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The Journal of Experimental Biology 205, 2583-2590 (2002)
© 2002 The Company of Biologists Limited

Rapid patterning and zonal differentiation in a two-dimensional Dictyostelium cell mass: the role of pH and ammonia

Satoshi Sawai1,*, Takashi Hirano2, Yasuo Maeda2 and Yasuji Sawada3

1 Graduate School of Information Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
2 Biological Institute, Graduate School of Science, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
3 Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan

* Author for correspondence at present address: Princeton University, Department of Molecular Biology, Princeton, NJ 08544, USA (e-mail: ssawai{at}molbio.princeton.edu)

Accepted 20 May 2002

Recently it was demonstrated that a rapidly forming, self-organizing pattern that emerges within two-dimensional Dictyostelium discoideum cell cultures could later give rise to stripes of distinct zones, each comprising different cell types. Here we report physiological aspects of the initial rapid patterning and its relationship to cell differentiation. We found that as the temperature is lowered the characteristic length of the pattern increases. From this we estimated the activation energy of the patterning kinetics. Fluorescence of fluorescein-conjugated dextran revealed that the cytosolic pH of cells in the inside zone becomes lower than that in the outer zone facing the air. The patterning could be inhibited by addition of the plasma-membrane proton pump inhibitors diethystilbestrol (DES) or miconazole. Preincubation of cells with weak acid delayed the timing of the patterning, whereas weak base hastened it. A pH-indicating dye revealed localized accumulation of ammonia in the extracellular space. These results suggest that gradients of secreted metabolites may be directly responsible for the rapid patterning and its consequence on cell differentiation in a confined geometrical situation. Possible diffusible candidate molecules and a reaction scheme coupled to the imposed oxygen gradient are discussed.

Key words: oxygen, pH, ammonia, H+-ATPase, reaction-diffusion, Dictyostelium discoideum


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© The Company of Biologists Ltd 2002