Fig. 1. Apc1 loss results in apoptosis of photoreceptors. (A) Schematic of the retina. High levels of Wg signaling induce apoptosis of photoreceptors (orange), intermediate levels induce photoreceptors to adopt a DRA fate (pink), and low levels result in ommatidia that lack bristles (blue). (B-I) Pupal retinas were stained with antibodies against activated caspase (green) and Elav (blue). Elav is expressed in all photoreceptors. (B,C) In wild-type pupal retinas at 38 hours after puparium formation (APF), activated caspases are present only at the periphery. (D-I) In Apc1^Q8 mutants, activated caspases are observed throughout the pupal retina. Caspase activation in photoreceptors is initially observed in the posterior retina at 35 hours APF (D,E), and, over the next four hours, extends to cover the entire retina (F-I).