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Jara JS, Avci HX, Kouremenou I, Doulazmi M, Bakouche J, Dubacq C, Goyenvalle C, Mariani J, Lohof AM, Sherrard RM. Pax3 induces target-specific reinnervation through axon collateral expression of PSA-NCAM. Prog Neurobiol 2024; 232:102560. [PMID: 38097036 DOI: 10.1016/j.pneurobio.2023.102560] [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: 07/11/2023] [Revised: 11/07/2023] [Accepted: 12/08/2023] [Indexed: 12/24/2023]
Abstract
Damaged or dysfunctional neural circuits can be replaced after a lesion by axon sprouting and collateral growth from undamaged neurons. Unfortunately, these new connections are often disorganized and rarely produce clinical improvement. Here we investigate how to promote post-lesion axonal collateral growth, while retaining correct cellular targeting. In the mouse olivocerebellar path, brain-derived neurotrophic factor (BDNF) induces correctly-targeted post-lesion cerebellar reinnervation by remaining intact inferior olivary axons (climbing fibers). In this study we identified cellular processes through which BDNF induces this repair. BDNF injection into the denervated cerebellum upregulates the transcription factor Pax3 in inferior olivary neurons and induces rapid climbing fiber sprouting. Pax3 in turn increases polysialic acid-neural cell adhesion molecule (PSA-NCAM) in the sprouting climbing fiber path, facilitating collateral outgrowth and pathfinding to reinnervate the correct targets, cerebellar Purkinje cells. BDNF-induced reinnervation can be reproduced by olivary Pax3 overexpression, and abolished by olivary Pax3 knockdown, suggesting that Pax3 promotes axon growth and guidance through upregulating PSA-NCAM, probably on the axon's growth cone. These data indicate that restricting growth-promotion to potential reinnervating afferent neurons, as opposed to stimulating the whole circuit or the injury site, allows axon growth and appropriate guidance, thus accurately rebuilding a neural circuit.
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Affiliation(s)
- J Sebastian Jara
- Sorbonne Université & CNRS, IBPS-B2A, Biological Adaptation and Ageing, Paris France
| | - Hasan X Avci
- Sorbonne Université & CNRS, IBPS-B2A, Biological Adaptation and Ageing, Paris France
| | - Ioanna Kouremenou
- Sorbonne Université & CNRS, IBPS-B2A, Biological Adaptation and Ageing, Paris France
| | - Mohamed Doulazmi
- Sorbonne Université & CNRS, IBPS-B2A, Biological Adaptation and Ageing, Paris France
| | - Joelle Bakouche
- Sorbonne Université & CNRS, IBPS-B2A, Biological Adaptation and Ageing, Paris France
| | - Caroline Dubacq
- Sorbonne Université, CNRS & INSERM, IBPS-NPS, Neurosciences Paris Seine, Paris France
| | - Catherine Goyenvalle
- Sorbonne Université & CNRS, IBPS-B2A, Biological Adaptation and Ageing, Paris France
| | - Jean Mariani
- Sorbonne Université & CNRS, IBPS-B2A, Biological Adaptation and Ageing, Paris France
| | - Ann M Lohof
- Sorbonne Université & CNRS, IBPS-B2A, Biological Adaptation and Ageing, Paris France
| | - Rachel M Sherrard
- Sorbonne Université & CNRS, IBPS-B2A, Biological Adaptation and Ageing, Paris France.
