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Kim KL, Rahme GJ, Goel VY, El Farran CA, Hansen AS, Bernstein BE. Dissection of a CTCF topological boundary uncovers principles of enhancer-oncogene regulation. Mol Cell 2024; 84:1365-1376.e7. [PMID: 38452764 PMCID: PMC10997458 DOI: 10.1016/j.molcel.2024.02.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2023] [Revised: 01/03/2024] [Accepted: 02/08/2024] [Indexed: 03/09/2024]
Abstract
Enhancer-gene communication is dependent on topologically associating domains (TADs) and boundaries enforced by the CCCTC-binding factor (CTCF) insulator, but the underlying structures and mechanisms remain controversial. Here, we investigate a boundary that typically insulates fibroblast growth factor (FGF) oncogenes but is disrupted by DNA hypermethylation in gastrointestinal stromal tumors (GISTs). The boundary contains an array of CTCF sites that enforce adjacent TADs, one containing FGF genes and the other containing ANO1 and its putative enhancers, which are specifically active in GIST and its likely cell of origin. We show that coordinate disruption of four CTCF motifs in the boundary fuses the adjacent TADs, allows the ANO1 enhancer to contact FGF3, and causes its robust induction. High-resolution micro-C maps reveal specific contact between transcription initiation sites in the ANO1 enhancer and FGF3 promoter that quantitatively scales with FGF3 induction such that modest changes in contact frequency result in strong changes in expression, consistent with a causal relationship.
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Affiliation(s)
- Kyung Lock Kim
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Gene Regulation Observatory, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA; Departments of Cell Biology and Pathology, Harvard Medical School, Boston, MA 02215, USA
| | - Gilbert J Rahme
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Gene Regulation Observatory, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA; Departments of Cell Biology and Pathology, Harvard Medical School, Boston, MA 02215, USA
| | - Viraat Y Goel
- Gene Regulation Observatory, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA; Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Koch Institute for Integrative Cancer Research, Cambridge, MA 02139, USA
| | - Chadi A El Farran
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Gene Regulation Observatory, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA; Departments of Cell Biology and Pathology, Harvard Medical School, Boston, MA 02215, USA
| | - Anders S Hansen
- Gene Regulation Observatory, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA; Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Koch Institute for Integrative Cancer Research, Cambridge, MA 02139, USA
| | - Bradley E Bernstein
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Gene Regulation Observatory, Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA; Departments of Cell Biology and Pathology, Harvard Medical School, Boston, MA 02215, USA.
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Salahudeen AA, Seoane JA, Yuki K, Mah AT, Smith AR, Kolahi K, De la O SM, Hart DJ, Ding J, Ma Z, Barkal SA, Shukla ND, Zhang CH, Cantrell MA, Batish A, Usui T, Root DE, Hahn WC, Curtis C, Kuo CJ. Functional screening of amplification outlier oncogenes in organoid models of early tumorigenesis. Cell Rep 2023; 42:113355. [PMID: 37922313 PMCID: PMC10841581 DOI: 10.1016/j.celrep.2023.113355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Revised: 08/30/2023] [Accepted: 10/12/2023] [Indexed: 11/05/2023] Open
Abstract
Somatic copy number gains are pervasive across cancer types, yet their roles in oncogenesis are insufficiently evaluated. This inadequacy is partly due to copy gains spanning large chromosomal regions, obscuring causal loci. Here, we employed organoid modeling to evaluate candidate oncogenic loci identified via integrative computational analysis of extreme copy gains overlapping with extreme expression dysregulation in The Cancer Genome Atlas. Subsets of "outlier" candidates were contextually screened as tissue-specific cDNA lentiviral libraries within cognate esophagus, oral cavity, colon, stomach, pancreas, and lung organoids bearing initial oncogenic mutations. Iterative analysis nominated the kinase DYRK2 at 12q15 as an amplified head and neck squamous carcinoma oncogene in p53-/- oral mucosal organoids. Similarly, FGF3, amplified at 11q13 in 41% of esophageal squamous carcinomas, promoted p53-/- esophageal organoid growth reversible by small molecule and soluble receptor antagonism of FGFRs. Our studies establish organoid-based contextual screening of candidate genomic drivers, enabling functional evaluation during early tumorigenesis.
