Abstract:
The southern cattle tick, Rhipicephalus microplus, is an economically important pest, especially for
resource-poor countries, both as a highly adaptive invasive species and prominent vector of disease.
The increasing prevalence of resistance to chemical acaricides and variable efficacy of current tick vaccine
candidates highlight the need for more effective control methods. In the absence of a fully annotated genome,
the wealth of available expressed sequence tag sequence data for this species presents a unique
opportunity to study the genes that are expressed in tissues involved in blood meal acquisition, digestion
and reproduction during feeding. Utilising a custom oligonucleotide microarray designed from available
singletons (BmiGI Version 2.1) and expressed sequence tag sequences of R. microplus, the expression profiles
in feeding adult female midgut, salivary glands and ovarian tissues were compared. From 13,456
assembled transcripts, 588 genes expressed in all three tissues were identified from fed adult females
20 days post infestation. The greatest complement of genes relate to translation and protein turnover.
Additionally, a number of unique transcripts were identified for each tissue that relate well to their
respective physiological/biological function/role(s). These transcripts include secreted anti-hemostatics
and defense proteins from the salivary glands for acquisition of a blood meal, proteases as well as
enzymes and transporters for digestion and nutrient acquisition from ingested blood in the midgut,
and finally proteins and associated factors involved in DNA replication and cell-cycle control for oogenesis
in the ovaries. Comparative analyses of adult female tissues during feeding enabled the identification
of a catalogue of transcripts that may be essential for successful feeding and reproduction in the cattle
tick, R. microplus. Future studies will increase our understanding of basic tick biology, allowing the identification
of shared proteins/pathways among different tissues that may offer novel targets for the development
of new tick control strategies.
