The myelin basic proteins are a set of peripheral membrane polypeptide
s which play an essential role in myelination. Their most well-documen
ted property is the unique ability to 'seal' the cytoplasmic aspects o
f the myelin membrane, but this is probably not the only function for
these highly charged molecules. Despite extensive homology, the indivi
dual myelin basic proteins (MBPs) exhibit different expression pattern
s and biochemical properties, and so it is now believed that the vario
us isoforms are not functionally equivalent in myelinating cells. We n
ow think that while the major MBPs are intracellular adhesion molecule
s, some of the quantitatively less abundant isoforms that are expresse
d very early in development may have regulatory effects on the myelina
tion program.