HaCaT cell. Immunofluorescence light micrograph of a HaCaT cell dividing into two. The nucleus, which contains the cell's genetic information, is purple. The yellow strands are microtubules, which are involved in cell division. HaCaT cells are human skin cells (keratinocytes) that have been transformed (mutated) to be immortal. They have unlimited growth potential, but unlike other immortal cell lines they are not tumourigenic (tumour forming). This means they grow in an orderly fashion and retain all the structural and functional features of human skin. HaCaT cells are grown in the laboratory and are used in research, including wound healing research. Magnification: x980 when printed 10cm wide.