title: Lmx1b is required for the glutamatergic fates of a subset of spinal cord neurons.
abstract: Alterations in neurotransmitter phenotypes of specific neurons can cause imbalances in excitation and inhibition in the central nervous system (CNS), leading to diseases. Therefore, the correct specification and maintenance of neurotransmitter phenotypes is vital. As with other neuronal properties, neurotransmitter phenotypes are often specified and maintained by particular transcription factors. However, the specific molecular mechanisms and transcription factors that regulate neurotransmitter phenotypes remain largely unknown.
  
  
  
  In this paper we use single mutant, double mutant and transgenic zebrafish embryos to elucidate the functions of Lmx1ba and Lmx1bb in the regulation of spinal cord interneuron neurotransmitter phenotypes.
  
  
  
  We demonstrate that lmx1ba and lmx1bb are both expressed in zebrafish spinal cord and that lmx1bb is expressed by both V0v cells and dI5 cells. Our functional analyses demonstrate that these transcription factors are not required for neurotransmitter fate specification at early stages of development, but that in embryos with at least two lmx1ba and/or lmx1bb mutant alleles there is a reduced number of excitatory (glutamatergic) spinal interneurons at later stages of development. In contrast, there is no change in the numbers of V0v or dI5 cells. These data suggest that lmx1b-expressing spinal neurons still form normally, but at least a subset of them lose, or do not form, their normal excitatory fates. As the reduction in glutamatergic cells is only seen at later stages of development, Lmx1b is probably required either for the maintenance of glutamatergic fates or to specify glutamatergic phenotypes of a subset of later forming neurons. Using double labeling experiments, we also show that at least some of the cells that lose their normal glutamatergic phenotype are V0v cells. Finally, we also establish that Evx1 and Evx2, two transcription factors that are required for V0v cells to acquire their excitatory neurotransmitter phenotype, are also required for lmx1ba and lmx1bb expression in these cells, suggesting that Lmx1ba and Lmx1bb act downstream of Evx1 and Evx2 in V0v cells.
  
  
  
  Lmx1ba and Lmx1bb function at least partially redundantly in the spinal cord and three functional lmx1b alleles are required in zebrafish for correct numbers of excitatory spinal interneurons at later developmental stages. Taken together, our data significantly enhance our understanding of how spinal cord neurotransmitter fates are regulated.
authors.affiliation: Department of Biology, Syracuse University, 107 College Place, Syracuse, NY, 13244, USA.|Department of Neuroscience and Physiology, SUNY Upstate Medical University, 505 Irving Avenue, Syracuse, NY, 13210, USA.
authors.forename: William C
authors.initials: WC
authors.lastname: Hilinski
authors.affiliation: Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI, 53226, USA.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Bostrom
authors.affiliation: Department of Biology, Syracuse University, 107 College Place, Syracuse, NY, 13244, USA.
authors.forename: Samantha J
authors.initials: SJ
authors.lastname: England
authors.affiliation: Department of Biology, Syracuse University, 107 College Place, Syracuse, NY, 13244, USA.
authors.forename: José L
authors.initials: JL
authors.lastname: Juárez-Morales
authors.affiliation: Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3DY, UK.
authors.forename: Sarah
authors.initials: S
authors.lastname: de Jager
authors.affiliation: Institute of Toxicology and Genetics, Karlsruhe Institute of Technology (KIT), Postfach 3640, 76021, Karlsruhe, Germany.
authors.forename: Olivier
authors.initials: O
authors.lastname: Armant
authors.affiliation: Institute of Toxicology and Genetics, Karlsruhe Institute of Technology (KIT), Postfach 3640, 76021, Karlsruhe, Germany.
authors.forename: Jessica
authors.initials: J
authors.lastname: Legradi
authors.affiliation: Institute of Toxicology and Genetics, Karlsruhe Institute of Technology (KIT), Postfach 3640, 76021, Karlsruhe, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Strähle
authors.affiliation: Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI, 53226, USA.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Link
authors.affiliation: Department of Biology, Syracuse University, 107 College Place, Syracuse, NY, 13244, USA. kelewi02@syr.edu.
authors.forename: Katharine E
authors.initials: KE
authors.lastname: Lewis
mesh_terms: D000818:Animals; D016923:Cell Death; D018698:Glutamic Acid / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000378:metabolism; D007395:Interneurons / Q000378:metabolism*; D010641:Phenotype; D013116:Spinal Cord / Q000254:growth & development* / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D050599:Vesicular Glutamate Transport Protein 2 / Q000378:metabolism; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology
chemical_list: C484089:Evx2 protein, zebrafish; D018398:Homeodomain Proteins; D014157:Transcription Factors; D050599:Vesicular Glutamate Transport Protein 2; D029961:Zebrafish Proteins; C425331:evx1 protein, zebrafish; C543330:lmx1bb protein, zebrafish; D018698:Glutamic Acid
keywords: CNS; Excitatory; Interneuron; Lmx1b; Neurotransmitter; Spinal cord; Transcription factor; V0v; Zebrafish; dI5