ABSTRACT
Mechanisms coordinating neural progenitor cell cycle exit and differentiation are incompletely understood. The cyclin-dependent kinase inhibitor p27Kip1 is transcriptionally induced, switching specific neural progenitors from proliferation to differentiation. However, neuronal differentiation-specific transcription factors mediating p27Kip1 transcription have not been identified. We
demonstrate the homeodomain transcription factor Phox2a, required for central nervous system (CNS)- and neural crest (NC)-derived
noradrenergic neuron differentiation, coordinates cell cycle exit and differentiation by inducing p27Kip1 transcription. Phox2a
transcription and activation in the CNS-derived CAD cell line and primary NC cells is mediated by combined cyclic AMP (cAMP) and bone
morphogenetic protein 2 (BMP2) signaling. In the CAD cellular model, cAMP and BMP2 signaling initially induces proliferation of the
undifferentiated precursors, followed by p27Kip1 transcription, G1 arrest, and neuronal differentiation.
Small interfering RNA silencing of either Phox2a or p27Kip1 suppresses p27Kip1 transcription and neuronal
differentiation, suggesting a causal link between p27Kip1 expression and differentiation. Conversely, ectopic Phox2a expression
via the Tet-off expression system promotes accelerated CAD cell neuronal differentiation and p27Kip1 transcription only in
the presence of cAMP signaling. Importantly, endogenous or ectopically expressed Phox2a activated by cAMP signaling binds homeodomain
cis-acting elements of the p27Kip1 promoter in vivo and mediates p27Kip1-luciferase expression in CAD and NC cells. We conclude that developmental cues of cAMP signaling causally link Phox2a activation with p27Kip1 transcription, thereby coordinating neural progenitor cell cycle exit and differentiation.
Coupling Cell Cycle Exit, Neuronal Differentiation and Migration in Cortical Neurogenesis
