AXONAL VERSUS DENDRITIC OUTGROWTH IS DIFFERENTIALLY AFFECTED BY RADIAL GLIA IN DISCRETE LAYERS OF THE RETINA

Formation of neural cell polarity defined by oriented extension of axo ns and dendrites is a crucial event during the development of the nerv ous system, Ganglion cells of the chicken retina extend axons exclusiv ely into the inner retina, whereas their dendrites grow into the outer retina, To analyze guidance cues for specific neurite extension, nove l in vitro systems were established, Ganglion cells were purified by e nzymatically facilitated detachment of the ganglion cell layer, A newl y developed retrograde labeling technique and the expression analysis of the cell type-specific 2A1 antigen were used to monitor ganglion ce ll purification. In highly purified ganglion cells explanted onto reti nal cryosections (cryoculture), axon formation was induced when the ce lls were positioned on the inner retina, In contrast, on outer layers of the developing retina dendritic outgrowth was prevalent. Because ra dial glia have been demonstrated to be instructive in neuritogenesis, distinct glial cell compartments located in inner and outer retina, re spectively, were isolated for functional assays. Glial end feet were p urified by a physical detachment technique, Glial somata were purified by complement mediated cytolysis of all nonglial cells. When ganglion cells were cultured on different glial compartments, axon formation o ccurred on end feet but not on glial somata, In striking contrast, on glial somata dendrites were formed, The data support the notion that g anglion cell polarity is affected by the retinal microenvironment, whi ch in turn is possibly influenced by radial glia, being themselves pol arized.