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Affiliation(s)
- Ameen A Salahudeen
- Stanford University School of Medicine, Department of Medicine, Divisions of Hematology, Stanford, CA 94305, USA; University of Illinois at Chicago College of Medicine, Department of Medicine, Division of Hematology and Oncology, Chicago, IL 60612, USA; Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago College of Medicine, Chicago, IL 60612, USA; University of Illinois Cancer Center, Chicago, IL 60612, USA.
| | - Jose A Seoane
- Stanford University School of Medicine, Department of Medicine, Divisions of Oncology, Stanford, CA 94305, USA; Cancer Computational Biology Group, Vall d'Hebron Institute of Oncology (VHIO), 08035 Barcelona, Spain.
| | - Kanako Yuki
- Stanford University School of Medicine, Department of Medicine, Divisions of Hematology, Stanford, CA 94305, USA
| | - Amanda T Mah
- Stanford University School of Medicine, Department of Medicine, Divisions of Hematology, Stanford, CA 94305, USA
| | - Amber R Smith
- Stanford University School of Medicine, Department of Medicine, Divisions of Hematology, Stanford, CA 94305, USA
| | - Kevin Kolahi
- Stanford University School of Medicine, Department of Medicine, Divisions of Hematology, Stanford, CA 94305, USA
| | - Sean M De la O
- Stanford University School of Medicine, Department of Medicine, Divisions of Hematology, Stanford, CA 94305, USA
| | - Daniel J Hart
- Stanford University School of Medicine, Department of Medicine, Divisions of Hematology, Stanford, CA 94305, USA
| | - Jie Ding
- Stanford University School of Medicine, Department of Medicine, Divisions of Oncology, Stanford, CA 94305, USA
| | - Zhicheng Ma
- Stanford University School of Medicine, Department of Medicine, Divisions of Oncology, Stanford, CA 94305, USA
| | - Sammy A Barkal
- Stanford University School of Medicine, Department of Medicine, Divisions of Hematology, Stanford, CA 94305, USA
| | - Navika D Shukla
- Stanford University School of Medicine, Department of Medicine, Divisions of Hematology, Stanford, CA 94305, USA
| | - Chuck H Zhang
- Stanford University School of Medicine, Department of Medicine, Divisions of Hematology, Stanford, CA 94305, USA
| | - Michael A Cantrell
- Stanford University School of Medicine, Department of Medicine, Divisions of Hematology, Stanford, CA 94305, USA
| | - Arpit Batish
- Stanford University School of Medicine, Department of Medicine, Divisions of Hematology, Stanford, CA 94305, USA
| | - Tatsuya Usui
- Stanford University School of Medicine, Department of Medicine, Divisions of Hematology, Stanford, CA 94305, USA
| | - David E Root
- Broad Institute of MIT and Harvard, 415 Main Street, Cambridge, MA 02142, USA
| | - William C Hahn
- Broad Institute of MIT and Harvard, 415 Main Street, Cambridge, MA 02142, USA; Dana-Farber Cancer Institute, Department of Medical Oncology, 450 Brookline Avenue, Boston, MA 02215, USA
| | - Christina Curtis
- Stanford University School of Medicine, Department of Medicine, Divisions of Oncology, Stanford, CA 94305, USA; Stanford University School of Medicine, Department of Medicine, Divisions of Genetics, Stanford, CA 94305, USA
| | - Calvin J Kuo
- Stanford University School of Medicine, Department of Medicine, Divisions of Hematology, Stanford, CA 94305, USA.
