DIFFERENT CELL-SURFACE AREAS OF POLARIZED RADIAL GLIA HAVING OPPOSITEEFFECTS ON AXONAL OUTGROWTH

During neuronal development neurites are likely to be specifically gui ded to their targets. Within the chicken retina, ganglion cell axons a re extended exclusively into the optic fibre layer, but not into the o uter retina. We investigated, whether radial glial cells having endfee t at the optic fibre layer and somata in the outer retina, might be in volved in neurite guidance. In order to analyse distinct cell surface areas, endfeet and somata of these glial cells were purified. Glial en dfeet were isolated from flat mounted retina by a specific detachment procedure. Glial somata were purified by negative selection using a mo noclonal antibody/complement mediated cytolysis of all non-glial cells . Retinal tissue strips were explanted either onto pure glial endfeet or onto glial somata. As revealed by scanning and fluorescence microsc opy, essentially no ganglion cell axons were evident on glial somata, whereas axonal outgrowth was abundant on glial endfeet. However, when glial somata were heat treated and employed thereafter as the substrat um, axon extension was significantly increased, Time-lapse video recor ding studies indicated that purified cell membranes of glial somata bu t not of endfeet induced collapse of growth cones. Collapsing activity was destroyed by heat treatment of glial membranes, The collapsing ac tivity of retinal glia was found to be specific for retinal ganglion c ell neurites, because growth cones from dorsal root ganglia remained u naffected, Employing four different kinase inhibitors revealed that th e investigated protein kinase types were unlikely to be involved in th e collapse reaction, The data show for the first time that radial glia l cells are functionally polarized having permissive endfeet and inhib itory somata with regard to outgrowing axons. This finding underscores the pivotal role of radial glia in structuring developing nervous sys tems.