[Glial lineage of the peripheral nervous system]

Glial cells are classified into 4 types. Two kinds of Schwann cells, myelinating and non-myelinating, are associated with the nerve fibres; satellite cells surround the neuronal soma in the ganglia, and enteric glial cells can be in contact with different neurons, that are incompletely ensheathed. A basal lamina is formed at the outer cell membrane of Schwann and satellite cells, but not inside the enteric plexuses. All the peripheral glial cells derive from the neural crest. The crest population of each axial level has both neuronal and glial potential, but it was unclear if common or separate precursors for the neuronal and glial lineages exist in this population, as is the case for some cranial ganglia were neurons are of placodal origin. To follow gliogenesis in the avian system we defined new molecular markers specific for glial cells by using the monoclonal antibody strategy. One of these markers is the Schwann cell Myelin Protein (SMP). It is a surface glycoprotein, belonging to the immunoglobulin superfamily. The SMP protein in vivo is restricted to oligodendrocytes and myelinating and non-myelinating Schwann cells, while satellite cells and enteric glia are SMP-negative. It is first expressed in the sciatic nerve of the quail embryo around E6, preceding myelination by 5 days. Thus in the PNS the appearance of SMP indicates an early stage of Schwann cell differentiation. The anti-SMP Mab was used to study the segregation of the glial lineage in the clonal culture system developed in our laboratory. We demonstrated that differently committed glial ancestors coexist in the cephalic neural crest during the migration stage.(ABSTRACT TRUNCATED AT 250 WORDS)