Pigmented epithelium induces complete retinal reconstitution from dispersed embryonic chick retinae in reaggregation culture.

Reaggregation of dispersed retinal cells of the chick embryo leads to histotypic retinospheroids in which the laminar organization remains incomplete: photoreceptors form rosettes which are surrounded by constituents of the other retinal layers. Here, for the first time, a complete arrangement of layers is achieved in cellular spheres (stratoids), provided that fully dispersed retinal cells are younger than embryonic day E6, and are reaggregated in the presence of a monolayer of retinal pigmented epithelium (RPE). A remarkable mechanism of stratoid formation from 1 to 15 days in vitro is revealed by the establishment of a radial Müller glia scaffold and of photoreceptors. During the first two days of reaggregation on RPE, rosettes are still observed. At this stage immunostaining with vimentin and F11 antibodies for radial Müller glia reveal a disorganized pattern. Subsequently, radial glia processes organize into long parallel fibre bundles which are arranged like spokes to stabilize the surface and centre of the stratoid. The opsin-specific antibody CERN 901 detects photoreceptors as they gradually build up an outer nuclear layer at the surface. These findings assign to the RPE a decisive role for the genesis and regeneration of a vertebrate retina.