Cell patterning in Dictyostelium.

We summarize studies on stalk and spore cell formation in D. discoideum cell monolayers, aimed at revealing factors involved in controlling the prestalk:prespore pattern in this organism. We propose that there are no cell interactions dependent on cell contact per se. Formation of mature stalk cells from isolated amoebae incubated in a buffered salts medium requires only cyclic AMP and a lipid-like factor (DIF) released by cells developing at high density. In addition, a variety of sporogenous mutants can form spores rapidly and efficiently when incubated at low density in tissue culture dishes containing a similar cyclic AMP and salts medium. In some cases spore formation is improved by the addition of one or other of a variety of protective agents such as bovine serum albumin. Wild-type amoebae at low density form prespore cells under the same conditions. We present some evidence that DIF is the activator of prestalk cell formation in a two-component patterning mechanism of the kind proposed by Wolpert et al. (Symp. Soc. exp. Biol. 25, 391-415 (1971)) and Gierer & Meinhardt (Kybernetik 12, 30-39 (1972)). We also provide data indicating that the role of inhibitor is played by ammonia, an idea first mooted by Sussman & Schindler (Differentiation 10, 1-5 (1978)).