Professor Kansas State University Manhattan, Kansas
The lone star tick (Amblyomma americanum) is broadly distributed in the United States and it is an important disease vector to humans and animals. Ticks spend over 90% of their lifetime off the host, thus; their survival during non-feeding periods largely depends on their osmoregulation in hot environments. A. americanum can secrete liquid through their dermal glands, located under the cuticle, after contact with a heated probe (~40 to 50ºC). We have previously proposed that the secretion is a function of evaporative cooling, like sweating in higher animals. In the current work, we characterized the type II dermal glands (source of the secretion), in A. americanum. We observed that the glands consisted of paired two cells each having a thin membrane sac, which is similar to the previous description for Rhipicephalus sanguineus type II glands. Immunohistochemistry of the glands and the dermal layer suggests the absence of neuronal projections, indicating that dermal gland control is unlikely neuronal, but instead, hormonal. We have identified that the tick dermal secretion is elicited by serotonin and the process is inhibited by ouabain (a Na+/K+-ATPase inhibitor) revealing molecular components involved in the secretory response. An RNAseq analysis of the dermal enriched tick cuticle and bioinformatics search revealed one candidate serotonin receptor (5HT-1A) associated with this response. We successfully cloned this receptor and heterologous expression assays showed response to serotonin. Elucidating the signaling pathways in the dermal secretion will allow us to utilize this knowledge for developing a tick management strategy by targeting this physiology.
