title: The actin binding domain of βI-spectrin regulates the morphological and functional dynamics of dendritic spines.
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.
authors.affiliation: Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Nestor
authors.forename: Xiang
authors.initials: X
authors.lastname: Cai
authors.forename: Michele R
authors.initials: MR
authors.lastname: Stone
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Bloch
authors.forename: Scott M
authors.initials: SM
authors.lastname: Thompson
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D001665:Binding Sites; D056547:CA1 Region, Hippocampal / Q000378:metabolism; D048430:Cell Shape; D049229:Dendritic Spines / Q000502:physiology* / Q000648:ultrastructure; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; D051381:Rats; D013049:Spectrin / Q000378:metabolism / Q000502:physiology*; D020744:rac GTP-Binding Proteins / Q000378:metabolism
chemical_list: D000199:Actins; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; D013049:Spectrin; D020744:rac GTP-Binding Proteins