ABSTRACT
Multicellular organisms assemble cilia and flagella of precise lengths differing from one cell to another, yet little is known about the mechanisms governing these differences. Similarly, protists assemble flagella of different lengths according to the stage of their life cycle. Trypanosoma brucei assembles flagella of 3 to 30 µm during its development in the tsetse fly. This provides an opportunity to examine how cells naturally modulate organelle length. Flagella are constructed by addition of new blocks at their distal end via intraflagellar transport (IFT). Immunofluorescence assays, 3D electron microscopy and live-cell imaging revealed that IFT was present in all T. brucei life cycle stages. IFT proteins are concentrated at the base, and IFT trains are located along doublets 3–4 and 7–8 and travel bidirectionally in the flagellum. Quantitative analysis demonstrated that the total amount of flagellar IFT proteins correlates with the length of the flagellum. Surprisingly, the shortest flagellum exhibited a supplementary large amount of dynamic IFT material at its distal end. The contribution of IFT and other factors to the regulation of flagellum length is discussed.
Footnotes
Author contributions
Conceptualization: E.B., B.R., P.B.; Methodology: E.B., A.M.; Formal analysis: E.B., A.M.; Writing - original draft: E.B., P.B.; Writing - review & editing: E.B., A.M., B.R., P.B.; Supervision: B.R., P.B.; Funding acquisition: P.B.
Funding
E.B. was supported by fellowships from French National Ministry for Research and Technology (doctoral school CDV515) and from La Fondation pour la Recherche Médicale (FDT20170436836). This work was funded by La Fondation pour la Recherche Médicale (Equipe FRM DEQ20150734356) and by a French Government (Agence Nationale de la Recherche) Investissement d'Avenir programme, Laboratoire d'Excellence “Integrative Biology of Emerging Infectious Diseases” (ANR-10-LABX-62-IBEID). We are also grateful for support for FESEM Zeiss Auriga and Elyra PS1 equipment from the French Government Programme Investissements d'Avenir France BioImaging (FBI, N° ANR-10-INSB-04-01) and from a DIM-Malinf grant from the Région Ile-de-France.
