Osteosarcoma cells. Immunofluorescence light micrograph of human osteosarcoma cells stained to show cell proteins and organelles. These cells are stained for tubulin (green), the stress responsive protein and enzyme sirtuin 6 (SIRT6, red), and mitochondria (blue). Tubulin is the main component of microtubes, cytoskeletal structures critical to mitosis and movement. Sirtuins may function as intracellular regulatory proteins with mono-ADP-ribosyltransferase activity. Magnification: x1030 when printed at 10 centimetres wide.