Breast epithelial cells. Fluorescence light micrograph of mammary epithelial cells from a human breast. Epithelial tissues form the lining of many body structures. Fluorescent markers have been used to highlight proteins in the cytoskeleton (red), cell membranes (green), and cell nuclei (blue-purple). The proteins stained here are: cytokeratin 18 in the intermediate filaments of the intracytoplasmic cytoskeleton; and E-cadherin, a calcium-dependent cell-cell adhesion glycoprotein. Cell nuclei have been stained with DAPI.