Neuronal differentiation is a protracted process during which newly generated neurons express distinct cellular and molecular programs at precise times during their maturation: long-distance axon outgrowth, subsequent terminal branching, and finally synaptogenesis. Many important aspects of neuronal character appear to be acquired through the expression of transcription factors at progenitor cell stages, whereas others depend on expression immediately upon cell cycle exit [1]. But whether the orderly expression and activity of transcriptional programs at much later developmental stages, well after cell cycle exit, is an essential step in the progression of neuronal differentiation and circuit assembly has yet to be resolved.