Exon-intron structure and sequence variation of the calreticulin gene among Rhipicephalus sanguineus group ticks

Abstract

BackgroundCalreticulin proteins (CRTs) are important components of tick saliva, which is involved in the blood meal success, pathogen transmission and host allergic responses. The characterization of the genes encoding for salivary proteins, such as CRTs, is pivotal to understand the mechanisms of tick-host interaction during blood meal and to develop tick control strategies based on their inhibition. In hard ticks, crt genes were shown to have only one intron with conserved position among species. In this study we investigated the exon-intron structure and variation of the crt gene in Rhipicephalus spp. ticks in order to assess the crt exon-intron structure and the potential utility of crt gene as a molecular marker.MethodsWe sequenced the exon-intron region of crt gene in ticks belonging to so-called tropical and temperate lineages of Rhipicephalus sanguineus (sensu lato), Rhipicephalus sp. I, Rhipicephalus sp. III, Rhipicephalus sp. IV, R. guilhoni, R. muhsamae and R. turanicus. Genetic divergence and phylogenetic relationships between the sequences obtained were estimated.ResultsAll individuals belonging to the tropical lineage of R. sanguineus (s.l.), R. guilhoni, R. muhsamae, R. turanicus, Rhipicephalus sp. III and Rhipicephalus sp. IV analysed showed crt intron-present alleles. However, both crt intron-present and intron-absent alleles were found in Rhipicephalus sp. I and the temperate lineage of R. sanguineus (s.l.), showing the occurrence of an intraspecific intron presence-absence polymorphism. Phylogenetic relationships among the crt intron-present sequences showed distinct lineages for all taxa, with the tropical and temperate lineages of R. sanguineus (s.l.) being more closely related to each other.ConclusionsWe expanded previous studies about the characterization of crt gene in hard ticks. Our results highlighted a previously overlooked variation in the crt structure among Rhipicephalus spp., and among hard ticks in general. Notably, the intron presence/absence polymorphism observed herein can be a candidate study-system to investigate the early stages of intron gain/loss before fixation at species level and some debated questions about intron evolution. Finally, the sequence variation observed supports the suitability of the crt gene for molecular recognition of Rhipicephalus spp. and for phylogenetic studies in association with other markers.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1909-3) contains supplementary material, which is available to authorized users.

The many faces of parasite calreticulin

“…Indeed, oral immunization with TsCalr results in 37% reduction in worm burden and delayed development in a taenisosis experimental model. In addition, TsCalr is expressed in the tegumentary and muscle cytons, neutralization by specific anti-TsCalr IgA could interfere with nutrition across the tegument ( 17 , 57 ). In T. solium organs involved in infection, such as the suckers, showed upregulation of Calr.…”

Beyond taxonomy: species complexes in New World phlebotomine sand flies

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“…Szcześniak et al, 2011), ongoing presence/absence polymorphism has never been observed in sponges and only rarely been detected in other groups. To our knowledge, it has only been described in a relatively small number of cases including a Drosophila species (Llopart et al, 2002), Daphnia pulex (Omilian et al, 2008), in a group of closely related Mycosphaerella species (Torriani et al, 2011), and in the tick Rhipicephalus sanguineus (Porretta et al, 2016). Given the rarity of such case studies, each one represents a valuable opportunity to increase our understanding of the evolutionary processes that lead to intron gains and losses in genomes and explain the enormous variation in intron number across eukaryotes.…”

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