Sorting out in pseudoplasmodia of Dictyostelium discoideum

During its period of migration the pseudoplasmodium of D. discoideum changes from a homogeneous mass of cells to one in which the cells of the front part stain more darkly with neutral red than those of the rear part. It has been asked whether this color change represents differentiation in situ of two cell type or sorting out of previously differentiated cell types. Experiments are described which (1) show that the transition of the pseudo‐plasmodia from one type to another is long continued process, and (2) show by means of labeling parts of pseudoplasmodia with vital dyes or C 14 thymidine, that exchange of cells across the color boundary separating tip and rear parts is continuous during the life of a pseudoplasmodium. From the results it appears that sorting out of cell types is probably a major cause of the color change. When combined with previous work, our results suggest that sorting out and redifferentiation are active together both in maintaining and restoring the normal proportions of cell types in a slug. It may prove useful to compare these processes with the components of regeneration in metazoan organisms.