POSITIVELY AND NEGATIVELY ACTING SIGNALS REGULATING STALK CELL AND ANTERIOR-LIKE CELL-DIFFERENTIATION IN DICTYOSTELIUM

The Dictyostelium ecmB gene encodes an extracellular matrix protein and is inducible by the stalk cell morphogen DIF. It is expressed in a subset of prestalk (pstB) cells in the slug and surrounding pstA cells first express it at culmination. A region of the ecmB promoter can direct transcription in all anterior prestalk cells, but a separate, downstream region acts to prevent its expression in pstA cells prior to culmination. Th is may be the site of interaction of a repressor, regulated by an extracellular antagonist to DIF. At culmination, expression of the ecmB gene also becomes greatly elevated in anterior-like cells as they move to surround the spore mass. A distal region of the ecmB promoter directs increased expression in those anterior-like cells that surmount the spore head. This divergence in gene expression suggests that anterior-like cells and anterior prestalk cells experience different inductive conditions at culmination.