%0 Book Section %1 statphys23_0386 %A Coniglio, A. %A Candia, A. De %A Gamba, A. %A Ferraro, T. %B Abstract Book of the XXIII IUPAP International Conference on Statistical Physics %C Genova, Italy %D 2007 %E Pietronero, Luciano %E Loreto, Vittorio %E Zapperi, Stefano %K cellular chemotaxis kinetics ordering phase processes separation signal statphys23 topic-10 trasduction %T A spin lattice model for eukaryotic directional sensing. %U http://st23.statphys23.org/webservices/abstract/preview_pop.php?ID_PAPER=386 %X Eukaryotic cells are able to sense spatial gradients of chemotactic signal. This ability governs the development of complex eukaryotic organisms. Experiments show that cells exposed to shallow chemoattractant gradients respond with strong accumulation of the phosphatidylinositol 3-kinase (PI3K) enzyme and its phosphoinositide product PIP3 on the plasma membrane side exposed to the highest chemoattractant concentration 1, whereas the PIP3-degrading enzyme PTEN and its product PIP2 localize in a complementary pattern. In physical terms, the process of directional sensing shows the characteristic phenomenology of phase separation 2,3. We propose a simple model which reproduces the main features of this process. The phosphoinositide species PIP2 and PIP3 are represented as states of an Ising spin and the chemoattractant signal plays the role of external field. The state of cells exposed to a uniform chemoattractant activation field is described as a metastable, uniform PIP3-rich state. The system dynamics leads to formation of PIP2 patches in the PIP3 sea and to a coarsening process culminating in the formation of two large domains, respectively rich in PIP2 and PIP3. In the presence of a uniform activation field the coarsening process is completely random, the size of PIP2 patches grows in time $t$ approximately as $t^1/2$, and the polarization process completes in a time $t_\astR^2$, where $R$ is the size of the system. In the presence of a slight anisotropic component $\epsilon$ in the activation field the process is completed after a time $t_\epsilon$, which can be much faster than $t_\ast$, thus leading to an effective amplification of the slight anisotropic component in the chemotactic signal. A threshold in the steepness of the smallest detectable anisotropic component is observed, along with a loss in sensitivity at higher concentrations of chemotactic signal, in agreement with recent experimental findings 4.\\ 1) C. Janetopoulos, L. Ma, P. N. Nevreotes, P. A. Iglesias Natl. Acad. Sci U.S.A. 101, 16606 (2004).\\ 2) A. Gamba, A.de Candia, A.Coniglio, F. Bussolino, G. Serini Proc. Natl. Acad. Sci U.S.A. 102, 16927 (2005).\\ 3) A. Gamba, A.de Candia, A.Coniglio, F. Bussolino, G. Serini Sci. STKE 378 (2007), pl1.\\ 4) L. Song, S. M. Nadkarni, H. U. Bodeker, C. Beta, A. Bae, C. Frank, W. J. Rappel, W.F. Loomis, E. Bodenschatz, Eur. J. Cell Biol. 85, 981 (2006).

@incollection{statphys23_0386, abstract = {Eukaryotic cells are able to sense spatial gradients of chemotactic signal. This ability governs the development of complex eukaryotic organisms. Experiments show that cells exposed to shallow chemoattractant gradients respond with strong accumulation of the phosphatidylinositol 3-kinase (PI3K) enzyme and its phosphoinositide product PIP3 on the plasma membrane side exposed to the highest chemoattractant concentration [1], whereas the PIP3-degrading enzyme PTEN and its product PIP2 localize in a complementary pattern. In physical terms, the process of directional sensing shows the characteristic phenomenology of phase separation [2,3]. We propose a simple model which reproduces the main features of this process. The phosphoinositide species PIP2 and PIP3 are represented as states of an Ising spin and the chemoattractant signal plays the role of external field. The state of cells exposed to a uniform chemoattractant activation field is described as a metastable, uniform PIP3-rich state. The system dynamics leads to formation of PIP2 patches in the PIP3 sea and to a coarsening process culminating in the formation of two large domains, respectively rich in PIP2 and PIP3. In the presence of a uniform activation field the coarsening process is completely random, the size of PIP2 patches grows in time $t$ approximately as $t^{1/2}$, and the polarization process completes in a time $t_\ast\sim R^2$, where $R$ is the size of the system. In the presence of a slight anisotropic component $\epsilon$ in the activation field the process is completed after a time $t_\epsilon$, which can be much faster than $t_\ast$, thus leading to an effective amplification of the slight anisotropic component in the chemotactic signal. A threshold in the steepness of the smallest detectable anisotropic component is observed, along with a loss in sensitivity at higher concentrations of chemotactic signal, in agreement with recent experimental findings [4].\\ 1) C. Janetopoulos, L. Ma, P. N. Nevreotes, P. A. Iglesias Natl. Acad. Sci U.S.A. 101, 16606 (2004).\\ 2) A. Gamba, A.de Candia, A.Coniglio, F. Bussolino, G. Serini Proc. Natl. Acad. Sci U.S.A. 102, 16927 (2005).\\ 3) A. Gamba, A.de Candia, A.Coniglio, F. Bussolino, G. Serini Sci. STKE 378 (2007), pl1.\\ 4) L. Song, S. M. Nadkarni, H. U. Bodeker, C. Beta, A. Bae, C. Frank, W. J. Rappel, W.F. Loomis, E. Bodenschatz, Eur. J. Cell Biol. 85, 981 (2006).}, added-at = {2007-06-20T10:16:09.000+0200}, address = {Genova, Italy}, author = {Coniglio, A. and Candia, A. De and Gamba, A. and Ferraro, T.}, biburl = {https://www.bibsonomy.org/bibtex/2288d11b4e3713b9141f848a7a6b66c59/statphys23}, booktitle = {Abstract Book of the XXIII IUPAP International Conference on Statistical Physics}, editor = {Pietronero, Luciano and Loreto, Vittorio and Zapperi, Stefano}, interhash = {23fc12e046aa4aeebdda009b29119f6f}, intrahash = {288d11b4e3713b9141f848a7a6b66c59}, keywords = {cellular chemotaxis kinetics ordering phase processes separation signal statphys23 topic-10 trasduction}, month = {9-13 July}, timestamp = {2007-06-20T10:16:18.000+0200}, title = {A spin lattice model for eukaryotic directional sensing.}, url = {http://st23.statphys23.org/webservices/abstract/preview_pop.php?ID_PAPER=386}, year = 2007 }