Role of the Flagellum Throughout the Leishmania Life Cycle

The flagellum is dramatically remodeled during the Leishmania life cycle. This makes Leishmania an intriguing organism to study flagellar biology. While the extracellular stage within the sand fly vector (promastigote) is motile and has a long flagellum, the infective mammalian host stage of the parasite (amastigote) has a significantly shorter flagellum with no obvious role in motility. In this work, I studied the roles of the flagellum throughout the life cycle—particularly during the amastigote stage. This is because the remodeled flagellum is not only interesting from a cell biology perspective but also as a model for studying host-parasite interactions. One intriguing hypothesis is that the amastigote flagellum is critical for interactions with the host, but there is little data to support this as most work on the Leishmania flagellum has primarily made use of the promastigote stage, which is disadvantageous if the flagellum is important for virulence within the host. The work presented in this thesis is significant in establishing the first aflagellate Leishmania strain for probing flagellum functions throughout the life cycle. These viable, aflagellate promastigotes allowed me to investigate presumed requirements for flagellum assembly in viability, cell body morphology, cell size, flagellar pocket structure and function, and virulence. The results were significant in showing that most of these presumed functions were dispensable except for the role in virulence—aflagellate cells could not properly differentiate to virulent amastigotes. In addition to providing this aflagellate strain, this work is significant in providing tools for future RNAi studies in axenic amastigotes