Significance Fast transmission of nerve impulses with energetic efficiency along axons of nerve cells is essential for brain function. Toward this goal, axons are wrapped by the myelin membranes extended from oligodendrocytes, which is known as myelination of axons. Therefore, myelination is dependent on the formation of oligodendrocyte lineage cells. How the oligodendrocyte lineage is formed remains incompletely known. Previous studies suggest that signaling pathways of growth factors and amino acids might coordinate the regulation of oligodendrocyte formation, but the specific amino acid signaling pathway that participates in this regulation has not been identified. This study identifies the amino acid signaling complex GATOR2 (GAP activity towards Rags 2) as a positive regulator of oligodendrocyte formation and myelination that coordinately regulates brain myelination with growth factor signaling.