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García-Llorca A, Aspelund SG, Ogmundsdottir MH, Steingrimsson E, Eysteinsson T. The microphthalmia-associated transcription factor (Mitf) gene and its role in regulating eye function. Sci Rep 2019; 9:15386. [PMID: 31659211 PMCID: PMC6817937 DOI: 10.1038/s41598-019-51819-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2019] [Accepted: 10/08/2019] [Indexed: 12/17/2022] Open
Abstract
Mutations in the microphthalmia-associated transcription factor (Mitf) gene can cause retinal pigment epithelium (RPE) and retinal dysfunction and degeneration. We examined retinal and RPE structure and function in 3 month old mice homo- or heterozygous or compound heterozygous for different Mitf mutations (Mitfmi-vga9/+, Mitfmi-enu22(398)/Mitfmi-enu22(398), MitfMi-Wh/+ and MitfMi-Wh/Mitfmi) which all have normal eye size with apparently normal eye pigmentation. Here we show that their vision and retinal structures are differentially affected. Hypopigmentation was evident in all the mutants while bright-field fundus images showed yellow spots with non-pigmented areas in the Mitfmi-vga9/+ mice. MitfMi-Wh/+ and MitfMi-Wh/Mitfmi mice showed large non-pigmented areas. Fluorescent angiography (FA) of all mutants except Mitfmi-vga9/+ mice showed hyperfluorescent areas, whereas FA from both Mitf-Mi-Wh/+ and MitfMi-Wh/Mitfmi mice showed reduced capillary network as well as hyperfluorescent areas. Electroretinogram (ERG) recordings show that MitfMi-Wh/+ and MitfMi-Wh/Mitfmi mice are severely impaired functionally whereas the scotopic and photopic ERG responses of Mitfmi-vga9/+ and Mitfmi-enu22(398)/Mitfmi-enu22(398) mice were not significantly different from wild type mice. Histological sections demonstrated that the outer retinal layers were absent from the MitfMi-Wh/+ and MitfMi-Wh/Mitfmi blind mutants. Our results show that Mitf mutations affect eye function, even in the heterozygous condition and that the alleles studied can be arranged in an allelic series in this respect.
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Affiliation(s)
- Andrea García-Llorca
- Department of Physiology, Biomedical Center, Faculty of Medicine, University of Iceland, Vatnsmyrarvegur 16, 101, Reykjavík, Iceland.,Department of Ophthalmology, Landspitali National University Hospital, Eiriksgata 37, 101, Reykjavik, Iceland
| | | | - Margret Helga Ogmundsdottir
- Department of Anatomy, Biomedical Center, Faculty of Medicine, University of Iceland, Sturlugata 8, Reykjavík, Iceland
| | - Eiríkur Steingrimsson
- Department of Biochemistry and Molecular Biology, Biomedical Center, Faculty of Medicine, University of Iceland, Sturlugata 8, Reykjavík, Iceland
| | - Thor Eysteinsson
- Department of Physiology, Biomedical Center, Faculty of Medicine, University of Iceland, Vatnsmyrarvegur 16, 101, Reykjavík, Iceland. .,Department of Ophthalmology, Landspitali National University Hospital, Eiriksgata 37, 101, Reykjavik, Iceland.
