[Changes in methylation of tumor cells: a new in situ quantitative approach on interphase nuclei and chromosomes]

DNA methylation is known to be related to the regulation of gene expression. DNA methylation patterns are modified in tumors compared to normal tissue, and in some cases, these variations are linked to cancer progression. Molecular biology techniques are generally used to evaluate DNA methylation status. We describe here a simple and fast immunofluorescent method to quantitate in situ DNA methylation using an image analyser and a CCD camera. Quantification of relative methylation levels in interphase nuclei and metaphase chromosomes was performed on digital images of two types of cells with known methylation levels. The results from image cytometry corresponded to those obtained by molecular studies. Advantages of this approach are that all the DNA of a cell may be examined rather than a limited restriction sequence, and that it may be done on a cell by cell basis rather than on a heterogenous population. In addition, with this method, changes in methylation patterns during tumor progression could be followed and eventually used as a marker for prognosis.