DUAL REGULATION OF THE GLYCOGEN-PHOSPHORYLASE-2 GENE OF DICTYOSTELIUM-DISCOIDEUM - THE EFFECTS OF DIF-1, CAMP, NH3 AND ADENOSINE

Cell differentiation in Dictyostelium results in the formation of two cell types, stalk and spore cells. The stalk cells undergo programmed cell death, whereas spore cells retain viability. The current evidence suggests that stalk cell differentiation is induced by Differentiatio n Inducing Factor (DIF), while spore cell differentiation occurs in re sponse to cAMP. We have discovered the first developmentally regulated Dictyostelium gene, the glycogen phosphorylase gene 2 (gp2) gene, tha t can be induced by both DIF-1 and cAMP, suggesting the possibility of a new group of developmentally regulated genes that have DIF-1 and cA MP dual responsiveness. The gp2 gene was found to be expressed in both prestalk/stalk cells and prespore/spore cells. The DIF-1 competence o f the gp2 gene required uninterrupted development, whereas the cAMP-co mpetence for the gene required only starvation. Both DIF-1 and cAMP in duction of the gene could be inhibited by NH3, a factor that is though t to act as a developmental signal in Dictyostelium. Another developme ntal signal, adenosine, was found to repress the DIP-1 induction of th e gp2 gene. Two introns in the gp2 gene were examined for their involv ement in the regulation of the gene, but no regulatory function was de tected. A model for the regulation of the gp2 gene during the developm ent is proposed.