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2
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Travnickova J, Wojciechowska S, Khamseh A, Gautier P, Brown DV, Lefevre T, Brombin A, Ewing A, Capper A, Spitzer M, Dilshat R, Semple CA, Mathers ME, Lister JA, Steingrimsson E, Voet T, Ponting CP, Patton EE. Zebrafish MITF-Low Melanoma Subtype Models Reveal Transcriptional Subclusters and MITF-Independent Residual Disease. Cancer Res 2019; 79:5769-5784. [PMID: 31582381 DOI: 10.1158/0008-5472.can-19-0037] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2019] [Revised: 06/28/2019] [Accepted: 09/23/2019] [Indexed: 12/17/2022]
Abstract
The melanocyte-inducing transcription factor (MITF)-low melanoma transcriptional signature is predictive of poor outcomes for patients, but little is known about its biological significance, and animal models are lacking. Here, we used zebrafish genetic models with low activity of Mitfa (MITF-low) and established that the MITF-low state is causal of melanoma progression and a predictor of melanoma biological subtype. MITF-low zebrafish melanomas resembled human MITF-low melanomas and were enriched for stem and invasive (mesenchymal) gene signatures. MITF-low activity coupled with a p53 mutation was sufficient to promote superficial growth melanomas, whereas BRAFV600E accelerated MITF-low melanoma onset and further promoted the development of MITF-high nodular growth melanomas. Genetic inhibition of MITF activity led to rapid regression; recurrence occurred following reactivation of MITF. At the regression site, there was minimal residual disease that was resistant to loss of MITF activity (termed MITF-independent cells) with very low-to-no MITF activity or protein. Transcriptomic analysis of MITF-independent residual disease showed enrichment of mesenchymal and neural crest stem cell signatures similar to human therapy-resistant melanomas. Single-cell RNA sequencing revealed MITF-independent residual disease was heterogeneous depending on melanoma subtype. Further, there was a shared subpopulation of residual disease cells that was enriched for a neural crest G0-like state that preexisted in the primary tumor and remained present in recurring melanomas. These findings suggest that invasive and stem-like programs coupled with cellular heterogeneity contribute to poor outcomes for MITF-low melanoma patients and that MITF-independent subpopulations are an important therapeutic target to achieve long-term survival outcomes. SIGNIFICANCE: This study provides a useful model for MITF-low melanomas and MITF-independent cell populations that can be used to study the mechanisms that drive these tumors as well as identify potential therapeutic options.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/22/5769/F1.large.jpg.
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Affiliation(s)
- Jana Travnickova
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom.,CRUK Edinburgh Centre, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom
| | - Sonia Wojciechowska
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom.,CRUK Edinburgh Centre, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom
| | - Ava Khamseh
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom.,Higgs Centre for Theoretical Physics, School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom
| | - Philippe Gautier
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom
| | - Daniel V Brown
- Department of Human Genetics, University of Leuven, KU Leuven, Leuven, Belgium.,Immunology Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, Australia
| | - Thomas Lefevre
- Department of Human Genetics, University of Leuven, KU Leuven, Leuven, Belgium
| | - Alessandro Brombin
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom.,CRUK Edinburgh Centre, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom
| | - Ailith Ewing
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom
| | - Amy Capper
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom.,CRUK Edinburgh Centre, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom
| | - Michaela Spitzer
- Open Targets, Wellcome Genome Campus, Hinxton, Cambridge, United Kingdom; and European Bioinformatics Institute (EMBL-EBI), Wellcome Genome Campus, Hinxton, Cambridge, United Kingdom
| | - Ramile Dilshat
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Iceland, Reykjavik, Iceland
| | - Colin A Semple
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom
| | - Marie E Mathers
- Department of Pathology, Western General Hospital, Edinburgh, United Kingdom
| | - James A Lister
- Department of Human and Molecular Genetics and Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, Virginia
| | - Eiríkur Steingrimsson
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Iceland, Reykjavik, Iceland
| | - Thierry Voet
- Department of Human Genetics, University of Leuven, KU Leuven, Leuven, Belgium.,Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton, Cambridge, United Kingdom
| | - Chris P Ponting
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom
| | - E Elizabeth Patton
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom. .,CRUK Edinburgh Centre, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom
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3
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Ogmundsdottir MH, Fock V, Sooman L, Pogenberg V, Dilshat R, Bindesbøll C, Ogmundsdottir HM, Simonsen A, Wilmanns M, Steingrimsson E. A short isoform of ATG7 fails to lipidate LC3/GABARAP. Sci Rep 2018; 8:14391. [PMID: 30258106 PMCID: PMC6158294 DOI: 10.1038/s41598-018-32694-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Accepted: 09/10/2018] [Indexed: 12/13/2022] Open
Abstract
Autophagy is a degradation pathway important for cellular homeostasis. The E1-like enzyme ATG7 is a key component of the autophagy machinery, with the main function of mediating the lipidation of LC3/GABARAP during autophagosome formation. By analysing mRNA-sequencing data we found that in addition to the full-length ATG7 isoform, various tissues express a shorter isoform lacking an exon of 27 amino acids in the C-terminal part of the protein, termed ATG7(2). We further show that ATG7(2) does not bind LC3B and fails to mediate the lipidation of members of the LC3/GABARAP family. We have thus identified an isoform of ATG7 that is unable to carry out the best characterized function of the protein during the autophagic response. This short isoform will have to be taken into consideration when further studying the role of ATG7.
