Fig. 10. Model for the role of GtaC in the regulation of DIF responses. (A) At the mound stage, stochastic differences due to growth history result in two populations of DIF-hypersensitive cells. Those with highest GtaC activity (blue) will behave as pstB cells while the rest will differentiate as pstO cells. (B) At the slug stage, pstB cells (blue) with highest GtaC activity have sorted to the prestalk/prespore boundary, with pstO cells (red) lying just anterior, where they continue to respond to DIF produced by prespore cells. (C) In the monolayer assay, DIF induces outer basal disc cell differentiation. DIF activity is dependent on the transcription factors GtaC, DimA and DimB, and is inhibited by the GskA protein kinase.