Osteosarcoma cells. Fluorescence light micrograph of bone cancer cells in a case of an osteosarcoma. The colours within the cell nuclei (oval) show nuclear material such as DNA (deoxyribonucleic acid) and cellular proteins. Undamaged DNA (blue) contrasts with sites of DNA damage (red) in the cell nucleus. The Smurf2 protein (green, in nuclei), may help suppress tumours by protecting DNA from damage. This protein is localized to the damaged DNA.