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Altbürger C, Rath M, Wehrle J, Driever W. The proneural factors Ascl1a and Ascl1b contribute to the terminal differentiation of dopaminergic GABAergic dual transmitter neurons in zebrafish. Dev Biol 2024; 505:58-74. [PMID: 37931393 DOI: 10.1016/j.ydbio.2023.10.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Revised: 10/06/2023] [Accepted: 10/23/2023] [Indexed: 11/08/2023]
Abstract
The proneural factor Ascl1 is involved in several steps of neurogenesis, from neural progenitor maintenance to initiation of terminal differentiation and neuronal subtype specification. In neural progenitor cells, Ascl1 initiates the cell-cycle exit of progenitors, and contributes to their differentiation into mainly GABAergic neurons. Several catecholaminergic neuron groups in the forebrain of zebrafish use GABA as co-transmitter, but a potential role of the two paralogues Ascl1a and Ascl1b in their neurogenesis is not understood. Here, we show that ascl1a, ascl1b double mutant embryos develop a significantly reduced number of neurons in all GABAergic and catecholaminergic dual transmitter neuron anatomical clusters in the fore- and hindbrain, while glutamatergic catecholaminergic clusters develop normally. However, none of the affected catecholaminergic cell clusters are lost completely, suggesting an impairment in progenitor pools, or a requirement of Ascl1a/b for differentiation of a subset of neurons in each cluster. Early progenitors which are dlx2a+, fezf2 + or emx2 + are not reduced whereas late progenitors and differentiating neurons marked by the expression of dlx5a, isl1 and arxa are severely reduced in ascl1a, ascl1b double mutant embryos. This suggests that Ascl1a and Ascl1b play only a minor or no role in the maintenance of their progenitor pools, but rather contribute to the initiation of terminal differentiation of GABAergic catecholaminergic neurons.
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Affiliation(s)
- Christian Altbürger
- Department of Developmental Biology, Faculty of Biology, Institute Biology 1, Albert Ludwigs University, Freiburg, Hauptstrasse 1, 79104, Freiburg, Germany; CIBSS and BIOSS - Centres for Biological Signalling Studies, University of Freiburg, Schänzlestrasse 18, 79104, Freiburg, Germany
| | - Meta Rath
- Department of Developmental Biology, Faculty of Biology, Institute Biology 1, Albert Ludwigs University, Freiburg, Hauptstrasse 1, 79104, Freiburg, Germany
| | - Johanna Wehrle
- Department of Developmental Biology, Faculty of Biology, Institute Biology 1, Albert Ludwigs University, Freiburg, Hauptstrasse 1, 79104, Freiburg, Germany; MeInBio Research Training Group, University of Freiburg, 79104, Freiburg, Germany
| | - Wolfgang Driever
- Department of Developmental Biology, Faculty of Biology, Institute Biology 1, Albert Ludwigs University, Freiburg, Hauptstrasse 1, 79104, Freiburg, Germany; CIBSS and BIOSS - Centres for Biological Signalling Studies, University of Freiburg, Schänzlestrasse 18, 79104, Freiburg, Germany.
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2
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Coltogirone RA, Sherfinski EI, Dobler ZA, Peterson SN, Andlinger AR, Fadel LC, Patrick RL, Bergeron SA. Gsx2, but not Gsx1, is necessary for early forebrain patterning and long-term survival in zebrafish. Dev Dyn 2023; 252:377-399. [PMID: 36184733 PMCID: PMC9992111 DOI: 10.1002/dvdy.542] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Revised: 07/23/2022] [Accepted: 08/10/2022] [Indexed: 11/11/2022] Open
Abstract
BACKGROUND Homeobox transcription factor encoding genes, genomic screen homeobox 1 and 2 (gsx1 and gsx2), are expressed during neurodevelopment in multiple vertebrates. However, we have limited knowledge of the dynamic expression of these genes through developmental time and the gene networks that they regulate in zebrafish. RESULTS We confirmed that gsx1 is expressed initially in the hindbrain and diencephalon and later in the optic tectum, pretectum, and cerebellar plate. gsx2 is expressed in the early telencephalon and later in the pallium and olfactory bulb. gsx1 and gsx2 are co-expressed in the hypothalamus, preoptic area, and hindbrain, however, rarely co-localize in the same cells. gsx1 and gsx2 mutant zebrafish were made with TALENs. gsx1 mutants exhibit stunted growth, however, they survive to adulthood and are fertile. gsx2 mutants experience swim bladder inflation failure that prevents survival. We also observed significantly reduced expression of multiple forebrain patterning distal-less homeobox genes in mutants, and expression of foxp2 was not significantly affected. CONCLUSIONS This work provides novel tools with which other target genes and functions of Gsx1 and Gsx2 can be characterized across the central nervous system to better understand the unique and overlapping roles of these highly conserved transcription factors.
