Schwann cell expression of a major myelin glycoprotein in the absence of myelin assembly

Quiescent Schwann cells in the distal segment of the permanently transected nerve produced basal levels of the major myelin glycoprotein, P₀, in the absence of myelin assembly. Low levels of P₀ could be detected at 35 days after transection by autoradiographic analysis of radioiodinated lectin binding after protein separation by high-resolution sodium dodecyl sulfate pore gradient electrophoresis and by fluorographic analysis after electrophoresis of [³H]fucose-and [³H]mannose-labeled glycoproteins after incorporation into endoneurial slices. Immunoreactivity to P₀ in the transected nerve could also be demonstrated with antisera against P₀ as evaluated by direct 'immune overlay' after electrophoresis. These results indicate that the requirement for continuing signals from appropriate axons to make detectable amounts of myelin-specific proteins and glycolipids is not absolute. Schwann cells, therefore, like oligodendrocytes, can synthesize myelin components in the absence of neuronal influence, although information from neuronal elements probably is required for myelin assembly by Schwann cells and for myelin compaction by oligodendrocytes.