Dynamics of insulin signaling in the black-legged tick, Ixodes scapularis

Ticks are obligate hematophagous parasites and are important vectors of a wide variety of pathogens. Lyme disease (LD) caused by the spirochete Borrelia burgdorferi and vectored by the black-legged tick, Ixodes scapularis, is the most prevalent vector-borne disease in the United States. Despite their importance, our knowledge of the biology of the ticks on a molecular level is limited. Insulin-like peptides (ILPs) have been identified in several invertebrates, particularly insects, and work on these ILPs has revealed many roles including regulation of energy homeostasis, growth, development, and lifespan to name a few. However, information on arthropod ILPs outside of insects is sparse. Studies of Ixodid tick ILPs are particularly scarce, despite their importance as vectors of infectious agents, most notably Lyme disease.
The publication of the tick genome and the recent development of functional genomics tools in ticks have advanced opportunities to study these organisms on a molecular level. Through bioinformatics searches of the tick genome and other available I. scapularis databases, we identified four putative ILP sequences, one IR, and two putative relaxin receptors. Full-length sequences of these ILP transcripts were confirmed, and quantitative RT-PCR was used to examine expression levels of these ILPs in different life stages, feeding states, and adult tissues. This work serves as an initial characterization of ILP expression in ticks and provides the foundation for further exploration of the roles of ILPs in these important arthropod vectors.