title: Pet-1 Switches Transcriptional Targets Postnatally to Regulate Maturation of Serotonin Neuron Excitability.
abstract: Newborn neurons enter an extended maturation stage, during which they acquire excitability characteristics crucial for development of presynaptic and postsynaptic connectivity. In contrast to earlier specification programs, little is known about the regulatory mechanisms that control neuronal maturation. The Pet-1 ETS (E26 transformation-specific) factor is continuously expressed in serotonin (5-HT) neurons and initially acts in postmitotic precursors to control acquisition of 5-HT transmitter identity. Using a combination of RNA sequencing, electrophysiology, and conditional targeting approaches, we determined gene expression patterns in maturing flow-sorted 5-HT neurons and the temporal requirements for Pet-1 in shaping these patterns for functional maturation of mouse 5-HT neurons. We report a profound disruption of postmitotic expression trajectories in Pet-1(-/-) neurons, which prevented postnatal maturation of 5-HT neuron passive and active intrinsic membrane properties, G-protein signaling, and synaptic responses to glutamatergic, lysophosphatidic, and adrenergic agonists. Unexpectedly, conditional targeting revealed a postnatal stage-specific switch in Pet-1 targets from 5-HT synthesis genes to transmitter receptor genes required for afferent modulation of 5-HT neuron excitability. Five-HT1a autoreceptor expression depended transiently on Pet-1, thus revealing an early postnatal sensitive period for control of 5-HT excitability genes. Chromatin immunoprecipitation followed by sequencing revealed that Pet-1 regulates 5-HT neuron maturation through direct gene activation and repression. Moreover, Pet-1 directly regulates the 5-HT neuron maturation factor Engrailed 1, which suggests Pet-1 orchestrates maturation through secondary postmitotic regulatory factors. The early postnatal switch in Pet-1 targets uncovers a distinct neonatal stage-specific function for Pet-1, during which it promotes maturation of 5-HT neuron excitability.
  
  
  CONCLUSIONS
  The regulatory mechanisms that control functional maturation of neurons are poorly understood. We show that in addition to inducing brain serotonin (5-HT) synthesis and reuptake, the Pet-1 ETS (E26 transformation-specific) factor subsequently globally coordinates postmitotic expression trajectories of genes necessary for maturation of 5-HT neuron excitability. Further, Pet-1 switches its transcriptional targets as 5-HT neurons mature from 5-HT synthesis genes to G-protein-coupled receptors, which are necessary for afferent synaptic modulation of 5-HT neuron excitability. Our findings uncover gene-specific switching of downstream targets as a previously unrecognized regulatory strategy through which continuously expressed transcription factors control acquisition of neuronal identity at different stages of development.
authors: Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio 44106.
authors: Steven C
authors: SC
authors: Wyler
authors: Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio 44106.
authors: W Clay
authors: WC
authors: Spencer
authors: Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235, and.
authors: Noah H
authors: NH
authors: Green
authors: Department of Anesthesiology and Critical Care, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104.
authors: Benjamin D
authors: BD
authors: Rood
authors: Department of Anesthesiology and Critical Care, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104.
authors: LaTasha
authors: http://orcid.org/0000-0002-8553-9894
authors: L
authors: Crawford
authors: Department of Anesthesiology and Critical Care, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104.
authors: Caryne
authors: C
authors: Craige
authors: Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235, and.
authors: Paul
authors: P
authors: Gresch
authors: Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235, and.
authors: Douglas G
authors: DG
authors: McMahon
authors: Department of Anesthesiology and Critical Care, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104.
authors: Sheryl G
authors: SG
authors: Beck
authors: Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio 44106, esd@case.edu.
authors: Evan
authors: E
authors: Deneris
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000254:growth & development* / Q000378:metabolism*; D005260:Female; D051379:Mice; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D055495:Neurogenesis / Q000502:physiology; D009924:Organ Culture Techniques; D059326:Serotonergic Neurons / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology*
chemical_list: C484684:Fev protein, mouse; D014157:Transcription Factors
keywords: Pet-1; adrenergic signaling; gene regulatory network; genomics; neuronal maturation; serotonin