A MARKER OF TERMINAL STALK CELL TERMINAL DIFFERENTIATION IN DICTYOSTELIUM

We describe the isolation of staB, a Dictyostelium gene that is select ively expressed in stalk cells. If an aggregate enters culmination imm ediately staB is ex pressed in the bottom half of the stalk and in the basal disc but if a migratory slug is formed it is also expressed in the top of the stalk and in a disc of cells that surmounts the spore h ead. The latter two populations of cells derive from the rear part of the prestalk region, the pstO cells, which would therefore seem to cha nge their transcription al competency during slug migration. The staB promoter contains a distal region that is required for expression with in both the stalk and the basal disc and a proximal region that is req uired only for expression within the basal disc. This uncoupling of tr anscriptional specificities suggests that the signalling mechanisms th at direct terminal differentiation in these two tissues differ in some way.