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3
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Huang H, Chen Q, Xu Z, Liu F. FGF3 Directs the Pathfinding of Prethalamic GABAergic Axons. Int J Mol Sci 2023; 24:14998. [PMID: 37834446 PMCID: PMC10573444 DOI: 10.3390/ijms241914998] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2023] [Revised: 09/26/2023] [Accepted: 10/05/2023] [Indexed: 10/15/2023] Open
Abstract
The thalamus plays a crucial role in ensuring the faithful transfer of sensory information, except olfactory signals, to corresponding cortical areas. However, thalamic function is not simply restricted to relaying information to and from the cerebral cortex. The ability to modulate the flow of sensory information is supported by a second abundant neuronal type in the prethalamus, the inhibitory gamma-aminobutyric acid (GABAergic) neurons, which project inhibitory GABAergic axons to dorsal thalamic glutamatergic neurons. Interestingly, during the trajectory of pioneer prethalamic axons, morphogen fibroblast growth factor (FGF)-3 is expressed in the ventral chick hypothalamus. Using in vitro analyses in chick explants, we identify a chemorepellent effect of FGF3 on nearby prethalamic GABAergic axons. Furthermore, inhibition of FGF3 guidance functions indicates that FGF3 signaling is necessary to navigate prethalamic axons correctly. Gene expression analyses and loss of function studies demonstrate that FGF3 mediates prethalamic axonal guidance through the downstream pathway of the FGF receptor (FGFR)-1. Together, these results suggest that FGF3 expressed in the hypothalamus functions as a chemorepellent molecule to direct the pathway selection of neighboring GABAergic axons.
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Affiliation(s)
- Hong Huang
- Department of Cell Biology, School of Basic Medical Sciences, Nanchang University, Nanchang 330031, China
- Medical Experimental Teaching Center, School of Basic Medical Sciences, Nanchang University, Nanchang 330031, China
| | - Qingyi Chen
- Department of Cell Biology, School of Basic Medical Sciences, Nanchang University, Nanchang 330031, China
- Medical Experimental Teaching Center, School of Basic Medical Sciences, Nanchang University, Nanchang 330031, China
| | - Zhengang Xu
- Medical Experimental Teaching Center, School of Basic Medical Sciences, Nanchang University, Nanchang 330031, China
| | - Fang Liu
- Department of Cell Biology, School of Basic Medical Sciences, Nanchang University, Nanchang 330031, China
- Medical Experimental Teaching Center, School of Basic Medical Sciences, Nanchang University, Nanchang 330031, China
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Hutchings C, Sela-Donenfeld D. Primer on FGF3. Differentiation 2023:S0301-4681(23)00069-5. [PMID: 37741710 DOI: 10.1016/j.diff.2023.09.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2023] [Revised: 08/30/2023] [Accepted: 09/11/2023] [Indexed: 09/25/2023]
Abstract
Though initially discovered as a proto-oncogene in virally induced mouse mammary tumors, FGF3 is primarily active in prenatal stages, where it is found at various sites at specific times. FGF3 is crucial during development, as its roles include tail formation, inner ear development and hindbrain induction and patterning. FGF3 expression and function are highly conserved in vertebrates, while it also interacts with other FGFs in various developmental processes. Intriguingly, while it is classified as a classical paracrine signaling factor, murine FGF3 was uniquely found to also act in an intracrine manner, depending on alternative translation initiation sites. Corresponding with its conserved role in inner ear morphogenesis, mutations in FGF3 in humans are associated with LAMM syndrome, a disorder that include hearing loss and inner ear malformations. While recent studies indicate of some FGF3 presence in post-natal stages, emerging evidences of its upregulation in various human tumors and cariogenic processes in mouse models, highlights the importance of its close regulation in adult tissues. Altogether, the broad and dynamic expression pattern and regulation of FGF3 in embryonic and adult tissues together with its link to congenital malformations and cancer, calls for further discoveries of its diverse roles in health and disease.
