Scientific correspondence Observations on the structure of myelin lacking the major proteolipid protein.

Proteolipid protein (PLP) and its smaller DM20 isoform account for approximately 50% of protein in central nervous system myelin, suggesting an important role in myelination. PLP/DM20-deficient mice generated by gene targeting techniques assemble large amounts of myelin, although it displays a variety of defects at the intraperiod line (IPL) when prepared for conventional electron microscopy. The appearance of the PLP/DM20-deficient myelin prepared by freeze substitution showed a similar range of IPL defects to that prepared by conventional fixation and also included regions containing a normal IPL.