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Affiliation(s)
- M H Ogmundsdottir
- Department of Biochemistry and Molecular Biology, Biomedical Center, Faculty of Medicine, University of Iceland, Sturlugata 8, 101, Reykjavik, Iceland.
| | - V Fock
- Department of Biochemistry and Molecular Biology, Biomedical Center, Faculty of Medicine, University of Iceland, Sturlugata 8, 101, Reykjavik, Iceland
| | - L Sooman
- Department of Biochemistry and Molecular Biology, Biomedical Center, Faculty of Medicine, University of Iceland, Sturlugata 8, 101, Reykjavik, Iceland
| | - V Pogenberg
- European Molecular Biology Laboratory, Hamburg Unit, Notkestrasse 85, 22607, Hamburg, Germany
| | - R Dilshat
- Department of Biochemistry and Molecular Biology, Biomedical Center, Faculty of Medicine, University of Iceland, Sturlugata 8, 101, Reykjavik, Iceland
| | - C Bindesbøll
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Sognsvannsveien 9, N-0317, Oslo, Norway
| | - H M Ogmundsdottir
- Cancer Research Laboratory, Biomedical Center, Faculty of Medicine, University of Iceland, Sturlugata 8, 101, Reykjavik, Iceland
| | - A Simonsen
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Sognsvannsveien 9, N-0317, Oslo, Norway
| | - M Wilmanns
- European Molecular Biology Laboratory, Hamburg Unit, Notkestrasse 85, 22607, Hamburg, Germany
| | - E Steingrimsson
- Department of Biochemistry and Molecular Biology, Biomedical Center, Faculty of Medicine, University of Iceland, Sturlugata 8, 101, Reykjavik, Iceland.
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Garcia Llorca A, Gudmundsdóttir Aspelund S, Ogmundsdóttir M, Steingrimsson E, Eysteinsson T. Retinal function and morphology in Mitf mutant mice. Acta Ophthalmol 2016. [DOI: 10.1111/j.1755-3768.2016.0601] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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5
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Garcia Llorca A, Ogmundsdóttir M, Steingrimsson E, Eysteinsson T. Autophagy is affected by Mitf in mouse primary RPE cells. Acta Ophthalmol 2016. [DOI: 10.1111/j.1755-3768.2016.0605] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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6
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Pogenberg V, Milewski M, Deineko V, Schepsky A, Steingrimsson E, Wilmanns M. The particular mechanisms of DNA recognition and dimerization of MITF. Acta Crystallogr A 2011. [DOI: 10.1107/s0108767311082584] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Steingrimsson E, Tessarollo L, Pathak B, Hou L, Arnheiter H, Copeland NG, Jenkins NA. Mitf and Tfe3, two members of the Mitf-Tfe family of bHLH-Zip transcription factors, have important but functionally redundant roles in osteoclast development. Proc Natl Acad Sci U S A 2002; 99:4477-82. [PMID: 11930005 PMCID: PMC123673 DOI: 10.1073/pnas.072071099] [Citation(s) in RCA: 168] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Mitf-Tfe family of basic helix-loop-helix-leucine zipper (bHLH-Zip) transcription factors encodes four family members: Mitf, Tfe3, Tfeb, and Tfec. In vitro, each protein in the family can bind DNA as a homo- or heterodimer with other family members. Mutational studies in mice have shown that Mitf is essential for melanocyte and eye development, whereas Tfeb is required for placental vascularization. Here, we uncover a role for Tfe3 in osteoclast development, a role that is functionally redundant with Mitf. Although osteoclasts seem normal in Mitf or Tfe3 null mice, the combined loss of the two genes results in severe osteopetrosis. We also show that Tfec mutant mice are phenotypically normal, and that the Tfec mutation does not alter the phenotype of Mitf, Tfeb, or Tfe3 mutant mice. Surprisingly, our studies failed to identify any phenotypic overlap between the different Mitf-Tfe mutations. These results suggest that heterodimeric interactions are not essential for Mitf-Tfe function in contrast to other bHLH-Zip families like Myc/Max/Mad, where heterodimeric interactions seem to be essential.
