Embryonic smooth muscle cell, immunofluorescence micrograph. Actin filaments are green, the protein vinculin is light blue. Actin is part of the cytoskeleton. The cytoskeleton maintains the cell's shape, allows some cellular mobility and is involved in intracellular transport. Vinculin is a membrane-cytoskeletal protein that is present at focal adhesions, where the cytoskeleton connects to the extracellular matrix.