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J Cell Biol. 2018 Dec 3;217(12):4298-4313. doi: 10.1083/jcb.201804141. Epub 2018 Sep 14.

Proteins that control the geometry of microtubules at the ends of cilia.

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Department of Cellular Biology, University of Georgia, Athens, GA.
Laboratory of Cytoskeleton and Cilia Biology, Nencki Institute of Experimental Biology of Polish Academy of Sciences, Warsaw, Poland.
Department of Mechanics, LadHyX, Ecole Polytechnique-Centre National de la Recherche Scientifique, Palaiseau, France.
UMR-S1174 Institut National de la Santé et de la Recherche Médicale, Université Paris-Sud, Bat 443, Orsay, France.
École Supérieure de Physique et de Chimie Industrielles de la Ville de Paris, Paris, France.
Department of Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, Aurora, CO.
Departments of Biophysics and Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX.
Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA.
Department of Molecular Biosciences, University of Kansas, Lawrence, KS
Department of Cellular Biology, University of Georgia, Athens, GA


Cilia, essential motile and sensory organelles, have several compartments: the basal body, transition zone, and the middle and distal axoneme segments. The distal segment accommodates key functions, including cilium assembly and sensory activities. While the middle segment contains doublet microtubules (incomplete B-tubules fused to complete A-tubules), the distal segment contains only A-tubule extensions, and its existence requires coordination of microtubule length at the nanometer scale. We show that three conserved proteins, two of which are mutated in the ciliopathy Joubert syndrome, determine the geometry of the distal segment, by controlling the positions of specific microtubule ends. FAP256/CEP104 promotes A-tubule elongation. CHE-12/Crescerin and ARMC9 act as positive and negative regulators of B-tubule length, respectively. We show that defects in the distal segment dimensions are associated with motile and sensory deficiencies of cilia. Our observations suggest that abnormalities in distal segment organization cause a subset of Joubert syndrome cases.

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