Mislocalization of RDGB and onset of retinal degeneration in dEsyt ^CaBM result from the loss of contact sites. (A) TEM images of a single photoreceptor from flies (i) Exposed to constant illumination for 6 days (ii) Aged for 6 days in dark Genotypes: Rh1>, Rh1>dEsyt::GFP and Rh1>dEsyt^CaBM::GFP as indicated on the left. (Ai-ii) Scale bar: 200 µm. (Aiii-vi) Scale bar: 500 µm. (B) Quantification of the number of MCS per photoreceptor of flies of the indicated genotypes reared in constant illumination for 6 days. X-axis indicates the genotype and Y-axis indicates the number of MCS/photoreceptor. n = 25 photoreceptors from three separate flies (R1–R6) (N = 3; n = 25]. (C) Quantification of the number of MCS per photoreceptor of flies of the indicated genotypes reared in constant dark for 6 days. X-axis indicates the genotype and Y-axis indicates the number of MCS/photoreceptors. n = 25 photoreceptors from three separate flies (R1–R6) (N = 3; n = 25). (D) Confocal images showing the localization of RDGB in Rh1>, Rh1>dEsyt::GFP and Rh1>dEsyt^CaBM::GFP photoreceptors of 6-day-old constant dark-reared flies. RDGB visualized is detected using an antibody against the endogenous protein (Cyan). Rhabdomeres are outlined using phalloidin which marks F-actin (Red). A single ommatidium is shown. Scale bar: 2 µm. (B and C) Violin plots with mean ± SD are shown. Statistical tests: One-way ANOVA with post hoc Tukey’s multiple pairwise comparison. ns - Not significant; ****P value <0.0001.