RT Journal Article SR Electronic T1 CCAAT/Enhancer-Binding Protein Phosphorylation Biases Cortical Precursors to Generate Neurons Rather Than Astrocytes In Vivo JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 10747 OP 10758 DO 10.1523/JNEUROSCI.2662-05.2005 VO 25 IS 46 A1 Annie Paquin A1 Fanie Barnabé-Heider A1 Ryoichiro Kageyama A1 Freda D. Miller YR 2005 UL http://www.jneurosci.org/content/25/46/10747.abstract AB The intracellular mechanisms that bias mammalian neural precursors to generate neurons versus glial cells are not well understood. We demonstrated previously that the growth factor-regulated mitogen-activated protein kinase kinase (MEK) and its downstream target, the CCAAT/enhancer-binding protein (C/EBP) family of transcription factors, are essential for neurogenesis in cultured cortical precursor cells (Ménard et al., 2002). Here, we examined a role for this pathway during cortical cell fate determination in vivo using in utero electroporation of the embryonic cortex. These studies demonstrate that inhibition of the activity of either MEK or the C/EBPs inhibits the genesis of neurons in vivo. Moreover, the MEK pathway mediates phosphorylation of C/EBPβ in cortical precursors, and expression of a C/EBPβ construct in which the MEK pathway phosphorylation sites are mutated inhibits neurogenesis. Conversely, expression of a C/EBPβ construct, in which the same sites are mutated to glutamate and therefore are “constitutively” phosphorylated, enhances neurogenesis in the early embryonic cortex. A subpopulation of precursors in which C/EBP activity is inhibited are maintained as cycling precursors in the ventricular/subventricular zone of the cortex until early in postnatal life, when they have an enhanced propensity to generate astrocytes, presumably in response to gliogenic signals in the neonatal environment. Thus, activation of an MEK-C/EBP pathway in cortical precursors in vivo biases them to become neurons and against becoming astrocytes, thereby acting as a growth factor-regulated switch.