Catalogue of stage-specific transcripts in Ixodes ricinus and their potential functions during the tick life-cycle

Abstract

Background: The castor bean tick Ixodes ricinus is an important vector of several clinically important diseases, whose prevalence increases with accelerating global climate changes. Characterization of a tick life-cycle is thus of great importance. However, researchers mainly focus on specific organs of fed life stages, while early development of this tick species is largely neglected. Methods: In an attempt to better understand the life-cycle of this widespread arthropod parasite, we sequenced the transcriptomes of four life stages (egg, larva, nymph and adult female), including unfed and partially blood-fed individuals. To enable a more reliable identification of transcripts and their comparison in all five transcriptome libraries, we validated an improved-fit set of five I. ricinus-specific reference genes for internal standard normalization of our transcriptomes. Then, we mapped biological functions to transcripts identified in different life stages (clusters) to elucidate life stage-specific processes. Finally, we drew conclusions from the functional enrichment of these clusters specifically assigned to each transcriptome, also in the context of recently published transcriptomic studies in ticks. Results: We found that reproduction-related transcripts are present in both fed nymphs and fed females, underlining the poorly documented importance of ovaries as moulting regulators in ticks. Additionally, we identified transposase transcripts in tick eggs suggesting elevated transposition during embryogenesis, co-activated with factors driving developmental regulation of gene expression. Our findings also highlight the importance of the regulation of energetic metabolism in tick eggs during embryonic development and glutamate metabolism in nymphs. Conclusions: Our study presents novel insights into stage-specific transcriptomes of I. ricinus and extends the current knowledge of this medically important pathogen, especially in the early phases of its development.

Iripin-3, a New Salivary Protein Isolated From Ixodes ricinus Ticks, Displays Immunomodulatory and Anti-Hemostatic Properties In Vitro

“…Cycling conditions were 95°C for 10 min followed by 45 cycles of 95°C for 15 s, 60°C for 10 s and 72°C for 30 s. The relative quantification of iripin-3 transcripts in tick tissues was performed using the ΔΔCt method ( 60 ). The I. ricinus gene encoding ribosomal protein S4 ( rps4 , GenBank accession number MN728897.1) was utilized as a reference gene for the calculation of relative expression ratios ( 61 , 62 ). Nucleotide sequences of forward and reverse primers as well as amplicon lengths are provided in Supplementary Table 3 .…”

Tick salivary gland transcriptomics and proteomics

“…Further transcriptomics or proteomics studies could even propagate problematic sequences; however, the use of well-established bioinformatics approaches and high-efficiency pipelines together with good quality assessment make it possible to construct reliable tick transcriptome assemblies. 11,34,35…”

“…Bioinformatics advances are therefore needed to refine tick transcript annotation and data submission to a single, accurate, tick‐specific database to solve the problems produced by poor sequence annotation and artefacts. Further transcriptomics or proteomics studies could even propagate problematic sequences; however, the use of well‐established bioinformatics approaches and high‐efficiency pipelines together with good quality assessment make it possible to construct reliable tick transcriptome assemblies 11,34,35 …”

Alternation between taxonomically divergent hosts is not the major determinant of flavivirus evolution

“…These data are in agreement with the view that the genetic diversification of TBFVs mainly occurs during horizontal transmission to the vertebrate hosts ( Grubaugh et al 2016b ). However, due to the life cycle of ticks, which takes approximately three years to complete, such transmissions occur infrequently, eventually resulting in slow viral evolution ( Grubaugh et al 2016b ; Vechtova et al 2020 ). Moreover, transstadial transmission in ticks most likely imposes additional bottlenecks, although available evidence suggests that these are relaxed ( Grubaugh et al 2016b ).…”