Dynamin-like proteins in Trypanosoma brucei: A division of labour between two paralogs?

Dynamins and dynamin-like proteins (DLPs) belong to a family of large GTPases involved in membrane remodelling events. These include both fusion and fission processes with different dynamin proteins often having a specialised function within the same organism. Trypanosoma brucei is thought to have only one multifunctional DLP ( Tb DLP). While this was initially reported to function in mitochondrial division only, an additional role in endocytosis and cytokinesis was later also proposed. Since there are two copies of Tb DLP present in the trypanosome genome, we investigated potential functional differences between these two paralogs by re-expressing either protein in a Tb DLP RNAi background. These paralogs, called Tb DLP1 and Tb DLP2, are almost identical bar a few amino acid substitutions. Our results, based on cell lines carrying tagged and RNAi-resistant versions of each protein, show that overexpression of Tb DLP1 alone is able to rescue the observed endocytosis and growth defects in the mammalian bloodstream form (BSF) of the parasite. While Tb DLP2 shows no rescue in our experiments in BSF, this might also be due to lower expression levels of the protein in this life stage. In contrast, both Tb DLP proteins apparently play more complementary roles in the insect procyclic form (PCF) since neither Tb DLP1 nor Tb DLP2 alone can fully restore wildtype growth and morphology in Tb DLP-depleted parasites.