Institute of Neuroscience/Institute of Molecular Biology, Howard Hughes Medical Institute, 1254 University of Oregon, Eugene, OR 97403, USA.
Neural precursors often generate distinct cell types in a specific order, but the intrinsic or extrinsic cues regulating the timing of cell fate specification are poorly understood. Here we show that Drosophila neural precursors (neuroblasts) sequentially express the transcription factors Hunchback --> Krüppel --> Pdm --> Castor, with differentiated progeny maintaining the transcription factor profile present at their birth. Hunchback is necessary and sufficient for first-born cell fates, whereas Krüppel is necessary and sufficient for second-born cell fates; this is observed in multiple lineages and is independent of the cell type involved. We propose that Hunchback and Krüppel control early-born temporal identity in neuroblast cell lineages.