Abstract
Illumina and 454 pyrosequencing were used to characterize genes from the synganglion of female Ixodes scapularis. GO term searching success for biological processes was similar for samples sequenced by both methods. However, for molecular processes, it was more successful for the Illumina samples than for 454 samples. Functional assignments of transcripts predicting neuropeptides, neuropeptide receptors, neurotransmitter receptors and other genes of interest was done, supported by strong e-values (<−6), and high consensus sequence alignments. Transcripts predicting 15 putative neuropeptide prepropeptides ((allatostatin, allatotropin, bursicon α, corticotropin releasing factor (CRF), CRF-binding protein, eclosion hormone, FMRFamide, glycoprotein A, insulin-like peptide, ion transport peptide, myoinhibitory peptide, inotocin ( = neurophysin-oxytocin), Neuropeptide F, sulfakinin and SIFamide)) and transcripts predicting receptors for 14 neuropeptides (allatostatin, calcitonin, cardioacceleratory peptide, corazonin, CRF, eclosion hormone, gonadotropin-releasing hormone/AKH-like, insulin-like peptide, neuropeptide F, proctolin, pyrokinin, SIFamide, sulfakinin and tachykinin) are reported. Similar to Dermacentor variabilis, we found transcripts matching pro-protein convertase, essential for converting neuropeptide hormones to their mature form. Additionally, transcripts predicting 6 neurotransmitter/neuromodulator receptors (acetylcholine, GABA, dopamine, glutamate, octopamine and serotonin) and 3 neurotransmitter transporters (GABA transporter, noradrenalin-norepinephrine transporter and Na+-neurotransmitter/symporter) are described. Further, we found transcripts predicting genes for pheromone odorant receptor, gustatory receptor, novel GPCR messages, ecdysone nuclear receptor, JH esterase binding protein, steroidogenic activating protein, chitin synthase, chitinase, and other genes of interest. Also found were transcripts predicting genes for spermatogenesis-associated protein, major sperm protein, spermidine oxidase and spermidine synthase, genes not normally expressed in the female CNS of other invertebrates. The diversity of messages predicting important genes identified in this study offers a valuable resource useful for understanding how the tick synganglion regulates important physiological functions.
Highlights
Ticks are obligate blood-feeding ectoparasites that serve as vectors of the causative agents of many important diseases affecting humans and animals, e.g., Lyme disease, Rocky Mountain spotted fever, tick-borne encephalitis, anaplasmosis, babesiosis and many others [1,2]
Comparing our findings with the transcriptome of D. variabilis done by 454 pyrosequencing [26,27], we found transcripts encoding for several of the same neuropeptides, encoding for allatostatin, and encoding for the peptides bursicon, glycoprotein A, eclosion hormone, insulin-like peptide, ion transport peptide, orcokinin, and sulfakinin
We found transcripts encoding for 7 other neuropeptides, namely, allatotropin, corticotropin-releasing factor (CRF), FMRFamide, myoinhibitory peptide, neurophysinisotocin, neuropeptide F, and SIFamide that were not found in the transcriptome of the D. variabilis synganglion
Summary
Ticks are obligate blood-feeding ectoparasites that serve as vectors of the causative agents of many important diseases affecting humans and animals, e.g., Lyme disease, Rocky Mountain spotted fever, tick-borne encephalitis, anaplasmosis, babesiosis and many others [1,2]. The molecular basis for understanding just how these complex neurohormone-controlled networks regulate tick physiological functions remains to be determined To this end, a global search to identify and characterize the numerous molecules expressed in the synganglion is needed. Transcriptome analysis of the synganglion of the brown dog tick, Rhipicephalus sanguineus, was done with cDNA library construction in phage resistant Escherichia coli This method yielded a total of only 1008 ESTs sequenced, with only 603 remaining after removal of vector contamination that could be clustered into unique transcripts [20]. Neuropeptides and their receptors have been predicted in several species of hard ticks using bioinformatics [28] and immunohistochemistry [24] and identified by MALDI-TOF/ TOF mass spectrometry [29]. We believe that the assembled, annotated transcriptomes described in this report will provide an invaluable resource for future studies of the role of the genes involved in neurologic functioning of the tick nervous system
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