Abstract
The cattle tick, Rhipicephalus microplus, is a monoxenous tick that co-evolved with indicine cattle on the Indian subcontinent. It causes massive damage to livestock worldwide. Cattle breeds present heritable, contrasting phenotypes of tick loads, taurine breeds carrying higher loads of the parasite than indicine breeds. Thus, a useful model is available to analyze mechanisms that determine outcomes of parasitism. We sought to gain insights on these mechanisms and used RNA sequencing and Multidimensional Protein Identification Technology (MudPIT) to generate a transcriptome from whole larvae and salivary glands from nymphs, males and females feeding on genetically susceptible and resistant bovine hosts and their corresponding proteomes. 931,698 reads were annotated into 11,676 coding sequences (CDS), which were manually curated into 116 different protein families. Male ticks presented the most diverse armamentarium of mediators of parasitism. In addition, levels of expression of many genes encoding mediators of parasitism were significantly associated with the level and stage of host immunity and/or were temporally restricted to developmental stages of the tick. These insights should assist in developing novel, sustainable technologies for tick control.
Highlights
The cattle tick, Rhipicephalus microplus, is a monoxenous tick that co-evolved with indicine cattle on the Indian subcontinent
We recently demonstrated that a multicomponent vaccine formulated with salivary proteins from R. micro‐ plus significantly reduced tick loads in immunized cattle of a tick-susceptible breed and that this protection was accompanied by increased levels of antigen-specific IgG1 and IgG2 antibodies against two of the antigens; levels of antibodies were boosted during a challenge infestation[23]
Three focused on the salivary glands of R. microplus: we examined a transcriptome generated with Sanger sequencing of transcripts from larvae and salivary glands of nymphs, male and female ticks feeding on genetically tick-resistant and susceptible breeds of c attle[23]; with a microarray built from expressed sequence tags (ESTs) from a transcriptome generated with Sanger sequencing of a pool of many tick t issues[26], Mercado-Curiel and colleagues examined salivary glands from male ticks fed on uninfected or Anaplasma marginale-infected cattle of a tick-susceptible b reed[25]; with Multidimensional Protein Identification Technology (MudPIT), Tirloni and colleagues generated the first proteome of cattle tick saliva and salivary glands from partially and fully fed females fed on a tick-susceptible breed of c attle[27]
Summary
The cattle tick, Rhipicephalus microplus, is a monoxenous tick that co-evolved with indicine cattle on the Indian subcontinent. Levels of expression of many genes encoding mediators of parasitism were significantly associated with the level and stage of host immunity and/or were temporally restricted to developmental stages of the tick These insights should assist in developing novel, sustainable technologies for tick control. When resistance to acaricides arose, studies showing that immunity against salivary antigens decreased tick loads were again u ndertaken[20,21] Another factor that favors salivary antigens in vaccines is the fact that persistent exposure to antigens is thought to be necessary to maintain immune memory[22]; another advantage of employing salivary antigens instead of concealed antigens would be the natural boosts that cattle will receive when exposed to tick-infested pastures. The efficacy of this vaccine needs to be improved; among the many secreted salivary proteins that ticks produce, two were targeted, possibly more proteins are needed
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