title: Cortical Polarity of the RING Protein PAR-2 Is Maintained by Exchange Rate Kinetics at the Cortical-Cytoplasmic Boundary.
abstract: Cell polarity arises through the spatial segregation of polarity regulators. PAR proteins are polarity regulators that localize asymmetrically to two opposing cortical domains. However, it is unclear how the spatially segregated PAR proteins interact to maintain their mutually exclusive partitioning. Here, single-molecule detection analysis in Caenorhabditis elegans embryos reveals that cortical PAR-2 diffuses only short distances, and, as a result, most PAR-2 molecules associate and dissociate from the cortex without crossing into the opposing domain. Our results show that cortical PAR-2 asymmetry is maintained by the local exchange reactions that occur at the cortical-cytoplasmic boundary. Additionally, we demonstrate that local exchange reactions are sufficient to maintain cortical asymmetry in a parameter-free mathematical model. These findings suggest that anterior and posterior PAR proteins primarily interact through the cytoplasmic pool and not via cortical diffusion.
authors.affiliation: Cellular Informatics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan. Electronic address: arata@riken.jp.
authors.forename: Yukinobu
authors.initials: Y
authors.lastname: Arata
authors.affiliation: Cellular Informatics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan; Laboratory for Cell Signaling Dynamics, Quantitative Biology Center (QBiC), RIKEN, Suita, Osaka 565-0874, Japan.
authors.forename: Michio
authors.initials: M
authors.lastname: Hiroshima
authors.affiliation: Cellular Informatics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan; Asan Institute for Life Sciences, University of Ulsan, College of Medicine, Asan Medical Center, Seoul 138-736, Republic of Korea.
authors.forename: Chan-Gi
authors.initials: CG
authors.lastname: Pack
authors.affiliation: Temasek Life Sciences Laboratory, Mechanobiology Institute, Department of Biological Sciences, National University of Singapore, Singapore 117604, Singapore.
authors.forename: Ravikrishna
authors.initials: R
authors.lastname: Ramanujam
authors.affiliation: Temasek Life Sciences Laboratory, Mechanobiology Institute, Department of Biological Sciences, National University of Singapore, Singapore 117604, Singapore.
authors.forename: Fumio
authors.initials: F
authors.lastname: Motegi
authors.affiliation: Theoretical Biology Laboratory, RIKEN, Wako, Saitama 351-0198, Japan.
authors.forename: Kenichi
authors.initials: K
authors.lastname: Nakazato
authors.affiliation: Cellular Informatics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Shindo
authors.affiliation: Department of Physics, McGill University, Montréal, QC H3A 2T8, Canada; Department of Chemistry, McGill University, Montréal, QC H3A 0B8, Canada.
authors.forename: Paul W
authors.initials: PW
authors.lastname: Wiseman
authors.affiliation: Multicellular Organization Laboratory, National Institute of Genetics, Mishima 411-8540, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sawa
authors.affiliation: Institute of Industrial Science, University of Tokyo, Tokyo 153-8505, Japan.
authors.forename: Tetsuya J
authors.initials: TJ
authors.lastname: Kobayashi
authors.affiliation: Department of Physics, McGill University, Montréal, QC H3A 2T8, Canada; Graduate Program in Biophysics, Harvard University, Boston, MA 02115, USA.
authors.forename: Hugo B
authors.initials: HB
authors.lastname: Brandão
authors.affiliation: Laboratory for Physical Biology, RIKEN Center for Developmental Biology (CDB), Chuo-ku Kobe, Hyogo 650-0047, Japan.
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Shibata
authors.affiliation: Cellular Informatics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan. Electronic address: sako@riken.jp.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Sako
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D002451:Cell Compartmentation; D016764:Cell Polarity; D003593:Cytoplasm / Q000378:metabolism* / Q000648:ultrastructure; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000378:metabolism*; D005786:Gene Expression Regulation; D007700:Kinetics; D015233:Models, Statistical; D010766:Phosphorylation; D021381:Protein Transport; D000072760:Single Molecule Imaging
chemical_list: D029742:Caenorhabditis elegans Proteins; C553666:LGL-1 protein, C elegans; C087977:par-2 protein, C elegans