Project Summary An intact blood-retinal barrier (BRB) is critical for the maintenance of the health of the retina. The endothelial cells of the retinal blood vessels along with the surrounding pericytes and astrocytes form a neurovascular unit with strong barrier properties. Very little is known about the molecular and cellular mechanisms that regulate the development and maintenance of the BRB. We hypothesize that retinoic acid (RA) plays a critical role in the regulation of BRB formation as well as maintenance. We will test this hypothesis using a novel zebrafish model that we have developed, which allows the longitudinal in vivo visualization and testing of the BRB.