The Actin Binding Domain of βI-Spectrin Regulates the Morphological and Functional Dynamics of Dendritic Spines

Michael W Nestor,Xiang Cai,Scott M Thompson,Robert J Bloch,Michele R Stone,Lin Mei

doi:10.1371/journal.pone.0016197

Michael W Nestor, Xiang Cai + Show 4 more

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https://doi.org/10.1371/journal.pone.0016197

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Journal: PloS one	Publication Date: Jan 31, 2011
Citations: 72	License type: CC BY 4.0

Affiliation: University of Maryland, Baltimore

Abstract

Actin microfilaments regulate the size, shape and mobility of dendritic spines and are in turn regulated by actin binding proteins and small GTPases. The βI isoform of spectrin, a protein that links the actin cytoskeleton to membrane proteins, is present in spines. To understand its function, we expressed its actin-binding domain (ABD) in CA1 pyramidal neurons in hippocampal slice cultures. The ABD of βI-spectrin bundled actin in principal dendrites and was concentrated in dendritic spines, where it significantly increased the size of the spine head. These effects were not observed after expression of homologous ABDs of utrophin, dystrophin, and α-actinin. Treatment of slice cultures with latrunculin-B significantly decreased spine head size and decreased actin-GFP fluorescence in cells expressing the ABD of α-actinin, but not the ABD of βI-spectrin, suggesting that its presence inhibits actin depolymerization. We also observed an increase in the area of GFP-tagged PSD-95 in the spine head and an increase in the amplitude of mEPSCs at spines expressing the ABD of βI-spectrin. The effects of the βI-spectrin ABD on spine size and mEPSC amplitude were mimicked by expressing wild-type Rac3, a small GTPase that co-immunoprecipitates specifically with βI-spectrin in extracts of cultured cortical neurons. Spine size was normal in cells co-expressing a dominant negative Rac3 construct with the βI-spectrin ABD. We suggest that βI-spectrin is a synaptic protein that can modulate both the morphological and functional dynamics of dendritic spines, perhaps via interaction with actin and Rac3.

Highlights

Most excitatory synapses are positioned on dendritic spines, which display a range of sizes and shapes
The actin-binding domain (ABD) of bI-spectrin induces actin bundling in CA1 pyramidal neurons
To investigate the interaction between spectrin family proteins and the actin cytoskeleton, we created constructs of the highly homologous ABDs of bI-spectrin, a-actinin-2, utrophin, dystrophin, and filamin, all fused to the fluorophore DsRed, and introduced them biolistically into CA1 pyramidal cells in hippocampal slice cultures

Summary

Introduction

Most excitatory synapses are positioned on dendritic spines, which display a range of sizes and shapes. Changes in dendritic spine size accompany synapse maturation [1] and are correlated with synaptic strength [2,3,4]. Spine morphology is altered by changes in synaptic activity [5,6] and can accompany changes in synaptic strength in some, but not all, forms of long-term potentiation [7,8,9]. The signaling mechanisms that regulate spine structure and couple changes in synaptic structure and function are being actively explored. Actin, both G-actin monomers and filamentous, polymerized Factin, is highly concentrated in dendritic spines [10] and regulates spine morphology. Actin and its binding proteins, as well as the signaling molecules that regulate their interaction, are essential for synapse structure and function

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