Tales of retinogenesis told by human stem cells

Vision begins when light enters the eye and falls onto the neural retina, a thin tissue in the back of the eye. In the neural retina, photoreceptor cells (cones for high visual acuity; rods for night vision) capture and transform the light into electrophysiological signals, which are relayed by retinal ganglion cells to the brain. Lining the neural retina is a single-layered, often darkly pigmented, transporting epithelium—the retinal pigment epithelium (RPE)—that forms the outer blood–retinal barrier and regulates retinal physiology. The RPE interacts intimately with cones and rods, and together they constitute the outer retina. Atrophy of the RPE or photoreceptors leads to vision loss, as in age-related macular degeneration, a leading cause of blindness in people age 65 and older in developed countries (1). How the humanretina forms is both scientifically fascinating and clinically important because such knowledge may lead to better diagnosis, prevention, and treatment of visual impairment. However, direct examinations of the molecular events unfolding as a cell begins its journey to becoming a retinal cell in our own species have been limited; current knowledge is mostly extrapolated from studies of other mammals, mice in particular, as well as a range of nonmammalian vertebrates. This landscape is changing, as a study by Meyer et al. (2) in this issue of PNAS offers a way to look into early events in human retinogenesis. …