Molecular Mechanism in Regulation of Neuronal Dendritic Morphology

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(1) In order to find out the relationships between drebrin and other actin associated proteins, drebrin, myosin, actin, toropomyosin, alpha-actinin, caldeson and gelsoin were purified, and various co-purification study with actin filament have been done. Drebrin binds to actin filaments at a stoichiometry of 1 : 5, with a dissociation constant (Kd) of 1.2x10^<-7>M.Drebrin does not exhibit any actin-nucleating, actin-severing or actin-capping activity, nor does it crosslink actin filaments. Drebrin did not affect the activity of gelsolin or actin binding activity of caldesmon and filamin, but strongly inhibited the actin binding activity of tropomyosin, and the actin binding and actin cross-linking activities of alpha-actinin and fascin. Drebrin has an inhibitory effect on actomyosin interation and might be an actin-linked regulatory protein of actomyosin interaction within neurons.(2) The morphological changes of dendritic spines of neurons have been postulated to participate in the expression of synaptic plasticity. We have examined the molecular mechanisms responsible for the changes in spine morphology, focusing on a protein that binds to actin filaments, drebrin, that is concentrated in neurons. We found that adult-type drebrin is localized in the dendritic spines in the forebrain of the rat, where it binds to the cytoskeleton of the spine. The drebrin-containing cytoskeleton consisted of drebrin, actin, myosin and gelsolin. In vitro, drebrin inhibited the movement of actin filaments on a glass surface that had been coated with myosin and reduced the actin-dependent ATPase activity of myosin. These results suggest that drebrin modulates the acto-myosin activity within spines and plays a role in the structure-based plasticity of synapses.