True divergent differentiation in a cellular slime mold, Polysphondylium pallidum.

Three abstract models of divergent cell differentiation to multiple cell types are presented. These differ primarily in the proportion of developmental events common to the pathways leading to each cell type. Two experimental approaches are outlined to determine which type best describes divergent differentiation occurring in a particular organism. The first technique is to describe and compare changes in labeling of specific polypeptides which characterize development to the several cell types. The second is to observe the ability of mutants which are blocked in one pathway to develop along alternate pathways. These approaches are applied to the case of Polysphondylium pallidum, where amebae develop into stalk cells, spores, or microcysts. It is concluded that cell differentiation in P. pallidum is of the truly divergent type in which developing cells show identical sequences of events until a branch point, and thereafter very different sequences of events.