Time: Wednesday, April 9, 2003 at 4:00 pm
Place: 102 DeBartolo Hall
Speaker: Prof. Dale Kaiser, Professor of Biochemistry
From: Department of Biochemistry, Stanford University

Topic: Dynamics of Pattern Formation

Abstract:
How do cells cooperate to build accurately shaped multicellular structures? Myxobacteria offer an experimental system to answer this question that is amenable to genetic and behavioral studies. They migrate as an organized swarm for feeding. Swarming genetic studies have shown that Myxococcus xanthus cells are propelled by two polar gliding engines, a pulling engine on one end and a pushing engine of the other. We are trying to develop a model of swarm behavior in terms of the mechanical properties of the two engines. When myxobacteria exhaust their food sources, they stop swarming and move to construct multicellular fruiting bodies. Building requires cell-cell signaling and leads to cell differentiation. Fruiting body development parallels the early stages of long bone development in vertebrates, for example. As fruiting body develop, heaps of cells form train of traveling waves. The waves decay as the rounded aggregates of cells enlarge, as if cells can leave wave crests by stopping on an early aggregate. Both the wave and aggregation patterns depend on the C-signal, a 17 kDa, surface-bound morphogenetic protein. In collaboration with Oleg Igoshin and George Oster, we have developed a mathematical model of cell movement and signaling in the traveling waves that agrees with the recorded trajectories of rippling cells (1,2). The wave model depends on signaling by cell-contact, rather then diffusible morphogens. The challenge is how to extend the signaling model into the realm of aggregation.

(1) Igoshin, O., Mogilner, A., Welch, R., Kaiser, D., and Oster, G. (2001) Pattern formation and traveling waves in myxobacteria: Theory and modeling. Proc. Natl. Acad. Sci. USA 98: 14913 - 14918.
(2). Welch, R., and Kaiser, D. (2001) Cell behavior in traveling wave patterns of myxobacteria. Proc. Natl. Acad. Sci. USA 98: 14907 - 14912.