Genomics of tick reproduction and development

Abstract

The major hemelipoglyco-carrier protein (CP) found throughout the development of male and female adult American dog ticks, Dermacentor variabilis (Say) was sequenced. DvCP is a single transcript coding for two protein subunits that together contain three motifs—(a) a lipoprotein n-terminal domain that is a common attribute of proteins that bind lipids, carbohydrates and metals, (b) a domain of unknown function characteristic of proteins with several large open beta sheets and (c) a von Willebrand factor type D domain near the carboxy-terminus apparently important for multimerization. These motifs also found in tick vitellogenin are not shared by heme-binding proteins studied thus far in other hematophagous insects. DvCP message was highest in fat body and salivary gland but was also found in midgut and ovary. Expression was initiated by blood feeding in virgin females and not by mating typical of tick vitellogenin (Vg); and the message was found in fed males at levels similar to part fed, virgin females. CP appears to be highly conserved among the Ixodida and shares a common origin with Vg. In the second part of this study, the tick synganglion transcriptome was studied by pyrosequencing to identify neuropeptides that regulated reproduction and development. Greater than 500,000 reads were assembled into 21,119 contiguous sequences of which 10,674 could be putatively identified. Twelve putative neuropeptides and five neuropeptide receptors from the synganglion of D. variabilis were selected for further study. Many of these neuropeptides such as an allatostatin, insulin-like peptide, eclosion hormone, bursicon alpha and beta and glycoprotein hormone alpha and beta have not been previously described in the Chelicerata. An insulin receptor substrate protein was also found indicating that at insulin signaling network is present in ticks. A putative type-2 proprotein processing convertase was sequenced that may be involved in cleavage at monobasic and dibasic endoproteolytic cleavage sites in prohormone peptides. Synganglion specific quantitative real-time PCR data were obtained for all of the putative neuropeptides, neuropeptide receptors and proprotein processing convertase in order to gain an initial understanding of their role in the synganglion during adult tick blood feeding and reproduction.