SCANNING ION ANALYTICAL MICROSCOPY FOR HIGH-RESOLUTION DETECTION OF 5-BROMO-2'-DEOXYURIDINE INCORPORATION IN METAPHASE CHROMOSOMES

We investigated the possibilities of using scanning ion analytical mic roscopy (SIAM) to detect bromine in human metaphase chromosomes. The e xperiments were performed after incorporation of the thymidine analogu e, 5-bromo-2'-deoxyuridine (BrdU), into the DNA or by In situ hybridiz ation of a BrdU-labelled probe for the subcentromeric repeated DNA seq uences. The possibilities offered by this microanalytical method were compared with immunofluorescent staining techniques. Well-defined maps of bands containing bromine were obtained with metaphase chromosomes that had incorporated BrdU during the late S-phase. Their patterns wer e similar to the labelling obtained by immunofluorescence. In addition , SIAM reveals the presence of bromine within constitutive heterochrom atic regions in which BrdU is poorly detected by immunofluorescence. T he comparison of the (CN)-C-12-N-14, P-31 and Br-81 maps of controls a nd fluorescence plus Giemsa (FPG) metaphase chromosomes, shows the los s of bromine from DNA during this treatment. SIAM emerges as a new pow erful microanalytical technology for investigating chromosome structur e further.