The expression of myelin-associated glycoprotein in regenerating cat sciatic nerve.

A model of peripheral nerve regeneration in the cat in which freshly severed proximal axons penetrate a permanently transected distal stump, composed of quiescent Schwann cells has been used to study the pattern of myelin protein expression during myelination associated with axonal regeneration. The expression of the myelin-associated glycoprotein (MAG) and the compact myelin proteins P0 and P1 has been analyzed by immunoassays at sequential distances down the regenerating nerve. In the most proximal regenerating zone of this model, MAG is expressed at a significantly higher level (7.9% of normal) than P0 (2.3% of normal) or P1 (1.7% of normal). In addition, elevated levels of MAG are sustained farther into the distal stump than those of P0 and P1. These results are similar to the pattern of accumulation of myelin proteins seen during normal feline development and indicate that MAG, which is localized in part to the periaxonal Schwann cell membranes, may play an important role in the early events of establishing and maintaining the relationship between Schwann cell and axon. Neither MAG, nor P0, were detected in non-myelinating Schwann cells in the distal stump, although it is possible that they are present at levels below the detection threshold of the assays, which are approximately 0.1% of normal.