Required for normal morphogenesis and cell-type stability. Expressed strongly in presumptive spore (prespore or psp) cells during the late G2 phase of cell cycle. Present at a low level in vegetative cells. High expression during late G2-S phases. During development, expression level peaks at 12-15 hr post-starvation, and falls thereafter. Up-regulated by starvation. Mutant shows pleiotropic effects that include an inability of the spore mass to go all the way to the top. The upper cup, a tissue that derives from prestalk cells and anterior-like cells (ALCs), does not develop properly; it is unable to lift the spore mass to the top of the fruiting body, likely due to defective intercellular adhesion. The differentiated state becomes unstable; prespore cells transdifferentiate into prestalk and vice versa. Cells that find themselves in the wrong environment sort out to the zone that is appropriate to their new identity. The functional barrier that prevents intermixing between the prestalk and prespore zones becomes weakened. This permits prespore cells to move to the slug anterior and prestalk cells to the posterior. Cells that have moved to the wrong zone switch their state of differentiation in accord with their new location.