We have investigated the formation of the prestalk-prespore pattern in Dictyostelium discoideum. Pattern formation occurs in clumps of Dictyostelium cells embedded in agar under a 100% oxygen atmosphere. Agar embedding allows us to control spatially the environment surrounding the cell clumps. Our results suggest that the ambient oxygen concentration plays a role in controlling the size of the multicellular mass. Further, oxygen gradients established across clumps embedded in agar or held in holes in a plastic barrier cause orientation of the prestalk-prespore pattern such that the anterior prestalk region forms at the highest end of the gradient. The results also indicate that developing cells have the ability to migrate up a gradient of oxygen.

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