M. Yoshida et Dr. Colman, PARALLEL EVOLUTION AND COEXPRESSION OF THE PROTEOLIPID PROTEINS AND PROTEIN ZERO IN VERTEBRATE MYELIN, Neuron, 16(6), 1996, pp. 1115-1126
Vertebrate myelin contains two proteins that mediate compaction: prote
in zero (P-0), an immunoglobulin gene superfamily member, or proteolip
id proteins, 4-hydrophobic domain-motif proteins biogenetically unrela
ted to P-0. The prevailing view has been that expression of P-0 and pr
oteolipid proteins is mutually exclusive; P-0, which mediates myelin c
ompaction in fish, is thought to be completely replaced by the newer p
roteolipid proteins in the terrestrial vertebrate CNS. However, we now
find that proteolipid proteins are actually major myelin constituents
in bony fish and amphibia, and so are coexpressed with P-0. Clearly,
myelin proteolipids are not new additions to the myelin protein repert
oire, but instead were ancestral sheath components, expressed similar
to 440 million years ago in the first myelinated fish that existed at
least similar to 100 million years before the origin of amphibians. In
conclusion, P-0 and the proteolipid proteins are evolving in parallel
in myelinating cells of most vertebrate species.