Chromosome painting reveals specific patterns of chromosome occurrence in mitomycin C- and diethylstilboestrol-induced micronuclei

Cultures of human blood lymphocytes from three subjects were incubated with the clastogen mitomycin C (MMC, 500 ng/ml) and the aneugen diethylstilboes trol (DES, 80 muM) 23 h before harvesting, to induce formation of micronucl ei (MN) and numerical and structural alterations in metaphase chromosomes. We used fluorescence in situ hybridization (FISH) with painting probes for all human chromosomes to determine which chromosomes had contributed materi al to the induced MN. MMC treatment induced an similar to 18-fold increase in MN and led to a significant increase in hypodiploidy and structural chro mosome aberrations in metaphase preparations. Undercondensation of pericent romeric heterochromatin of chromosomes 9 and 1 occurred in 20-75% of metaph ases and FISH disclosed an abundance of material from these chromosomes in induced MN (62-69% from chromosome 9 and 7-12% from chromosome 1), DES trea tment of lymphocytes induced a seven-fold increase in MN frequency and four -fold increase in the frequency of numerical aberrations; structural aberra tions were not significantly increased. FISH analysis showed that material from all chromosomes was present in DES-induced MN, with material from chro mosome 1 present in 16% of MN and material from each other chromosomes bein g present in 2-10% of MN. Material from chromosomes 14, 19 and 21 was signi ficantly more frequent material from chromosome Y significantly less freque nt in DES-treated cells than in controls. The findings of the MMC studies i ndicate that the heterochromatin block of chromosome 9 is a specific target for MMC-induced undercondensation, which induces a preferential occurrence of chromosome 9 material in MN. DES, in contrast, does not trigger heteroc hromatin decondensation and fails to induce such a significant appearance o f material of particular chromosomes in MN.