Fig. 5. npc2a and npc2b act redundantly in regulating sterol homeostasis in Drosophila. Filipin staining patterns of third-instar larval tracheas (A) and brains (B) in different genetic backgrounds. (A) npc2a and npc2b act redundantly in regulating sterol homeostasis in trachea. A small number of filipin-stained particles of sterol accumulation (arrow) was found in npc2a animals. By contrast, there was no sterol accumulation phenotype in npc2b mutants or in wild-type animals (not shown). However, massive sterol accumulation (arrow) was found in npc1a animals as well as npc2a; npc2b double mutants. (B) In brains, the punctated filipin-stained pattern (arrows) was found in both npc2a single and npc2a; npc2b double mutants but not wild type or npc2b single mutants.