Fig. 2. Clones of scrib mutant eye tissue are eliminated by JNK pathway-mediated apoptosis. (A and B) By using a w+ gene to mark wild-type tissue in the adult eye, an ey-FLP control eye incorporates an equal amount of w+ and w– tissue (A). An ey-FLP scrib1 mosaic eye incorporates little scrib– tissue (w–) in the adult, the eyes are reduced in size and necrotic spots are often observed in the centre of the eye (B). (C and D) Acridine orange staining of third instar larval eye discs reveals few apoptotic cells in a wild-type eye/antennal disc (C), but in an ey-FLP scrib1 mosaic eye/antennal disc (D) many apoptotic cells are detected. (E–J) The MARCM system was used to generate ey-FLP clones expressing different transgenes, with GFP as a positive clonal marker, in either wild-type control clones (E, G and I) or scrib1 clones (F, H and J). Developing photoreceptor cells in third instar larval eye discs are shown by Elav staining. In wild-type clones, only expressing GFP as a clonal marker, clonal tissue makes up ∼50% of the tissue (E2 and 3) and the adult eyes are normal (E4). In scrib1 clones, mutant tissue is significantly less represented than wild-type tissue (F2 and 3), and the adult eyes are often reduced in size and disorganized (F4). Ectopic activation of the JNK pathway by expressing an activated allele of JNKK (HepACT) in control wild-type clones (G1–3) nearly eliminates all clonal tissue, resulting in slightly roughened adult eyes (G4). Blocking the JNK pathway, by expressing a dominant-negative form of JNK (BskDN), in scrib1 clones (H1–3) causes a pronounced expansion of the scrib– tissue in the eye disc (H2; compared with scrib1 clones, F2), and complete pupal lethality. Expression of BskDN in control clones (I1–3) results in adult flies with only slight eye disorganization (I4). The expression of the pan-caspase inhibitor, p35, in scrib1 mutant clones (J1–3) results in an increase in the size of scrib– clonal tissue compared with clones of scrib1 alone (F2), and the eyes of the resulting adult flies are more disorganized and necrotic (J4) compared with scrib1 clones alone (F4).