Fig. 12.

Model of regulatory interactions between Six1, Eya1 and SoxB1 genes in placodal ectoderm. Blue and red arrows and bars indicate positive and negative regulatory interactions, respectively, of Eya1 + Six1 (red) and SoxB1 (blue) proteins supported by present study. The circle encloses a network of proteins known to cross-regulate during early stages of neuronal determination. High levels of Eya1 and Six1 in the placodes (red squares) maintain proliferative neuronal progenitors. These levels decrease as cells leave the placodes (pink squares), permitting cell cycle exit and onset of neuronal determination and promoting neuronal differentiation. See text for details.