Disruption of Leishmania flagellum attachment zone architecture causes flagellum loss.

Leishmania are flagellated eukaryotic parasites that cause leishmaniasis and are closely related to the other kinetoplastid parasites such as Trypanosoma brucei. In all these parasites there is a cell membrane invagination at the base of the flagellum called the flagellar pocket, which is tightly associated with and sculpted by cytoskeletal structures including the flagellum attachment zone (FAZ). The FAZ is a complex interconnected structure linking the flagellum to the cell body and has critical roles in cell morphogenesis, function and pathogenicity. However, this structure varies dramatically in size and organisation between these different parasites, suggesting changes in protein localisation and function. Here, we screened the localisation and function of the Leishmania orthologues of T. brucei FAZ proteins identified in the genome-wide protein tagging project TrypTag. We identified 27 FAZ proteins and our deletion analysis showed that deletion of two FAZ proteins in the flagellum, FAZ27 and FAZ34 resulted in a reduction in cell body size, and flagellum loss in some cells. Furthermore, after null mutant generation, we observed distinct and reproducible changes to cell shape, demonstrating the ability of the parasite to adapt to morphological perturbations resulting from gene deletion. This process of adaptation has important implications for the study of Leishmania mutants.

Cell-to-flagellum attachment and surface architecture in kinetoplastids.

A key morphological feature of kinetoplastid parasites is the position and length of flagellum attachment to the cell body. This lateral attachment is mediated by the flagellum attachment zone (FAZ), a large complex cytoskeletal structure, which is essential for parasite morphogenesis and pathogenicity. Despite the complexity of the FAZ only two transmembrane proteins, FLA1 and FLA1BP, are known to interact and connect the flagellum to the cell body. Across the different kinetoplastid species, each only has a single FLA/FLABP pair, except in Trypanosoma brucei and Trypanosoma congolense where there has been an expansion of these genes. Here, we focus on the selection pressure behind the evolution of the FLA/FLABP proteins and the likely impact this will have on host-parasite interactions.