WS3 is a novel small molecule that promotes β cell proliferation with EC50 of 28 nM (induced R7T1 proliferation). More recently, WS3 has been found to mediate proliferation of primary retinal pigment epithelial cells. After WS3 removal, the retinal cells differentiated into a functional monolayer and remained functional in vivo, preserving vision when they were transplanted into RCS rats used as a model of retinal degeneration.