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Sibuea S, Ho JK, Pouton CW, Haynes JM. TGFβ3, dibutyryl cAMP and a notch inhibitor modulate phenotype late in stem cell-derived dopaminergic neuron maturation. Front Cell Dev Biol 2023; 11:1111705. [PMID: 36819101 PMCID: PMC9928866 DOI: 10.3389/fcell.2023.1111705] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Accepted: 01/19/2023] [Indexed: 02/04/2023] Open
Abstract
The generation of midbrain dopaminergic neurons (mDAs) from pluripotent stem cells (hPSC) holds much promise for both disease modelling studies and as a cell therapy for Parkinson's disease (PD). Generally, dopaminergic neuron differentiation paradigms rely on inhibition of smad signalling for neural induction followed by hedgehog signalling and an elevation of β-catenin to drive dopaminergic differentiation. Post-patterning, differentiating dopaminergic neuron cultures are permitted time for maturation after which the success of these differentiation paradigms is usually defined by expression of tyrosine hydroxylase (TH), the rate limiting enzyme in the synthesis of dopamine. However, during maturation, culture media is often supplemented with additives to promote neuron survival and or promote cell differentiation. These additives include dibutyryl cyclic adenosine monophosphate (dbcAMP), transforming growth factor β3 (TGFβ3) and or the γ-secretase inhibitor (DAPT). While these factors are routinely added to cultures, their impact upon pluripotent stem cell-derived mDA phenotype is largely unclear. In this study, we differentiate pluripotent stem cells toward a dopaminergic phenotype and investigate how the omission of dbcAMP, TGFβ3 or DAPT, late in maturation, affects the regulation of multiple dopaminergic neuron phenotype markers. We now show that the removal of dbcAMP or TGFβ3 significantly and distinctly impacts multiple markers of the mDA phenotype (FOXA2, EN1, EN2, FOXA2, SOX6), while commonly increasing both MSX2 and NEUROD1 and reducing expression of both tyrosine hydroxylase and WNT5A. Removing DAPT significantly impacted MSX2, OTX2, EN1, and KCNJ6. In the absence of any stressful stimuli, we suggest that these culture additives should be viewed as mDA phenotype-modifying, rather than neuroprotective. We also suggest that their addition to cultures is likely to confound the interpretation of both transplantation and disease modelling studies.
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Affiliation(s)
- Shanti Sibuea
- Stem Cell Biology Group, Monash Institute of Pharmaceutical Sciences Monash University, Parkville, VIC, Australia,National Agency of Drug and Food Control, Jakarta, Indonesia
| | - Joan K. Ho
- Stem Cell Biology Group, Monash Institute of Pharmaceutical Sciences Monash University, Parkville, VIC, Australia
| | - Colin W. Pouton
- Stem Cell Biology Group, Monash Institute of Pharmaceutical Sciences Monash University, Parkville, VIC, Australia
| | - John M. Haynes
- Stem Cell Biology Group, Monash Institute of Pharmaceutical Sciences Monash University, Parkville, VIC, Australia,*Correspondence: John M. Haynes,
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Giliberti A, Currò A, Papa FT, Frullanti E, Ariani F, Coriolani G, Grosso S, Renieri A, Mari F. MEIS2 gene is responsible for intellectual disability, cardiac defects and a distinct facial phenotype. Eur J Med Genet 2020; 63:103627. [DOI: 10.1016/j.ejmg.2019.01.017] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Revised: 01/25/2019] [Accepted: 01/29/2019] [Indexed: 12/25/2022]
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Rapacioli M, Fiszer de Plazas S, Flores V. The developing optic tectum: An asymmetrically organized system and the need for a redefinition of the notion of sensitive period. Int J Dev Neurosci 2018; 73:1-9. [PMID: 30572015 DOI: 10.1016/j.ijdevneu.2018.12.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2018] [Revised: 12/13/2018] [Accepted: 12/14/2018] [Indexed: 10/27/2022] Open
Abstract
The present article summarizes the main events involved in the isthmic organizer and optic tectum determination and analyses how optic tectum patterning is translated, by the organized operation of several specific cell behaviors, into the terminally differentiated optic tectum. The paper proposes that this assembling of temporally/spatially organized cell behaviors could be incorporated into a wider notion of patterning and that, given the asymmetric organization of the developing optic tectum, the notion of "sensitive period" does not capture the whole complexity of midbrain development and the pathogenesis of congenital disorders. The cell behaviors involved in the optic tectum development are organized in time and space by the isthmic organizer. A comprehensive description of the normal optic tectum development, and also its alterations, should consider both domains. Significantly, the identity of each neuronal cohort depends critically on its "time and place of birth". Both parameters must be considered at once to explain how the structural and functional organization of the optic tectum is elaborated. The notion of "patterning" applies only to the early events of the optic tectum development. Besides, the notion of "sensitive period" considers only a temporal domain and disregards the asymmetric organization of the developing optic tectum. The present paper proposes that these notions might be re-defined: (a) a wider meaning of the term patterning and (b) a replacement of the term "sensitive period" by a more precise concept of "sensitive temporal/spatial window".
