PATTERNS OF CELL-MOVEMENT WITHIN THE DICTYOSTELIUM SLUG REVEALED BY CELL-TYPE-SPECIFIC, SURFACE LABELING OF LIVING CELLS

There are cells scattered in the rear, prespore region of the Dictyost elium slug that share many of the properties of the prestalk cells and that are therefore called anterior-like cells (ALCs). By placing the gene encoding a cell surface protein under the central of an ALC-speci fic promoter and immunologically labeling the living cells, we analyze the movement of ALCs within the slug. There Is a posterior to anterio r cellular flow, and the ALCs change their movement pattern as they en ter the prestalk zone. Prestalk cells are periodically shed from the m igrating slug. They must be replaced if the correct ratio of prestalk to prespore eels is to be maintained, and we present evidence for the transdifferentiation of prespore into prestalk cells, with ALCs functi oning as intermediates in the transition. The slug has, therefore, a s urprisingly dynamic structure, both with respect to cellular different iation and cell movement.