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Affiliation(s)
| | - Emma I. Sherfinski
- Department of Biology, West Virginia University, Morgantown, West, Virginia, USA
| | - Zoë A. Dobler
- Department of Biology, West Virginia University, Morgantown, West, Virginia, USA
| | - Sarah N. Peterson
- Department of Biology, West Virginia University, Morgantown, West, Virginia, USA
| | | | - Lindsay C. Fadel
- Department of Biology, West Virginia University, Morgantown, West, Virginia, USA
| | - Regina L. Patrick
- Department of Biology, West Virginia University, Morgantown, West, Virginia, USA
| | - Sadie A. Bergeron
- Department of Biology, West Virginia University, Morgantown, West, Virginia, USA
- Department of Neuroscience, West Virginia University, Morgantown, West, Virginia, USA
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3
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Wang R, Guo S, Yang L. Tal2 is required for generation of GABAergic neurons in the zebrafish midbrain. Dev Dyn 2023; 252:263-275. [PMID: 36063149 DOI: 10.1002/dvdy.534] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Revised: 08/22/2022] [Accepted: 08/28/2022] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND In the zebrafish midbrain, GABAergic neurons develop from precursors located in the nucleus of the medial longitudinal fasciculus (nMLF). However, the precise mechanisms that underline generation of the nMLF GABAergic neuron are poorly understood. RESULTS GABAergic neurons in the nMLF co-express transcription factors tal2, gata2a, gata3, and nkx1.2lb. The Nodal-related gene and shh signaling are required for differentiation of nMLF GABAergic neuron precursors. Tal2 is important for nMLF GABAergic neurogenesis. Disruption of Tal2, embryos completely lack the GABA-synthesizing enzyme glutamic acid decarboxylase 67 gene (gad67) expressing cells in the nMLF, and the whole nkx1.2lb expressing cells in the midbrain. Although almost all tal2-expressing cells in the diencephalon and/or nMLF are gata2a- and gata3-positive, simultaneous knockdown of gata2a and gata3 does not affect either tal2 or gad67 expression. CONCLUSIONS In the zebrafish midbrain, expression of tal2, gata2a, and/or gata3 is independent of each other. The function of gata2a and gata3 is dispensable for generation of GABAergic neuron in the nMLF. This suggests that the functional connections of the regulatory genes leading to generation of nMLF GABAergic neurons have diverged between mouse and zebrafish.
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Affiliation(s)
- Ruihong Wang
- State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, China
| | - Shaojuan Guo
- State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, China
| | - Lixin Yang
- State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, China
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4
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Leung RF, George AM, Roussel EM, Faux MC, Wigle JT, Eisenstat DD. Genetic Regulation of Vertebrate Forebrain Development by Homeobox Genes. Front Neurosci 2022; 16:843794. [PMID: 35546872 PMCID: PMC9081933 DOI: 10.3389/fnins.2022.843794] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Accepted: 03/14/2022] [Indexed: 01/19/2023] Open
Abstract
Forebrain development in vertebrates is regulated by transcription factors encoded by homeobox, bHLH and forkhead gene families throughout the progressive and overlapping stages of neural induction and patterning, regional specification and generation of neurons and glia from central nervous system (CNS) progenitor cells. Moreover, cell fate decisions, differentiation and migration of these committed CNS progenitors are controlled by the gene regulatory networks that are regulated by various homeodomain-containing transcription factors, including but not limited to those of the Pax (paired), Nkx, Otx (orthodenticle), Gsx/Gsh (genetic screened), and Dlx (distal-less) homeobox gene families. This comprehensive review outlines the integral role of key homeobox transcription factors and their target genes on forebrain development, focused primarily on the telencephalon. Furthermore, links of these transcription factors to human diseases, such as neurodevelopmental disorders and brain tumors are provided.
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Affiliation(s)
- Ryan F. Leung
- Murdoch Children’s Research Institute, The Royal Children’s Hospital Melbourne, Parkville, VIC, Australia
- Department of Paediatrics, University of Melbourne, Parkville, VIC, Australia
| | - Ankita M. George
- Murdoch Children’s Research Institute, The Royal Children’s Hospital Melbourne, Parkville, VIC, Australia
| | - Enola M. Roussel
- Murdoch Children’s Research Institute, The Royal Children’s Hospital Melbourne, Parkville, VIC, Australia
| | - Maree C. Faux
- Murdoch Children’s Research Institute, The Royal Children’s Hospital Melbourne, Parkville, VIC, Australia
- Department of Paediatrics, University of Melbourne, Parkville, VIC, Australia
- Department of Surgery, Royal Melbourne Hospital, The University of Melbourne, Parkville, VIC, Australia
| | - Jeffrey T. Wigle
- Department of Biochemistry and Medical Genetics, Max Rady College of Medicine, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, MB, Canada
- Institute of Cardiovascular Sciences, St. Boniface Hospital Albrechtsen Research Centre, Winnipeg, MB, Canada
| | - David D. Eisenstat
- Murdoch Children’s Research Institute, The Royal Children’s Hospital Melbourne, Parkville, VIC, Australia
- Department of Paediatrics, University of Melbourne, Parkville, VIC, Australia
- Department of Medical Genetics, University of Alberta, Edmonton, AB, Canada
- Department of Pediatrics, University of Alberta, Edmonton, AB, Canada
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5
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Yu EPY, Perin S, Saxena V, Ekker M. Novel cross-regulation interactions between dlx genes in larval zebrafish. Gene 2021; 801:145848. [PMID: 34293450 DOI: 10.1016/j.gene.2021.145848] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Accepted: 07/13/2021] [Indexed: 11/19/2022]
Abstract
The homeodomain-containing transcription factors dlx1a, dlx2a, dlx5a and dlx6a are expressed in the zebrafish brain in overlapping patterns and are important in vertebrate development. Previous work in mice have suggested the overlapping expression pattern is in part due to cross-regulatory interactions among the aforementioned dlx genes. However, the extent of these interactions and whether they are conserved among vertebrates remains to be determined. Through whole-mount in situ hybridization in zebrafish dlx mutants produced by CRISPR-Cas9 mutagenesis, cross-regulatory interactions between dlx1a, dlx2a, dlx5a and dlx6a were examined from 24 to 72 h post fertilization (hpf). Notably, and different from previous work done in mouse, zebrafish dlx2a-/- mutants continue to express dlx5a until 72hpf, whereas deletion of both enhancers within the dlx5a/dlx6a locus resulted in delayed dlx5a/dlx6a expression and relative increased dlx2a expression. These results suggest alternative regulatory elements and pathways exist to mediate dlx expression in zebrafish and may highlight evolutionary differences in gene interactions between vertebrates.
