Effects of distamycin A & netropsin on condensation of mitotic chromosomes in early embryos and larval brain cells of Drosophila nasuta

Abstract

Effects of distamycin A (DA) and netropsin (NP) treatments on mitotic chromosome condensation in early embryonic and late larval brain cells of D. nasuta cultured in vitro have been compared. These A-T specific DNA ligands cause inhibition of condensation or the heterochromatin segments much more frequently in embryonic cells than in larval brain cells. Examination of colchicine induced tetraploid cells in DA treated larval brain preparations reveals that the mitotic cells. which have completed 2 cell cycles in the presence of the DNA ligand, remain as frequently unaffected as those exposed to DA for less than one cycle. Analysis of metaphase chromosomes in brain ganglia labelled with ³H-thymidine and chased in DA containing medium reveals that the mitotic cells which were in DNA synthesis or gap (GI or G2) period just before the DA treatment remain equally often unaffected. It appears that reduced sensitivity of mitotic chromosomes in larval brain ganglia to the condensation inhibitory effect of the A-T specific DNA ligands is related to differences in chromosome organization in early embryonic and larval brain cells.