Tag Archives: paul matsudaira

Traction stress analysis and modeling reveal amoeboid migration in confined spaces is accompanied by expansive forces and requires the structural integrity of the  membrane-cortex interactions

by Ai Kia Yip, Keng-Hwee Chiam and Paul Matsudaira

Integrative Biology, 2015, DOI: 10.1039/C4IB00245H. First published online 27 May 2015

Cell migration is crucial in many biological processes such as embryonic development, wound closure, as part of the body’s inflammatory response, as well as during cancer cell metastasis. A cell can translocate across a surface by either a mesenchymal or amoeboid cell migration mechanism. While cells are known to adhere to the extracellular matrix and generate contractile cell traction forces during integrin-dependent mesenchymal migration, little is known about the nature of the traction forces required for amoeboid migration in the absence of cell-matrix adhesions.

In this paper, we have combined 3-dimensional traction force microscopy with a confinement assay, where neutrophil-like cells are confined between two pieces of polyacrylamide gels. In the absence of cell-matrix adhesions, confined cells migrate by amoeboid “chimneying”, that is, generate traction by applying expansive and divergent forces against opposing surfaces. This chimneying speed was shown, both experimentally and computationally, to depend on both the magnitude of the intracellular pressure and the location where blebs are formed as determined by the membrane-cortex adhesion strength.


AiKiaYip-cellPic-sm

Picture caption: A cell confined between two pieces of non-adhesive polyacrylamide gels. 3D traction forces can be calculated based on gel deformations detected by the displacements of the embedded beads (orange).

Movie caption: An amoeboid neutrophil-like, differentiated HL60 cell migrating in between two pieces of non-adhesive polyacrylamide gels (DIC image, far left). Cell nuclei were stained with Hoechst (middle left panel, blue) and cells were transfected with Lifeact-GFP (middle right panel, green), which labels the F-actin. The three channels are overlaid in the far right panel. The number on the top of the images indicates the time in hour: minute: second.

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Direct observation of stick-slip movements of water nanodroplets induced by an electron beam

by Utkur Mirsaidov, Haimei Zheng, Dipanjan Bhattacharya, Yosune Casana, Paul Matsudaira

Proc Natl Acad Sci USA 109(19), 7187-7190 (2012)

Dynamics of the first few nanometers of water at the interface are encountered in a wide range of physical, chemical, and biological phenomena. A simple but critical question is whether interfacial forces at these nanoscale dimensions affect an externally induced movement of a water droplet on a surface.

At the bulk-scale water droplets spread on a hydrophilic surface and slip on a nonwetting, hydrophobic surface. Here we report the experimental description of the electron beam-induced dynamics of nanoscale water droplets by direct imaging the translocation of 10- to 80-nm-diameter water nanodroplets by transmission electron microscopy. These nanodroplets move on a hydrophilic surface not by a smooth flow but by a series of stick-slip steps.

We observe that each step is preceded by a unique characteristic deformation of the nanodroplet into a toroidal shape induced by the electron beam. We propose that this beam-induced change in shape increases the surface free energy of the nanodroplet that drives its transition from stick to slip state. 

Pictured is a snapshot of 50nm-diameter water droplet formed by the electron beam of a TEM. When irradiated with electrons, the droplet moves by a stick-slip mechanism in which the dome-shape droplet deforms into a high-energy toroidal shape and then translocates by extending a thin lamella from one edge.

Read online: PNAS.

Learn more about Utkur Mirsaidov‘s and Paul Matsudaira‘s research.