title: Drebrin-dependent actin clustering in dendritic filopodia governs synaptic targeting of postsynaptic density-95 and dendritic spine morphogenesis.
abstract: Dendritic spines have two major structural elements: postsynaptic densities (PSDs) and actin cytoskeletons. PSD proteins are proposed to regulate spine morphogenesis. However, other molecular mechanisms should govern spine morphogenesis, because the initiation of spine morphogenesis precedes the synaptic clustering of these proteins. Here, we show that synaptic clustering of drebrin, an actin-binding protein highly enriched in dendritic spines, governs spine morphogenesis. We immunocytochemically analyzed developing hippocampal neurons of low-density cultures. Filopodia-like dendritic protrusions were classified into two types: diffuse-type filopodia, which have diffuse distribution of drebrin, and cluster-type filopodia, which have drebrin clusters with filamentous actin (F-actin). Most cluster-type filopodia were synaptic filopodia. Postsynaptic drebrin clusters were found in both most synaptic filopodia and spines. Postsynaptic PSD-95 clusters, however, were found in only one-half of synaptic filopodia but in most spines. These data indicate that cluster-type filopodia are not mature spines but their precursors. Suppression of the upregulation of drebrin adult isoform (drebrin A) by antisense oligonucleotides against it attenuated synaptic clustering of PSD-95, as well as clustering of drebrin and F-actin. Furthermore, the restoration of drebrin A expression by injection of the expression vectors of drebrin A tagged with green fluorescent protein into the neurons treated with the antisense oligonucleotides induced synaptic reclustering of PSD-95 on clusters of the labeled drebrin A. These data indicated that the synaptic clustering of drebrin is necessary for that of PSD-95 in developing neurons. Together, these data suggest that synaptic clustering of drebrin is an essential step for spine morphogenesis.
authors.affiliation: Department of Neurobiology and Behavior, Gunma University School of Medicine, Maebashi 371-8511, Japan. tshirao@med.gunma-u.ac.jp
authors.forename: Hideto
authors.initials: H
authors.lastname: Takahashi
authors.forename: Yuko
authors.initials: Y
authors.lastname: Sekino
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tanaka
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Mizui
authors.forename: Shoji
authors.initials: S
authors.lastname: Kishi
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Shirao
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D002454:Cell Differentiation; D022081:Cell Surface Extensions / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000235:genetics / Q000378:metabolism; D003712:Dendrites / Q000378:metabolism* / Q000648:ultrastructure; D000076122:Disks Large Homolog 4 Protein; D049452:Green Fluorescent Proteins; D006624:Hippocampus / Q000166:cytology; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins / Q000235:genetics; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009024:Morphogenesis; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D009479:Neuropeptides / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D011554:Pseudopodia / Q000145:classification / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D013569:Synapses / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors
chemical_list: D000199:Actins; D000076122:Disks Large Homolog 4 Protein; C501449:Dlg4 protein, rat; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; D016376:Oligonucleotides, Antisense; C053386:drebrins; C033652:postsynaptic density proteins; D049452:Green Fluorescent Proteins