title: Ultrastructural study of Rac1 and its effectors beneath the substratum-facing membrane.
abstract: The cytoskeletal architecture and adhesion apparatus are tightly controlled during embryogenesis, tissue development, and carcinogenesis. The Rho family GTPases play central roles in regulation of the cytoskeleton and adhesions. Rac1, one of the Rho family GTPases, appears to be activated at the plasma membrane and exert its functions through its effectors. However, where Rac1 and its effectors function at the molecular level remains to be determined. In this study, we examined the molecular organization on the cytoplasmic surface of the substratum-facing plasma membrane, focusing on Rac1 and its effectors, IQGAP1 and Sra-1, by electron microscopy. We employed deep-etch immunoreplica methods to observe the membrane cytoskeletal architecture while determining molecular locations. Beneath the plasma membrane, Rac1 and its effectors showed similar, but distinct, destinations. Rac1 localized on the membrane and associated with the membrane cytoskeleton. IQGAP1 predominantly localized beside actin filaments and occasionally near microtubules together with Rac1. On the other hand, Sra-1 localized at actin filaments, microtubules, and the plasma membrane. Sra-1 colabeled with Rac1 was mainly found at the membrane and actin filaments. These results suggest that IQGAP1 and Sra-1 colocalize with Rac1 at distinct places, including the plasma membrane and cytoskeletal architecture, for their specific functions.
authors.affiliation: Institute for Advanced Research, Nagoya University, Aichi, Japan. takashiw@med.nagoya-u.ac.jp
authors.forename: Takashi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Shujie
authors.initials: S
authors.lastname: Wang
authors.forename: Mai
authors.initials: M
authors.lastname: Kakeno
authors.forename: Jiro
authors.initials: J
authors.lastname: Usukura
authors.forename: Kozo
authors.initials: K
authors.lastname: Kaibuchi
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry / Q000648:ultrastructure; D048868:Adaptor Proteins, Signal Transducing / Q000032:analysis* / Q000737:chemistry; D000818:Animals; D002462:Cell Membrane / Q000737:chemistry* / Q000648:ultrastructure; D002522:Chlorocebus aethiops; D003599:Cytoskeleton / Q000737:chemistry* / Q000648:ultrastructure; D005613:Freeze Etching; D046529:Microscopy, Electron, Transmission; D008870:Microtubules / Q000737:chemistry* / Q000648:ultrastructure; D014709:Vero Cells; D020830:rac1 GTP-Binding Protein / Q000032:analysis*; D020703:ras GTPase-Activating Proteins / Q000032:analysis* / Q000737:chemistry
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C101203:IQ motif containing GTPase activating protein 1; D020703:ras GTPase-Activating Proteins; D020830:rac1 GTP-Binding Protein