Insulator body formation and disassembly occurs rapidly, and bodies are highly dynamic. (A and B) Frames taken at 2-min intervals after gradual 250 mM NaCl media addition at time 0 min in S2 cells expressing Su(Hw)::EGFP and BEAF-32::mCherry. Bodies form in a matter of minutes from diffuse speckles (A) and can undergo rounds of fusion (bodies 1 and 2) to produce larger structures (body 3*; B). Boxed regions are enlarged in insets at the bottom. (C) The dynamic movement of body 1 starting with its formation at 4 min until its fusion with body 2 at 20 min (blue line) and the movement of the fused body (white line) until the final frame was acquired (36 min). (D) A polytene nucleus from a third instar salivary gland expressing Su(Hw)::EGFP subjected to 250 mM NaCl osmostress (10 min) followed by recovery in isotonic media (23 min). Blue numbers denote media treatment time points, and green numbers indicate stress treatment time points. Arrowheads (9 and 25 min) mark bands of Su(Hw). Bars: (A, B [top], and D) 3 µm; (B [bottom] and C) 2 µm. Also see Videos 1, 2, 3, and 4.