Drosophila neuroblasts sequentially express transcription factors which specify the temporal identity of their neuronal progeny

Neural precursors often generate distinct cell types in a specific order, b ut the intrinsic or extrinsic cues regulating the timing of cell fate speci fication are poorly understood. Here we show that Drosophila neural precurs ors (neuroblasts) sequentially express the transcription factors Hunchback --> Kruppel --> Pdm --> Castor, with differentiated progeny maintaining the transcription factor profile present at their birth. Hunchback is necessar y and sufficient for first-born cell fates, whereas Kruppel is necessary an d sufficient for second-born cell fates; this is observed in multiple linea ges and is independent of the cell type involved. We propose that Hunchback and Kruppel control early-born temporal identity in neuroblast cell lineag es.