Abstract
Cilia and flagella are required for cell motility and sensing the external environment and can vary in both length and stability. Stable flagella maintain their length without shortening and lengthening and are proposed to "lock" at the end of growth, but molecular mechanisms for this lock are unknown. We show that CEP164C contributes to the locking mechanism at the base of the flagellum in Trypanosoma brucei. CEP164C localizes to mature basal bodies of fully assembled old flagella, but not to growing new flagella, and basal bodies only acquire CEP164C in the third cell cycle after initial assembly. Depletion of CEP164C leads to dysregulation of flagellum growth, with continued growth of the old flagellum, consistent with defects in a flagellum locking mechanism. Inhibiting cytokinesis results in CEP164C acquisition on the new flagellum once it reaches the old flagellum length. These results provide the first insight into the molecular mechanisms regulating flagella growth in cells that must maintain existing flagella while growing new flagella.
Highlights
Cilia and flagella are highly conserved microtubule-based or- the boundary between the axoneme and basal bodies and have ganelles that have important roles in cell motility and sensing. been shown to be important for allowing selective entry ofThey can be highly dynamic and short lived, such as primary molecules into cilia/flagella (Gonçalves and Pelletier, 2017).cilia or those in Chlamydomonas reinhardtii (Marshall and Trypanosomes are pathogenic protists that have a single fla-Rosenbaum, 2001), or very stable and long lived, such as those gellum, which remains assembled throughout the cell cycle, in spermatozoa (San Agustin et al, 2015), photoreceptors (Jiang with a new flagellum assembling alongside (Kohl and Bastin, et al, 2015), or the flagella of many protists
We show that CEP164C is important for the locking mechanism, and our results illustrate a novel concept in the regulation of flagella growth for cells with stable flagella that need to maintain the length of existing flagella during growth of new flagella
CEP164C is recruited to transition fibers in the third cell cycle after basal body formation Recent worked showed that assembled flagella are prevented from further elongation via a lock mechanism (Bertiaux et al, 2018)
Summary
Cilia and flagella are highly conserved microtubule-based or- the boundary between the axoneme and basal bodies and have ganelles that have important roles in cell motility and sensing. been shown to be important for allowing selective entry ofThey can be highly dynamic and short lived, such as primary molecules into cilia/flagella (Gonçalves and Pelletier, 2017).cilia or those in Chlamydomonas reinhardtii (Marshall and Trypanosomes are pathogenic protists that have a single fla-Rosenbaum, 2001), or very stable and long lived, such as those gellum, which remains assembled throughout the cell cycle, in spermatozoa (San Agustin et al, 2015), photoreceptors (Jiang with a new flagellum assembling alongside (Kohl and Bastin, et al, 2015), or the flagella of many protists. CEP164C is recruited to transition fibers in the third cell cycle after basal body formation Recent worked showed that assembled flagella are prevented from further elongation via a lock mechanism (Bertiaux et al, 2018). At cytokinesis, the daughter cell with the old flagellum had a CEP164C signal, but the daughter cell with the new flagellum did not (Fig. 1 D).
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