Expression of a novel Muller glia specific antigen during development and after optic nerve lesion

To generate monoclonal antibodies, immunogen fractions were purified from embryonic chick retinae by temperature-induced detergent-phase separation employing Triton X-114. Under reducing conditions, the monoclonal antibody (mAb) 2M6 identifies a protein doublet at 40 and 46 × 10(3) Mr, which appears to form disulfide-coupled multimers. The 2M6 antigen is regulated developmentally during retinal histogenesis and its expression correlates with Muller glial cell differentiation. Isolated glial endfeet and retinal glial cells in vitro were found to be 2M6-positive, identified with the aid of the general glia marker mAb R5. mAb 2M6 does not bind to any other glial cell type in the CNS as judged from immunohistochemical data. Cell-type specificity was further substantiated by employing retinal explant and single cell cultures on laminin in conjunction with two novel neuron-specific monoclonal antibodies. MAb 2M6 does not bind either to neurites or to neuronal cell bodies. Incubation of retinal cells in vitro with bromodeoxyuridine (BrdU) and subsequent immunodouble labelling with mAb 2M6 and anti-BrdU reveal that mitotic Muller cells can also express the 2M6 antigen. To investigate whether Muller cell differentiation depends on interactions with earlier differentiating ganglion cells, transections of early embryonic optic nerves in vivo were performed. This operation eliminates ganglion cells. Muller cell development and 2M6 antigen expression were not affected, suggesting a ganglion-cell-independent differentiation process. If, however, the optic nerve of juvenile chicken was crushed to induce a transient degeneration/regeneration process in the retina, a significant increase of 2M6 immunoreactivity became evident. These data are in line with the hypothesis that Muller glial cells, in contrast to other distinct glial cell types, might facilitate neural regeneration.