Abstract

Classical embryological studies have led to the suggestion that cells in developing tissues may be directed to differentiate along a particular pathway by the concentrations of molecules called morphogens. Studies of the slime mould Dictyostelium discoideum, which has a simple tissue pattern consisting of only two cell types, have revealed several molecules which may act as morphogens. Cyclic AMP and ammonia promote the formation of spores, while adenosine and a novel class of compounds called DIFs promote the formation of stalk cells, the alternative cell fate. The constant proportions of the two differentiated cell types observed in this organism may result from a balance among the influences of these compounds.