptide (MIP) and pigment dispersing factor (PDF) showing the nervous projections innervating the acini of salivary glands. We also used peptidomics tools (proteomics) to identify the neuropeptides in synganglia extract using matrix-assisted laser desorption ionization-time of flight/time of flight (MALDI-TOF/TOF). We identified a 1322 Da peptide with the sequence ASDWNRLSGMWamide, having the signature of typical MIP W(6X)Wamide motif. The gene encoding MIP was also identified in the genome sequence. It encodes two consecutive MIP-like mature peptides including the peptide identified in MALDI as ASDWNRLSGMWamide. This study opens a new area in the neuropeptidergic system of tick, particularly, for understanding the roles of neuropeptides in the control of salivary glands, which has not been studied before.