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Affiliation(s)
- Carmel Hutchings
- Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agricultural, Food and Environmental Sciences, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Dalit Sela-Donenfeld
- Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agricultural, Food and Environmental Sciences, The Hebrew University of Jerusalem, Rehovot, Israel.
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5
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Fiore M, Taddia A, Indio V, Bertuccio SN, Messelodi D, Serravalle S, Bandini J, Spreafico F, Perotti D, Collini P, Di Cataldo A, Pasquinelli G, Chiarini F, Fois M, Melchionda F, Pession A, Astolfi A. Molecular Signature of Biological Aggressiveness in Clear Cell Sarcoma of the Kidney (CCSK). Int J Mol Sci 2023; 24. [PMID: 36835166 DOI: 10.3390/ijms24043743] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Revised: 02/06/2023] [Accepted: 02/07/2023] [Indexed: 02/16/2023] Open
Abstract
Clear cell sarcoma of the kidney (CCSK) is a rare pediatric renal tumor with a worse prognosis than Wilms' tumor. Although recently, BCOR internal tandem duplication (ITD) has been found as a driver mutation in more than 80% of cases, a deep molecular characterization of this tumor is still lacking, as well as its correlation with the clinical course. The aim of this study was to investigate the differential molecular signature between metastatic and localized BCOR-ITD-positive CCSK at diagnosis. Whole-exome sequencing (WES) and whole-transcriptome sequencing (WTS) were performed on six localized and three metastatic BCOR-ITD-positive CCSKs, confirming that this tumor carries a low mutational burden. No significant recurrences of somatic or germline mutations other than BCOR-ITD were identified among the evaluated samples. Supervised analysis of gene expression data showed enrichment of hundreds of genes, with a significant overrepresentation of the MAPK signaling pathway in metastatic cases (p < 0.0001). Within the molecular signature of metastatic CCSK, five genes were highly and significantly over-expressed: FGF3, VEGFA, SPP1, ADM, and JUND. The role of FGF3 in the acquisition of a more aggressive phenotype was investigated in a cell model system obtained by introducing the ITD into the last exon of BCOR by Crispr/Cas9 gene editing of the HEK-293 cell line. Treatment with FGF3 of BCOR-ITD HEK-293 cell line induced a significant increase in cell migration versus both untreated and scramble cell clone. The identification of over-expressed genes in metastatic CCSKs, with a particular focus on FGF3, could offer new prognostic and therapeutic targets in more aggressive cases.
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Liu K, Lv Z, Huang H, Yu S, Xiao L, Li X, Li G, Liu F. FGF3 from the Hypothalamus Regulates the Guidance of Thalamocortical Axons. Dev Neurosci 2021; 42:208-216. [PMID: 33684917 DOI: 10.1159/000513534] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2020] [Accepted: 12/02/2020] [Indexed: 11/19/2022] Open
Abstract
Thalamus is an important sensory relay station: afferent sensory information, except olfactory signals, is transmitted by thalamocortical axons (TCAs) to the cerebral cortex. The pathway choice of TCAs depends on diverse diffusible or substrate-bound guidance cues in the environment. Not only classical guidance cues (ephrins, slits, semaphorins, and netrins), morphogens, which exerts patterning effects during early embryonic development, can also help axons navigate to their targets at later development stages. Here, expression analyses reveal that morphogen Fibroblast growth factor (FGF)-3 is expressed in the chick ventral diencephalon, hypothalamus, during the pathfinding of TCAs. Then, using in vitro analyses in chick explants, we identify a concentration-dependent effect of FGF3 on thalamic axons: attractant 100 ng/mL FGF3 transforms to a repellent at high concentration 500 ng/mL. Moreover, inhibition of FGF3 guidance functions indicates that FGF3 signaling is necessary for the correct navigation of thalamic axons. Together, these studies demonstrate a direct effect for the member of FGF7 subfamily, FGF3, in the axonal pathfinding of TCAs.
