Salivary glands are vital to tick feeding success and also play a crucial role in tick-borne pathogen transmission. In previous studies of Ixodes scapularis salivary glands, we demonstrated that saliva-producing type II and III acini are innervated by neuropeptidergic axons which release different classes of neuropeptides via their terminals (Šimo et al., 2009b, 2013). Among these, the neuropeptide SIFamide-along with its cognate receptor-were postulated to control the basally located acinar valve via basal epithelial and myoepithelial cells (Vancová et al., 2019). Here, we functionally characterized a second SIFamide receptor (SIFa_R2) from the I. scapularis genome and proved that it senses a low nanomolar level of its corresponding ligand. Insect SIFamide paralogs, SMYamides, also activated the receptor but less effectively compared to SIFamide. Bioinformatic and molecular dynamic analyses suggested that I. scapularis SIFamide receptors are class A GPCRs where the peptide amidated carboxy-terminus is oriented within the receptor binding cavity. The receptor was found to be expressed in Ixodes ricinus salivary glands, synganglia, midguts, trachea, and ovaries, but not in Malpighian tubules. Investigation of the temporal expression patterns suggests that the receptor transcript is highly expressed in unfed I. ricinus female salivary glands and then decreases during feeding. In synganglia, a significant transcript increase was detected in replete ticks. In salivary gland acini, an antibody targeting the SIFa_R2 recognized basal epithelial cells, myoepithelial cells, and basal granular cells in close proximity to the SIFamide-releasing axon terminals. Immunoreactivity was also detected in specific neurons distributed throughout various I. ricinus synganglion locations. The current findings, alongside previous reports from our group, indicate that the neuropeptide SIFamide acts via two different receptors that regulate distinct or common cell types in the basal region of type II and III acini in I. ricinus salivary glands. Our study investigates the peptidergic regulation of the I. ricinus salivary gland in detail, emphasizing the complexity of this system.
- MeSH
- klíště * genetika metabolismus MeSH
- neurony metabolismus MeSH
- neuropeptidy * genetika metabolismus MeSH
- slinné žlázy metabolismus MeSH
- sliny MeSH
- zvířata MeSH
- Check Tag
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Ticks are hematophagous ectoparasites that transmit a wide range of pathogens. The lone star tick, Amblyomma americanum, is one of the most widely distributed ticks in the Midwest and Eastern United States. Lone star ticks, as other three-host ixodid ticks, can survive in harsh environments for extended periods without a blood meal. Physiological mechanisms that allow them to survive during hot and dry seasons include thermal tolerance and water homeostasis. Dermal fluid secretions have been described in metastriate ticks including A. americanum. We hypothesized that tick dermal secretion in the unfed tick plays a role in thermoregulation, as described in other hematophagous arthropods during blood feeding. In this study, we found that physical contact with a heat probe at 45 °C or high environmental temperature at ∼50 °C can trigger dermal secretion in A. americanum and other metastriate ticks in the off-host period. We demonstrated that dermal secretion plays a role in evaporative cooling when ticks are exposed to high temperatures. We find that type II dermal glands, having paired two cells and forming large glandular structures, are the source of dermal secretion. The secretion was triggered by an injection of serotonin, and the serotonin-mediated secretion was suppressed by a pretreatment with ouabain, a Na/K-ATPase blocker, implying that the secretion is controlled by serotonin and the downstream Na/K-ATPase.
- MeSH
- adenosintrifosfatasy MeSH
- Amblyomma MeSH
- Ixodidae * fyziologie MeSH
- klíšťata * MeSH
- serotonin MeSH
- termoregulace MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- Geografické názvy
- Spojené státy americké MeSH
Regulatory factors controlling tick salivary glands (SGs) are direct upstream neural signaling pathways arising from the tick's central nervous system. Here we investigated the cholinergic signaling pathway in the SG of two hard tick species. We reconstructed the organization of the cholinergic gene locus, and then used in situ hybridization to localize mRNA encoding choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT) in specific neural cells in the Ixodes synganglion. Immunohistochemical staining revealed that cholinergic axonal projections exclusively reached type I acini in the SG of both Ixodes species. In type I acini, the rich network of cholinergic axons terminate within the basolateral infoldings of the lamellate cells. We also characterized two types (A and B) of muscarinic acetylcholine receptors (mAChRs), which were expressed in Ixodes SG. We pharmacologically assessed mAChR-A to monitor intracellular calcium mobilization upon receptor activation. In vivo injection of vesamicol-a VAChT blocker-at the cholinergic synapse, suppressed forced water uptake by desiccated ticks, while injection of atropine, an mAChR-A antagonist, did not show any effect on water volume uptake. This study has uncovered a novel neurotransmitter signaling pathway in Ixodes SG, and suggests its role in water uptake by type I acini in desiccated ticks.
