Why are growth factors important in oligodendrocyte physiology?

Recent studies in chicken, rodents and transgenic mice have provided new in sight on the nature of factors essential to oligodendrocyte development. He re we first review how sonic hedgehog (shh) graded signalling induces emerg ence of oligodendrocytes in the embryonic spinal cord from birds to man. We then discuss the way in which thyroid hormone successively signals differe nt thyroid receptors to control fate determination, growth and differentiat ion in the oligodendrocyte lineage. Platelet-derived growth factor (PDGF) i s a potent regulator of oligodendrocyte progenitor (OP) migration and proli feration, while insulin-like growth factor 1 (IGF-1) acts both on neurons a nd myelin-forming cells to promote myelination. The balance between OP prol iferation and differentiation appears to be controlled by different sets of growth factors locally synthesized in the central nervous system (CNS) as well as glutamate. In experimental models of multiple sclerosis (MS), the n euregulin isoform glial growth factor 2, IGF-1 and some neurotrophins can p romote remyelination after an episode of inflammatory demyelination. A futu re challenge is to determine how to induce multipotential neural precursors to generate migratory OP and enhance the remyelination process in the adul t CNS. (C) 2000 Editions scientifiques et medicales Elsevier SAS.