Gut transcriptome analysis on females of Ornithodoros mimon (Acari: Argasidae) and phylogenetic inference of ticks

Abstract

Ornithodoros mimon is an argasid tick that parasitizes bats, birds and opossums and is also harmful to humans. Knowledge of the transcripts present in the tick gut helps in understanding the role of vital molecules in the digestion process and parasite-host relationship, while also providing information about the evolution of arthropod hematophagy. Thus, the present study aimed to know and ascertain the main molecules expressed in the gut of argasid after their blood meal, through analysis on the gut transcriptome of engorged females of O. mimon using 454-based RNA sequencing. The gut transcriptome analysis reveals several transcripts associated with hemoglobin digestion, such as serine, cysteine, aspartic proteases and metalloenzymes. The phylogenetic analysis on the peptidases confirmed that most of them are clustered with other tick genes. We recorded the presence a cathepsin O peptidase-coding transcript in ticks. The topology of the phylogenetic inferences, based on transcripts of inferred families of homologues, was similar to that of previous reports based on mitochondrial genome and nuclear rRNA sequences. We deposited 2,213 sequence of O. mimon to the public databases. Our findings may help towards better understanding of important argasid metabolic processes, such as digestion, nutrition and immunity.Keywords: Argasidae, transcriptome, gut, phylogeny, Ornithodoros mimon. ResumoOrnithodoros mimon é um carrapato argasídeo parasita de morcegos, aves e marsupiais, além de ser bastante agressivo aos humanos. O conhecimento dos transcritos presentes no intestino dos carrapatos auxilia no entendimento do papel de moléculas vitais no processo de digestão e na relação parasito-hospedeiro, além de fornecer também informações sobre a evolução dos artrópodes hematófagos. Desta maneira, o presente estudo teve como objetivo conhecer e identificar as principais moléculas expressas no intestino de uma espécie de carrapato argasídeo após o repasto sanguíneo, através de uma análise transcritômica descritiva do intestino de fêmeas ingurgitadas de O. mimon, utilizando um sequenciamento de RNA de nova geração da plataforma 454. Além de inferir a relação filogenética de carrapatos através de um conjunto de dados transcritômicos. O transcriptoma do intestino revelou diversos transcritos associados com a digestão da hemoglobina, como proteinases das classes serino, cisteína, aspártica e metalo. Registramos a presença de um transcrito de uma cisteína peptidase do tipo catepsina O em carrapatos. A inferência filogenética baseada em conjunto de dados transcritos homólogos tem uma resolução topológica similar a de outros conjuntos de dados moleculares. Foram depositados no banco de dados gênico público 2213 transcritos de O. mimon. Os achados obtidos no presente estudo podem contribuir para compreensão dos importantes processos, como digestão, nutrição e imunidade dos carrapatos da família Argasidae, além de fornecer informações sobre a filogenia da ordem Ixodida.

RNA-seq analysis of the salivary glands and midgut of the Argasid tick Ornithodoros rostratus

“…Most of the other protease inhibitor contigs belonged to the classes of the serine protease inhibitors (Serpins), cystatins and thyropin and were all highly expressed in the MG. Those were also the main classes of protease inhibitors found in O. mimon MG 15 . Serpin domains were also found in MG of O. moubata 9 .…”

“…These domains are normally described as cysteine-protease inhibitors and binding partners of heparin 59 . They have been found in transcriptomes of ticks’ SG and MG, including the Ornithodoros genus 15,60 . Their function for ticks, however, remains unknown.…”

A physiologic overview of the organ-specific transcriptome of the cattle tick Rhipicephalus microplus

“…To address this singularity of the biology of ticks, we prepared cDNA libraries from DIG that were isolated from (1) partially engorged adult females (DIG-P) that were still engaged in the process blood feeding and were in the "big sip" stage, and (2) fully engorged females (DIG-F) that had already completed blood meal and have detached from the host. To our knowledge, this is the first transcriptomic analysis of this cell type, as other previous studies on gene expression in tick gut have used whole organ extracts 16,82,83 .…”

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

“…Due to an increase in its epidemiological importance, I. ricinus has become a species featured in many recent transcriptomic studies, the majority of them focused on the transcription in salivary glands and/or midgut, which are the key organs in the tick-borne pathogens' lifecycle. Studying these organs in response to blood-feeding can be instrumental for the identification of factors that underlie survival and dissemination of pathogens within their vector and their transmission into the final host [24,[31][32][33][34][35][36][37] . More specifically, expression analyses using tick haemocytes, the main actors in tick immunity, can unveil the character of the immunity barrier for tick-borne pathogens [29].…”