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Affiliation(s)
- Emily P Y Yu
- Department of Biology, University of Ottawa, Marie-Curie Private, Ottawa, ON K1N9A4, Canada
| | - Sofia Perin
- Department of Biology, University of Ottawa, Marie-Curie Private, Ottawa, ON K1N9A4, Canada
| | - Vishal Saxena
- Department of Biology, University of Ottawa, Marie-Curie Private, Ottawa, ON K1N9A4, Canada
| | - Marc Ekker
- Department of Biology, University of Ottawa, Marie-Curie Private, Ottawa, ON K1N9A4, Canada.
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6
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Puelles L, Diaz C, Stühmer T, Ferran JL, Martínez‐de la Torre M, Rubenstein JLR. LacZ-reporter mapping of Dlx5/6 expression and genoarchitectural analysis of the postnatal mouse prethalamus. J Comp Neurol 2021; 529:367-420. [PMID: 32420617 PMCID: PMC7671952 DOI: 10.1002/cne.24952] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2019] [Revised: 05/10/2020] [Accepted: 05/11/2020] [Indexed: 12/22/2022]
Abstract
We present here a thorough and complete analysis of mouse P0-P140 prethalamic histogenetic subdivisions and corresponding nuclear derivatives, in the context of local tract landmarks. The study used as fundamental material brains from a transgenic mouse line that expresses LacZ under the control of an intragenic enhancer of Dlx5 and Dlx6 (Dlx5/6-LacZ). Subtle shadings of LacZ signal, jointly with pan-DLX immunoreaction, and several other ancillary protein or RNA markers, including Calb2 and Nkx2.2 ISH (for the prethalamic eminence, and derivatives of the rostral zona limitans shell domain, respectively) were mapped across the prethalamus. The resulting model of the prethalamic region postulates tetrapartite rostrocaudal and dorsoventral subdivisions, as well as a tripartite radial stratification, each cell population showing a characteristic molecular profile. Some novel nuclei are proposed, and some instances of potential tangential cell migration were noted.
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Affiliation(s)
- Luis Puelles
- Department of Human Anatomy and Psychobiology and IMIB‐Arrixaca InstituteUniversity of MurciaMurciaSpain
| | - Carmen Diaz
- Department of Medical Sciences, School of Medicine and Institute for Research in Neurological DisabilitiesUniversity of Castilla‐La ManchaAlbaceteSpain
| | - Thorsten Stühmer
- Nina Ireland Laboratory of Developmental Neurobiology, Department of PsychiatryUCSF Medical SchoolSan FranciscoCaliforniaUSA
| | - José L. Ferran
- Department of Human Anatomy and Psychobiology and IMIB‐Arrixaca InstituteUniversity of MurciaMurciaSpain
| | | | - John L. R. Rubenstein
- Nina Ireland Laboratory of Developmental Neurobiology, Department of PsychiatryUCSF Medical SchoolSan FranciscoCaliforniaUSA
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7
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Weinschutz Mendes H, Taktek M, Duret T, Ekker M. Expression of dlx genes in the normal and regenerating brain of adult zebrafish. PLoS One 2020; 15:e0229549. [PMID: 32497078 PMCID: PMC7272068 DOI: 10.1371/journal.pone.0229549] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Accepted: 05/16/2020] [Indexed: 12/12/2022] Open
Abstract
Dysfunctions in the GABAergic system lead to various pathological conditions and impaired inhibitory function is one of the causes behind neuropathies characterized by neuronal hyper excitability. The Dlx homeobox genes are involved in the development of nervous system, neural crest, branchial arches and developing appendages. Dlx genes also take part in neuronal migration and differentiation during development, more precisely, in the migration and differentiation of GABAergic neurons. Functional analysis of dlx genes has mainly been carried out in developing zebrafish embryos and larvae, however information regarding the expression and roles of these genes in the adult zebrafish brain is still lacking. The extensive neurogenesis that takes place in the adult zebrafish brain, makes them a good model for the visualization of mechanisms involving dlx genes during adulthood in physiological conditions and during regeneration of the nervous system. We have identified the adult brain regions where transcripts of dlx1a, dlx2a, dlx5a and dlx6a genes are normally found and have confirmed that within telencephalic domains, there is high overlapping expression of the four dlx paralogs with a marker for GABAergic neurons. Co-localization analyses carried with the Tg(dlx6a-1.4kbdlx5a/dlx6a:GFP) reporter line have also shown that in some areas of the diencephalon, cells expressing the dlx5a/6a bigene may have a neural stem cell identity. Furthermore, investigations in a response to stab wound lesions, have demonstrated a possible participation of the dlx5a/6a bigene, most likely of dlx5a, during regeneration of the adult zebrafish brain. These observations suggest a possible participation of dlx-expressing cells during brain regeneration in adult zebrafish and also provide information on the role of dlx genes under normal physiological conditions in adults.
