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Protist. 2017 Dec;168(6):697-717. doi: 10.1016/j.protis.2017.10.001. Epub 2017 Oct 20.

Tetrahymena Cilia Cap is Built in a Multi-step Process: A Study by Atomic Force Microscopy.

Author information

1
Instituto Gulbenkian de Ciência, Apartado 14, 2781-901 Oeiras, Portugal.
2
Instituto Gulbenkian de Ciência, Apartado 14, 2781-901 Oeiras, Portugal; Centro de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Edifício C8, 1749-016 Lisboa, Portugal.
3
Physics Department, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal; INESC-MN, Rua Alves Redol, 9, 1000-029, Lisboa, Portugal.
4
Instituto Gulbenkian de Ciência, Apartado 14, 2781-901 Oeiras, Portugal; Centro de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Edifício C8, 1749-016 Lisboa, Portugal; Escola Superior de Tecnologia da Saúde de Lisboa, 1990-096 Lisboa, Instituto Politécnico de Lisboa, Portugal. Electronic address: mhsoares@fc.ul.pt.

Abstract

Cilia are complex and dynamic organelles that have motility and sensory functions. Defects in cilia biogenesis and function are at the origin of human ciliopathies. In motile cilia, a basal body organizes the axoneme composed of nine microtubule doublets surrounding a central pair of singlet microtubules. The distal ends of axonemal microtubules are attached to the membrane by microtubule-capping structures. Little is known about the early steps of cilium assembly. Although cilia grow and resorb from their distal tips, it remains poorly understood where and when the components of the caps are first assembled. By using Atomic Force Microscopy in tapping mode, with resolution at the nanometer range and with minimum sample manipulation, we show that Tetrahymena cilia assembly requires transient assembly of structures, composed of three components that are placed asymmetrically on an early elongating axoneme. In small uncapped axonemes the microtubule central pair was never observed. Additionally, we show that cilia cap assembly is a multi-step process in which structures of different sizes and shapes are put together in close proximity before the axoneme appears capped. We propose that the cap modifies the axoneme microtubule rate of polymerization and present a model for Tetrahymena cilia cap assembly.

KEYWORDS:

AFM; Tetrahymena; cap assembly; cilia assembly; re-ciliation.

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