Discussion

Trypanosoma brucei undergoes a complex life cycle progression in the tsetse vector. The parasite encounters many challenges involving migration and colonization of several tsetse tissues, which are accompanied by a series of developmental changes. After the "stumpy" form differentiates into the procyclic stage, it is assumed that the parasite first colonises the midgut (MG) ectoperitrophic space and then invades the proventriculus (PV) or cardia, where transformation into epimastigotes occurs. The last step of the journey involves migration to and establishment of a salivary gland (SG) infection to ensure transmission of infectious metacyclic trypomastigotes. In order to understand what parasite genes are important for a successful life cycle completion in the fly, we used RNA-seq to compare the gene expression profiles of a fly-transmissible strain with that of a trypanosome strain that is unable to progress beyond the PV. Overall, we found 786 and 867 genes that were significantly up-regulated or down-regulated in the transmissible strain, respectively, compared with the impaired one. Among the top up-regulated genes we identified several encoding metabolic enzymes (i.e. folate transporters and glutamate dehydrogenase) and RNA-binding proteins (RBPs), including RBP6, whose overexpression in procyclics leads to the differentiation up to the metacyclic stage in vitro (Kolev et al. 2012). To validate the role of these genes in parasite development in the fly, we overexpressed them in procyclic trypanosomes and characterized their phenotypes in vitro. In vivo studies are on their way to determine if the overexpression of these genes rescues the limited infectivity of the impaired strain in the tsetse.