From stem cells towards neural layers: a lesson from re-aggregated embryonic retinal cells

Cells from dissociated embryonic avian retinae have the capacity to re-aggr egate in rotation culture and form cellular spheres reconstituting a comple te arrangement of all retina[ layers. This exquisite phenomenon is based up on in vitro proliferation of multipotent precursor stem cells and spatial o rganization of their differentiating descendants. The addition of soluble f actors from cultured retinal pigmented epithelial (RPE) or radial glial cel ls is essential to revert inside-out spheres (rosetted retinal spheres) int o correctly laminated outside-out-spheres (stratified spheres). Such comple te restoration of a laminated brain tissue by cell re-aggregation has been achieved only for the embryonic avian retina, but not the mammalian retina, nor for other brain parts. This review summarises the history of the re-ag gregation approach, presents avian retinal re-aggregate models, and analyse s roles of the RPE and Muller cells for successful retinal tissue regenerat ion. It is predicted that these results will become biomedically relevant, as stem cell biology will soon open ways to produce large amounts of human retinal precursors. NeuroReport 12:39-46 (C) 2001 Lippincott Williams & Wil kins.