Light-induced retinal degeneration in ktub mutant. Young adults flies (<1 day) were reared in the dark (A, B), or under constant light (500 lux) (C, D) for 6 days. Confocal images indicate that photoreceptor cells arrayed as a typical trapezoid, and the rhabdomere appeared as an oval shape in the wild type and ktub mutant in dark condition (A, C). When flies were reared under constant light for 6 days, wild type photoreceptor cells remained normal (B), but the ktub mutant photoreceptor cells showed significant degeneration (D). The photoreceptor R7 was not affected, and remained as in the wild type (D, arrows). The scale bar is 5 μm.