Microtubule-severing proteins are involved in flagellar length control and mitosis in Trypanosomatids.

Summary Microtubules are key players in the biology of Trypa- nosomatid parasites, not only as classical compo- nents of the mitotic spindle, microtubule-organizing centres and flagellum but also as the essential con- stituent of the cytoskeleton. Their length dynamics are regulated by, among others, microtubule-severing proteins. Four and six genes encoding microtubule- severing proteins can be found bioinformatically in the Leishmania major and Trypanosoma brucei genome respectively. We investigated all these pro- teins in these organisms, which include the katanin, katanin-like, spastin and fidgetin, and looked at their subcellular localization as well as their putative func- tion by examining 'loss-of-function' phenotypes. The katanin-like KAT60b was found implicated in flagellar length reduction, but not in its size increase, while the katanin p80 subunit appeared clearly involved in cytokinesis. Fidgetin and spastin homologues were both localized in the nucleus: the first as a discrete and variable number of dots during most of the cell cycle, redistributing to the spindle and midbody during mitosis; the second concentrated as 5 peri- nucleolar punctuations, similar to the electron-dense plaques identified in T. brucei, which were assimi- lated to kinetochores. This first study of microtubule- severing proteins in 'divergent' eukaryotes gives further insight into the multiple functions of these proteins identified in the hitherto studied models.