Thu, 21 Aug 2008 15:29:30 BST CiteULike: lechristophe Kasai http://www.citeulike.org/user/lechristophe/author/Kasai CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/lechristophe/article/2669700 <i>Neuron, Vol. 57, No. 5. (13 March 2008), pp. 719-729.</i><br /><br />Summary Synapse function and plasticity depend on the physical structure of dendritic spines as determined by the actin cytoskeleton. We have investigated the organization of filamentous (F-) actin within individual spines on CA1 pyramidal neurons in rat hippocampal slices. Using two-photon photoactivation of green fluorescent protein fused to [beta]-actin, we found that a dynamic pool of F-actin at the tip of the spine quickly treadmilled to generate an expansive force. The size of a stable F-actin pool at the base of the spine depended on spine volume. Repeated two-photon uncaging of glutamate formed a third pool of F-actin and enlarged the spine. The spine often released this "enlargement pool" into the dendritic shaft, but the pool had to be physically confined by a spine neck for the enlargement to be long-lasting. Ca2+/calmodulin-dependent protein kinase II regulated this confinement. Thus, spines have an elaborate mechanical nature that is regulated by actin fibers. The Subspine Organization of Actin Fibers Regulates the Structure and Plasticity of Dendritic Spines Naoki Honkura Masanori Matsuzaki Jun Noguchi Graham Ellis-Davies Haruo Kasai doi:10.1016/j.neuron.2008.01.013 Neuron, Vol. 57, No. 5. (13 March 2008), pp. 719-729. 2008-04-14T16:24:42-00:00 2008 Neuron 57 5 719 729 actin cytosqueleton dendritic_spines photoactivation http://www.citeulike.org/user/lechristophe/article/918597 <i>Annu Rev Biophys Biomol Struct, Vol. 34 (2005), pp. 351-378.</i><br /><br />Recent advancements in single-molecule tracking methods with nanometer-level precision now allow researchers to observe the movement, recruitment, and activation of single molecules in the plasma membrane in living cells. In particular, on the basis of the observations by high-speed single-particle tracking at a frame rate of 40,000 frames s(1), the partitioning of the fluid plasma membrane into submicron compartments throughout the cell membrane and the hop diffusion of virtually all the molecules have been proposed. This could explain why the diffusion coefficients in the plasma membrane are considerably smaller than those in artificial membranes, and why the diffusion coefficient is reduced upon molecular complex formation (oligomerization-induced trapping). In this review, we first describe the high-speed single-molecule tracking methods, and then we critically review a new model of a partitioned fluid plasma membrane and the involvement of the actin-based membrane-skeleton "fences" and anchored-transmembrane protein "pickets" in the formation of compartment boundaries. Paradigm shift of the plasma membrane concept from the two-dimensional continuum fluid to the partitioned fluid: high-speed single-molecule tracking of membrane molecules. A Kusumi C Nakada K Ritchie K Murase K Suzuki H Murakoshi RS Kasai J Kondo T Fujiwara doi:10.1146/annurev.biophys.34.040204.144637 Annu Rev Biophys Biomol Struct, Vol. 34 (2005), pp. 351-378. 2006-10-30T15:58:28-00:00 2005 Annu Rev Biophys Biomol Struct 1056-8700 34 351 378 biophysics cytosqueleton membrane_diffusion model review http://www.citeulike.org/user/lechristophe/article/894197 <i>J. Cell Biol., Vol. 174, No. 6. (11 September 2006), pp. 851-862.</i><br /><br />Three-dimensional images of the undercoat structure on the cytoplasmic surface of the upper cell membrane of normal rat kidney fibroblast (NRK) cells and fetal rat skin keratinocytes were reconstructed by electron tomography, with 0.85-nm-thick consecutive sections made [~]100 nm from the cytoplasmic surface using rapidly frozen, deeply etched, platinum-replicated plasma membranes. The membrane skeleton (MSK) primarily consists of actin filaments and associated proteins. The MSK covers the entire cytoplasmic surface and is closely linked to clathrin-coated pits and caveolae. The actin filaments that are closely apposed to the cytoplasmic surface of the plasma membrane (within 10.2 nm) are likely to form the boundaries of the membrane compartments responsible for the temporary confinement of membrane molecules, thus partitioning the plasma membrane with regard to their lateral diffusion. The distribution of the MSK mesh size as determined by electron tomography and that of the compartment size as determined from high speed single-particle tracking of phospholipid diffusion agree well in both cell types, supporting the MSK fence and MSK-anchored protein picket models. 10.1083/jcb.200606007 Three-dimensional reconstruction of the membrane skeleton at the plasma membrane interface by electron tomography Nobuhiro Morone Takahiro Fujiwara Kotono Murase Rinshi Kasai Hiroshi Ike Shigeki Yuasa Jiro Usukura Akihiro Kusumi doi:10.1083/jcb.200606007 J. Cell Biol., Vol. 174, No. 6. (11 September 2006), pp. 851-862. 2006-10-12T11:56:54-00:00 2006 J. Cell Biol. 174 6 851 862 cytosqueleton electron_microscopy membrane_diffusion trafficking http://www.citeulike.org/user/lechristophe/article/768774 <i>Nat Cell Biol, Vol. 5, No. 7. (July 2003), pp. 626-632.</i><br /><br />The formation and maintenance of polarized distributions of membrane proteins in the cell membrane are key to the function of polarized cells. In polarized neurons, various membrane proteins are localized to the somatodendritic domain or the axon. Neurons control polarized delivery of membrane proteins to each domain, and in addition, they must also block diffusional mixing of proteins between these domains. However, the presence of a diffusion barrier in the cell membrane of the axonal initial segment (IS), which separates these two domains, has been controversial: it is difficult to conceive barrier mechanisms by which an even diffusion of phospholipids could be blocked. Here, by observing the dynamics of individual phospholipid molecules in the plasma membrane of developing hippocampal neurons in culture, we found that their diffusion was blocked in the IS membrane. We also found that the diffusion barrier is formed in neurons 7-10 days after birth through the accumulation of various transmembrane proteins that are anchored to the dense actin-based membrane skeleton meshes being formed under the IS membrane. We conclude that various membrane proteins anchored to the dense membrane skeleton function as rows of pickets, which even stop the overall diffusion of phospholipids, and may represent a universal mechanism for formation of diffusion barriers in the cell membrane. Accumulation of anchored proteins forms membrane diffusion barriers during neuronal polarization. C Nakada K Ritchie Y Oba M Nakamura Y Hotta R Iino RS Kasai K Yamaguchi T Fujiwara A Kusumi doi:10.1038/ncb1009 Nat Cell Biol, Vol. 5, No. 7. (July 2003), pp. 626-632. 2006-07-21T17:11:45-00:00 2003 Nat Cell Biol 1465-7392 5 7 626 632 ais axon cytosqueleton membrane_diffusion single_molecule