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Affiliation(s)
| | - Mariam Taktek
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - Thomas Duret
- Faculté des Sciences Fondamentales et Appliquées, Université de Poitiers, Poitiers, France
| | - Marc Ekker
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
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8
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Chan S, Shen D, Sang Y, Wang S, Wang Y, Chen C, Gao B, Song C. Development of enhancer-trapping and -detection vectors mediated by the Tol2 transposon in zebrafish. PeerJ 2019; 7:e6862. [PMID: 31106068 PMCID: PMC6499061 DOI: 10.7717/peerj.6862] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2018] [Accepted: 03/28/2019] [Indexed: 01/02/2023] Open
Abstract
Enhancers are key transcriptional drivers of gene expression. The identification of enhancers in the genome is central for understanding gene-expression programs. Although transposon-mediated enhancer trapping (ET) is a powerful approach to the identification of enhancers in zebrafish, its efficiency varies considerably. To improve the ET efficiency, we constructed Tol2-mediated ET vectors with a reporter gene (mCherry) expression box driven by four minimal promoters (Gata, Myc, Krt4 and Oct4), respectively. The ET efficiency and expression background were compared among the four promoters by zebrafish embryo injection at the one-cell stage. The results showed that the Gata minimal promoter yielded the lowest basic expression and the second-highest trapping efficiency (44.6% at 12 hpf (hour post-fertilization) and 23.1% at 72 hpf, n = 305 and n = 307). The Krt4 promoter had the highest trapping efficiency (64% at 12 hpf and 67.1% at 72 hpf, n = 302 and n = 301) and the strongest basic expression. To detect enhancer activity, chicken 5′HS4 double insulators were cloned into the two ET vectors with the Gata or Krt4 minimal promoter, flanking the mCherry expression box. The resulting detection vectors were injected into zebrafish embryos. mCherry expression driven by the Gata promoter (about 5%, n = 301) was decreased significantly compared with that observed for embryos injected with the ET vectors (23% at 72 hpf, n = 308). These results suggest that the insulators block the genome-position effects and that this vector is fit for enhancer-activity evaluation. To assess the compatibility between the enhancers and the minimal promoters, four enhancers (CNS1, Z48, Hand2 and Hs769) were cloned upstream of the Gata or Beta-globin minimal promoter in the enhancer-activity-detection vectors. The resulting recombinant vectors were assayed by zebrafish embryo injection. We found that Z48 and CNS1 responded to the Gata minimal promoter, and that Hand2 only responded to the Beta-globin minimal promoter. In contrast, Hs769 did not respond to either the Gata or Beta-globin minimal promoters. These results suggest the existence of compatibility between enhancers and minimal promoters. This study represents a systematic approach to the discovery of optional ET and enhancer-detection vectors. We are eager to provide a superior tool for understanding functional genomics.
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Affiliation(s)
- Shuheng Chan
- Yangzhou University, Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou, Jiangsu, China
| | - Dan Shen
- Yangzhou University, Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou, Jiangsu, China
| | - Yatong Sang
- Yangzhou University, Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou, Jiangsu, China
| | - Saisai Wang
- Yangzhou University, Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou, Jiangsu, China
| | - Yali Wang
- Yangzhou University, Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou, Jiangsu, China
| | - Cai Chen
- Yangzhou University, Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou, Jiangsu, China
| | - Bo Gao
- Yangzhou University, Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou, Jiangsu, China
| | - Chengyi Song
- Yangzhou University, Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou, Jiangsu, China
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9
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Narboux-Neme N, Ekker M, Levi G, Heude E. Posterior axis formation requires Dlx5/Dlx6 expression at the neural plate border. PLoS One 2019; 14:e0214063. [PMID: 30889190 PMCID: PMC6424422 DOI: 10.1371/journal.pone.0214063] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2019] [Accepted: 03/06/2019] [Indexed: 11/18/2022] Open
Abstract
Neural tube defects (NTDs), one of the most common birth defects in human, present a multifactorial etiology with a poorly defined genetic component. The Dlx5 and Dlx6 bigenic cluster encodes two evolutionary conserved homeodomain transcription factors, which are necessary for proper vertebrate development. It has been shown that Dlx5/6 genes are essential for anterior neural tube closure, however their role in the formation of the posterior structures has never been described. Here, we show that Dlx5/6 expression is required during vertebrate posterior axis formation. Dlx5 presents a similar expression pattern in neural plate border cells during posterior neurulation of zebrafish and mouse. Dlx5/6-inactivation in the mouse results in a phenotype reminiscent of NTDs characterized by open thoracic and lumbar vertebral arches and failure of epaxial muscle formation at the dorsal midline. The dlx5a/6a zebrafish morphants present posterior NTDs associated with abnormal delamination of neural crest cells showing altered expression of cell adhesion molecules and defects of motoneuronal development. Our findings provide new molecular leads to decipher the mechanisms of vertebrate posterior neurulation and might help to gather a better understanding of human congenital NTDs etiology.
