Sun, 06 Jul 2008 12:51:13 BST CiteULike: dchen's Brangwynne http://www.citeulike.org/user/dchen/author/Brangwynne CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/dchen/article/2767406 <i>Physical Review Letters, Vol. 100, No. 11. (2008)</i><br /><br />Biological activity gives rise to nonequilibrium fluctuations in the cytoplasm of cells; however, there are few methods to directly measure these fluctuations. Using a reconstituted actin cytoskeleton, we show that the bending dynamics of embedded microtubules can be used to probe local stress fluctuations. We add myosin motors that drive the network out of equilibrium, resulting in an increased amplitude and modified time dependence of microtubule bending fluctuations. We show that this behavior results from steplike forces on the order of 10 pN driven by collective motor dynamics. Nonequilibrium Microtubule Fluctuations in a Model Cytoskeleton Clifford Brangwynne Gijsje Koenderink Frederick Mackintosh David Weitz doi:10.1103/PhysRevLett.100.118104 Physical Review Letters, Vol. 100, No. 11. (2008) 2008-05-07T21:19:39-00:00 2008 Physical Review Letters 100 11 APS 2008 biology weitz http://www.citeulike.org/user/dchen/article/954119 <i>J. Cell Biol., Vol. 173, No. 5. (5 June 2006), pp. 733-741.</i><br /><br />Cytoskeletal microtubules have been proposed to influence cell shape and mechanics based on their ability to resist large-scale compressive forces exerted by the surrounding contractile cytoskeleton. Consistent with this, cytoplasmic microtubules are often highly curved and appear buckled because of compressive loads. However, the results of in vitro studies suggest that microtubules should buckle at much larger length scales, withstanding only exceedingly small compressive forces. This discrepancy calls into question the structural role of microtubules, and highlights our lack of quantitative knowledge of the magnitude of the forces they experience and can withstand in living cells. We show that intracellular microtubules do bear large-scale compressive loads from a variety of physiological forces, but their buckling wavelength is reduced significantly because of mechanical coupling to the surrounding elastic cytoskeleton. We quantitatively explain this behavior, and show that this coupling dramatically increases the compressive forces that microtubules can sustain, suggesting they can make a more significant structural contribution to the mechanical behavior of the cell than previously thought possible. 10.1083/jcb.200601060 Microtubules can bear enhanced compressive loads in living cells because of lateral reinforcement Clifford Brangwynne Frederick Mackintosh Sanjay Kumar Nicholas Geisse Jennifer Talbot L Mahadevan Kevin Parker Donald Ingber David Weitz doi:10.1083/jcb.200601060 J. Cell Biol., Vol. 173, No. 5. (5 June 2006), pp. 733-741. 2006-11-20T22:19:20-00:00 2006 J. Cell Biol. 173 5 733 741 biology microrheology weitz http://www.citeulike.org/user/dchen/article/2688177 <i>Current Opinion in Cell Biology, Vol. 19, No. 1. (February 2007), pp. 101-107.</i><br /><br />To elucidate the dynamic and functional role of a cell within the tissue it belongs to, it is essential to understand its material properties. The cell is a viscoelastic material with highly unusual properties. Measurements of the mechanical behavior of cells are beginning to probe the contribution of constituent components to cell mechanics. Reconstituted cytoskeletal protein networks have been shown to mimic many aspects of the mechanical properties of cells, providing new insight into the origin of cellular behavior. These networks are highly nonlinear, with an elastic modulus that depends sensitively on applied stress. Theories can account for some of the measured properties, but a complete model remains elusive. The cell as a material Karen Kasza Amy Rowat Jiayu Liu Thomas Angelini Clifford Brangwynne Gijsje Koenderink David Weitz doi:10.1016/j.ceb.2006.12.002 Current Opinion in Cell Biology, Vol. 19, No. 1. (February 2007), pp. 101-107. 2008-04-18T15:21:56-00:00 2007 Current Opinion in Cell Biology 19 1 101 107 biology review weitz http://www.citeulike.org/user/dchen/article/2265040 <i>Proceedings of the National Academy of Sciences, Vol. 104, No. 41. (9 October 2007), pp. 16128-16133.</i><br /><br />Microtubules are highly dynamic biopolymer filaments involved in a wide variety of biological processes including cell division, migration, and intracellular transport. Microtubules are very rigid and form a stiff structural scaffold that resists deformation. However, despite their rigidity, inside of cells they typically exhibit significant bends on all length scales. Here, we investigate the origin of these bends using a Fourier analysis approach to quantify their length and time dependence. We show that, in cultured animal cells, bending is suppressed by the surrounding elastic cytoskeleton, and even large intracellular forces only cause significant bending fluctuations on short length scales. However, these lateral bending fluctuations also naturally cause fluctuations in the orientation of the microtubule tip. During growth, these tip fluctuations lead to microtubule bends that are frozen-in by the surrounding elastic network. This results in a persistent random walk of the microtubule, with a small apparent persistence length of approx30 microm, approx100 times smaller than that resulting from thermal fluctuations alone. Thus, large nonthermal forces govern the growth of microtubules and can explain the highly curved shapes observed in the microtubule cytoskeleton of living cells. 10.1073/pnas.0703094104 Force fluctuations and polymerization dynamics of intracellular microtubules Clifford Brangwynne FC Mackintosh David Weitz doi:10.1073/pnas.0703094104 Proceedings of the National Academy of Sciences, Vol. 104, No. 41. (9 October 2007), pp. 16128-16133. 2008-01-21T00:56:00-00:00 2007 Proceedings of the National Academy of Sciences 104 41 16128 16133 2007 biology microfluid weitz