Fig. 11. A proposed model for signaling events controlling DV patterning of the eye. Interaction of high levels of Hh and FGFR with low levels of RA signaling repress Pax6 and induce the expression of Vax1, Pax2 and Vax2, leading to OS specification. High levels of RA in collaboration with low levels of Hh and FGFR signaling repress ET and induce the expression of Vax2 in the absence of Vax1 and Pax2, but in the presence of Pax6, thus specifying VR identity. BMP signaling inhibits Vax2 and induces ET expression, causing DR specification. In addition, high levels of RA repress the expression of Hh and FGFR signals, while Hh and FGFR signaling crossactivate each other at the transcriptional level.