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Affiliation(s)
- Nicolas Narboux-Neme
- Département Adaptations du Vivant, Centre National de la Recherche Scientifique UMR 7221, Muséum National d’Histoire Naturelle, Paris, France
| | - Marc Ekker
- Department of Biology, Centre for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, Ontario, Canada
| | - Giovanni Levi
- Département Adaptations du Vivant, Centre National de la Recherche Scientifique UMR 7221, Muséum National d’Histoire Naturelle, Paris, France
| | - Eglantine Heude
- Département Adaptations du Vivant, Centre National de la Recherche Scientifique UMR 7221, Muséum National d’Histoire Naturelle, Paris, France
- * E-mail:
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10
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Newman EA, Wu D, Taketo MM, Zhang J, Blackshaw S. Canonical Wnt signaling regulates patterning, differentiation and nucleogenesis in mouse hypothalamus and prethalamus. Dev Biol 2018; 442:236-248. [PMID: 30063881 DOI: 10.1016/j.ydbio.2018.07.021] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Revised: 07/26/2018] [Accepted: 07/26/2018] [Indexed: 01/10/2023]
Abstract
The hypothalamus is a small, but anatomically and functionally complex region of the brain whose development is poorly understood. In this study, we have explored its development by studying the canonical Wnt signaling pathway, generating gain and loss of function mutations of beta-catenin (Ctnnb1) in both hypothalamic and prethalamic neuroepithelium. Deletion of Ctnnb1 resulted in an anteriorized and hypoplastic hypothalamus. Posterior structures were lost or reduced, and anterior structures were expanded. In contrast, overexpression of a constitutively active mutant form of Ctnnb1 resulted in severe hyperplasia of prethalamus and hypothalamus, and expanded expression of a subset of posterior and premamillary hypothalamic markers. Moderate defects in differentiation of Arx-positive GABAergic neural precursors were observed in both prethalamus and hypothalamus of Ctnnb1 loss of function mutants, while in gain of function mutants, their differentiation was completely suppressed, although markers of prethalamic progenitors were preserved. Multiple other region-specific markers, including several specific posterior hypothalamic structures, were also suppressed in Ctnnb1 gain of function mutations. Severe, region-specific defects in hypothalamic nucleogenesis were also observed in both gain and loss of function mutations of Ctnnb1. Finally, both gain and loss of function of Ctnnb1 also produced severe, non-cell autonomous disruptions of pituitary development. These findings demonstrate a central and multifaceted role for canonical Wnt signaling in regulating growth, patterning, differentiation and nucleogenesis in multiple diencephalic regions.
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Affiliation(s)
- Elizabeth A Newman
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Dan Wu
- Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Makoto Mark Taketo
- Division of Experimental Therapeutics, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Jiangyang Zhang
- Department of Radiology, NYU Langone School of Medicine, New York, NY, USA
| | - Seth Blackshaw
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, USA; Department of Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, MD, USA; Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA; Center for Human Systems Biology, Johns Hopkins University School of Medicine, Baltimore, MD, USA; Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
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11
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Silva N, Louro B, Trindade M, Power DM, Campinho MA. Transcriptomics reveal an integrative role for maternal thyroid hormones during zebrafish embryogenesis. Sci Rep 2017; 7:16657. [PMID: 29192226 PMCID: PMC5709499 DOI: 10.1038/s41598-017-16951-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2017] [Accepted: 11/20/2017] [Indexed: 02/06/2023] Open
Abstract
Thyroid hormones (THs) are essential for embryonic brain development but the genetic mechanisms involved in the action of maternal THs (MTHs) are still largely unknown. As the basis for understanding the underlying genetic mechanisms of MTHs regulation we used an established zebrafish monocarboxylic acid transporter 8 (MCT8) knock-down model and characterised the transcriptome in 25hpf zebrafish embryos. Subsequent mapping of differentially expressed genes using Reactome pathway analysis together with in situ expression analysis and immunohistochemistry revealed the genetic networks and cells under MTHs regulation during zebrafish embryogenesis. We found 4,343 differentially expressed genes and the Reactome pathway analysis revealed that TH is involved in 1681 of these pathways. MTHs regulated the expression of core developmental pathways, such as NOTCH and WNT in a cell specific context. The cellular distribution of neural MTH-target genes demonstrated their cell specific action on neural stem cells and differentiated neuron classes. Taken together our data show that MTHs have a role in zebrafish neurogenesis and suggest they may be involved in cross talk between key pathways in neural development. Given that the observed MCT8 zebrafish knockdown phenotype resembles the symptoms in human patients with Allan-Herndon-Dudley syndrome our data open a window into understanding the genetics of this human congenital condition.
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Affiliation(s)
- Nadia Silva
- Comparative Endocrinology and Integrative Biology Group, Centre for Marine Sciences (CCMAR), Universidade do Algarve, Faro, Portugal
| | - Bruno Louro
- Comparative Endocrinology and Integrative Biology Group, Centre for Marine Sciences (CCMAR), Universidade do Algarve, Faro, Portugal
| | - Marlene Trindade
- Comparative Endocrinology and Integrative Biology Group, Centre for Marine Sciences (CCMAR), Universidade do Algarve, Faro, Portugal
| | - Deborah M Power
- Comparative Endocrinology and Integrative Biology Group, Centre for Marine Sciences (CCMAR), Universidade do Algarve, Faro, Portugal
| | - Marco A Campinho
- Comparative Endocrinology and Integrative Biology Group, Centre for Marine Sciences (CCMAR), Universidade do Algarve, Faro, Portugal.
