Abstract
BackgroundRhipicephalus (Boophilus) microplus is an obligate blood feeder which is host specific to cattle. Existing knowledge pertaining to the host or host breed effects on tick transcript expression profiles during the tick - host interaction is poor.ResultsGlobal analysis of gene expression changes in whole R. microplus ticks during larval, pre-attachment and early adult stages feeding on Bos indicus and Bos taurus cattle were compared using gene expression microarray analysis. Among the 13,601 R. microplus transcripts from BmiGI Version 2 we identified 297 high and 17 low expressed transcripts that were significantly differentially expressed between R. microplus feeding on tick resistant cattle [Bos indicus (Brahman)] compared to R. microplus feeding on tick susceptible cattle [Bos taurus (Holstein-Friesian)] (p ≤ 0.001). These include genes encoding enzymes involved in primary metabolism, and genes related to stress, defence, cell wall modification, cellular signaling, receptor, and cuticle formation. Microarrays were validated by qRT-PCR analysis of selected transcripts using three housekeeping genes as normalization controls.ConclusionThe analysis of all tick stages under survey suggested a coordinated regulation of defence proteins, proteases and protease inhibitors to achieve successful attachment and survival of R. microplus on different host breeds, particularly Bos indicus cattle. R. microplus ticks demonstrate different transcript expression patterns when they encounter tick resistant and susceptible breeds of cattle. In this study we provide the first transcriptome evidence demonstrating the influence of tick resistant and susceptible cattle breeds on transcript expression patterns and the molecular physiology of ticks during host attachment and feeding.The microarray data used in this analysis have been submitted to NCBI GEO database under accession number GSE20605 http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE20605.
Highlights
Rhipicephalus (Boophilus) microplus is an obligate blood feeder which is host specific to cattle
We report that unfed larvae have elevated expression of 47 transcripts compared to larvae exposed to B. taurus host for 5 hours but not allowed to feed (’frustrated larvae’) and adult ticks feeding on B. indicus cattle have elevated expression of 43 transcripts compared to adult ticks feeding on B. taurus
1-Assessment of gene expression on primary stages of unfed and frustrated larvae a) Transcripts highly expressed B-FL and H-FL versus unattached/unfed larvae The tick attachment and feeding process involves sequential behavioural and molecular changes which can be examined both during host recognition of newly hatched larvae and during larval host attachment while responding to feeding stimuli following host recognition. In this microarray comparison, unattached/unfed larvae versus frustrated larvae obtained after 5 hrs of exposure to Bos indicus (Brahman, B-FL) and B. taurus (Holstein-Friesian, H-FL) cattle resulted in the identification of 128 transcripts highly expressed in frustrated larvae on Brahman and HolsteinFriesian (Figure 1A.1, 1B.1)
Summary
Rhipicephalus (Boophilus) microplus is an obligate blood feeder which is host specific to cattle. Vaccination has become a potentially effective alternative for controlling tick and tick-borne diseases as demonstrated by the commercial vaccines (Gavac® and TickGard®) derived from the Bm86 antigen of R. microplus [7,8]. The development of novel tick control strategies requires enhanced knowledge about the proteins expressed by different R. microplus stages during development, in particular during tick interactions with the host. The recent rapid development of genomic technologies is having an impact on tick - host interaction research and can help to identify potential antigens for tick vaccine development. Harvard.edu/tgi/cgi-bin/tgi/gimain.pl?gudb=b_microplus; [14,15,16] This gene index consists of 13, 643 unique transcripts derived from various tick life stages and tick strains exposed to various environmental conditions. The first draft of the I. scapularis genome became available early 2008 and will be the first available complete tick genome sequence [21]
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