Further observation on Hoechst 33258 plus hypotonic treatment induced supercondensation of interphase heterochromatin in Drosophila nasuta cells

Abstract

Extending our earlier observation [Exp Cell Res, 132 (198I) 423] on the effects of Hoechst 33258 and hypotonic treatments on condensation of heterochromatin in interphase nuclei of D. nasuta, we now show by Feulgen-DNA cytophotometry that the chromocentre heterochromatin in Hoechst 33258 + hypotonic treated interphase cells of D. nasuta is supercondensed. Like the Hoechst 33258 effect, exposure of live embryonic (2 hr) or larval brain cells (16 hr) of D. nasuta to 20 μg/ml Netropsin or Distamycin A (both A-T specific DNA ligands) when followed by a pre-fixation hypotonic treatment, also causes supercondensation of chromocentre in majority of the treated cells; without ihe hypotonic treatment chromocentre is not supercondensed in any of the drug treated cells. A G-C specific DNA ligand, Olivomycin, does not cause any such effect. It is suggested that, only A-T specific ligands can cause the supercondensation of interphase heterochromatin when the treated cells are exposed to hypotonic solution prior to fixation. By reverting 16 hr Hoechst 33258 + 15min hypotonic treated larval brain ganglia to isotonic culture medium for I or 4 hr, the supercondensation of chromocentre can be reversed, although a second hypotonic treatment after 4 hr in Hoechst 33258 free isotonic culture medium restores the supercondensation of chromocentre. It appears that the A-T specific drug binding to DNA modifies the nucleoprotein interactions in interphase heterochromatin in such a way that a hypotonic treatment causes a very rapid but reversible reorganization of chromatin constituents to cause the supercondensation.