title: Ascl1 Is Required for the Development of Specific Neuronal Subtypes in the Enteric Nervous System.
abstract: The enteric nervous system (ENS) is organized into neural circuits within the gastrointestinal wall where it controls the peristaltic movements, secretion, and blood flow. Although proper gut function relies on the complex neuronal composition of the ENS, little is known about the transcriptional networks that regulate the diversification into different classes of enteric neurons and glia during development. Here we redefine the role of Ascl1 (Mash1), one of the few regulatory transcription factors described during ENS development. We show that enteric glia and all enteric neuronal subtypes appear to be derived from Ascl1-expressing progenitor cells. In the gut of Ascl1(-/-) mutant mice, neurogenesis is delayed and reduced, and posterior gliogenesis impaired. The ratio of neurons expressing Calbindin, TH, and VIP is selectively decreased while, for instance, 5-HT(+) neurons, which previously were believed to be Ascl1-dependent, are formed in normal numbers. Essentially the same differentiation defects are observed in Ascl1(KINgn2) transgenic mutants, where the proneural activity of Ngn2 replaces Ascl1, demonstrating that Ascl1 is required for the acquisition of specific enteric neuronal subtype features independent of its role in neurogenesis. In this study, we provide novel insights into the expression and function of Ascl1 in the differentiation process of specific neuronal subtypes during ENS development.
  
  
  CONCLUSIONS
  The molecular mechanisms underlying the generation of different neuronal subtypes during development of the enteric nervous system are poorly understood despite its pivotal function in gut motility and involvement in gastrointestinal pathology. This report identifies novel roles for the transcription factor Ascl1 in enteric gliogenesis and neurogenesis. Moreover, independent of its proneurogenic activity, Ascl1 is required for the normal expression of specific enteric neuronal subtype characteristics. Distinct enteric neuronal subtypes are formed in a temporally defined order, and we observe that the early-born 5-HT(+) neurons are generated in Ascl1(-/-) mutants, despite the delayed neurogenesis. Enteric nervous system progenitor cells may therefore possess strong intrinsic control over their specification at the initial waves of neurogenesis.
authors.affiliation: Division of Molecular Neurobiology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-17177 Stockholm, Sweden.
authors.forename: Fatima
authors.identifier: http://orcid.org/0000-0002-8876-1212
authors.initials: F
authors.lastname: Memic
authors.affiliation: Division of Molecular Neurobiology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-17177 Stockholm, Sweden.
authors.forename: Viktoria
authors.initials: V
authors.lastname: Knoflach
authors.affiliation: Division of Molecular Neurobiology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-17177 Stockholm, Sweden.
authors.forename: Rebecca
authors.identifier: http://orcid.org/0000-0002-7727-8129
authors.initials: R
authors.lastname: Sadler
authors.affiliation: Department of Clinical Science, Intervention and Technology, Karolinska University Hospital, Huddinge, Karolinska Institutet, S-17177 Stockholm, Sweden.
authors.forename: Gunilla
authors.initials: G
authors.lastname: Tegerstedt
authors.affiliation: Division of Neurodegeneration, Department of Neurobiology, Care Sciences and Society, Novum, Karolinska Institutet, S-14186 Stockholm, Sweden, Stockholms Sjukhem Foundation, R & D Unit, S-10226 Stockholm, Sweden, and.
authors.forename: Erik
authors.initials: E
authors.lastname: Sundström
authors.affiliation: Francis Crick Institute, Mill Hill Laboratory, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom.
authors.forename: Francois
authors.identifier: http://orcid.org/0000-0003-0432-5067
authors.initials: F
authors.lastname: Guillemot
authors.affiliation: Francis Crick Institute, Mill Hill Laboratory, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom.
authors.forename: Vassilis
authors.initials: V
authors.lastname: Pachnis
authors.affiliation: Division of Molecular Neurobiology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-17177 Stockholm, Sweden, Ulrika.Marklund@ki.se.
authors.forename: Ulrika
authors.identifier: http://orcid.org/0000-0003-1426-1271
authors.initials: U
authors.lastname: Marklund
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000502:physiology*; D064026:Calbindins / Q000378:metabolism; D002454:Cell Differentiation / Q000235:genetics; D017615:Enteric Nervous System / Q000254:growth & development*; D005260:Female; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009154:Mutation / Q000235:genetics; D058953:Neural Stem Cells / Q000502:physiology; D055495:Neurogenesis / Q000235:genetics / Q000502:physiology; D009457:Neuroglia / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D011247:Pregnancy; D059326:Serotonergic Neurons / Q000502:physiology; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D064026:Calbindins; D014446:Tyrosine 3-Monooxygenase; D014660:Vasoactive Intestinal Peptide; C065500:ASCL1 protein, human; C499317:Ascl1 protein, mouse
keywords: differentiation; enteric nervous system; gliogenesis; mutant mice; neurogenesis; transcription factor