Whole-genome sequencing of the protozoan pathogen Trypanosoma cruzi revealed that the diploid genome contains a predicted 22,570 proteins encoded by genes, of which 12,570 represent allelic pairs. Over 50% of the genome consists of repeated sequences, such as retrotransposons and genes for large families of surface molecules, which include trans-sialidases, mucins, gp63s, and a large novel family (>1300 copies) of mucin-associated surface protein (MASP) genes. Analyses of the T. cruzi, T. brucei, and Leishmania major (Tritryp) genomes imply differences from other eukaryotes in DNA repair and initiation of replication and reflect their unusual mitochondrial DNA. Although the Tritryp lack several classes of signaling molecules, their kinomes contain a large and diverse set of protein kinases and phosphatases; their size and diversity imply previously unknown interactions and regulatory processes, which may be targets for intervention.

The Trypanosoma brucei flagellum is unusual as it is attached along the cell body and contains, in addition to an apparently conventional axoneme, a structure called the paraflagellar rod, which is essential for cell motility. Here, we investigated flagellum behaviour in normal and mutant trypanosome cell lines where expression of genes encoding various axoneme proteins (PF16, PF20, DNAI1, LC2) had been silenced by RNAi. First, we show that the propulsive wave (normally used for forward motility) is abolished in the absence of outer dynein arms, whereas the reverse wave (normally used for changing direction) still occurs. Second, in contrast to Chlamydomonas - but like metazoa, the central pair adopts a fixed orientation during flagellum beating. This orientation becomes highly variable in central-pair- and outer-dynein-arm-mutants. Third, the paraflagellar rod contributes to motility by facilitating three-dimensional wave propagation and controlling cell shape. Fourth, motility is required to complete the last stage of cell division in both insect and bloodstream stages of the parasite. Finally, our study also reveals the conservation of molecular components of the trypanosome flagellum. Coupled to the ease of reverse genetics, it raises the interest of trypanosomes as model organisms to study cilia and flagella.

To perform their multiple functions, cilia and flagella are precisely positioned at the cell surface by mechanisms that remain poorly understood. The protist Trypanosoma brucei possesses a single flagellum that adheres to the cell body where a specific cytoskeletal structure is localised, the flagellum attachment zone (FAZ). Trypanosomes build a new flagellum whose distal tip is connected to the side of the old flagellum by a discrete structure, the flagella connector. During this process, the basal body of the new flagellum migrates towards the posterior end of the cell. We show that separate inhibition of flagellum assembly, base-to-tip motility or flagella connection leads to reduced basal body migration, demonstrating that the flagellum contributes to its own positioning. We propose a model where pressure applied by movements of the growing new flagellum on the flagella connector leads to a reacting force that in turn contributes to migration of the basal body at the proximal end of the flagellum.

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