PHENOTYPIC PLASTICITY OF SCHWANN-CELLS AND ENTERIC GLIAL-CELLS IN RESPONSE TO THE MICROENVIRONMENT

We produced earlier a monoclonal antibody against Schwann cell myelin protein (SMP), a glycoprotein expressed on Schwann cells (SC) but not on satellite cells of the ganglia or enteric glial cells. We now studied whether SMP expression is environmentally regulated in the different compartments of the peripheral nervous system. Quail neural-crest cells from either mes-metencephalic, vagal, or truncal levels of the neuraxis were heterochronically associated with gut wall, skin, or muscle tissues from embryonic day (E) 7 to Ell chickens. Coculture of these chimeric organs revealed that as in normal development glial cells, characterized by HNK1 immunoreactivity and the quail nuclear marker, expressed the SMP phenotype exclusively in skin and muscle, failing to do so in gut. However, when SMP+ SC from quail sciatic nerves were cocultured with chicken gut, these cells rapidly lost their initial SMP immunoreactivity. In contrast, when associated with muscle and skin, SC remained SMP+, even in the complete absence of neuronal cells. Enteric plexuses from E8 to E15 quail gut express SMP+ and laminin when withdrawn from the intestinal-mesenchyme environment. These results show that SMP can be expressed by enteric glial cells and that the SC SMP phenotype is strongly inhibited by the gut-wall environment. Moreover, these results strongly suggest that these two types of glial cells belong to the same lineage and that their terminal phenotype is modulated through cell-to-cell interactions.