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12
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GABAergic Interneuron Differentiation in the Basal Forebrain Is Mediated through Direct Regulation of Glutamic Acid Decarboxylase Isoforms by Dlx Homeobox Transcription Factors. J Neurosci 2017; 37:8816-8829. [PMID: 28821666 DOI: 10.1523/jneurosci.2125-16.2017] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2016] [Revised: 06/25/2017] [Accepted: 08/03/2017] [Indexed: 01/09/2023] Open
Abstract
GABA is the key inhibitory neurotransmitter in the cortex but regulation of its synthesis during forebrain development is poorly understood. In the telencephalon, members of the distal-less (Dlx) homeobox gene family are expressed in, and regulate the development of, the basal ganglia primodia from which many GABAergic neurons originate and migrate to other forebrain regions. The Dlx1/Dlx2 double knock-out mice die at birth with abnormal cortical development, including loss of tangential migration of GABAergic inhibitory interneurons to the neocortex (Anderson et al., 1997a). We have discovered that specific promoter regulatory elements of glutamic acid decarboxylase isoforms (Gad1 and Gad2), which regulate GABA synthesis from the excitatory neurotransmitter glutamate, are direct transcriptional targets of both DLX1 and DLX2 homeoproteins in vivo Further gain- and loss-of-function studies in vitro and in vivo demonstrated that both DLX1 and DLX2 are necessary and sufficient for Gad gene expression. DLX1 and/or DLX2 activated the transcription of both Gad genes, and defects in Dlx function disrupted the differentiation of GABAergic interneurons with global reduction in GABA levels in the forebrains of the Dlx1/Dlx2 double knock-out mouse in vivo Identification of Gad genes as direct Dlx transcriptional targets is significant; it extends our understanding of Dlx gene function in the developing forebrain beyond the regulation of tangential interneuron migration to the differentiation of GABAergic interneurons arising from the basal telencephalon, and may help to unravel the pathogenesis of several developmental brain disorders.SIGNIFICANCE STATEMENT GABA is the major inhibitory neurotransmitter in the brain. We show that Dlx1/Dlx2 homeobox genes regulate GABA synthesis during forebrain development through direct activation of glutamic acid decarboxylase enzyme isoforms that convert glutamate to GABA. This discovery helps explain how Dlx mutations result in abnormal forebrain development, due to defective differentiation, in addition to the loss of tangential migration of GABAergic inhibitory interneurons to the neocortex. Reduced numbers or function of cortical GABAergic neurons may lead to hyperactivity states such as seizures (Cobos et al., 2005) or contribute to the pathogenesis of some autism spectrum disorders. GABAergic dysfunction in the basal ganglia could disrupt the learning and development of complex motor and cognitive behaviors (Rubenstein and Merzenich, 2003).
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Solek CM, Feng S, Perin S, Weinschutz Mendes H, Ekker M. Lineage tracing of dlx1a/2a and dlx5a/6a expressing cells in the developing zebrafish brain. Dev Biol 2017; 427:131-147. [PMID: 28479339 DOI: 10.1016/j.ydbio.2017.04.019] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2016] [Revised: 04/28/2017] [Accepted: 04/29/2017] [Indexed: 02/06/2023]
Abstract
Lineage tracing of specific populations of progenitor cells provides crucial information about developmental programs. Four members of the Dlx homeobox gene family, Dlx1,2, 5 and 6, are involved in the specification of γ-aminobutyric acid (GABA)ergic neurons in the vertebrate forebrain. Orthologous genes in mammals and teleost show similarities in expression patterns and transcriptional regulation mechanisms. We have used lineage tracing to permanently label dlx-expressing cells in the zebrafish and have characterized the progeny of these cells in the larva and in the juvenile and adult brain. We have found that dlx1a/2a and dlx5a/6a expressing progenitors give rise, for the most part, to small populations of cells which constitute only a small proportion of GABAergic cells in the adult brain tissue. Moreover, some of the cells do not acquire a neuronal phenotype suggesting that, regardless of the time a cell expresses dlx genes in the brain, it can potentially give rise to cells other than neurons. In some instances, labeling larval dlx5a/6a-expressing cells, but not dlx1a/2a-expressing cells, results in massively expanding, widespread clonal expansion throughout the adult brain. Our data provide a detailed lineage analysis of the dlx1a/2a and dlx5a/6a expressing progenitors in the zebrafish brain and lays the foundation for further characterization of the role of these transcription factors beyond the specification of GABAergic neurons.
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Affiliation(s)
- Cynthia M Solek
- CAREG, Department of Biology, University of Ottawa, 20 Marie-Curie Private, Ottawa, ON, Canada K1N 6N5; Montreal Neurological Institute, McGill University, 3801 University Street, Montreal, QC, Canada H3A 2B4
| | - Shengrui Feng
- CAREG, Department of Biology, University of Ottawa, 20 Marie-Curie Private, Ottawa, ON, Canada K1N 6N5; Department of Medical Biophysics, University of Toronto, 610 University Avenue, Toronto, ON, Canada M5G 2M9
| | - Sofia Perin
- CAREG, Department of Biology, University of Ottawa, 20 Marie-Curie Private, Ottawa, ON, Canada K1N 6N5
| | - Hellen Weinschutz Mendes
- CAREG, Department of Biology, University of Ottawa, 20 Marie-Curie Private, Ottawa, ON, Canada K1N 6N5
| | - Marc Ekker
- CAREG, Department of Biology, University of Ottawa, 20 Marie-Curie Private, Ottawa, ON, Canada K1N 6N5.
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Characterization of the γ-aminobutyric acid signaling system in the zebrafish (Danio rerio Hamilton) central nervous system by reverse transcription-quantitative polymerase chain reaction. Neuroscience 2016; 343:300-321. [PMID: 27453477 DOI: 10.1016/j.neuroscience.2016.07.018] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2016] [Revised: 07/11/2016] [Accepted: 07/11/2016] [Indexed: 11/20/2022]
Abstract
In the vertebrate brain, inhibition is largely mediated by γ-aminobutyric acid (GABA). This neurotransmitter comprises a signaling machinery of GABAA, GABAB receptors, transporters, glutamate decarboxylases (gads) and 4-aminobutyrate aminotransferase (abat), and associated proteins. Chloride is intimately related to GABAA receptor conductance, GABA uptake, and GADs activity. The response of target neurons to GABA stimuli is shaped by chloride-cation co-transporters (CCCs), which strictly control Cl- gradient across plasma membranes. This research profiled the expression of forty genes involved in GABA signaling in the zebrafish (Danio rerio) brain, grouped brain regions and retinas. Primer pairs were developed for reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The mRNA levels of the zebrafish GABA system share similarities with that of mammals, and confirm previous studies in non-mammalian species. Proposed GABAA receptors are α1β2γ2, α1β2δ, α2bβ3γ2, α2bβ3δ, α4β2γ2, α4β2δ, α6bβ2γ2 and α6bβ2δ. Regional brain differences were documented. Retinal hetero- or homomeric ρ-composed GABAA receptors could exist, accompanying α1βyγ2, α1βyδ, α6aβyγ2, α6aβyδ. Expression patterns of α6a and α6b were opposite, with the former being more abundant in retinas, the latter in brains. Given the stoichiometry α6wβyγz, α6a- or α6b-containing receptors likely have different regulatory mechanisms. Different gene isoforms could originate after the rounds of genome duplication during teleost evolution. This research depicts that one isoform is generally more abundantly expressed than the other. Such observations also apply to GABAB receptors, GABA transporters, GABA-related enzymes, CCCs and GABAA receptor-associated proteins, whose presence further strengthens the proof of a GABA system in zebrafish.
