Fluorescent light micrograph of a cell during cytokinesis (cell division). Fluorescent markers have been used to highlight alpha tubulin (green), a component of microtubules, and DNA (deoxyribonucleic acid, pink). At centre is a midbody, a bridge of cytoplasm between two separating cells. Division of a cell's cytoplasm follows shortly after division of the nucleus (mitosis). A contractile ring of actin filaments gradually narrows the bridge between the two cells until it breaks the microtubule fibres of the spindle (bright green) and divides the cells. The spindle is involved in division of chromosomes during mitosis, the formation of two daughter nuclei from one parent nucleus.