title: Increased dopaminergic innervation in the brain of conditional mutant mice overexpressing Otx2: effects on locomotor behavior and seizure susceptibility.
abstract: The homeobox-containing transcription factor Otx2 controls the identity, fate and proliferation of mesencephalic dopaminergic (mesDA) neurons. Transgenic mice, in which Otx2 was conditionally overexpressed by a Cre recombinase expressed under the transcriptional control of the Engrailed1 gene (En1(Cre/+); tOtx2(ov/+)), show an increased number of mesDA neurons during development. In adult mice, Otx2 is expressed in a subset of neurons in the ventral tegmental area (VTA) and its overexpression renders mesDA more resistant to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-HCl (MPTP) neurotoxin. Here we further investigated the neurological consequences of the increased number of mesDA neurons in En1(Cre/+); tOtx2(ov/+) adult mice. Immunohistochemistry for the active, glycosylated form of the dopamine transporter (glyco-Dat) showed that En1(Cre/+); tOtx2(ov/+) adult mice display an increased density of mesocortical DAergic fibers, as compared to control animals. Increased glyco-Dat staining was accompanied by a marked hypolocomotion in En1(Cre/+); tOtx2(ov/+) mice, as detected in the open field test. Since conditional knockout mice lacking Otx2 in mesDA precursors (En1(Cre/+); Otx2(floxv/flox) mice) show a marked resistance to kainic acid (KA)-induced seizures, we investigated the behavioral response to KA in En1(Cre/+); tOtx2(ov/+) and control mice. No difference was observed between mutant and control mice, but En1(Cre/+); tOtx2(ov/+) mice showed a markedly different c-fos mRNA induction profile in the cerebral cortex and hippocampus after KA seizures, as compared to controls. Accordingly, an increased density of parvalbumin (PV)-positive inhibitory interneurons was detected in the deep layers of the frontal cortex of naïve En1(Cre/+); tOtx2(ov/+) mice, as compared to controls. These data indicate that Otx2 overexpression results in increased DAergic innervation and PV cell density in the fronto-parietal cortex, with important consequences on spontaneous locomotor activity and seizure-induced gene expression. Our results strengthen the notion that Otx2 mutant mouse models are a powerful genetic tool to unravel the molecular and behavioral consequences of altered development of the DAergic system.
authors.affiliation: Institute of Neuroscience, CNR, Pisa, Italy; Laboratory of Neurobiology, Scuola Normale Superiore, Pisa, Italy.
authors.forename: P P
authors.initials: PP
authors.lastname: Tripathi
authors.affiliation: Institute of Genetics and Biophysics 'A. Buzzati-Traverso', CNR, Naples, Italy.
authors.forename: L G
authors.initials: LG
authors.lastname: Di Giovannantonio
authors.affiliation: Institute of Neuroscience, CNR, Pisa, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Sanguinetti
authors.affiliation: Institute of Genetics and Biophysics 'A. Buzzati-Traverso', CNR, Naples, Italy; IRCCS Neuromed, 86077 Pozzilli, Isernia, Italy.
authors.forename: D
authors.initials: D
authors.lastname: Acampora
authors.affiliation: Institute of Neuroscience, CNR, Pisa, Italy; Laboratory of Neurobiology, Scuola Normale Superiore, Pisa, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Allegra
authors.affiliation: Institute of Neuroscience, CNR, Pisa, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Caleo
authors.affiliation: Institute of Developmental Genetics, Helmholtz Zentrum and Max-Planck-Institute of Psychiatry, Molecular Neurogenetics, Munich, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Wurst
authors.affiliation: Institute of Genetics and Biophysics 'A. Buzzati-Traverso', CNR, Naples, Italy; IRCCS Neuromed, 86077 Pozzilli, Isernia, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Simeone
authors.affiliation: Institute of Neuroscience, CNR, Pisa, Italy; Laboratory of Molecular Neuropathology, Centre for Integrative Biology, University of Trento, Italy. Electronic address: bozzi@science.unitn.it.
authors.forename: Y
authors.initials: Y
authors.lastname: Bozzi
mesh_terms: D000818:Animals; D001921:Brain / Q000166:cytology* / Q000502:physiology* / Q000503:physiopathology; D002452:Cell Count; D004298:Dopamine / Q000378:metabolism*; D050483:Dopamine Plasma Membrane Transport Proteins / Q000378:metabolism; D059290:Dopaminergic Neurons / Q000502:physiology*; D007608:Kainic Acid; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D008822:Mice, Transgenic; D009043:Motor Activity / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D051857:Otx Transcription Factors / Q000235:genetics / Q000378:metabolism*; D010320:Parvalbumins / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012640:Seizures / Q000503:physiopathology*
chemical_list: D050483:Dopamine Plasma Membrane Transport Proteins; D051857:Otx Transcription Factors; C497660:Otx2 protein, mouse; D010320:Parvalbumins; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D007608:Kainic Acid; D004298:Dopamine
keywords: Otx2; dopamine; epilepsy; hippocampus; limbic system; prefrontal cortex