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Affiliation(s)
- Eiríkur Steingrimsson
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Iceland, 101 Reykjavik, Iceland.
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Kristinsson SY, Thorolfsdottir ET, Talseth B, Steingrimsson E, Thorsson AV, Helgason T, Hreidarsson AB, Arngrimsson R. MODY in Iceland is associated with mutations in HNF-1alpha and a novel mutation in NeuroD1. Diabetologia 2001; 44:2098-103. [PMID: 11719843 DOI: 10.1007/s001250100016] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
AIMS/HYPOTHESIS Five different types of maturity-onset diabetes of the young (MODY) have been identified until now but mutation screening suggests that more MODY genes exist. Mutations in genes encoding transcription factors essential for normal development and function of pancreatic beta cells has recently become important in studying the genetics of Type II (non-insulin-dependent) diabetes mellitus. Patients with MODY and their families in Iceland were screened for mutations in the transcription factor genes. METHODS Clinical and biochemical information on individuals with MODY was collected and their family trees constructed. Linkage analysis was carried out on chromosomal regions known to harbour genes previously shown to be associated with MODY. Mutations were identified by direct sequencing. RESULTS Three families were identified. Two of these showed linkage to chromosome 12 and carried mutations in exon 4 of the HNF-1alpha gene (290fsdelC and R272C). However, the third family showed no linkage to the previously described MODY genes but shared a novel mutation in the NeuroD1 gene on chromosome 2q32. This mutation, a glutamate to lysine substitution at codon 110, resides in the basic domain of the protein. CONCLUSION/INTERPRETATION Mutations in MODY subjects have been identified in the Icelandic population. In addition this study identified the NeuroD1 gene as the gene responsible for the sixth type of MODY.
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Affiliation(s)
- S Y Kristinsson
- Unit of Medical Genetics, Faculty of Medicine, University of Iceland, Reykjavik, Iceland
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9
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Mao NC, Steingrimsson E, DuHadaway J, Wasserman W, Ruiz JC, Copeland NG, Jenkins NA, Prendergast GC. The murine Bin1 gene functions early in myogenesis and defines a new region of synteny between mouse chromosome 18 and human chromosome 2. Genomics 1999; 56:51-8. [PMID: 10036185 DOI: 10.1006/geno.1998.5709] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
We cloned and functionally characterized the murine Bin1 gene as a first step to investigate its physiological roles in differentiation, apoptosis, and tumorigenesis. The exon-intron organization of the >/=55-kb gene is similar to that of the human gene. Consistent with a role for Bin1 in apoptosis, the promoter included a functional consensus motif for activation by NF-kappaB, an important regulator of cell death. A muscle regulatory module defined in the human promoter that includes a consensus recognition site for myoD family proteins was not conserved in the mouse promoter. However, Bin1 is upregulated in embryonic development by E10.5 in myotomes, the progenitors of skeletal muscle, supporting a role in myogenesis and suggesting that the mouse and human genes may be controlled somewhat differently during development. In C2C12 myoblasts antisense Bin1 prevents induction of the cell cycle kinase inhibitor p21WAF1, suggesting that it acts at an early time during the muscle differentiation program. Interspecific mouse backcross mapping located the Bin1 locus between Mep1b and Apc on chromosome 18. Since the human gene was mapped previously to chromosome 2q14, the location of Bin1 defines a previously unrecognized region of synteny between human chromosome 2 and mouse chromosome 18.
