Acf7

Kodama, Atsuko; Karakesisoglou, Iakowos; Wong, Edmund; Vaezi, Alec; Fuchs, Elaine

doi:10.1016/s0092-8674(03)00813-4

Cited by 279 publications

(151 citation statements)

References 61 publications

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“…Additionally, there is evidence for a burst of actin polymerization during synaptic potentiation, both in the pre-and post-synaptic compartments (24,27,29,30), and we find phosphorylated STOP in the vicinity of pre-and post-synaptic protein clusters, in differentiated neurons. Finally, cross-talk between microtubule and actin assemblies have been a subject of great interest in recent times, and several proteins with dual microtubule/actin binding properties have been identified as crucial integrators of the cytoskeleton (8,31,32). Our findings suggest that STOP protein may function as such integrators in nerve terminals.…”

Section: Discussionmentioning

confidence: 64%

Phosphorylation of Microtubule-associated Protein STOP by Calmodulin Kinase II

Baratier

Peris

Brocard

et al. 2006

Journal of Biological Chemistry

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STOP proteins are microtubule-associated, calmodulinregulated proteins responsible for the high degree of stabilization displayed by neuronal microtubules. STOP suppression in mice induces synaptic defects affecting both short and long term synaptic plasticity in hippocampal neurons. Interestingly, STOP has been identified as a component of synaptic structures in neurons, despite the absence of microtubules in nerve terminals, indicating the existence of mechanisms able to induce a translocation of STOP from microtubules to synaptic compartments. Here we have tested STOP phosphorylation as a candidate mechanism for STOP relocalization. We show that, both in vitro and in vivo, STOP is phosphorylated by the multifunctional enzyme calcium/calmodulin-dependent protein kinase II (CaMKII), which is a key enzyme for synaptic plasticity. This phosphorylation occurs on at least two independent sites. Phosphorylated forms of STOP do not bind microtubules in vitro and do not co-localize with microtubules in cultured differentiating neurons. Instead, phosphorylated STOP co-localizes with actin assemblies along neurites or at branching points. Correlatively, we find that STOP binds to actin in vitro. Finally, in differentiated neurons, phosphorylated STOP co-localizes with clusters of synaptic proteins, whereas unphosphorylated STOP does not. Thus, STOP phosphorylation by CaMKII may promote STOP translocation from microtubules to synaptic compartments where it may interact with actin, which could be important for STOP function in synaptic plasticity.

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Section: Discussionmentioning

confidence: 64%

Phosphorylation of Microtubule-associated Protein STOP by Calmodulin Kinase II

Baratier

Peris

Brocard

et al. 2006

Journal of Biological Chemistry

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“…Cells that frequently make turns will yield a k value close to 0, whereas cells that persistently move along one direction will yield a k value close to 1. In addition to the direction of cell motility, v and k are important parameters that define cell motility (18). For all shapes, v and k are constant within experimental errors.…”

Section: Resultsmentioning

confidence: 99%

“…Currently the most widely used method to study polarized, moving cells is to scratch a wound in a confluent monolayer of cells and to observe the cells at the margin of the wound as they spontaneously polarize and migrate toward the wound (11,18,20). This method does not allow researchers to study single, isolated cells, because each cell contacts others.…”

