Mus musculus strain:C57BL/6J Raw sequence reads. Mus musculus strain:C57BL/6J

How gene expression temporally unfolds and is regulated to shape post-differentiation development of neuronal identity is poorly understood. Here, RNA-sequencing of flow sorted serotonin (5-HT) neurons uncovers multiple discretegene expression trajectories during 5-HT neuron maturation. Integration of ChIP-seq and RNA-seq datasets shows that transcription factor, Pet-1/FEV, regulatestrajectories of diverse targets including a transcription factor network and pan-neuronal and neuron-type identity features. The profound disruption ofexpression patterns in Pet-1-/- 5-HT neurons permanently stalled maturation oftheir active and passive membrane characteristics. Collapse of specifictrajectories blocked acquisition of glutamatergic and G-protein coupled receptor-signaling pathways required for mature afferent responses of 5-HT neurons.Moreover, continuous transcriptional activity was required to shape trajectories ofkey identity features defining mature 5-HT neurons. Our findings identify atranscriptional program that promotes maturation of serotonergic efferent andafferent connectivity and provides a framework for understanding how immatureserotonergic activity may contribute to psychiatric disorders.