Receptors for the neuropeptides, myoinhibitory peptide and SIFamide, in control of the salivary glands of the blacklegged tick Ixodes scapularis

Abstract

Tick salivary glands are important organs that enable the hematophagous feeding of the tick. We previously described the innervation of the salivary gland acini types II and III by a pair of protocerebral salivary gland neurons that produce both myoinhibitory peptide (MIP) and SIFamide (Šimo et al., 2009b). In this study we identified authentic receptors expressed in the salivary glands for these neuropeptides. Homology-based searches for these receptors in the Ixodes scapularis genome sequence were followed by gene cloning and functional expression of the receptors. Both receptors were activated by low nanomolar concentrations of their respective ligands. The temporal expression patterns of the two ligands and their respective receptors suggest that the SIFamide signaling system pre-exists in unfed salivary glands, while the MIP system is activated upon initiation of feeding. Immunoreactivity for the SIFamide receptor in the salivary gland was detected in acini types II and III, surrounding the acinar valve and extending to the basal region of the acinar lumen. The location of the SIFamide receptor in the salivary glands suggests three potential target cell types and their probable functions: myoepithelial cells that may function in the contraction of the acini and/or the control of the valve; large, basally located dopaminergic granular cells for regulation of paracrine dopamine; and neck cells that may be involved in the control of the acinar duct and its valve.

Ancestral reconstruction of tick lineages

“…Cholinergic stimulants do not act on isolated salivary glands of hard or soft ticks (Kaufman, 1978;Mans, 2002;Maritz-Olivier, 2005), suggesting that they act on the central nervous system, whereas stimulation of isolated argasid and ixodid salivary glands with dopamine induces secretion (Kaufman, 1977;Mans, 2002;Maritz-Olivier, 2005). Sequence homologs for the receptor for SIFamide (sifa-r) have been detected in salivary gland transcriptomes of ixodid and argasid ticks, suggesting that the SIFamide-dopamine system may be conserved in all ticks (Egekwu et al 2016;Šimo et al 2013; B.J. Mans, unpublished observation).…”

Neuropeptidergic control of the hindgut in the black-legged tick Ixodes scapularis

“…All monoclonal antibodies or polyclonal antisera originally raised against insect neuropeptides were previously described in tick or insect immunohistochemistry (Šimo et al, 2009a, b; Yamanaka et al, 2011). Characterization of affinity-purified antisera against Ixodes SIFamide receptor (SIFa-R) and MIP receptor 1 (MIP-R1) were previously described (Šimo et al, 2013). The negative controls for the immunohistochemistry of the RS for neuropeptide receptors were performed with the primary antibodies preadsorbed with 1 μM of the 20 antigenic amino acid peptides for 4 h at room temperature (RT) or incubation of tissue in pre-immune serum.…”

“…The phylogenetic tree for FGLa/AST-Rs was constructed by a neighbor-joining method using 500 bootstrap replicates in MEGA5 (Kumar et al, 2008) to confirm the orthology with Drosophila FGLa/AST-R. Each FGLa/AST and orcokinin gene in I. scapularis was previously described (Christie, 2008; Donohue et al, 2010; Šimo et al, 2014). Receptors for the MIP and SIFamide, including their ligands, in I. scapularis were described by Šimo et al (2013) and were further investigated in hindgut tissues in this study.…”

“…Due to high nucleotide identity among all four fgla/ast receptors 1 to 4 , we designed primers in untranslated regions to achieve specificity. The primers for mip-r1 and sifa-r were previously used in quantitative real-time PCR in Šimo et al (2013). The 80 bp-long amplicon encoding ribosomal protein S4 (rps4, GenBank Accession No.…”

Myoinhibitory peptide regulates feeding in the marine annelidPlatynereis

“…Many neuropeptides are known to have roles in regulating different aspects of feeding [26][27][28]. MIPs/Wamides are also pleiotropic [29][30][31][32][33][34][35] and regulate aspects of feeding and gut muscle activity in some insects and cnidarians. The first MIP described had a myoinhibitory function on adult locust hindgut [36].…”