Human retinal progenitor cells grown as neurospheres demonstrate time-dependent changes in neuronal and glial cell fate potential.

The spatiotemporal birth order of the seven major classes of retinal cells is highly conserved among vertebrates. During retinal development, long projection neurons (ganglion cells) are produced first from resident progenitors, followed by the appearance of retinal interneurons, photoreceptors, and Muller glia. This sequence is maintained through the complex orchestration of cell-intrinsic and cell-extrinsic events and factors, including local influences between neighboring cells. Here we asked whether cultures of human prenatal retinal cells might also yield different ratios of cell types based on gestational age and time spent in vitro, thus recapitulating in vivo development. An established chopping technique was used to passage human prenatal retinal cells as neurospheres, avoiding the use of proteases and preserving cell-cell contacts and native microenvironments present in vivo. Retinal neurospheres cultured in this manner demonstrated specific patterns of growth over a limited time period, possibly reflecting trends in normal retinal development. Upon differentiation, immunocytochemical analysis revealed that retinal neurospheres produce predominantly glial cells with increasing gestational age and time in culture. Conversely, the percentage of betaIII tubulin-positive neurons declined over time. This provides information for optimizing culture systems aimed at the study of human retinal development and the generation of specific retinal cell types for therapeutic use or drug testing.