A pulse BrdU method for SCE.

Using 'reverse' harlequin staining (bromouracil-substituted chromatin staining dark), it is possible to detect at metaphase a pulse of bromodeoxyuridine (BrdU) incorporated during S-phase. Provided that this pulse is of reasonable duration, fairly uniform staining along the chromatids of some S-cells is achieved, and no difficulty is encountered in observing and scoring SCE in such cells at second division. Thus, it is possible to define within an asynchronous population a narrow cohort of target cells and recover these for SCE scoring at second division irrespective of treatment induced perturbation. This serves to reduce the heterogeneity found in the usual terminal BrdU SCE protocols for such populations and should lead to more reliable and repeatable quantitative results. The method is illustrated for mitomycin C given to dividing human blood lymphocytes using both simultaneous and delayed pulse modes.