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Yin C, Zhang J, Shi Z, Sun W, Zhang H, Fu Y. Identification and expression of the target gene emx2 of miR-26a and miR-26b in Paralichthys olivaceus. Gene 2015; 570:205-12. [PMID: 26079439 DOI: 10.1016/j.gene.2015.06.030] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2015] [Revised: 06/05/2015] [Accepted: 06/06/2015] [Indexed: 11/26/2022]
Abstract
MicroRNAs (miRNAs) can regulate specific gene expression by binding to target mRNA further involution to diverse biological processes. Our previous miRNA sequencing showed that pol-miR-26a and pol-miR-26b have a sex-biased expression in ovary and testis of Paralichthys olivaceus (P. olivaceus). And the gene empty spiracles homeobox 2 (emx2) was proposed to be a candidate target by bioinformatics prediction. In this study, we cloned the P. olivaceus emx2 cDNA, including a coding region of 741 bp and a 3'-untranslated region (UTR) of 912 bp and the 5'-UTR of 12 bp. The Emx2 protein is highly conserved and especially its homeodomain region is 100% identical from teleosts to mammals. Real-time PCR results showed that the emx2 is not only highly expressed in embryonic neurula stage and adult brain but also has abundant expression in adult gonad, moreover, it exhibits higher expression in ovary than testis. To determine the relationship between emx2 and miRNAs, a luciferase reporter assay was performed and verified that the emx2 is a common target gene of pol-miR-26a and pol-miR-26b. These data thus helps further clarify that miR-26a and miR-26b are involved in regulating gonad development partially through its target on emx2 expression in P. olivaceus.
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Affiliation(s)
- Cui Yin
- Key laboratory of Freshwater Aquatic Genetic Resources, Shanghai Ocean University, Ministry of Agriculture, Shanghai 201306, China
| | - Junling Zhang
- Key laboratory of Freshwater Aquatic Genetic Resources, Shanghai Ocean University, Ministry of Agriculture, Shanghai 201306, China
| | - Zhiyi Shi
- Key laboratory of Freshwater Aquatic Genetic Resources, Shanghai Ocean University, Ministry of Agriculture, Shanghai 201306, China.
| | - Wenhui Sun
- Key laboratory of Freshwater Aquatic Genetic Resources, Shanghai Ocean University, Ministry of Agriculture, Shanghai 201306, China
| | - Hongmei Zhang
- Key laboratory of Freshwater Aquatic Genetic Resources, Shanghai Ocean University, Ministry of Agriculture, Shanghai 201306, China
| | - Yuanshuai Fu
- Key laboratory of Freshwater Aquatic Genetic Resources, Shanghai Ocean University, Ministry of Agriculture, Shanghai 201306, China
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Bedont JL, Newman EA, Blackshaw S. Patterning, specification, and differentiation in the developing hypothalamus. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2015; 4:445-68. [PMID: 25820448 DOI: 10.1002/wdev.187] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Revised: 02/10/2015] [Accepted: 02/12/2015] [Indexed: 12/21/2022]
Abstract
Owing to its complex structure and highly diverse cell populations, the study of hypothalamic development has historically lagged behind that of other brain regions. However, in recent years, a greatly expanded understanding of hypothalamic gene expression during development has opened up new avenues of investigation. In this review, we synthesize existing work to present a holistic picture of hypothalamic development from early induction and patterning through nuclear specification and differentiation, with a particular emphasis on determination of cell fate. We will also touch on special topics in the field including the prosomere model, adult neurogenesis, and integration of migratory cells originating outside the hypothalamic neuroepithelium, and how these topics relate to our broader theme.
