Muller glia cells reorganize reaggregating chicken retinal cells into correctly laminated in vitro retinae

Muller cells, that belong to the family of radial glia cells, have central functions during retinogenesis. They form a stabilizing scaffold, they are candidate targets for the mediation of extraneous retinogenetic factors, an d they are an important source for retina-borne retinogenetic factors. Reag gregate cultures allow the analysis of retinogenesis from dispersed cells t o fully laminated tissues. Reaggregating cells from the embryonic chick ret ina reassemble to reversed laminated cellular spheres including constituent s of all retinal layers, yet the outer nuclear layer is represented by inte rnal rosettes. Using spheroids, we tested whether Muller cells have a decis ive function in establishing retinal polarity and in determining the lamina tion pattern. To this end, we established confluent monolayers of highly en riched Muller cells derived from E6 or E13 chicken retinas, and then let di spersed E5.5 retinal cells reaggregate either in the absence of these monol ayers or on top of them. In the presence of Muller cells, the reversed lami na polarity of rosetted spheroids progressively transformed within a week i nto correctly laminated retinal spheres, whereas all initial rosettes vanis hed. Moreover, photoreceptors formed a regular outer nuclear layer, as visu alized by the rod-specific CERN901 antibody. In correctly laminated spheroi ds, staining for vimentin and glutamine synthetase was much more pronounced than in rosetted spheroids; in particular, a well-established inner limiti ng membrane stood out wherever the retinal lamination was complete. Because these effects can be similarly achieved by supernatants derived from Mulle r cells, direct cell-cell contacts or cellular replenishment from the monol ayer do not account for these effects. We conclude that Muller cells are in volved in the establishment of a correct retinal lamination and in the arra ngement of the cells in the reaggregate cultures. In particular, rosette fo rmation is counteracted and the formation of an inner limiting membrane is induced. Because rosettes are objects of concern in several ophthalmologica l defects, these results are highly relevant, both biomedically and also fo r normal retinogenesis. GLIA 29:45-57, 2000. (C) 2000 Wiley-Liss, Inc.