Actomyosin contractility controls cell surface area of oligodendrocytes

<p>Abstract</p> <p>Background</p> <p>To form myelin oligodendrocytes expand and wrap their plasma membrane multiple times around an axon. How is this expansion controlled?</p> <p>Results</p> <p>Here we show that cell surface area depends on actomyosin contractility and is regulated by physical properties of the supporting matrix. Moreover, we find that chondroitin sulfate proteoglycans (CSPG), molecules associated with non-permissive growth properties within the central nervous system (CNS), block cell surface spreading. Most importantly, the inhibitory effects of CSPG on plasma membrane extension were completely prevented by treatment with inhibitors of actomyosin contractility and by RNAi mediated knockdown of myosin II. In addition, we found that reductions of plasma membrane area were accompanied by changes in the rate of fluid-phase endocytosis.</p> <p>Conclusion</p> <p>In summary, our results establish a novel connection between endocytosis, cell surface extension and actomyosin contractility. These findings open up new possibilities of how to promote the morphological differentiation of oligodendrocytes in a non-permissive growth environment.</p> <p>See related minireview by Bauer and ffrench-Constant: <url>http://www.jbiol.com/content/8/8/78</url></p

Straight GDP-Tubulin Protofilaments Form in the Presence of Taxol

International audienceMicrotubules exist in dynamic equilibrium, growing and shrinking by the addition or loss of tubulin dimers from the ends of protofilaments. The hydrolysis of GTP in b-tubulin destabilizes the microtubule lattice by increasing the curvature of protofilaments in the microtubule and putting strain on the lattice. The ob- servation that protofilament curvature depends on GTP hydrolysis suggests that microtubule destabil- izers and stabilizers work by modulating the curvature of the microtubule lattice itself. Indeed, the microtu- bule destabilizer MCAK has been shown to increase the curvature of protofilaments during depolymeriza- tion. Here, we show that the atomic force microscopy (AFM) of individual tubulin protofilaments provides sufficient resolution to allow the imaging of single pro- tofilaments in their native environment. By using this assay, we confirm previous results for the effects of GTP hydrolysis and MCAK on the conformation of pro- tofilaments. We go on to show that taxol stabilizes microtubules by straightening the GDP protofilament and slowing down the transition of protofilaments from straight to a curved configuration

Force probing surfaces of living cells to molecular resolution

Biological processes rely on molecular interactions that can be directly measured using force spectroscopy techniques. Here we review how atomic force microscopy can be applied to force probe surfaces of living cells to single-molecule resolution. Such probing of individual interactions can be used to map cell surface receptors, and to assay the receptors' functional states, binding kinetics and landscapes. This information provides unique insight into how cells structurally and functionally modulate the molecules of their surfaces to interact with the cellular environment

In PC3 prostate cancer cells ephrin receptors crosstalk to beta(1)-integrins to strengthen adhesion to collagen type I

Eph receptor (Eph) and ephrin signaling can play central roles in prostate cancer and other cancer types. Exposed to ephrin-A1 PC3 prostate cancer cells alter adhesion to extracellular matrix (ECM) proteins. However, whether PC3 cells increase or reduce adhesion, and by which mechanisms they change adhesion to the ECM remains to be characterized. Here, we assay how ephrin-A1 stimulates PC3 cells to adhere to ECM proteins using single-cell force spectroscopy. We find that PC3 cells binding to immobilized ephrin-A1 but not to solubilized ephrin-A1 specifically strengthen adhesion to collagen I. This Eph-ephrin-A1 signaling, which we suppose is based on mechanotransduction, stimulates β1-subunit containing integrin adhesion via the protein kinase Akt and the guanine nucleotide-exchange factor cytohesin. Inhibiting the small GTPases, Rap1 or Rac1, generally lowered adhesion of PC3 prostate cancer cells. Our finding suggests a mechanism by which PC3 prostate cancer cells exposed to ephrins crosstalk to β1-integrins and preferably metastasize in bone, a collagen I rich tissue.ISSN:2045-232

The depolymerizing kinesin MCAK uses lattice diffusion to rapidly target microtubule ends

The microtubule cytoskeleton is a dynamic structure in which the lengths of the microtubules are tightly regulated. One regulatory mechanism is the depolymerization of microtubules by motor proteins in the kinesin-13 family1. These proteins are crucial for the control of microtubule length in cell division2–4, neuronal development5 and interphase microtubule dynamics6,7. The mechanism by which kinesin-13 proteins depolymerize microtubules is poorly understood. A central question is how these proteins target to microtubule ends at rates exceeding those of standard enzyme–substrate kinetics8. To address this question we developed a single-molecule microscopy assay for MCAK, the founding member of the kinesin-13 family9. Here we show that MCAK moves along the microtubule lattice in a one-dimensional (1D) random walk. MCAK–microtubule interactions were transient: the average MCAK molecule diffused for 0.83 s with