EST-based gene indices for the cattle fever tick, the horn fly, and the screwworm fly.

The southern cattle tick, Rhip,cephalus (Boophilus) microplus, the horn fly, Haematobia irritans, and the New World screwworm, Cochl,omyia hominivorax, are economically important parasites of cattle throughout the world. Understanding the biology and genomics of these pests is critical to developing novel control methods. We developed EST sequence databases for these parasites and used bioinformatic analysis to identify conceptual open reading frames and assigned Gene Ontology (GO) terms to those database transcripts that had informative BlasIX hits. Bloinformatic analysis showed that a large fraction of the tick database entries have no clear matches in other sequenced genomes. Several putative tick G protein-coupled receptors (GPCRs) were identified that mightserve as starting points to develop novel control technologies.

Expressed cDNAS from embryonic and larval stages of the horn fly (Diptera: Muscidae).

We used an expressed sequence tag approach to initiate a study of the genome of the horn fly, Hematobia irritans (L.) (Diptera: Muscidae). Two normalized cDNA libraries were synthesized from RNA isolated from embryos and first instars from a field population of horn flies. Approximately 10,000 clones were sequenced from both the 5' and 3' directions. Sequence data from each library was assembled into a database of tentative consensus sequences (TCs) and singletons and used to search public protein databases and annotate the sequences. Additionally, the sequences from both the egg and larval libraries were combined into a single database consisting of 16,702 expressed sequence tags (ESTs) assembling into 2886 TCs and 1,522 singleton entries. Several sequences were identified that may have roles in the horn fly's resistance to insecticides. The availability of this database will facilitate the design of microarray and other experiments to study horn fly gene expression on a larger scale than previously possible. This would include studies designed to investigate metabolic-based insecticide resistance, identify novel antigens for vaccine-based control approaches, and discover new proteins to serve as targets for new pesticide development.

Tick genomics: the Ixodes genome project and beyond.

Ticks and mites (subphylum Chelicerata; subclass Acari) include important pests of animals and plants worldwide. The Ixodes scapularis (black-legged tick) genome sequencing project marks the beginning of the genomics era for the field of acarology. This project is the first to sequence the genome of a blood-feeding tick vector of human disease and a member of the subphylum Chelicerata. Genome projects for other species of Acari are forthcoming and their genome sequences will likely feature significantly in the future of tick research. Parasitologists interested in advancing the field of tick genomics research will be faced with specific challenges. The development of genetic tools and resources, and the size and repetitive nature of tick genomes are important considerations. Innovative approaches may be required to sequence, assemble, annotate and analyse tick genomes. Overcoming these challenges will enable scientists to investigate the genes and genome organisation of this important group of arthropods and may ultimately lead to new solutions for control of ticks and tick-borne diseases.

Serial analysis of gene expression in the southern cattle tick following acaricide treatment of larvae from organophosphate resistant and susceptible strains.

Organophosphate resistant and susceptible tick larvae from laboratory strains of the southern cattle tick, Rhipicephalus (Boophilus) microplus were exposed to low doses of the organophosphate (OP) acaricide, coumaphos. Serial analysis of gene expression (SAGE) was used to analyse differential gene expression in response to OP treatment and to compare the responses of OP-treated and -untreated resistant and susceptible tick larvae. An R. microplus Gene Index was used as an EST database to identify genes which corresponded to SAGE tags whose abundance changed in response to acaricide exposure. Relative quantitative RT-PCR was used to confirm the differential expression results from the SAGE experiments. Of particular interest is a SAGE tag which corresponds to a cytochrome P450-like EST in the Gene Index which was more abundant in untreated OP resistant larvae compared to untreated OP susceptible larvae. This SAGE tag was also more abundant in OP resistant larvae treated with OP compared to OP susceptible larvae treated with OP.