title: Testing the evolutionary conservation of vocal motoneurons in vertebrates.
abstract: Medullary motoneurons drive vocalization in many vertebrate lineages including fish, amphibians, birds, and mammals. The developmental history of vocal motoneuron populations in each of these lineages remains largely unknown. The highly conserved transcription factor Paired-like Homeobox 2b (Phox2b) is presumed to be expressed in all vertebrate hindbrain branchial motoneurons, including laryngeal motoneurons essential for vocalization in humans. We used immunohistochemistry and in situ hybridization to examine Phox2b protein and mRNA expression in caudal hindbrain and rostral spinal cord motoneuron populations in seven species across five chordate classes. Phox2b was present in motoneurons dedicated to sound production in mice and frogs (bullfrog, African clawed frog), but not those in bird (zebra finch) or bony fish (midshipman, channel catfish). Overall, the pattern of caudal medullary motoneuron Phox2b expression was conserved across vertebrates and similar to expression in sea lamprey. These observations suggest that motoneurons dedicated to sound production in vertebrates are not derived from a single developmentally or evolutionarily conserved progenitor pool.
authors.affiliation: Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: Jacob
authors.initials: J
authors.lastname: Albersheim-Carter
authors.affiliation: Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Blubaum
authors.affiliation: Department of Biological Sciences, Columbia University, New York, NY 10027, USA; Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Irene H
authors.initials: IH
authors.lastname: Ballagh
authors.affiliation: Department of Exercise Science, Faculté des Sciences, Université du Québec à Montréal, Montréal, Québec H3C 3P8, Canada; Department of Neuroscience, Université de Montréal, Montréal, Québec H3C 3J7, Canada.
authors.forename: Kianoush
authors.initials: K
authors.lastname: Missaghi
authors.affiliation: Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: Edward R
authors.initials: ER
authors.lastname: Siuda
authors.affiliation: Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: George
authors.initials: G
authors.lastname: McMurray
authors.affiliation: Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Andrew H
authors.initials: AH
authors.lastname: Bass
authors.affiliation: Department of Exercise Science, Faculté des Sciences, Université du Québec à Montréal, Montréal, Québec H3C 3P8, Canada; Department of Neuroscience, Université de Montréal, Montréal, Québec H3C 3J7, Canada.
authors.forename: Réjean
authors.initials: R
authors.lastname: Dubuc
authors.affiliation: Department of Biological Sciences, Columbia University, New York, NY 10027, USA.
authors.forename: Darcy B
authors.initials: DB
authors.lastname: Kelley
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Marc F
authors.initials: MF
authors.lastname: Schmidt
authors.affiliation: Hotchkiss Brain Institute and ACH Research Institute, Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta T2N4N1, Canada.
authors.forename: Richard J A
authors.initials: RJ
authors.lastname: Wilson
authors.affiliation: Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110, USA. Electronic address: pgray@mac.com.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Gray
mesh_terms: D000818:Animals; D005075:Biological Evolution; D009046:Motor Neurons / Q000502:physiology*; D014714:Vertebrates / Q000502:physiology*; D014828:Vocalization, Animal / Q000502:physiology*
keywords: Hypoglossal; Lamprey; Midshipman; Respiration; Vocalization; Zebra Finch