Differential gene expression of Trypanosoma brucei in the tsetse vector

African trypanosomes of the Trypanosoma brucei complex cause devastating human and animal disease in sub-Saharan Africa. These protozoan parasites are transmitted by the bite of an infected tsetse fly ( Glossina spp.). While trypanosome development in the mammalian host is well investigated, less is known about parasite development in tsetse. Trypanosomes undergo several differentiation processes during development in the tsetse fly. Upon ingestion, bloodstream trypanosomes differentiate into the procyclic form and inhabit the fly midgut. They migrate to the proventriculus and differentiate into epimastigote cells. Epimastigotes continue to the salivary glands where they attach and differentiate to mammalian infective metacyclic trypomastigotes. Finally, metacyclics develop into the bloodstream form in the mammalian host after inoculation by the fly during a blood meal. To characterize the corresponding transcriptome of T. brucei in the tsetse host, global gene expression analysis was attempted. Abundant host transcripts prevented the analysis of the less abundant trypanosome transcripts. To overcome this challenge, a means to selectively manipulate only trypanosome transcripts from a heterogeneous pool was successfully developed. In lieu of global gene analysis, an in-silico screen of the T. brucei genome yielded 162 putative proteins with glycosylphosphatidylinisotol (GPI) anchor attachment domains. GPI anchored proteins are predicted to be expressed on the cell surface. Of the 162 genes, 111 were unknown. These were analyzed by semi-quantitative RT-PCR on normalized cDNAs from parasite infected tsetse salivary glands, proventriculus, midguts and infected mammalian blood for stage specific expression. The validity of this approach was confirmed using quantitative RT-PCR. A large proportion of the detectible genes were found to be expressed in the unculturable parasite stages infecting the salivary glands and proventriculus. Two genes families, TbSGM1 and TbSGM2, with salivary gland specific expression profiles were investigated further. Analyses using a polyclonal anti-recTbSGM2 antibody demonstrated that the TbSGM2 protein is expressed on the surface of metacyclic parasites infecting tsetse salivary glands. These data provide the foundation for future detailed functional characterizations of unknown proteins likely to be surface coat associated, and that can provide unique avenues to interfere either in fly transmission or host infection processes Implications for disease control are discussed.