Fig. 7. Eye specifying gene hierarchy depends on the cell type and the stage of development. The network of regulatory genes specifying eye development is modified based on this study and other recently published results. (A) In the embryonic eye precursor cells, toy directly activates ey through the ey-enhancer (Czerny et al., 1999) without ey activating its downstream genes so/eya (Kumar and Moses, 2001). (B) In the eye disc of late L2 and early L3 ey and toy directly regulate so in a complex network by using different sites on the same enhancer element in different sets of cells to direct the development of the compound eyes and the ocelli.