A-T specific DNA ligands and hypotonic induced supercondensation of chromocentre in brain cells of Drosophila nasuta larvae in relation to their synthetic activities

Abstract

When A-T base specific DNA ligands like Hoechst 33258 (H) or Distamycin A (DA) treated brain ganglia of D. nasura larvae are exposed 10 a pre-fixation hypotonic (hy) solution, the heterochromatic chromocentre (cc) becomes supercondensed in 40-60% interphase nuclei. In the present study, the effects of these DNA ligands on DNA and RNA synthesis in larval brain ganglia and the relationship of cc supercondensation with these synthetic activities of a cell has been examined by autoradiography. It is seen that both the frequency of replicating cells and the rate of ³H-thymidine uptake are inhibited by the treatment, more so in the population of cells in which the cc is supercondensed. H treatment has no effect on the rate of ³H-uridine uptake in transcribing nuclei although, compared to the control ganglia, the frequency of labelled nuclei is reduced after treatment. The cc supercondensation is shown to occur preferentially in nuclei which are active in DNA and/or RNA synthesis.