Hypotheses regarding myelination derived from comparisons of myelin subfractions.

Patterns of myelin-associated proteins and glycoproteins in subfractions of central nervous system myelin and changes in these during development have been reviewed. Several hypotheses are put forward regarding classification of these proteins as structural components of myelin, as components of the membranes from which myelin is derived or as molecules present to play a role in myelin formation rather than as true components of compact myelin. 2′, 3′-Cyclic nucleotide 3′-phosphohydrolase is considered to fit into this last category and two different hypothesis are proposed for its role. The major myelin glycoprotein is postulated to serve a function in recognition of axons by oligodendrocytes, a function not needed in the peripheral nervous system where Schwann cells and axons develop in close contact.