Tick saliva: secret to blood feeding success

The salivary glands of ticks serve several functions that are essential for successful blood feeding. They help establish the feeding lesion and secrete a remarkably complex mixture of antihemostatic proteins, lipids, and other molecules that disarm skin resident and invading immune cells, dilute blood vessels and prevents blood coagulation. Tick saliva effectively anesthetizes the skin surrounding the tick's mouth parts, blocks blood coagulation, wound healing and compromises anti-tick immunity. In hard ticks, the salivary glands also secrete cement that binds the tick tightly to the host, facilitating long-term feeding while also excreting excess blood meal water, enabling them to greatly increase the volume of blood consumed. Tick saliva also extracts moisture from humid atmospheres, helping to maintain body water balance during lengthy periods between blood feeding. Precisely how they accomplish these remarkable feats and the pathogens that exploit these processes is explored in the scientific articles included in this special research topic.

Although a great deal has been learned about the composition of tick saliva and the functions of many of its numerous molecules, the story is still not complete. Recent reviews have reported more than 500 proteins and peptides secreted during blood feeding, many of which have no known orthologs with salivary proteins in other haematophagous arthropods and no known function. Many of the secreted proteins are grouped in well recognized protein families, e.g., chitinases, mucins, cystatins, defensins, hyaluronidases, Kunitz-type, lipocalins, metalloproteases, but others have not been categorized. Often, annotations assigned to these molecules are tenuous and need verification. In addition, mRNAs and microRNAs also have been reported in the saliva of some ticks. The goal of this research topic is to focus attention on the proteins, peptides, and other salivary molecules of unknown function as well as genetic changes in known proteins as they adapt to host immune challenge. More specifically, the goal is to encourage studies using modern genetic tools (e.g., CRISPR, RNAi, etc.) to determine the precise roles of all these proteins, both known and unknown, in the blood feeding process.

The specific themes of the research topic are to encourage studies using modern genetic tools to determine the functional roles of tick salivary peptides and proteins, both known and unknown, to gain a more comprehensive understanding the way they are used to orchestrate blood feeding in ticks. We wish to encourage studies that look for phenotypic changes in the dynamics of tick feeding 1) following CRISPR-mediated gene modifications/deletions; 2) following RNAi knockdown of genes coding for specific salivary proteins; or 3) following vaccination with specific tick salivary molecules, or combinations of molecules, in ticks feeding on appropriate model animals. We also would like to tie these discoveries to specific salivary gland acini and their cell types, and to learn how their expression is regulated by neuropeptides/neurotransmitters from the synganglion. We invite manuscripts that address any and or all of these themes.