An integrin-contactin complex regulates CNS myelination by differential Fyn phosphorylation.
The understanding of how adhesion molecules mediate the axon-glial interactions in the CNS that ensure target-dependent survival of oligodendrocytes and initiate myelination remains incomplete. Here, we investigate how signals from adhesion molecules can be integrated to regulate these initial steps of myelination. We first demonstrate that the Ig superfamily molecule contactin is associated in oligodendrocytes with integrins, extracellular matrix receptors that regulate target-dependent survival by amplification of growth factor signaling. This amplification is inhibited by small interfering RNA-mediated knockdown of contactin in oligodendrocytes. In contrast, the presence of L1-Fc, the extracellular portion of a contactin ligand expressed on axons, enhanced survival and additionally promoted myelination in cocultures of neurons and oligodendrocytes. We further demonstrate that the signals from contactin and integrin are integrated by differential phosphorylation of the Src family kinase Fyn. Integrin induced dephosphorylation of the inhibitory Tyr-531, whereas contactin increased phosphorylation of both Tyr-531 and the activating Tyr-420. The combined effect is an enhanced activity of Fyn and also a dynamic regulation of the phosphorylation/dephosphorylation balance of Fyn, as required for normal cell adhesion and spreading. We conclude, therefore, that a novel integrin/contactin complex coordinates signals from extracellular matrix and the axonal surface to regulate both oligodendrocyte survival and myelination by controlling Fyn activity.
Laursen
Lisbeth Schmidt
LS
Medical Research Council Centre for Regenerative Medicine, Centre for Inflammation Research, The Queen's Medical Research Institute, University of Edinburgh, EH16 4TJ Edinburgh, United Kingdom. ls.laursen@ed.ac.uk
Chan
Colin W
CW
ffrench-Constant
Charles
C
D000818:Animals; D001369:Axons / Q000502:physiology; D015816:Cell Adhesion Molecules, Neuronal / Q000378:metabolism*; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D018920:Coculture Techniques; D058966:Contactins; D005109:Extracellular Matrix / Q000378:metabolism; D055785:Gene Knockdown Techniques; D039121:Integrin alpha6beta1 / Q000378:metabolism; D016023:Integrins / Q000378:metabolism*; D008959:Models, Neurological; D009186:Myelin Sheath / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D009836:Oligodendroglia / Q000502:physiology*; D010766:Phosphorylation; D051076:Proto-Oncogene Proteins c-fyn / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D014443:Tyrosine / Q000378:metabolism
D015816:Cell Adhesion Molecules, Neuronal; D058966:Contactins; D039121:Integrin alpha6beta1; D016023:Integrins; D034741:RNA, Small Interfering; D014443:Tyrosine; C494961:Fyn protein, rat; D051076:Proto-Oncogene Proteins c-fyn