CNS integrins switch growth factor signalling to promote target-dependent survival

Depending on the stage of development, a growth factor can mediate cell proliferation, survival or differentiation. The interaction of cell-surface integrins with extracellular matrix ligands can regulate growth factor responses and thus may influence the effect mediated by the growth factor. Here we show, by using mice lacking the α₆ integrin receptor for laminins, that myelin-forming oligodendrocytes activate an integrin-regulated switch in survival signalling when they contact axonal laminins. This switch alters survival signalling mediated by neuregulin from dependence on the phosphatidylinositol-3-OH kinase (PI(3)K) pathway to dependence on the mitogen-activated kinase pathway. The consequent enhanced survival provides a mechanism for target-dependent selection during development of the central nervous system. This integrin-regulated switch reverses the capacity of neuregulin to inhibit the differentiation of precursors, thereby explaining how neuregulin subsequently promotes differentiation and survival in myelinating oligodendrocytes. Our results provide a general mechanism by which growth factors can exert apparently contradictory effects at different stages of development in individual cell lineages.