Neurons or glia? Can SHP2 know it all?

Normal development of the nervous system relies on the spatially and temporally well-controlled differentiation of neurons and glia. Here, we discuss the intra- and extracellular molecular mechanisms that underlie the sequential genesis of neurons and glia, emphasizing recent studies describing the role of a signaling molecule, the tyrosine phosphatase SHP2, in normal brain development. Activation of SHP2 simultaneously enhances downstream activation of the MEK-ERK pathway, which subsequently promotes neurogenesis, while inhibiting the JAK-STAT pathway, which is critical for astroglial differentiation. Mutations in SHP2 that increase its tyrosine phosphatase activity cause a mental retardation-related disorder, Noonan syndrome. An imbalance in neurogenesis versus gliogenesis due to SHP2 mutations may contribute to Noonan syndrome.