Image analysis tools for improved characterization of nuclear chromatin patterns by confocal fluorescence microscopy.

We have collected fluorescence images of fixed cell nuclei of two different types-HeLa and HepG2-with DNA labeled by a standard fluorophore, and have devised three different quantitative parameters aimed to describe the distribution of the nuclear chromatin. The parameters are the fractal dimension, associated with the intricacy and hierarchical structure of chromatin; the total perimeter of local maxima, associated with the amount of chromatin domains; and the radial distance of angularly averaged intensity profile maximum, associated with the possible occurrence of a peak density at a characteristic distance from the nucleus center. Our results suggested that it was possible to differentiate the two types of cells in the 3D space of the defined parameters. Therefore, these parameters appear promising in identifying specific functional patterns in chromatin. At the same time, the negative control of different runs of measurements on the same cell type also showed at least partial differentiation. Thus, the tool proposed here for nuclear chromatin pattern characterization is probably sensitive to the cell life cycle moment almost as much as to the cell type and should be tested further on cells synchronized at the same phase during their cycle.