Ryoki Ishikawa

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Morphological changes in the dendritic spines have been postulated to participate in the expression of synaptic plasticity. The cytoskeleton is likely to play a key role in regulating spine structure. Here we examine the molecular mechanisms responsible for the changes in spine morphology, focusing on drebrin, an actin-binding protein that is known to(More)
The dynamic behaviour of myosin V molecules translocating along actin filaments has been mainly studied by optical microscopy. The processive hand-over-hand movement coupled with hydrolysis of adenosine triphosphate was thereby demonstrated. However, the protein molecules themselves are invisible in the observations and have therefore been visualized by(More)
Multiple isoforms of tropomyosin (TM) of rat cultured cells show differential effects on actin-severing activity of gelsolin. Flow birefringence measurements have revealed that tropomyosin isoforms with high Mr values (high Mr TMs) partially protect actin filaments from fragmentation by gelsolin, while tropomyosins with low Mr values (low Mr TMs) have no(More)
Drebrin is a development-associated neuroprotein whose cDNA into fibroblasts causes the formation of dendrite-like structures (Shirao, T., Kojima, N., and Obata, K. (1992) Neuroreport 3, 109-112). To explore molecular functions of drebrin during brain development, we purified drebrin from brains of rat embryos. Drebrin bound to actin filaments at a(More)
The endoplasmic streaming in Characean cells is an actin-dependent movement. The motor protein responsible for the streaming was partially purified and characterized. It was soluble at low ionic strength, an ATPase of a molecular mass of 225 kDa and activated more than 100 times by muscle F-actin. Surprisingly, in an in vitro motility assay, the motor(More)
Drebrin is an actin-binding protein which is expressed at highly levels in neurons. When introduced into fibroblasts, it has been known to bind to F-actin and to cause remodeling of F-actin. Here, we performed a domain analysis of the actin-binding and actin-remodeling activities of drebrin. Various fragments of drebrin cDNA were fused with green(More)
Human fascin is an actin-bundling protein and is thought to play a role in the formation of microfilament bundles of microspikes and stress fibers in cultured cells. To explore the regulation of fascin-actin interaction, we have examined the effects of culture cell caldesmon and tropomyosin (TM) on actin binding activity of human fascin. Caldesmon alone or(More)
Myosin-Va is an actin-based processive motor that conveys intracellular cargoes. Synaptic vesicles are one of the most important cargoes for myosin-Va, but the role of mammalian myosin-Va in secretion is less clear than for its yeast homologue, Myo2p. In the current studies, we show that myosin-Va on synaptic vesicles interacts with syntaxin-1A, a t-SNARE(More)
In skeletal muscles, the sarcolemma is possibly stabilized and protected against contraction-imposed stress by intermediate filaments (IFs) tethered to costameric sarcolemma. Although there is emerging evidence that plectin links IFs to costameres through dystrophin-glycoprotein complexes (DGC), the molecular organization from plectin to costameres still(More)
Previous results from our laboratory have shown that 1) cultured rat cells contain two classes of tropomyosin (TM), one (high Mr TMs) with higher Mr values and greater affinity for actin than the other (low Mr TMs); 2) presaturation of F-actin with high Mr TMs, but not with low Mr TMs, inhibits both actin-severing and actin binding activities of gelsolin;(More)