Precise Temporal Regulation of Molecular Diffusion within Dendritic Spines by Actin Polymers during Structural Plasticity

Shigeo Okabe,Atsushi Matsuda,Kazuki Obashi,Yasuhiro Inoue

doi:10.1016/j.celrep.2019.04.006

Shigeo Okabe, Atsushi Matsuda + Show 2 more

Open Access

https://doi.org/10.1016/j.celrep.2019.04.006

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Journal: Cell Reports	Publication Date: Apr 1, 2019
Citations: 22	License type: cc-by

Affiliation: The University of Tokyo, Kyoto University

Abstract

The biochemical transduction of excitatory synaptic signals occurs in the cytoplasm within dendritic spines. The associated reaction kinetics are shaped by the mobility of the signaling molecules; however, accurate monitoring of diffusional events within the femtoliter-sized spine structures has not yet been demonstrated. Here, we applied two-photon fluorescence correlation spectroscopy and raster image correlation spectroscopy to monitor protein dynamics within spines, revealing that F-actin restricts the mobility of proteins with a molecular mass of >100kDa. This restriction is transiently removed during actin remodeling at the initial phase of spine structural plasticity. Photobleaching experiments combined with super-resolution imaging indicate that this increase in mobility facilitates molecular interactions, which may modulate the functions of key postsynaptic signaling molecules, such as Tiam1 and CaMKII. Thus, actin polymers in dendritic spines act as precise temporal regulators of molecular diffusion and modulate signal transduction during synaptic plasticity.

Highlights

Most excitatory synapses on excitatory neurons in the forebrain are formed onto dendritic spines, which contain postsynaptic densities, the actin cytoskeleton, membrane organelles (Sheng and Hoogenraad, 2007), and various molecules responsible for the postsynaptic functions (Sala and Segal, 2014)
Two-Photon fluorescence correlation spectroscopy (FCS) and Two-Photon raster image correlation spectroscopy (RICS) within Dendritic Spines We hypothesized that a physical barrier within the spine suppresses the mobility of high-molecular-weight proteins and protein multimers
The autocorrelation function of EGFP5 within spines shifted to the left, toward a shorter diffusion time, after latrunculin A treatment (Figure 1B), resulting in a higher diffusion coefficient (Figure 1E)

Summary

Introduction

Most excitatory synapses on excitatory neurons in the forebrain are formed onto dendritic spines, which contain postsynaptic densities, the actin cytoskeleton, membrane organelles (Sheng and Hoogenraad, 2007), and various molecules responsible for the postsynaptic functions (Sala and Segal, 2014). A lower molecular mobility reduces the rate at which signaling molecules encounter one another. One way this can be achieved is via cytoskeletal polymers, such as actin polymers (F-actin), which are enriched within dendritic spines (Lin et al, 2013; Luby-Phelps, 2000). These two factors, namely confinement and the reduction of mobility, may play complex roles during synaptic plasticity, a process associated with changes in spine structure. Real-time monitoring of the mobility of molecules within the spine cytoplasm is required to verify that this regulation occurs

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