Biological effects of a bifunctional DNA cross-linker. II. Generation of micronuclei and attached micronuclear-like structure

Madin-Darby bovine kidney (MDBK) cells were treated with the bifunctional D NA cross-linker, L-7, to examine the generation of micronuclei and other nu clear abnormalities. The preceding paper demonstrates that L-7 treatment in duces the formation of triradial and quadriradial chromosomes in MDBK cells . These chromosomes are believed to result from interduplex DNA cross-links formed between G-C rich centromeric satellite DNA regions on non-sister ch romatids. Treatment produces a majority of centromere-positive micronuclei. In addition, many daughter cells remain attached by chromatin bridges whic h are sometimes beaded with micronuclei. Up to 15% of cell nuclei become lo bular and fused with numerous micronuclear-like structures attached to thei r membranes, These attached structures are classified as attached micronucl ear-like structures (AMNLS), Fluorescence in situ hybridization (FISH) usin g a centromeric satellite sequence was performed on treated cells. Hybridiz ation reveals that intercellular bridges are composed of centromeric sequen ces and initiate at centromeric foci in daughter cells. Furthermore, the ma jority of junctions between AMNLS and nuclei contain an enhancement of cent romeric signal, The frequency of AMNLS appears dependent on the concentrati on of L-7 and the duration of treatment, Similar results were found for the generation of cross-linked chromosome products in the previous paper, We s uggest that AMNLS result from the abnormal mitotic segregation of cross-lin ked chromosome products. (C) 1999 Elsevier Science B.V. All rights reserved .