Fig. 9. Pre-placodes form from an unspecified placodal field independent of Hedgehog. (Bottom) At neural plate stages, pitx3 (blue) and dlx3b-dlx4b (red) expression domains demarcate placodal fields (Figs 2, 3). (Middle) Lens and pituitary pre-placode forms in a Hedgehog-independent process and has lens epithelial character (light blue). (Top) In a Hedgehog-dependent process, pituitary tissue (green) is specified (Figs 7, 8) (Herzog et al., 2003; Karlstrom et al., 1999; Kondoh et al., 2000; Sbrogna et al., 2003; Treier et al., 2001; Varga et al., 2001). Similarly, lens epithelial cells (light blue) differentiate into lens fiber cells (dark blue) under influence of BMPs (Belecky-Adams et al., 2002; Faber et al., 2002).