title: Two classes of short intraflagellar transport train with different 3D structures are present in Chlamydomonas flagella.
abstract: Intraflagellar transport (IFT) is responsible for the bidirectional trafficking of molecular components required for the elongation and maintenance of eukaryotic cilia and flagella. Cargo is transported by IFT 'trains', linear rows of multiprotein particles moved by molecular motors along the axonemal doublets. We have previously described two structurally distinct categories of 'long' and 'short' trains. Here, we analyse the relative number of these trains throughout flagellar regeneration and show that long trains are most abundant at the beginning of flagellar growth whereas short trains gradually increase in number as flagella elongate. These observations are incompatible with the previous hypothesis that short trains are derived solely from the reorganization of long trains at the flagellar tip. We demonstrate with electron tomography the existence of two distinct ultrastructural organizations for the short trains, we name these 'narrow' and 'wide', and provide the first 3D model of the narrow short trains. These trains are characterized by tri-lobed units, which repeat longitudinally every 16 nm and contact protofilament 7 of the B-tubule. Functional implications of the new structural evidence are discussed.
authors.affiliation: Department of Life Sciences, University of Siena, Via Aldo Moro 2, 53100 Siena, Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Vannuccini
authors.affiliation: Department of Life Sciences, University of Siena, Via Aldo Moro 2, 53100 Siena, Italy.
authors.forename: Eugenio
authors.initials: E
authors.lastname: Paccagnini
authors.affiliation: Dipartimento di Chimica, Università degli Studi di Milano, Via Camillo Golgi 19, 20133 Milan, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Cantele
authors.affiliation: Department of Life Sciences, University of Siena, Via Aldo Moro 2, 53100 Siena, Italy.
authors.forename: Mariangela
authors.initials: M
authors.lastname: Gentile
authors.affiliation: Department of Life Sciences, University of Siena, Via Aldo Moro 2, 53100 Siena, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Dini
authors.affiliation: Department of Life Sciences, University of Siena, Via Aldo Moro 2, 53100 Siena, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Fino
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, Yale University, 219 Prospect Street, New Haven, CT 06520, USA.
authors.forename: Dennis
authors.initials: D
authors.lastname: Diener
authors.affiliation: Department of Life Sciences, University of Siena, Via Aldo Moro 2, 53100 Siena, Italy.
authors.forename: Caterina
authors.initials: C
authors.lastname: Mencarelli
authors.affiliation: Department of Life Sciences, University of Siena, Via Aldo Moro 2, 53100 Siena, Italy pietro.lupetti@unisi.it.
authors.forename: Pietro
authors.identifier: 0000-0003-4316-9861
authors.initials: P
authors.lastname: Lupetti
mesh_terms: D054468:Axoneme / Q000378:metabolism / Q000648:ultrastructure; D001692:Biological Transport; D002696:Chlamydomonas / Q000235:genetics / Q000254:growth & development* / Q000648:ultrastructure; D002923:Cilia / Q000235:genetics / Q000648:ultrastructure; D055032:Electron Microscope Tomography; D005407:Flagella / Q000235:genetics / Q000648:ultrastructure*; D021381:Protein Transport; D012038:Regeneration / Q000235:genetics*
keywords: Chlamydomonas flagella; Electron tomography; Flagellar regeneration; Intraflagellar transport