Expression of the large myelin-associated glycoprotein isoform during the development in the mouse peripheral nervous system.

The developmental maximum expression of the large myelin-associated glycoprotein isoform (L-MAG) protein prior to that of the small myelin-associated glycoprotein isoform (S-MAG) in both the central and peripheral nervous systems (CNS, PNS) in mice was shown by immunoblotting techniques using specific antibodies to the L-MAG protein and the S-MAG protein. Both the L-MAG protein and the S-MAG protein were expressed earlier in the PNS than in the CNS, which reflects earlier myelination in the PNS. The peak of the L-MAG protein concentration was 8 days in the sciatic nerve and 15 days in the brainstem. The concentration of the S-MAG protein in the sciatic nerve reached a peak at 15 days, whereas in the brainstem it increased rapidly between 15 and 20 days and gradually thereafter. Thus, the preceding maximum expression of the L-MAG during active myelination in the PNS demonstrated here as well as in the CNS strongly suggests an important role for L-MAG in myelin formation.