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Article |
Essential role of B-Raf in oligodendrocyte maturation and myelination during postnatal central nervous system development
Correspondence to M. Baccarini: manuela.baccarini{at}univie.ac.at
Mutations in the extracellular signal-regulated kinase (ERK) pathway, particularly in the mitogen-activated protein kinase/ERK kinase (MEK) activator B-Raf, are associated with human tumorigenesis and genetic disorders. Hence, B-Raf is a prime target for molecule-based therapies, and understanding its essential biological functions is crucial for their success. B-Raf is expressed preferentially in cells of neuronal origin. Here, we show that in mice, conditional ablation of B-Raf in neuronal precursors leads to severe dysmyelination, defective oligodendrocyte differentiation, and reduced ERK activation in brain. Both B-Raf ablation and chemical inhibition of MEK impair oligodendrocyte differentiation in vitro. In glial cell cultures, we find B-Raf in a complex with MEK, Raf-1, and kinase suppressor of Ras. In B-Raf–deficient cells, more Raf-1 is recruited to MEK, yet MEK/ERK phosphorylation is impaired. These data define B-Raf as the rate-limiting MEK/ERK activator in oligodendrocyte differentiation and myelination and have implications for the design and use of Raf inhibitors.
Abbreviations used in this paper: CNS, central nervous system; ERK, extracellular signal-regulated kinase; KO, knockout; KSR, kinase suppressor of Ras; MBP, myelin basic protein; MEK, MAPK/ERK kinase; P, postnatal day; PDGFR
, PDGF receptor
; WT, wild type.
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