DETECTION OF HYDROQUINONE-INDUCED NONRANDOM BREAKAGE IN THE CENTROMERIC HETEROCHROMATIN OF MOUSE BONE-MARROW CELLS USING MULTICOLOR FLUORESCENCE IN-SITU HYBRIDIZATION WITH THE MOUSE MAJOR AND MINOR SATELLITE PROBES

Fluorescence in situ hybridization with a mouse major satellite probe and CREST staining were used to characterize the origin of micronuclei occurring in mouse bone marrow erythrocytes following administration of the benzene metabolite hydroquinone. Hydroquinone was administered to male CD-1 mice by i.p. injection on three consecutive days and the bone marrow cells were harvested 24 h later. A pronounced difference in the results was observed using the two approaches: 63% of the micronuclei induced by hydroquinone labeled with the major satellite probe whereas only 28% labeled with the CREST antibody. To determine whether the observed difference was due to a disruption of the kinetochore or a result of breakage within centromeric heterochromatin, we developed a tandem label multicolor hybridization assay, which requires the presence of both the mouse major and minor satellite probes in a micronucleus for a classification of chromosomal loss. The minor probe targets a centromeric region physically linked to the short arm of mouse chromosomes, whereas the major probe hybridizes to the centromeric heterochromatin adjacent to the long arm. Using this approach, 29% of the micronuclei induced by hydroquinone hybridized with both the major and minor satellite probes, indicating chromosome loss; an additional 37% labeled with only the major satellite probe indicating breakage within the centromeric heterochromatin. Although the region targeted by the major satellite probe comprises only 5-10% of the mouse genome, these major-probe containing micronuclei represent 53% of the micronuclei formed as the result of chromosome breakage. These results indicate that, in addition to chromosome loss and breakage throughout the euchromatin, hydroquinone induces nonrandom breakage within the centromeric heterochromatin. This new hybridization assay shows promise as an accurate technique for distinguishing micronuclei arising from chromosome loss from those originating from chromosome breakage, particularly when breakage occurs within the mouse heterochromatin, a breakage-prone region targeted by the major satellite probe.