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Affiliation(s)
- N C Mao
- The Wistar Institute, 3601 Spruce Street, Philadelphia, Pennsylvania, 19104, USA
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Tamimi RM, Steingrimsson E, Montgomery-Dyer K, Copeland NG, Jenkins NA, Tapscott SJ. NEUROD2 and NEUROD3 genes map to human chromosomes 17q12 and 5q23-q31 and mouse chromosomes 11 and 13, respectively. Genomics 1997; 40:355-7. [PMID: 9119405 DOI: 10.1006/geno.1996.4578] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
NEUROD2 and NEUROD3 are transcription factors involved in neurogenesis that are related to the basic helix-loop-helix protein NEUROD. NEUROD2 maps to human chromosome 17q12 and mouse chromosome 11. NEUROD3 maps to human chromosome 5q23-q31 and mouse chromosome 13.
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Affiliation(s)
- R M Tamimi
- Fred Hutchinson Cancer Research Center, Seattle, Washington 98104, USA
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11
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Tamimi R, Steingrimsson E, Copeland NG, Dyer-Montgomery K, Lee JE, Hernandez R, Jenkins NA, Tapscott SJ. The NEUROD gene maps to human chromosome 2q32 and mouse chromosome 2. Genomics 1996; 34:418-21. [PMID: 8786144 DOI: 10.1006/geno.1996.0306] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The Neurod gene is a basic-helix-loop-helix gene that regulates neurogenesis and is identical to the hamster beta2 gene that was cloned as a regulator of insulin transcription. Here we report the cloning of human NEUROD and mapping of the gene to human chromosome 2q32 and to mouse chromosome 2.
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Affiliation(s)
- R Tamimi
- Fred Hutchinson Cancer Research Center, 1124 Columbia Street, Seattle, Washington, 98104, USA
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12
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Cross JC, Flannery ML, Blanar MA, Steingrimsson E, Jenkins NA, Copeland NG, Rutter WJ, Werb Z. Hxt encodes a basic helix-loop-helix transcription factor that regulates trophoblast cell development. Development 1995; 121:2513-23. [PMID: 7671815 DOI: 10.1242/dev.121.8.2513] [Citation(s) in RCA: 230] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Trophoblast cells are the first lineage to form in the mammalian conceptus and mediate the process of implantation. We report the cloning of a basic helix-loop-helix (bHLH) transcription factor gene, Hxt, that is expressed in early trophoblast and in differentiated giant cells. A separate gene, Hed, encodes a related protein that is expressed in maternal deciduum surrounding the implantation site. Overexpression of Hxt in mouse blastomeres directed their development into trophoblast cells in blastocysts. In addition, overexpression of Hxt induced the differentiation of rat trophoblast (Rcho-1) stem cells as assayed by changes in cell adhesion and by activation of the placental lactogen-I gene promoter, a trophoblast giant cell-specific gene. In contrast, the negative HLH regulator, Id-1, inhibited Rcho-1 differentiation and placental lactogen-I transcription. These data demonstrate a role for HLH factors in regulating trophoblast development and indicate a positive role for Hxt in promoting the formation of trophoblast giant cells.
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Affiliation(s)
- J C Cross
- Department of Anatomy, University of California, San Francisco 94143, USA
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13
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Abstract
At the poles of the Drosophila embryo, cell fate is established by a pathway that begins with the activation of a membrane-associated tyrosine kinase (the torso gene product); this then leads to activation of a serine/threonine kinase (Drosophila Raf-1). Activated Raf-1 then leads, by an undefined mechanism, to the transcriptional activation of the tailless (tll) gene; the tll gene product, itself a transcription factor, subsequently regulates the expression of an array of target genes. To further define this pathway, we have utilized sequence comparison between Drosophila melanogaster and Drosophila virilis to identify conserved elements in the tll promoter region. As assessed by DNase I footprinting and promoter dissection experiments, two of these elements are potential regulatory targets of Raf-1-activated transcription factors. Sequence comparison also reveals that the unique residues in the DNA-binding domain of the tll protein, the next component in the pathway, are conserved. One of these residues, the alanine after the last cysteine in the first zinc finger, may be responsible for part of the difference between the tll protein DNA binding site and the closely related half-site of the retinoid/estrogen receptors. Consistent with the rapid turnover of the tll protein, it contains a PEST sequence (rich in proline, glutamate and aspartate, serine, and threonine) that is also conserved.
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Affiliation(s)
- G J Liaw
- Department of Biology, University of California, Los Angeles 90024
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