title: A bistable model of cell polarity.
abstract: Ultrasensitivity, as described by Goldbeter and Koshland, has been considered for a long time as a way to realize bistable switches in biological systems. It is not as well recognized that when ultrasensitivity and reinforcing feedback loops are present in a spatially distributed system such as the cell plasmamembrane, they may induce bistability and spatial separation of the system into distinct signaling phases. Here we suggest that bistability of ultrasensitive signaling pathways in a diffusive environment provides a basic mechanism to realize cell membrane polarity. Cell membrane polarization is a fundamental process implicated in several basic biological phenomena, such as differentiation, proliferation, migration and morphogenesis of unicellular and multicellular organisms. We describe a simple, solvable model of cell membrane polarization based on the coupling of membrane diffusion with bistable enzymatic dynamics. The model can reproduce a broad range of symmetry-breaking events, such as those observed in eukaryotic directional sensing, the apico-basal polarization of epithelium cells, the polarization of budding and mating yeast, and the formation of Ras nanoclusters in several cell types.
authors.affiliation: Department of Physics and Mathematics, Università dell'Insubria, Como, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Semplice
authors.forename: Andrea
authors.initials: A
authors.lastname: Veglio
authors.forename: Giovanni
authors.initials: G
authors.lastname: Naldi
authors.forename: Guido
authors.initials: G
authors.lastname: Serini
authors.forename: Andrea
authors.initials: A
authors.lastname: Gamba
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002462:Cell Membrane / Q000378:metabolism*; D002465:Cell Movement; D016764:Cell Polarity; D049109:Cell Proliferation; D002633:Chemotaxis; D003600:Cytosol / Q000378:metabolism; D004023:Dictyostelium / Q000378:metabolism; D020342:Finite Element Analysis; D008954:Models, Biological; D015233:Models, Statistical; D008962:Models, Theoretical; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D015398:Signal Transduction; D018631:ras Proteins / Q000378:metabolism
chemical_list: D018631:ras Proteins