A role for the parasite flagellum in virulence.
While the infective amastigote stage lacks an external flagellum, it maintains a ‘stub’ which has largely been ignored. Recently Gull’s lab proposed this may play a role in parasite virulence, as a conduit for virulence factors as well as a sensing organelle as seen in other eukaryotes. To test this we sought to knockout the Leishmania flagellum. Remarkably this proved easy to do through ablation of a gene implicated in intraflagellar transport, IFT140. In culture as the promastigote stage, these parasites completely lacked a flagellum, yet maintained a fairly normal flagellar pocket, and grew normally (other than being unable to swim). In contrast, the ift140 mutants were completely avirulent, in a mouse or in a macrophage model. Current work is now directed towards understanding the impact of this on virulence factor secretion into the host.
In 2010 we showed that while most Leishmania species lack the RNA interference pathway, species belonging to the L. braziliensis group have retained it. This permits the application of RNAi-based methods for functional genomics in this group of species, although the advent of CRISPR gene editing will likely supplant this going forward. The loss of RNAi in most Leishmania raises the interesting evolutionary question of what forces contribute to the loss of a pathway of such fundamental importance in other organisms. This is being pursued, through the study of RNAi-deficient null mutants many of which bear RNA viruses.
Other interests of the lab include molecular evolution of parasitism and virulence, and the use of genetically modified parasites as vaccines.