title: MicroRNA-9 promotes the switch from early-born to late-born motor neuron populations by regulating Onecut transcription factor expression.
abstract: Motor neurons in the vertebrate spinal cord are stereotypically organized along the rostro-caudal axis in discrete columns that specifically innervate peripheral muscle domains. Originating from the same progenitor domain, the generation of spinal motor neurons is orchestrated by a spatially and temporally tightly regulated set of secreted molecules and transcription factors such as retinoic acid and the Lim homeodomain transcription factors Isl1 and Lhx1. However, the molecular interactions between these factors remained unclear. In this study we examined the role of the microRNA 9 (miR-9) in the specification of spinal motor neurons and identified Onecut1 (OC1) as one of its targets. miR-9 and OC1 are expressed in mutually exclusive patterns in the developing chick spinal cord, with high OC1 levels in early-born motor neurons and high miR-9 levels in late-born motor neurons. miR-9 efficiently represses OC1 expression in vitro and in vivo. Overexpression of miR-9 leads to an increase in late-born neurons, while miR-9 loss-of-function induces additional OC1(+) motor neurons that display a transcriptional profile typical of early-born neurons. These results demonstrate that regulation of OC1 by miR-9 is a crucial step in the specification of spinal motor neurons and support a model in which miR-9 expression in late-born LMCl neurons downregulates Isl1 expression through inhibition of OC1. In conclusion, our study contributes essential factors to the molecular network specifying spinal motor neurons and emphasizes the importance of microRNAs as key players in the generation of neuronal diversity.
authors.affiliation: Institute of Developmental Genetics, Helmholtz Zentrum München - German Research Center for Environmental Health, Ingolstaedter Landstr. 1, 85764 Neuherberg, Germany.
authors.forename: Georg
authors.initials: G
authors.lastname: Luxenhofer
authors.affiliation: Institute of Developmental Genetics, Helmholtz Zentrum München - German Research Center for Environmental Health, Ingolstaedter Landstr. 1, 85764 Neuherberg, Germany. Electronic address: michaela.helmbrecht@helmholtz-muenchen.de.
authors.forename: Michaela S
authors.initials: MS
authors.lastname: Helmbrecht
authors.affiliation: Institute of Developmental Genetics, Helmholtz Zentrum München - German Research Center for Environmental Health, Ingolstaedter Landstr. 1, 85764 Neuherberg, Germany.
authors.forename: Jana
authors.initials: J
authors.lastname: Langhoff
authors.affiliation: Max Planck Institute of Psychiatry, Kraepelinstr. 2-10, 80804 Munich, Germany.
authors.forename: Sebastian A
authors.initials: SA
authors.lastname: Giusti
authors.affiliation: Max Planck Institute of Psychiatry, Kraepelinstr. 2-10, 80804 Munich, Germany.
authors.forename: Damian
authors.initials: D
authors.lastname: Refojo
authors.affiliation: Institute of Developmental Genetics, Helmholtz Zentrum München - German Research Center for Environmental Health, Ingolstaedter Landstr. 1, 85764 Neuherberg, Germany. Electronic address: andrea.huber@helmholtz-muenchen.de.
authors.forename: Andrea B
authors.initials: AB
authors.lastname: Huber
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001483:Base Sequence; D002642:Chick Embryo; D018274:Electroporation; D005453:Fluorescence; D018507:Gene Expression Regulation, Developmental / Q000235:genetics / Q000502:physiology*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008156:Luciferases; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009046:Motor Neurons / Q000378:metabolism / Q000502:physiology*; D051558:Onecut Transcription Factors / Q000235:genetics / Q000378:metabolism*; D013116:Spinal Cord / Q000196:embryology*
chemical_list: D035683:MicroRNAs; D051558:Onecut Transcription Factors; D008156:Luciferases
keywords: MicroRNA-9; Motor neuron development; Onecut