Section: Resultsmentioning

confidence: 99%

Directing cell migration with asymmetric micropatterns

Jiang

Bruzewicz²,

Wong³

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

425

343

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This report shows that the direction of polarization of attached mammalian cells determines the direction in which they move. Surfaces micropatterned with appropriately functionalized selfassembled monolayers constrain individual cells to asymmetric geometries (for example, a teardrop); these geometries polarize the morphology of the cell. After electrochemical desorption of the self-assembled monolayers removes these constraints and allows the cells to move across the surface, they move toward their blunt ends.motility ͉ polarity ͉ self-assembled monolayers T his report demonstrates that imposed polarity of an adherent mammalian cell, that is, its morphology as characterized by a wide front (typically the blunt end) and a narrow rear (typically the sharp end), determines its direction of motility (1, 2). We patterned self-assembled monolayers (SAMs) on gold to confine single cells initially to polarized shapes (3, 4). A brief pulse of voltage applied to the gold released the cells from their constraints and allowed them to move freely across the surface (4). The initial direction of motility of cells correlated with the polarity of their original shape; we conclude that polarization of the shape of cells is sufficient to determine their directions of motion.The migration of mammalian cells typically includes the following processes: (i) morphological polarization (characterized by a wide front and a narrow rear); (ii) extension of membranes toward the direction of motility; (iii) formation of attachments between these leading membranes and the substrate; (iv) movement of the bulk of the cell body; and (v) release of attachments from the substrate at the sharp end (2). These processes together result in net translocation of the cell body (Fig. 1A). Many types of motile mammalian cells adopt a ''teardrop'' shape with a wide leading edge (dominated by structures termed the lamellipodia) that extends in the front and a narrow tail that releases and retracts. Most types of cells can polarize and move without stimuli (2, 5). Under the influence of a stimulus (chemical or mechanical), cells can polarize and move directionally (toward or away from the stimulus). It is not clear, however, whether morphological polarity of the cell itself can determine the direction of motility. We addressed this uncertainty by defining the polarity of adherent cells using an asymmetrically patterned substrate without a gradient of stimulant. We then released the constraint on the shape and location of the cells and assessed the direction of motility for individual cells. This approach is, to our knowledge, the first test of the hypothesis that the shape of a cell determines the direction of its motion. Other parameters that characterize the motion of cells, such as their speed and their tendency to make turns, are not affected by the initial constraints.Recently, Parker et al. (6) showed that cells, when confined to a square shape, in the absence of gradients of stimulant, preferentially extended their lamellipodia from the corners (Fi...

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“…This suggests that in living cells, the MT-based motors can act as both passive cross-links that resist transport and active force generators, an emerging theme in the molecular motor field (Tao et al, 2006;Saunders et al, 2007). Alternatively, there may be a second set of molecules that passively cross-link, most likely to the stationary F-actin cytoskeleton, such as ACF7 (Chishti et al, 1998;Kodama et al, 2003). The anterograde movement of the MTs suggests that the motor that drives bending is either dynein or a minus-end-directed kinesin.…”

Section: Evidence For Microtubule-based Motor-driven Bucklingmentioning

confidence: 99%

Anterograde Microtubule Transport Drives Microtubule Bending in LLC-PK1 Epithelial Cells

Bicek

Tüzel

Demtchouk

et al. 2009

MBoC

103

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Microtubules (MTs) have been proposed to act mechanically as compressive struts that resist both actomyosin contractile forces and their own polymerization forces to mechanically stabilize cell shape. To identify the origin of MT bending, we directly observed MT bending and F-actin transport dynamics in the periphery of LLC-PK1 epithelial cells. We found that F-actin is nearly stationary in these cells even as MTs are deformed, demonstrating that MT bending is not driven by actomyosin contractility. Furthermore, the inhibition of myosin II activity through the use of blebbistatin results in microtubules that are still dynamically bending. In addition, as determined by fluorescent speckle microscopy, MT polymerization rarely results, if ever, in bending. We suppressed dynamic instability using nocodazole, and we observed no qualitative change in the MT bending dynamics. Bending most often results from anterograde transport of proximal portions of the MT toward a nearly stationary distal tip. Interestingly, we found that in an in vitro kinesin-MT gliding assay, MTs buckle in a similar manner. To make quantitative comparisons, we measured curvature distributions of observed MTs and found that the in vivo and in vitro curvature distributions agree quantitatively. In addition, the measured MT curvature distribution is not Gaussian, as expected for a thermally driven semiflexible polymer, indicating that thermal forces play a minor role in MT bending. We conclude that many of the known mechanisms of MT deformation, such as polymerization and acto-myosin contractility, play an inconsequential role in mediating MT bending in LLC-PK1 cells and that MT-based molecular motors likely generate most of the strain energy stored in the MT lattice. The results argue against models in which MTs play a major mechanical role in LLC-PK1 cells and instead favor a model in which mechanical forces control the spatial distribution of the MT array.

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Acf7

Cited by 279 publications

References 61 publications

Phosphorylation of Microtubule-associated Protein STOP by Calmodulin Kinase II

Phosphorylation of Microtubule-associated Protein STOP by Calmodulin Kinase II

Directing cell migration with asymmetric micropatterns

Anterograde Microtubule Transport Drives Microtubule Bending in LLC-PK1 Epithelial Cells

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