Neurodegeneration by mutations in ft. (A) Tangential eye sections through ftfd clones aged 1, 7 and 14 days, of ftfd,dDGC13 double mutant clones and of ftfd clones in a ykiB5 heterozygous background aged 14 days. Clones are marked by the absence of yellow pigment. Arrows point at degenerating photoreceptors, arrowheads point at intact wt photoreceptors in mosaic ommatidia. The circled ommatidium is genetically wt but non-autonomously flipped in its polarity and has not degenerated. Lower panels are masks that show clonal borders and quantification of PR number per ommatidia. After 14 days, almost all ftfd cells have degenerated, whereas almost all ftfd,dDGC13 and some ftfd,ykiB5/+ neuronal photoreceptors have not. (B) Histograms showing the quantification of degeneration in ftfd, ftfddDGC13 and ftfdykiB5/+ clones. Loss of ft leads to statistically significant loss of neurons and this is suppressed at 14 days by ykiB5and much more dramatically by dDGC13. ***P<0.001, **P<0.01; *P<0.05 in two-tailed t-test. (C) Degeneration in mosaic ommatidia in ftfd clones. At this stage of degeneration approximately half of the non-pigmented (genotypically mutant) PR cells display a degenerative phenotype, whereas virtually all pigmented (genotypically wt) PR cells are normal. χ2-test: 82.38; P<0.001. Total PR N=310 (pigmented) and 327 (not pigmented). (D) Tangential eye sections through MARCM clone mutants for ftfd that express either no transgene or an RNAi construct against yki (UAS–ykiIR) with Tub–Gal4 and aged 14 days at 29°C. Because the transgene UAS–ykiIR is on chromosomal arm 2 L, the same as ft, clones generated with this system carry two copies of UAS–ykiIR and therefore downregulate yki very effectively. No other cell outside the clones expresses the construct and is therefore wt for yki. Mask panel is presented on the right of each section. A quantification of photoreceptor numbers (far right) displays a very significant increase in the number of wt ommatidia (N=210 and 219 from four eyes). ***P<0.001 in two-tailed t-test. If all classes of ommatidia are considered, χ2-test=232.30; P<0.001 for 3 degrees of freedom.