Fig. 2.

Involvement of Ras/PI3K/MAPK pathway in remyelination. Migration: the proteoglycan NG2 contributes to front-rear polarity establishment in OPCs in response to growth factors and chemokines. NG2 maintains high RhoA activity at the rear of the cell whereas it stimulates Rac at the migration front via its switch of activity induced by RTK/GPCR dependent PKCα activation. Ras/Raf/MEK/ERK and PI3K/Akt pathways regulate this Rac activation. Conversely, removal of GSK3β mediated inhibition of p190A by Akt probably favours local RhoA inhibition. Proliferation/differentiation: Akt dependent regulation of mTORC1 and β-catenin plays a parallel role to ERK1/2 in proliferation and differentiation of oligodendrocytes. However, β-catenin can have opposite effects on this differentiation depending of its nuclear level. Arrows show activation and truncated red arrows show inhibition. PI3K-Akt pathway is shown in orange boxes, MAPK pathway in blue boxes and GSK3β/β-catenin in purple boxes. Factors shown in green favour establishment of the migration front