Radiation Induced Chromatin Conformation Changes Analysed by Fluorescent Localization Microscopy, Statistical Physics, and Graph Theory
Panel A. Radial pair correlation functions determined at different repair times after exposure to 0.5 Gy radiation dose. The radial pair correlation function g(r) shows that correlations between the positions of labeled H2B histones exist up to a distance of roughly 300 nm. Marker and thus chromatin densities in the surroundings of each marker are elevated compared to the average density of markers in the cell nucleus. Above 300 nm, however, histone positions are uncorrelated and the marked histones can be viewed as being positioned randomly relative to each other. Furthermore, the radial pair correlation function for cells exposed to 0.5 Gy γ-irradiation apparently does not differ from the one of untreated cells, regardless of the time passed after irradiation. Panel B. Rescaled distribution of the length of edges in a Delaunay triangulation of the H2B marker positions after different repair times post 0.5 Gy irradiation. The inset shows the original distributions for the different images. The differences in the edge length distributions are due to the different marker densities in the images. Therefore a rescaling of the distributions was performed with respect to the point density to clear out this effect. The rescaled distributions can be seen in the main panel and show that the distributions belong to the same family.