Insulator bodies have a defined structural organization. (A and B) S2 cells treated with or without 250 mM NaCl and stained for CP190 and Su(Hw) (A), dCTCF::mCherry and Su(Hw)::EGFP (B) and BEAF-32 and Su(Hw) after 60-min incubation in PBS. (C) BEAF-32 forms large donut structures around the spherical structures (arrowhead and insets). Bars: (A–C, main images) 2 µm; (C, insets) 0.5 µm.