TREATMENTS WITH SALINE SOLUTIONS AND DNASE-I HAVE DIFFERENT EFFECTS ON DNA CONTENT AND DISTRIBUTION IN HUMAN AND IN MOUSE CHROMOSOMES

The aim of this work was to re-examine, on a quantitative basis, the r elationship between banding pattern after Giemsa staining and the amou nt (and distribution) of DNA along the length of the chromatid arms. T o do this, we investigated by cytofluorometric methods the occurrence of possibly different extraction of chromosome DNA after some alternat ive G-banding procedure, i.e. treatment of chromosomes with saline sol utions, or DNasi I digestion in situ. The G-banding procedure entailin g trypsin pretreatment is known to be difficult to standardize; in the present investigation, it was also found that trypsin induced a massi ve, although quantitatively variable, extraction of DNA from fixed met aphase chromosomes. G-banding-like patterns may be obtained, by treati ng chromosome preparations with saline solutions. Both PBS and Tris-HC l treatment for the times considered induced a G-banding-like pattern after Giemsa staining, regardless of the age of chromosome preparation s; no banding was observed after staining DNA with PI, nor extraction of DNA was found to occur. DNase I digestion initially induced a G-ban ding in both human and mouse chromosomes after Giemsa staining, with c oncomitant extraction of DNA (but without apparent G-banding-like patt ern after PI staining); after 30 min digestion, a C-banding-like patte rn was observed after both Giemsa and PI staining. Exposure to PBS or Tris-HCl buffer at room temperature may therefore be recommended as a G-banding inducing treatment, since it allows the classification of si ngle chromosomes after Giemsa staining, without determining significan t displacement of genomic DNA, which can be submitted to further analy sis in situ.