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Affiliation(s)
- Melina Rapacioli
- Grupo Interdisciplinario de Biología Teórica, Instituto de Neurociencia Cognitiva y Traslacional (INCyT), Universidad Favaloro-INECO-CONICET, Buenos Aires, Argentina.
| | - Sara Fiszer de Plazas
- Instituto de Biología Celular y Neurociencias (IBCN) Dr. Eduardo de Robertis, Facultad de Medicina, CONICET, Universidad de Buenos Aires (UBA), Buenos Aires, Argentina
| | - Vladimir Flores
- Grupo Interdisciplinario de Biología Teórica, Instituto de Neurociencia Cognitiva y Traslacional (INCyT), Universidad Favaloro-INECO-CONICET, Buenos Aires, Argentina; Instituto de Biología Celular y Neurociencias (IBCN) Dr. Eduardo de Robertis, Facultad de Medicina, CONICET, Universidad de Buenos Aires (UBA), Buenos Aires, Argentina
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Rapacioli M, Palma V, Flores V. Morphogenetic and Histogenetic Roles of the Temporal-Spatial Organization of Cell Proliferation in the Vertebrate Corticogenesis as Revealed by Inter-specific Analyses of the Optic Tectum Cortex Development. Front Cell Neurosci 2016; 10:67. [PMID: 27013978 PMCID: PMC4794495 DOI: 10.3389/fncel.2016.00067] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Accepted: 03/01/2016] [Indexed: 12/11/2022] Open
Abstract
The central nervous system areas displaying the highest structural and functional complexity correspond to the so called cortices, i.e., concentric alternating neuronal and fibrous layers. Corticogenesis, i.e., the development of the cortical organization, depends on the temporal-spatial organization of several developmental events: (a) the duration of the proliferative phase of the neuroepithelium, (b) the relative duration of symmetric (expansive) versus asymmetric (neuronogenic) sub phases, (c) the spatial organization of each kind of cell division, (e) the time of determination and cell cycle exit and (f) the time of onset of the post-mitotic neuronal migration and (g) the time of onset of the neuronal structural and functional differentiation. The first five events depend on molecular mechanisms that perform a fine tuning of the proliferative activity. Changes in any of them significantly influence the cortical size or volume (tangential expansion and radial thickness), morphology, architecture and also impact on neuritogenesis and synaptogenesis affecting the cortical wiring. This paper integrates information, obtained in several species, on the developmental roles of cell proliferation in the development of the optic tectum (OT) cortex, a multilayered associative area of the dorsal (alar) midbrain. The present review (1) compiles relevant information on the temporal and spatial organization of cell proliferation in different species (fish, amphibians, birds, and mammals), (2) revises the main molecular events involved in the isthmic organizer (IsO) determination and localization, (3) describes how the patterning installed by IsO is translated into spatially organized neural stem cell proliferation (i.e., by means of growth factors, receptors, transcription factors, signaling pathways, etc.) and (4) describes the morpho- and histogenetic effect of a spatially organized cell proliferation in the above mentioned species. A brief section on the OT evolution is also included. This section considers how the differential operation of cell proliferation could explain differences among species.
