1. An individual-based model for cell division simulation Simulation and results The simulator allows us to reconstitute a virtual cell tissue. Each cell is taken as an autonomous agent carrying out a whole of rules: grow, divide and organize itself in space with the other cells. Simulations provide a better understanding of dynamical characteristics of cell population and cells with their environment. In addition, the model supposes that the same molecules which stimulate the volume growth of the cell also stimulate the molecules which order the division time. That allows, the growth of the cell and its division in two cells, to be in harmony. We remark that even if the model is simple and that rules of cell growth, the interactions cell/cell and cell/environnement are simple, we could reproduce some scenarios which are more or less compatible with the experimental observations. We also remark that the cells gradually form a colony and the population follows an exponential growth before to stabilize. We tested some parameters of IBM to see the effect on the population such as absorption rate of the nutrients and the environment parameter. We hope that the model will allow to explore phenomena of disordered state in a tissue using individual based model approach and to understand some collective behaviors which can result from local rules on the cells. We think to extend the model by introducing more complex interactions for example proteins evolution or genes into the cell cycle connecting the molecular level to the tissue behavior. We can also think of a better presentation of the model by an 3D interface or to introduce more than one kind of cells and/or spread cancerous cells in a healthy tissue. References: [1] Booth G.,”Gecko: A Continuous 2D World for Ecological Modeling”, Artificial Life, Vol. 3, Issue 3 - Summer 1997. [2} Kreft J.U, Booth G, BacSim, ”a simulator for individual-based modelling of bacterial colony growth”, Microbiology Wimpenny JWT, 144: 3275-3287 (1998). [3] Kreft J.U, ”Biofilms promote altruism”, Microbiology, 150: 2751-2760 (2004). cell population absorption rate’s Effect Effect of the environnement Introduction The growth and division of cells are important for almost all organisms, including humans. Following cell division, the daughter cells confront two possible fates. They may decide to enter immediately into another round of growth and division, thereby remaining in the active growth cycle. This leads to repeat rounds of cell division and results in turn in an exponentially increasing cell population. As an alternative, the daughter cells may decide to cease active growth for a while. In that case, they will exit the active cell cycle and enter into a state of quiescence. Growth will imply the build-up of new molecules by a cell and the associated increase in its mass and volume. Division implies the division of mother cell on two cells. Cells grow more or less by a factor of 2 between successive divisions but the mass of the 2 daughter cells is not always equal. Here, we use the individual based model approach to model cell growth and cell division. Each cell and their properties are modeled individually. We use a simple mathematical model for the growth and we give some rules for organization of cells in space according to platform Bacsim/Gecko [2]. F. Bekkal Brikci, A. Estacio Moreno, Alassane Bah UR GEODES Institut de Recherche pour le Développement, centre d’Ile de France 32 Avenue Henri Varagnat 93143 Bondy cedex, France Cell growth and cell division simulator catch of screen after many steps of simulation Parameters model We use the following rules for spatial organization: Cell grow according to the equation of volume The positions are updated for each step (coordinates of the cells on space’s simulator) Rearrangement of the neighbors to avoid the overlapping according to platform Gecko/Bacsim Division in two cells when the cell reaches the age of division (signal molecules reach a threshold) The number of feasible divisions of the initial cell is limited by 40 (Hayflick's limit). Cell spatial organization and neighborhood  The cells are represented by spheres in a continuous space.  They can move and grow in volume.  They maintain a minimal distance to the neighbours by shoving when they grow or divide. Individual based model (IBM) Cell growth Cell growth and cell division is regulated both by intracellular molecules and by extracellular substances that control these programs. Cells grow by absorbing substances from the environment through cell surface and form nutrients molecules (n) inside cells. Cell growth implies both volume cell growth and cell cycle progression until cell division. The timing of cell division is regulated by some molecules which we called signal molecules (s) regulated by nutrients molecules. In fact, cells divide when signal molecules reach a threshold. When s>s t the cell divide on two cells. Panel of and their functions Individual based- model structure