- MeSH
- acinární buňky metabolismus fyziologie MeSH
- axony metabolismus MeSH
- centrální nervový systém metabolismus MeSH
- cholin-O-acetyltransferasa genetika metabolismus MeSH
- cholinergní látky metabolismus MeSH
- klíště metabolismus MeSH
- messenger RNA metabolismus MeSH
- neurony cholinergní metabolismus fyziologie MeSH
- neurony metabolismus MeSH
- signální transdukce genetika MeSH
- slinné žlázy metabolismus fyziologie MeSH
- vezikulární transportní proteiny acetylcholinu genetika metabolismus MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Ixodid ticks are ectoparasites that feed exclusively on blood as their source of nutrients. Although ticks spend most of their life off the host, until now it has been assumed that the blood and the water vapor are the only sources of water to maintain water balance and prevent desiccation. Here we report for the first time that adult lone star ticks, Amblyomma americanum, also actively drink nutrient-free water, which greatly increases their survival. The volume of ingested water is greater in females than males (0.55 ± 0.06 vs 0.44 ± 0.07 µl) and most likely due to differences in tick size. Water uptake occurs through mouthparts and it can be later observed in the salivary glands and the midgut. We also exploited this behavior by adding a variety of inorganic compounds and microorganisms to water. Addition of inorganic salts to drinking water such as KH2PO4 + NaCl+KNO3 resulted in 100% tick mortality within 3 days. As a proof of concept for using the water drinking as a delivery route of toxic reagents for ticks, we also show that adding Pseudomonas aeruginosa to drinking water quickly leads to tick death. This tick behavior can be exploited to target important physiological systems, which would make ticks vulnerable to dehydration and microbial dysbiosis.
- MeSH
- infestace klíšťaty parazitologie MeSH
- Ixodidae účinky léků fyziologie MeSH
- pití MeSH
- soli aplikace a dávkování toxicita MeSH
- stravovací zvyklosti MeSH
- voda aplikace a dávkování MeSH
- vysoušení MeSH
- zvířata MeSH
- Check Tag
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Ticks can survive in harsh and fluctuating vegetated environments for long durations between blood feedings with highly developed osmoregulatory mechanisms. Like the unique life history of hematophagous ticks, osmoregulatory organs and their regulatory mechanisms are significantly different from those in the closely related insect taxa. Over the last ten years, research has uncovered several neuropeptidergic innervations of the primary osmoregulatory organ, the salivary glands: myoinhibitory peptide (MIP), SIFamide, and elevenin. These neuropeptides are thought to be modulators of dopamine's autocrine or paracrine actions controlling the salivary glands, including the activation of fluid transport into the lumen of salivary acini and the pumping and gating action of salivary acini for expelling fluids out into salivary ducts. These actions are through two different dopamine receptors, D1 receptor and invertebrate D1-like dopamine receptor, respectively. Interestingly, MIP and SIFamide are also involved in the control of another important excretory/osmoregulatory organ, the hindgut, where SIFamide is myostimulatory, with MIP having antagonistic effects. FGLamide related allatostatin is also found to have axonal projections located on the surface of the rectum. Investigations of the osmoregulatory mechanisms of these critical vector species will potentially lead to the development of a measure to control tick species.
- MeSH
- axony metabolismus ultrastruktura MeSH
- biologické modely MeSH
- dopamin metabolismus MeSH
- endokrinní systém metabolismus MeSH
- fluorescenční barviva metabolismus MeSH
- klíště metabolismus MeSH
- neurony metabolismus MeSH
- orgánová specificita * MeSH
- osmoregulace * MeSH
- slinné žlázy metabolismus MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
- Research Support, N.I.H., Extramural MeSH
The salivary gland of hard ticks is a highly innervated tissue where multiple intertwined axonal projections enter each individual acini. In the present study, we investigated the ultrastructural architecture of axonal projections within granular salivary gland type II and III acini of Ixodes ricinus female. Using immunogold labeling, we specifically examined the associations of SIFamide neuropeptide, SIFamide receptor (SIFa_R), neuropeptide pigment dispersing factor (PDF), and the invertebrate-specific D1-like dopamine receptor (InvD1L), with acinar cells. In both acini types, SIFamide-positive axons were found to be in direct contact with either basal epithelial cells or a single adlumenal myoepithelial cell in close proximity to the either the acinar duct or its valve, respectively. Accordingly, SIFa_R staining correlated with SIFamide-positive axons in both basal epithelial and myoepithelial cells. Immunoreactivity for both InvD1L and PDF (type II acini exclusively) revealed positive axons radiating along the acinar lumen. These axons were primarily enclosed by the adlumenal myoepithelial cell plasma membrane and interstitial projections of ablumenal epithelial cells. Our study has revealed the detailed ultrastructure of I. ricinus salivary glands, and provides a solid baseline for a comprehensive understanding of the cell-axon interactions and their functions in this essential tick organ.
- MeSH
- axony metabolismus ultrastruktura MeSH
- Ixodidae MeSH
- klíště ultrastruktura MeSH
- receptory dopaminové metabolismus MeSH
- slinné žlázy inervace metabolismus ultrastruktura MeSH
- transmisní elektronová mikroskopie MeSH
- zvířata MeSH
- Check Tag
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