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Affiliation(s)
- Melina Rapacioli
- Interdisciplinary Group in Theoretical Biology, Department of Biostructural Sciences, Favaloro UniversityBuenos Aires, Argentina
| | - Verónica Palma
- Laboratory of Stem Cell and Developmental Biology, Faculty of Science, University of ChileSantiago, Chile
| | - Vladimir Flores
- Interdisciplinary Group in Theoretical Biology, Department of Biostructural Sciences, Favaloro UniversityBuenos Aires, Argentina
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Louw JJ, Corveleyn A, Jia Y, Hens G, Gewillig M, Devriendt K. MEIS2involvement in cardiac development, cleft palate, and intellectual disability. Am J Med Genet A 2015; 167A:1142-6. [DOI: 10.1002/ajmg.a.36989] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Accepted: 01/04/2015] [Indexed: 11/11/2022]
Affiliation(s)
- Jacoba J. Louw
- Department of Congenital and Pediatric Cardiology; University Hospitals Leuven; Belgium
- Center of Human Genetics; University Hospitals Leuven; Katholieke Universiteit Leuven; Belgium
| | - Anniek Corveleyn
- Center of Human Genetics; University Hospitals Leuven; Katholieke Universiteit Leuven; Belgium
| | - Yaojuan Jia
- Center of Human Genetics; University Hospitals Leuven; Katholieke Universiteit Leuven; Belgium
| | - Greet Hens
- Department of Ear, Nose and Throat; University Hospitals Leuven; Belgium
| | - Marc Gewillig
- Department of Congenital and Pediatric Cardiology; University Hospitals Leuven; Belgium
| | - Koenraad Devriendt
- Center of Human Genetics; University Hospitals Leuven; Katholieke Universiteit Leuven; Belgium
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Johansson S, Berland S, Gradek GA, Bongers E, de Leeuw N, Pfundt R, Fannemel M, Rødningen O, Brendehaug A, Haukanes BI, Hovland R, Helland G, Houge G. Haploinsufficiency ofMEIS2is associated with orofacial clefting and learning disability. Am J Med Genet A 2014; 164A:1622-6. [DOI: 10.1002/ajmg.a.36498] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2013] [Accepted: 11/14/2013] [Indexed: 11/12/2022]
Affiliation(s)
- Stefan Johansson
- Center for Medical Genetics and Molecular Medicine; Haukeland University Hospital; Bergen Norway
- Department of Clinical Science; University of Bergen; Bergen Norway
| | - Siren Berland
- Center for Medical Genetics and Molecular Medicine; Haukeland University Hospital; Bergen Norway
| | - Gyri Aasland Gradek
- Center for Medical Genetics and Molecular Medicine; Haukeland University Hospital; Bergen Norway
| | - Ernie Bongers
- Department of Human Genetics; Radboud University Medical Centre; Nijmegen The Netherlands
| | - Nicole de Leeuw
- Department of Human Genetics; Radboud University Medical Centre; Nijmegen The Netherlands
| | - Rolph Pfundt
- Department of Human Genetics; Radboud University Medical Centre; Nijmegen The Netherlands
| | - Madeleine Fannemel
- Department of Medical Genetics; Oslo University Hospital; Ullevål Oslo Norway
| | - Olaug Rødningen
- Department of Medical Genetics; Oslo University Hospital; Ullevål Oslo Norway
| | - Atle Brendehaug
- Center for Medical Genetics and Molecular Medicine; Haukeland University Hospital; Bergen Norway
| | - Bjørn Ivar Haukanes
- Center for Medical Genetics and Molecular Medicine; Haukeland University Hospital; Bergen Norway
| | - Randi Hovland
- Center for Medical Genetics and Molecular Medicine; Haukeland University Hospital; Bergen Norway
| | - Gunnar Helland
- Department of Pediatrics; Levanger Hospital; Levanger Norway
| | - Gunnar Houge
- Center for Medical Genetics and Molecular Medicine; Haukeland University Hospital; Bergen Norway
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Agoston Z, Li N, Haslinger A, Wizenmann A, Schulte D. Genetic and physical interaction of Meis2, Pax3 and Pax7 during dorsal midbrain development. BMC DEVELOPMENTAL BIOLOGY 2012; 12:10. [PMID: 22390724 PMCID: PMC3313853 DOI: 10.1186/1471-213x-12-10] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/22/2011] [Accepted: 03/05/2012] [Indexed: 12/31/2022]
Abstract
Background During early stages of brain development, secreted molecules, components of intracellular signaling pathways and transcriptional regulators act in positive and negative feed-back or feed-forward loops at the mid-hindbrain boundary. These genetic interactions are of central importance for the specification and subsequent development of the adjacent mid- and hindbrain. Much less, however, is known about the regulatory relationship and functional interaction of molecules that are expressed in the tectal anlage after tectal fate specification has taken place and tectal development has commenced. Results Here, we provide experimental evidence for reciprocal regulation and subsequent cooperation of the paired-type transcription factors Pax3, Pax7 and the TALE-homeodomain protein Meis2 in the tectal anlage. Using in ovo electroporation of the mesencephalic vesicle of chick embryos we show that (i) Pax3 and Pax7 mutually regulate each other's expression in the mesencephalic vesicle, (ii) Meis2 acts downstream of Pax3/7 and requires balanced expression levels of both proteins, and (iii) Meis2 physically interacts with Pax3 and Pax7. These results extend our previous observation that Meis2 cooperates with Otx2 in tectal development to include Pax3 and Pax7 as Meis2 interacting proteins in the tectal anlage. Conclusion The results described here suggest a model in which interdependent regulatory loops involving Pax3 and Pax7 in the dorsal mesencephalic vesicle modulate Meis2 expression. Physical interaction with Meis2 may then confer tectal specificity to a wide range of otherwise broadly expressed transcriptional regulators, including Otx2, Pax3 and Pax7.
