Cortical Polarity of the RING Protein PAR-2 Is Maintained by Exchange Rate Kinetics at the Cortical-Cytoplasmic Boundary
Yukinobu Arata,
Michio Hiroshima,
Chan-Gi Pack,
Ravikrishna Ramanujam,
Fumio Motegi,
Kenichi Nakazato,
Yuki Shindo,
Paul W. Wiseman,
Hitoshi Sawa,
Tetsuya J. Kobayashi,
Hugo B. Brandão,
Tatsuo Shibata,
Yasushi Sako
Affiliations
Yukinobu Arata
Cellular Informatics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
Michio Hiroshima
Cellular Informatics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
Chan-Gi Pack
Cellular Informatics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
Ravikrishna Ramanujam
Temasek Life Sciences Laboratory, Mechanobiology Institute, Department of Biological Sciences, National University of Singapore, Singapore 117604, Singapore
Fumio Motegi
Temasek Life Sciences Laboratory, Mechanobiology Institute, Department of Biological Sciences, National University of Singapore, Singapore 117604, Singapore
Kenichi Nakazato
Theoretical Biology Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
Yuki Shindo
Cellular Informatics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
Paul W. Wiseman
Department of Physics, McGill University, Montréal, QC H3A 2T8, Canada
Hitoshi Sawa
Multicellular Organization Laboratory, National Institute of Genetics, Mishima 411-8540, Japan
Tetsuya J. Kobayashi
Institute of Industrial Science, University of Tokyo, Tokyo 153-8505, Japan
Hugo B. Brandão
Department of Physics, McGill University, Montréal, QC H3A 2T8, Canada
Tatsuo Shibata
Laboratory for Physical Biology, RIKEN Center for Developmental Biology (CDB), Chuo-ku Kobe, Hyogo 650-0047, Japan
Yasushi Sako
Cellular Informatics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
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.
