Non-enzymatic, low temperature fluorescence in situ hybridization of human chromosomes with a repetitive...

In all DNA-DNA in situ hybridization (ISH) procedures described so far in the literature, the production of single-stranded target DNA sequences plays a decisive role. This can be achieved either by enzymatic treatment at physiological temperatures or by the separation of double-stranded DNA sequences. Denaturation by heat and chemical agents (e.g. formamide) is regarded as a prerequisite for the non-enzymatic ISH process. However, additional mechanisms of a non-enzymatic ISH procedure are conceivable which do not require high temperature treatment combined with formamide. Here, we report on a non-enzymatic, non-formamide, low temperature, fluorescence, in situ hybridization (FISH) procedure which allowed a microscopic visualization and quantitative fluorescence analysis of the binding sites of a repetitive DNA probe. Following only probe denaturation at 94 degrees C, hybridization was performed at 52 degrees C for 30 min, i.e. at nearly physiological temperatures. Moreover, increasing the hybridization time to 3 hours indicated that hybridization sites became also visible at 37 degrees C. Since the protocols are based on recently described Fast FISH developments, the technique will be called Low Temperature Fast-FISH (LTFF).