Figure 4.

Cohesin Is Not Required for the Maintenance of Polytene-Chromosome Morphology

(A) Outline of the TEV-cleavage experiment in salivary glands.

(B) Western blot analysis of salivary gland extracts prepared either before (t = −0.75 hr) or at various time points after heat shock (red arrow) from GFP-negative larvae. The last lane shows a sample of salivary glands from Rad21^TEV-expressing flies that do not contain hs-TEV. Blots were probed with antibodies against myc (detecting full-length transgenic Rad21 [arrow] and the C-terminal TEV-cleavage fragment [arrowhead]) and v5 (detecting TEV protease [open circle]).

(C) Representative polytene-chromosome spreads of third-instar larvae that carry hs-TEV and express either transgenic Rad21 (left panel) or Rad21^TEV as their only source of Rad21 were prepared before (t = −0.75 hr) and at various time points after heat shock (red arrow). Polytene chromosomes were coimmunostained with antibodies against myc (recognizing Rad21) and CTCF. The morphology of the polytene chromosomes was visualized by DAPI staining (bottom row, higher magnification [2.5×]). All pictures were acquired by using the same acquisition settings. The scale bar is 20 μm.