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Biol. Bull. 207: 168. (October 2004)
© 2004 Marine Biological Laboratory

Abstract

Evolution of Myelin Proteins

Robert M. Gould1,2, Hilary Morrison3, Robert Campbell2 and Edwin Gilland2

1 University of Illinois at Chicago
2 Marine Biological Laboratory, Woods Hole, Massachusetts
3 Bay Paul Center for Molecular Evolution, Marine Biological Laboratory, Woods Hole, Massachusetts

The myelinated nervous system arose in a common ancestor of all modern-day gnathostomes (jawed animals). Modern-day agnathans (jawless animals, i.e., lamprey and hagfish) have nervous systems that contain large axons surrounded by glial cells, but no myelin. In order for myelination to evolve, both neurons and axons had to simultaneously develop appropriate communication pathways. Pathways from large axons were designed not only to attract glial cells, but also to induce them to form myelin internodes of appropriate size for the axon. The associating glial cells in turn need to signal neurons/axons to target ion channels and other proteins to specialized regions called nodes of Ranvier. The accumulation of ion channels at nodes of Ranvier is an essential feature of rapid saltatory nerve conduction.

With growing genomic and est databases, we felt that it would be possible to use structures of known myelination-associated proteins, both those expressed by glial cells and neurons, to identify homologues in animals that lack myelin. While there is a highly annotated and complete database from the sea squirt, Ciona intestinalis, < www.jgi.doe.gov/ciona>, there are very limited genomic and est sequences from species more closely related to myelination: amphioxus, lamprey, and hagfish. Hopefully, genomic sequencing projects involving these species will be available in the near future.

Protein sequence databases were generated for myelin basic protein, proteolipid protein/DM-20, protein zero, 2', 3'-cyclic nucleotide phosphodiesterase (CNP) mal, and PMP22. Using protein sequences from human and fish homologues, we identified homologous proteins for DM-20 and PMP22 in Ciona.

This research was supported by an NSF grant to RMG.





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