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Ning Wang's blog

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Mechanics dictates embryonic stem cell pluripotency

We demonstrate that a soft substrate of a stiffness that matches the embryonic stem cell stiffness can promote homogenous self-renewal and pluripotency of these cells, even in the absence of the growth factor-Leukemia Inhibitory Factor (LIF). These findings open the field of stem cell biology for long term culture of embryonic stem cells without generating a heterogeneous population of cells with varying degrees of differentiation and highlight the importance of mechanics in dictating embryonic stem cell pluripotency.

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Rac activation by stress does not depend on Src

It is known that platelet derived growth factor (PDGF) induced Rac activation depends on Src activity. However, we find that a local stress of physiologic magnitude via integrins can directly activate Rac GTPase rapidly, independent of the Src activity. Our finding on the stress-induced rapid Rac activation challenges the conventional wisdom on mechanotransduction and suggests that stress-induced signaling via focal adhesions does not follow signal transduction pathways induced by growth factors. To view the whole paper:

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Embryonic stem cell softness dictates stress-induced spreading and differentiation

We recently find that embryonic stem cells are very sensitive to a local cyclic stress applied to the focal adhesion.  They spread and differentiate (Oct3/4 downregulation) in response to this local force.

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Journal Club Theme of April 2009: Mechanobiology and Molecular Mechanomedicine

Professor YC Fung, the widely-recognized father of modern biomechanics, recently challenged the field by asking this fundamental question: “What axioms of the classical continuum mechanics have to be changed for biology?”

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Noncovalent bonds dictate cell rheology

Over the last ten years, a peculiar behavior of living cells is revealed: their modulus increases weakly with loading frequency (the so-called weak power law behavior) (for a pure elastic solid, the slope is 0; for a viscous fluid, the slope is 1).  The underlying mechanism is not clear at all; although a phenomenological soft glass rheology model (a model based on a disordered structure system) has been proposed, it cannot explain the multi-power laws at different loading frequencies (see Stamenovic et al, Biophys J Letter, 2007). 

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Podosomes are dynamic mechanosensors

We recently find that podosomes, very dynamic, self-organized structures, can function as mechanosensors.  For details, see the recent issue of Current Biology.

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A unique feature of mechanotransduction is revealed

It is generally believed that similar to soluble ligand-induced signal transduction, mechanotransduction initiates at the local force-membrane interface (e.g., at focal adhesions) by inducing local conformational changes or unfolding of membrane-bound proteins, followed by a cascade of diffusion-based or translocation-based signaling in the cytoplasm. However, all published reports, including past studies with the reporter type of construct extended here, were limited in timescale to address this fundamental issue.

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Long-distance propagation of forces in a cell

What might be the differences, if there is any, between mechanical signaling and chemical signaling in a living cell?

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