Erkennung strahleninduzierter Chromosomenaberrationen mittels Fluoreszenz-Hybridisierung und Bildanalyse

Optimized Fast-FISH with alpha-satellite probes: acceleration by microwave activation

It has been shown for several DNA probes that the recently introduced Fast-FISH (fluorescence in situ hybridization) technique is well suited for quantitative microscopy. For highly repetitive DNA probes the hybridization (renaturation) time and the number of subsequent washing steps were reduced considerably by omitting denaturing chemical agents (e.g., formamide). The appropriate hybridization temperature and time allow a clear discrimination between major and minor binding sites by quantitative fluorescence microscopy. The well-defined physical conditions for hybridization permit automatization of the procedure, e.g., by programmable thermal cycler. Here, we present optimized conditions for a commercially available X-specific alpha-satellite probe. Highly fluorescent major binding sites were obtained for 74 degrees C hybridization temperature and 60 min hybridization time. They were clearly discriminated from some low fluorescent minor binding sites on metaphase chromosomes as well as in interphase cell nuclei. On average, a total of 3.43 +/- 1.59 binding sites were measured in metaphase spreads, and 2.69 +/- 1.00 in interphase nuclei. Microwave activation for denaturation and hybridization was tested to accelerate the procedure. The slides with the target material and the hybridization buffer were placed in a standard microwave oven. After denaturation for 20 sec at 900 W, hybridization was performed for 4 min. at 90 W. The suitability of a microwave oven for Fast-FISH was confirmed by the application to a chromosome 1-specific alpha-satellite probe. In this case, denaturation was performed at 630 W for 60 sec and hybridization at 90 W for 5 min. In all cases, the results were analyzed quantitatively and compared to the results obtained by Fast-FISH. The major binding sites were clearly discriminated by their brightness.

Optimization of Fast-FISH for alpha-satellite DNA probes

It has been shown for several highly repetitive DNA probes that the newly introduced Fast-FISH (fast-fluorescence in situ hybridization) technique is well suited for quantitative microscopy. The advantage of omitting denaturing chemical agents (e.g., formamide) in the hybridization buffer results in a short hybridization time and a considerable reduction of the number of subsequent washing steps. Choosing the appropriate hybridization temperature and time allows to clearly discriminate major and minor binding sites by quantitative fluorescence microscopy. To further optimize the procedure with reference to reproducibility, a fully programmable thermal-cycler was applied for thermal de- and renaturation. Here, the optimized renaturation conditions for two commercially available alpha-satellite probes (specific for chromosomes 1 and X) are described. For the Boehringer chromosome-1-specific DNA probe, two highly fluorescent binding sites were obtained for 72 degrees C hybridization temperature and 60 min hybridization time. For the Oncor chromosome-X-specific DNA probe, the optimal conditions were found at 74 degrees C and 60 min hybridization time. In both cases the major binding sites were clearly discriminated from only a few weakly fluorescent minor binding sites on metaphase spreads as well as in interphase cell nuclei.