Fig. 3. npc2a mutants and their sterol accumulation phenotypes. (A) The gene structure of npc2a and the chromosome intervals deleted in three Drosophila npc2a alleles. (B-G) Filipin staining reveals the sterol distribution patterns in wild type (B,D,F) and npc2a mutants (C,E,G). B and C are filipin-stained wing imaginal discs from third-instar larvae: wild type (B) and npc2a mutant (C). The magnified views (B',C') show that in wild type, sterol is located mainly at cell-cell boundaries, whereas in npc2a mutants sterol accumulates in a punctate pattern that is not restricted to those boundaries. (D,E) Aberrant sterol accumulation was observed in a striped pattern in npc2a (E) but not wild-type eggs (D). (F,G) Filipin staining highlighted the lumen of the Malpighian tubules in wild type. In npc2a mutants, massive punctate accumulations of filipin staining were visible inside Malpighian tubules.