A Ras-like GTPase in African trypanosomes

Small Ras-like GTPases are conserved across eukaryotes and mediate many functions. Trypanosoma brucei encodes only three putative open reading frames belonging to Ras and Rho subfamilies, all highly divergent from other taxa. We investigated the most Ras-like gene product in T. brucei , TbRlp, evaluating essentiality, location and impact of blocking the GDP/GTP cycle. TbRlp is expressed in both life stages, with a clear fitness contribution in bloodstream forms in in vitro culture, without a specific block to the cell cycle or clear morphological defect. Overexpression of TbRlp and mutant forms results in moderate disruption of the cell cycle and altered proliferation indicating that GTP/GDP cycling and expression levels of these forms of TbRlp are important to proliferation. Epitope-tagged TbRlp is located predominantly on structures in the posterior of the cell, and suggesting the late endosomal system. Analyses also indicates a link between cell density and levels of TbRlp in the BSF, with a decrease in TbRlp protein but not RNA upon increased cell density. These data suggest that TbRlp is important in control of proliferation and opens possibilities for future research.