The blood-brain barrier consists of specialized endothelial cells that have an important function separate blood from the brain extracellular fluid. The endothelial cells of brain capillaries have very tight junctions to restrict passage of large solutes into the brain?s domain. The image on the left shows cultured human brain endothelial cells that have been labeled to identify ß-catenin (green), myosin light chains (red), and nuclei (blue). ß-catenin is an important junctional and signaling protein that helps maintain adherens junctions. Myosin light chains are a key element of the actin cytoskeleton, which determines cell shape and tensile forces within the cells. These forces can affect junctional integrity, and thus overall barrier function of the brain endothelium. Photo contributed and taken using a standard fluorescent microscope by Dr. Jerome Breslin. The specimen was produced by Dr. Rich Beard of Dr. Sarah Yuan's laboratory at the University of South Florida.