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Affiliation(s)
- Zsuzsa Agoston
- Institute of Neurology (Edinger Institute), J, W, Goethe University Medical School, Heinrich Hoffmannstr, 7, 50628 Frankfurt, Germany
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Agoston Z, Li N, Haslinger A, Wizenmann A, Schulte D. Genetic and physical interaction of Meis2, Pax3 and Pax7 during dorsal midbrain development. BMC DEVELOPMENTAL BIOLOGY 2012. [PMID: 22390724 DOI: 10.1186/1471‐213x‐12‐10] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
BACKGROUND During early stages of brain development, secreted molecules, components of intracellular signaling pathways and transcriptional regulators act in positive and negative feed-back or feed-forward loops at the mid-hindbrain boundary. These genetic interactions are of central importance for the specification and subsequent development of the adjacent mid- and hindbrain. Much less, however, is known about the regulatory relationship and functional interaction of molecules that are expressed in the tectal anlage after tectal fate specification has taken place and tectal development has commenced. RESULTS Here, we provide experimental evidence for reciprocal regulation and subsequent cooperation of the paired-type transcription factors Pax3, Pax7 and the TALE-homeodomain protein Meis2 in the tectal anlage. Using in ovo electroporation of the mesencephalic vesicle of chick embryos we show that (i) Pax3 and Pax7 mutually regulate each other's expression in the mesencephalic vesicle, (ii) Meis2 acts downstream of Pax3/7 and requires balanced expression levels of both proteins, and (iii) Meis2 physically interacts with Pax3 and Pax7. These results extend our previous observation that Meis2 cooperates with Otx2 in tectal development to include Pax3 and Pax7 as Meis2 interacting proteins in the tectal anlage. CONCLUSION The results described here suggest a model in which interdependent regulatory loops involving Pax3 and Pax7 in the dorsal mesencephalic vesicle modulate Meis2 expression. Physical interaction with Meis2 may then confer tectal specificity to a wide range of otherwise broadly expressed transcriptional regulators, including Otx2, Pax3 and Pax7.
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Affiliation(s)
- Zsuzsa Agoston
- Institute of Neurology (Edinger Institute), J, W, Goethe University Medical School, Heinrich Hoffmannstr, 7, 50628 Frankfurt, Germany
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Diercke K, Sen S, Kohl A, Lux C, Erber R. Compression-dependent Up-regulation of Ephrin-A2 in PDL Fibroblasts Attenuates Osteogenesis. J Dent Res 2011; 90:1108-15. [DOI: 10.1177/0022034511413926] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Members of the ephrin/Eph family have recently been shown to be involved in the regulation of bone homeostasis in a murine model. The activation of the EphB4 receptor on osteoblasts by its ligand ephrin-B2 led to stimulation of osteoblastogenesis and therefore to bone formation. The activation of ephrin-A2-EphA2 signaling on osteoblasts inhibited the activation of osteoblast-specific gene expression, leading to bone resorption. Fibroblasts within the periodontal ligament periodontal ligament may be one of the first responders to orthodontic forces. Periodontal ligament fibroblasts (PDLF) are mechanoresponsive. Members of the ephrin/Eph family might link mechanical forces received by PDLF with the regulation of osteoblastogenesis on osteoblasts of the alveolar bone. To study whether ephrin-A2 is modulated upon compression, we subjected human primary PDLF to static compressive forces (30.3 g/cm2). Static compressive forces significantly induced the expression of ephrin-A2, while the expression of ephrin-B2 was significantly down-regulated. Moreover, osteoblasts of the alveolar bone stimulated with ephrin-A2 in vitro significantly suppressed their osteoblastogenic gene expression (RUNX2, ALPL) and decreased signs of osteoblastic differentiation, as demonstrated by a significantly reduced ALP activity. Together, these findings establish a role for this ligand/receptor system linking mechanical forces with the regulation of osteogenesis during orthodontic tooth movement.