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Affiliation(s)
- Kuan Liu
- School of Basic Medical Sciences, Medical college of Nanchang University, Nanchang, China
| | - Zhongsheng Lv
- School of Basic Medical Sciences, Medical college of Nanchang University, Nanchang, China
| | - Hong Huang
- School of Basic Medical Sciences, Medical college of Nanchang University, Nanchang, China
| | - Shuyang Yu
- School of Basic Medical Sciences, Medical college of Nanchang University, Nanchang, China
| | - Li Xiao
- School of Basic Medical Sciences, Medical college of Nanchang University, Nanchang, China
| | - Xiang Li
- School of Basic Medical Sciences, Medical college of Nanchang University, Nanchang, China
| | - Gang Li
- School of Basic Medical Sciences, Medical college of Nanchang University, Nanchang, China
| | - Fang Liu
- School of Basic Medical Sciences, Medical college of Nanchang University, Nanchang, China,
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7
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Al Yassin A, D'Arco F, Morín M, Pagarkar W, Harrop-Griffiths K, Shaida A, Fernández E, Cullup T, De-Souza B, Moreno-Pelayo MA, Bitner-Glindzicz M. Three New Mutations and Mild, Asymmetrical Phenotype in the Highly Distinctive LAMM Syndrome: A Report of Eight Further Cases. Genes (Basel) 2019; 10:E529. [PMID: 31336982 DOI: 10.3390/genes10070529] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2019] [Revised: 07/04/2019] [Accepted: 07/04/2019] [Indexed: 11/17/2022] Open
Abstract
Labyrinthine aplasia, microtia, and microdontia (LAMM) is an autosomal recessive condition causing profound congenital deafness, complete absence of inner ear structures (usually Michel’s aplasia), microtia (usually type 1) and microdontia. To date, several families have been described with this condition and a number of mutations has been reported. We report on eight further cases of LAMM syndrome including three novel mutations, c. 173T>C p.L58P; c. 284G>A p.(Arg95Gln) and c.325_327delinsA p.(Glu109Thrfs*18). Congenital deafness was the primary presenting feature in all affected individuals and consanguinity in all but two families. We compare the features in our patients to those previously reported in LAMM, and describe a milder, asymmetrical phenotype associated with FGF3 mutations.
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Dos Santos ÍGD, Jorge EC, Copola AGL, Bertassoli BM, Goes AMD, Silva GAB. FGF2, FGF3 and FGF4 expression pattern during molars odontogenesis in Didelphis albiventris. Acta Histochem 2017; 119:129-141. [PMID: 28012573 DOI: 10.1016/j.acthis.2016.12.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Revised: 11/30/2016] [Accepted: 12/07/2016] [Indexed: 12/12/2022]
Abstract
Odontogenesis is guided by a complex signaling cascade in which several molecules, including FGF2-4, ensure all dental groups development and specificity. Most of the data on odontogenesis derives from rodents, which does not have all dental groups. Didelphis albiventris is an opossum with the closest dentition to humans, and the main odontogenesis stages occur when the newborns are in the pouch. In this study, D. albiventris postnatals were used to characterize the main stages of their molars development; and also to establish FGF2, FGF3 and FGF4 expression pattern. D. albiventris postnatals were processed for histological and indirect immunoperoxidase analysis of the tooth germs. Our results revealed similar dental structures between D. albiventris and mice. However, FGF2, FGF3 and FGF4 expression patterns were observed in a larger number of dental structures, suggesting broader functions for these molecules in this opossum species. The knowledge of the signaling that determinates odontogenesis in an animal model with complete dentition may contribute to the development of therapies for the replacement of lost teeth in humans. This study may also contribute to the implementation of D. albiventris as model for Developmental Biology studies.
