Transcriptome analysis of Rhipicephalus (Boophilus) microplus

Ticks, as blood-feeding ectoparasites, affect their hosts both directly and as vectors of viral, bacterial and protozoal diseases. The tick’s mode of feeding means it must maintain intimate contact with the host in the face of host defensive responses for a prolonged time. The parasite:host interactions are characterized by the host response and parasite counter-response which result in a highly complex biological system that is barely understood. We conducted trancriptomic analyses utilizing both suppressive subtractive hybridization (SSH) and the Nimblegen R. microplus tick array to identify transcripts associated with host attachment and feeding on both naturally susceptible and immune breeds of cattle (Holstein-Friesian and Brahman). Five SSH libraries were established from differentially expressed transcripts isolated from unattached frustrated larvae, feeding larvae, unattached frustrated female ticks, feeding female ticks and male ticks (590 clones). Unattached frustrated ticks are those held in fabric bags affixed to cattle for up to 24 hours – thus ‘frustrated’. Approximately half of the clones were unique R. microplus transcripts or predicted proteins of unknown function. Feeding stages demonstrated an abundance of transcripts associated with ribosomal protein production and increased metabolic function. Host modifying proteases were differentially expressed by frustrated larvae and frustrated female ticks as well as males. Microarray expression analysis was conducted on unfed/unattached larvae, frustrated larvae and adult females from both Brahman and Holstein-Friesian cattle. Preliminary microarray results show that 226 genes are up and 9 down regulated by ticks on Brahman in comparison to ticks on Holstein (based on ≥3 standard deviation). Of the up-regulated transcripts, approximately 100 were unique and a further 50 similar to hypothetical proteins of unknown function. Transcripts with <1e-5 significance included putative retroviral proteins, kinases