Super-resolved analysis of colocalization between replication and transcription along the cell cycle in a model of oncogene activation.

To understand how oncogenes affect genome organization, it is essential to visualize fundamental processes such as DNA replication and transcription at high resolution in intact cells. At the same time, it is important to determine the progression of the cell along the cell cycle, as cell cycle regulation is crucial for the control of cell proliferation and oncogenesis. Here, we present a super-resolution imaging-based method to analyze single cell nuclei sorted according to specific phases of the cell cycle. The sorting is based on the evaluation of the number and the intensity of pixels in the replication foci image and the colocalization analysis is based on image cross-correlation spectroscopy (ICCS). We evaluate the colocalization between replication and transcription, at different cell cycle phases, in a model of PML-RARα oncogene activation. We find that colocalization between replication and transcription is higher in cells in early S phase compared to cells in middle and late S phase. When we turn on the PML-RARα oncogene, this colocalization pattern is preserved but we detect an increase of colocalization between replication and transcription in the early S phase which points to an effect of the PML-RARα oncogene on the coordination between replication and transcription.