Fig. 6. Sterol requirement and sterol content of npc2 mutants. (A) Rescue of mutant Drosophila melanogaster by food supplementation with 20E or other sterols. The particular developmental stage in which the mutants died is shown as a percentage of the total. The x-axis indicates the developmental stage and the y-axis is the percentage of lethal. Without dietary supplements, nearly all mutants died by the pupal stage. Supplementation with 20E caused substantial rescue, allowing survival of more than 80% of the mutant animals until adulthood. Similarly, cholesterol and its immediate precursor 7-dehydrocholesterol allowed about 80% of the mutant animals to survive to adulthood. (B) The total sterol content of third-instar larvae was not changed in npc2 mutants. Three samples were measured for each genotype and error bars represent standard deviation.