Time: 3:15-4:15pm, Monday, December 2
Room: 318 DBRT
Host: Mark S. Alber (Mathematics)

Speaker: Dr. Stan Maree'

From: Department of Mathematics, University of British Columbia Vancouver, Canada

Title: Modeling Slime Mould Morphogenesis: the Culmination

Abstract:
Culmination of the morphogenesis of the cellular slime mould Dictyostelium discoideum involves complex cell movements which transform a mound of cells into a globule of spores on a slender stalk. The movement has been likened to a ``reverse fountain'', whereby prestalk cells in the upper part form a stalk that moves downwards and anchors itself to the substratum, while prespore cells in the lower part move upwards to form the spore head. We will demonstrate that the processes that are essential during the earlier stages of the morphogenesis are in fact sufficient to produce the dynamics of the culmination stage. These processes are cyclic AMP signaling, differential adhesion, cell differentiation and production of ECM.

We have simulated the culmination using a hybrid CA/PDE model. In the model, individual cells are represented as a group of connected automata, i.e. the basic scale of the model is subcellular. Initially we simulated in 2D, describing transverse sections through the culminant. Recently we have extended the model to 3D, in order to prove feasibility of the full model, and to open the road to describe the whole development as one continuous process.

With our model we are able to reproduce the main features that occur during culmination, namely the straight downward elongation of the stalk, its anchoring to the substratum and the formation of the long thin stalk topped by the spore head. We show that periodic upward movements, due to chemotactic motion, are essential for successful culmination, because the pressure waves they induce squeeze the stalk downwards through the cell mass, a mechanism which has a number of self-organizing and self-correcting properties and can explain many experimental observations.