3D Ground state depletion (GSD) micrograph of microtubules in a HeLa cell. Colour-coding shows the height of the microtuble above the surface the cell is growing on (scale at top right). Microtubules are polymers of the protein tubulin and are a component of the cytoskeleton. The cytoskeleton maintains the cell's shape, allows some cellular mobility and is involved in intracellular transport and nuclear division. The cell has been stained with anti-alpha-tubulin antibodies tagged with the fluorescent dye Alexa 647.