Fig. 3. Morphogenesis in the mound. (A) Within the mound, cell movement switches from directly towards the aggregation centre to rotation perpendicular to the tip axis. In addition, differentiation into the precursor cells of the fruiting body begins. The pstA and pstO cells move into the tip, and pstB cells move to the base. Pre-spore cells occupy the central region of the mound. (B) LagC/gp150 is required for cell-cell adhesion and, through the transcription factor GBF, for the switch in the direction of movement and cell differentiation. G-box-binding factor (GBF) is required for lagC/gp150 expression, which creates a feedback loop. (C) Cell differentiation requires GskA activity. This is regulated by extracellular cAMP through two receptors, cAR3 and cAR4. At low cAMP, cAR3 activates GskA activity through ZAK1; at high concentrations cAR4 inhibits GskA activity. GskA regulates the pstB–pre-spore ratio.