title: Superresolution microscopy reveals a dynamic picture of cell polarity maintenance during directional growth.
abstract: Polar (directional) cell growth, a key cellular mechanism shared among a wide range of species, relies on targeted insertion of new material at specific locations of the plasma membrane. How these cell polarity sites are stably maintained during massive membrane insertion has remained elusive. Conventional live-cell optical microscopy fails to visualize polarity site formation in the crowded cell membrane environment because of its limited resolution. We have used advanced live-cell imaging techniques to directly observe the localization, assembly, and disassembly processes of cell polarity sites with high spatiotemporal resolution in a rapidly growing filamentous fungus, Aspergillus nidulans. We show that the membrane-associated polarity site marker TeaR is transported on microtubules along with secretory vesicles and forms a protein cluster at that point of the apical membrane where the plus end of the microtubule touches. There, a small patch of membrane is added through exocytosis, and the TeaR cluster gets quickly dispersed over the membrane. There is an incessant disassembly and reassembly of polarity sites at the growth zone, and each new polarity site locus is slightly offset from preceding ones. On the basis of our imaging results and computational modeling, we propose a transient polarity model that explains how cell polarity is stably maintained during highly active directional growth.
authors.affiliation: Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany.
authors.forename: Yuji
authors.identifier: 0000-0002-6780-7154
authors.initials: Y
authors.lastname: Ishitsuka
authors.affiliation: Department of Functional and Comparative Genomics, Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK.
authors.forename: Natasha
authors.initials: N
authors.lastname: Savage
authors.affiliation: Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany.
authors.forename: Yiming
authors.identifier: 0000-0003-4109-3824
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Microbiology, Institute for Applied Biosciences, KIT, 76187 Karlsruhe, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Bergs
authors.affiliation: Department of Microbiology, Institute for Applied Biosciences, KIT, 76187 Karlsruhe, Germany.
authors.forename: Nathalie
authors.identifier: 0000-0002-8945-9023
authors.initials: N
authors.lastname: Grün
authors.affiliation: Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany.
authors.forename: Daria
authors.initials: D
authors.lastname: Kohler
authors.affiliation: Department of Functional and Comparative Genomics, Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Donnelly
authors.affiliation: Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany. ; Institute of Nanotechnology, KIT, 76344 Eggenstein-Leopoldshafen, Germany. ; Institute of Toxicology and Genetics, KIT, 76344 Eggenstein-Leopoldshafen, Germany. ; Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: G Ulrich
authors.identifier: 0000-0002-5027-3192
authors.initials: GU
authors.lastname: Nienhaus
authors.affiliation: Department of Microbiology, Institute for Applied Biosciences, KIT, 76187 Karlsruhe, Germany.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Fischer
authors.affiliation: Department of Microbiology, Institute for Applied Biosciences, KIT, 76187 Karlsruhe, Germany. ; Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Norio
authors.identifier: 0000-0003-2666-4991
authors.initials: N
authors.lastname: Takeshita
keywords: Aspergillus; Computational Modeling; PALM; exocytosis; filamentous fungi; microtubule; polarity maintenance; super-resolution microscopy