Skin cancer cells. Fluorescence light micrograph of two skin cancer cells connected by actin (green), a protein in the cellular skeleton (cytoskeleton). The cell nuclei are blue. Although actin is required by many cells for normal movement, it also enables cancer cells to spread to other parts of the body. Research aimed at understanding these processes may lead to new treatments for cancer. These cells are from a mouse, an animal commonly used to study human diseases (including many types of cancer) and to test the effectiveness of drugs.