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Affiliation(s)
- Íria Gabriela Dias Dos Santos
- Universidade Federal de Minas Gerais, Instituto de Ciências Biológicas, Departamento de Morfologia, Avenida Presidente Antônio Carlos 6627, CEP 31270-901 Belo Horizonte, Minas Gerais, Brazil.
| | - Erika Cristina Jorge
- Universidade Federal de Minas Gerais, Instituto de Ciências Biológicas, Departamento de Morfologia, Avenida Presidente Antônio Carlos 6627, CEP 31270-901 Belo Horizonte, Minas Gerais, Brazil.
| | - Aline Gonçalves Lio Copola
- Universidade Federal de Minas Gerais, Instituto de Ciências Biológicas, Departamento de Morfologia, Avenida Presidente Antônio Carlos 6627, CEP 31270-901 Belo Horizonte, Minas Gerais, Brazil.
| | - Bruno Machado Bertassoli
- Universidade Federal de Minas Gerais, Instituto de Ciências Biológicas, Departamento de Morfologia, Avenida Presidente Antônio Carlos 6627, CEP 31270-901 Belo Horizonte, Minas Gerais, Brazil.
| | - Alfredo Miranda de Goes
- Universidade Federal de Minas Gerais, Instituto de Ciências Biológicas, Departamento de Morfologia, Avenida Presidente Antônio Carlos 6627, CEP 31270-901 Belo Horizonte, Minas Gerais, Brazil.
| | - Gerluza Aparecida Borges Silva
- Universidade Federal de Minas Gerais, Instituto de Ciências Biológicas, Departamento de Morfologia, Avenida Presidente Antônio Carlos 6627, CEP 31270-901 Belo Horizonte, Minas Gerais, Brazil.
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Anderson MJ, Southon E, Tessarollo L, Lewandoski M. Fgf3-Fgf4-cis: A new mouse line for studying Fgf functions during mouse development. Genesis 2016; 54:91-8. [PMID: 26666435 DOI: 10.1002/dvg.22913] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2015] [Revised: 12/09/2015] [Accepted: 12/10/2015] [Indexed: 01/15/2023]
Abstract
The fibroblast growth factor (FGF) family consists of 22 ligands in mice and humans. FGF signaling is vital for embryogenesis and, when dysregulated, can cause disease. Loss-of-function genetic analysis in the mouse has been crucial for understanding FGF function. Such analysis has revealed that multiple Fgfs sometimes function redundantly. Exploring such redundancy between Fgf3 and Fgf4 is currently impossible because both genes are located on chromosome 7, about 18.5 kb apart, making the frequency of interallelic cross-over between existing mutant alleles too infrequent to be practicable. Therefore, we retargeted Fgf3 and Fgf4 in cis, generating an Fgf3 null allele and a conditional Fgf4 allele, subject to Cre inactivation. To increase the frequency of cis targeting, we used an F1 embryonic stem cell line that contained 129/SvJae (129) and C57BL/6J (B6) chromosomes and targeting constructs isogenic to the 129 chromosome. We confirmed cis targeting by assaying for B6/129 allele-specific single-nucleotide polymorphisms. We demonstrated the utility of the Fgf3(Δ)-Fgf4(flox)-cis mouse line by showing that the caudal axis extension defects found in the Fgf3 mutants worsen when Fgf4 is also inactivated. This Fgf3(Δ)-Fgf4(flox)-cis line will be useful to study redundancy of these genes in a variety of tissues and stages in development.
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Affiliation(s)
- Matthew J Anderson
- Cancer and Developmental Biology Laboratory, National Cancer Institute, Frederick, 21702, Maryland
| | - Eileen Southon
- Mouse Cancer Genetics Program, National Cancer Institute, Frederick, 21702, Maryland
| | - Lino Tessarollo
- Mouse Cancer Genetics Program, National Cancer Institute, Frederick, 21702, Maryland
| | - Mark Lewandoski
- Cancer and Developmental Biology Laboratory, National Cancer Institute, Frederick, 21702, Maryland
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