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Affiliation(s)
- Joseph L Bedont
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Elizabeth A Newman
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Seth Blackshaw
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,Department of Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,High-Throughput Biology Center, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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Filippi A, Mueller T, Driever W. vglut2 and gad expression reveal distinct patterns of dual GABAergic versus glutamatergic cotransmitter phenotypes of dopaminergic and noradrenergic neurons in the zebrafish brain. J Comp Neurol 2015; 522:2019-37. [PMID: 24374659 PMCID: PMC4288968 DOI: 10.1002/cne.23524] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2013] [Revised: 11/27/2013] [Accepted: 11/27/2013] [Indexed: 01/22/2023]
Abstract
Throughout the vertebrate lineage, dopaminergic neurons form important neuromodulatory systems that influence motor behavior, mood, cognition, and physiology. Studies in mammals have established that dopaminergic neurons often use γ-aminobutyric acid (GABA) or glutamatergic cotransmission during development and physiological function. Here, we analyze vglut2, gad1b and gad2 expression in combination with tyrosine hydroxylase immunoreactivity in 4-day-old larval and 30-day-old juvenile zebrafish brains to determine which dopaminergic and noradrenergic groups may use GABA or glutamate as a second transmitter. Our results show that most dopaminergic neurons also express GABAergic markers, including the dopaminergic groups of the olfactory bulb (homologous to mammalian A16) and the subpallium, the hypothalamic groups (A12, A14), the prethalamic zona incerta group (A13), the preoptic groups (A15), and the pretectal group. Thus, the majority of catecholaminergic neurons are gad1b/2-positive and coexpress GABA. A very few gad1/2-negative dopaminergic groups, however, express vglut2 instead and use glutamate as a second transmitter. These glutamatergic dual transmitter phenotypes are the Orthopedia transcription factor–dependent, A11-type dopaminergic neurons of the posterior tuberculum. All together, our results demonstrate that all catecholaminergic groups in zebrafish are either GABAergic or glutamatergic. Thus, cotransmission of dopamine and noradrenaline with either GABA or glutamate appears to be a regular feature of zebrafish catecholaminergic systems. We compare our results with those that have been described for mammalian systems, discuss the phenomenon of transmitter dualism in the context of developmental specification of GABAergic and glutamatergic regions in the brain, and put this phenomenon in an evolutionary perspective. J. Comp. Neurol. 522:2019–2037, 2014.
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Affiliation(s)
- Alida Filippi
- Developmental Biology, Institute of Biology I, Faculty of Biology, Albert-Ludwigs-University Freiburg, 79104, Freiburg, Germany
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Klarić T, Lardelli M, Key B, Koblar S, Lewis M. Activity-dependent expression of neuronal PAS domain-containing protein 4 (npas4a) in the developing zebrafish brain. Front Neuroanat 2014; 8:148. [PMID: 25538572 PMCID: PMC4255624 DOI: 10.3389/fnana.2014.00148] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2014] [Accepted: 11/18/2014] [Indexed: 11/26/2022] Open
Abstract
In rodents, the Npas4 gene has recently been identified as being an important regulator of synaptic plasticity and memory. Homologs of Npas4 have been found in invertebrate species though their functions appear to be too divergent for them to be studied as a proxy for the mammalian proteins. The aim of this study, therefore, was to ascertain the suitability of the zebrafish as a model organism for investigating the function of Npas4 genes. We show here that the expression and regulation of the zebrafish Npas4 homolog, npas4a, is remarkably similar to that of the rodent Npas4 genes. As in mammals, expression of the zebrafish npas4a gene is restricted to the brain where it is up-regulated in response to neuronal activity. Furthermore, we also show that knockdown of npas4a during embryonic development results in a number of forebrain-specific defects including increased apoptosis and misexpression of the forebrain marker genes dlx1a and shha. Our work demonstrates that the zebrafish is a suitable model organism for investigating the role of the npas4a gene and one that is likely to provide valuable insights into the function of the mammalian homologs. Furthermore, our findings highlight a potential role for npas4a in forebrain development.
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Affiliation(s)
- Thomas Klarić
- School of Molecular and Biomedical Sciences, The University of Adelaide Adelaide, SA, Australia
| | - Michael Lardelli
- School of Molecular and Biomedical Sciences, The University of Adelaide Adelaide, SA, Australia
| | - Brian Key
- School of Biomedical Sciences, The University of Queensland Brisbane, QLD, Australia
| | - Simon Koblar
- School of Medicine, The University of Adelaide Adelaide, SA, Australia
| | - Martin Lewis
- School of Molecular and Biomedical Sciences, The University of Adelaide Adelaide, SA, Australia
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Heude É, Shaikho S, Ekker M. The dlx5a/dlx6a genes play essential roles in the early development of zebrafish median fin and pectoral structures. PLoS One 2014; 9:e98505. [PMID: 24858471 PMCID: PMC4032342 DOI: 10.1371/journal.pone.0098505] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2014] [Accepted: 05/02/2014] [Indexed: 11/18/2022] Open
Abstract
The Dlx5 and Dlx6 genes encode homeodomain transcription factors essential for the proper development of limbs in mammalian species. However, the role of their teleost counterparts in fin development has received little attention. Here, we show that dlx5a is an early marker of apical ectodermal cells of the pectoral fin buds and of the median fin fold, but also of cleithrum precursor cells during pectoral girdle development. We propose that early median fin fold establishment results from the medial convergence of dlx5a-expressing cells at the lateral edges of the neural keel. Expression analysis also shows involvement of dlx5a during appendage skeletogenesis. Using morpholino-mediated knock down, we demonstrate that disrupted dlx5a/6a function results in pectoral fin agenesis associated with misexpression of bmp4, fgf8a, and1 and msx genes. In contrast, the median fin fold presents defects in mesenchymal cell migration and actinotrichia formation, whereas the initial specification seems to occur normally. Our results demonstrate that the dlx5a/6a genes are essential for the induction of pectoral fin outgrowth, but are not required during median fin fold specification. The dlx5a/6a knock down also causes a failure of cleithrum formation associated with a drastic loss of runx2b and col10a1 expression. The data indicate distinct requirements for dlx5a/6a during median and pectoral fin development suggesting that initiation of unpaired and paired fin formation are not directed through the same molecular mechanisms. Our results refocus arguments on the mechanistic basis of paired appendage genesis during vertebrate evolution.
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Affiliation(s)
- Églantine Heude
- Centre for Advanced Research in Environmental Genomics, Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - Sarah Shaikho
- Centre for Advanced Research in Environmental Genomics, Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - Marc Ekker
- Centre for Advanced Research in Environmental Genomics, Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
- * E-mail:
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