Figure 4.
Simplified schematic of major cell fate decisions that create the retinal mosaic in the fly (A) and mouse (B) eyes. A) In flies, Spalt specifies inner photoreceptor fate. Prospero (Pros) determines R7 fate and Senseless (Sens) R8 fate. Then, a choice is made for one of the four R7/8 subtypes. B) In the mouse retina, Crx is expressed in all photoreceptor precursor cells. Rods are distinguished from cones by the expression of Rorβ, Nrl and Nr2e3. Cones adopt either short (S) or medium (M) cone fate depending on the expression of either Rorβ or Trβ2, respectively. Note that Rorβ plays a dual role in the rod and S cone pathways. For details, see text.