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Affiliation(s)
- K. Diercke
- Department of Orthodontics and Dentofacial Orthopaedics, Dental School, University of Heidelberg, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany
| | - S. Sen
- Department of Orthodontics and Dentofacial Orthopaedics, Dental School, University of Heidelberg, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany
| | - A. Kohl
- Department of Orthodontics and Dentofacial Orthopaedics, Dental School, University of Heidelberg, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany
| | - C.J. Lux
- Department of Orthodontics and Dentofacial Orthopaedics, Dental School, University of Heidelberg, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany
| | - R. Erber
- Department of Orthodontics and Dentofacial Orthopaedics, Dental School, University of Heidelberg, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany
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Agoston Z, Schulte D. Meis2 competes with the Groucho co-repressor Tle4 for binding to Otx2 and specifies tectal fate without induction of a secondary midbrain-hindbrain boundary organizer. Development 2009; 136:3311-22. [DOI: 10.1242/dev.037770] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The transcription factor Otx2 is expressed throughout the anterior neuroectoderm and is required for the formation of all forebrain- and midbrain-derived structures. The molecular determinants that cooperate with Otx2 to subdivide its expression domain into distinct functional units are, however, poorly understood at present. We show here that the TALE-homeodomain protein Meis2 is expressed in the chick tectal anlage and is both necessary and sufficient for tectal development. Unlike known tectum-inducing genes, the ability of Meis2 to initiate tectal development does not involve the formation of a secondary midbrain-hindbrain boundary organizer, but instead requires direct interaction with Otx2. Using an Otx2-dependent reporter assay we demonstrate that Meis2 competes with the Groucho co-repressor Tle4 (Grg4) for binding to Otx2 and thereby restores Otx2 transcriptional activator function. Together, our data suggest a model in which the balance between a co-repressor and a co-activator, which compete for binding to Otx2 in the mesencephalic vesicle, provides spatial and temporal control over tectal development. Controlled formation of Meis2-containing higher order protein complexes might thus serve as a general mechanism to achieve subdivision of the anterior neuroectoderm into distinct functional units during embryogenesis.
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Affiliation(s)
- Zsuzsa Agoston
- Department of Neuroanatomy, Max-Planck Institute for Brain Research,Deutschordenstr. 46, Frankfurt, Germany
| | - Dorothea Schulte
- Department of Neuroanatomy, Max-Planck Institute for Brain Research,Deutschordenstr. 46, Frankfurt, Germany
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Abstract
The mid-hindbrain boundary (MHB) harbors an important organizing center for the adjacent brain regions. Here, we present evidence that the receptor protein tyrosine phosphatase lambda (RPTPlambda) is part of the complex molecular network that maintains and shapes the MHB region. RPTPlambda is expressed in a tight band of cells in the caudal midbrain, anterior to the transverse ring of Wnt1 expression. Forced expression of RPTPlambda across the mid-hindbrain region repressed expression of Wnt1, whereas RNA interference-mediated knock-down of RPTPlambda resulted in expansion and distortion of the Wnt1 domain. When ectopically expressed in the mesencephalon, RPTPlambda specifically inhibited the induction of Wnt1 expression after subsequent stimulation with Fgf8. Reduced Wnt1 expression after RPTPlambda transfection correlated with a decrease in Ras- mitogen-activated protein kinase activity at the MHB. We further show that in the embryonic midbrain, RPTPlambda can bind to beta-catenin, a central component of the canonical Wnt signaling pathway. Overexpression of RPTPlambda suppressed the activity of a beta-catenin responsive promoter in the midbrain and reduced progenitor cell proliferation. Cotransfection of Wnt1 or of a stabilized form of beta-catenin together with RPTPlambda partially rescued the RPTPlambda-mediated proliferation defect. Together, these data suggest that RPTPlambda may play a dual role in the control of midbrain development: as a negative modulator of Fgf8-induced Wnt1 expression at the MHB, which may help to confine the Wnt1 domain to it characteristic tight ring at the MHB; and as an inhibitor of canonical Wnt signaling through interaction with and presumably sequestration of beta-catenin.
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