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Moses A, Bhalla P, Thompson A, Lai L, Coskun FS, Seroogy CM, de la Morena MT, Wysocki CA, van Oers NSC. Comprehensive phenotypic analysis of diverse FOXN1 variants. J Allergy Clin Immunol 2023; 152:1273-1291.e15. [PMID: 37419334 PMCID: PMC11071152 DOI: 10.1016/j.jaci.2023.06.019] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2022] [Revised: 05/05/2023] [Accepted: 06/08/2023] [Indexed: 07/09/2023]
Abstract
BACKGROUND Thymus hypoplasia due to stromal cell problems has been linked to mutations in several transcription factors, including Forkhead box N1 (FOXN1). FOXN1 supports T-cell development by regulating the formation and expansion of thymic epithelial cells (TECs). While autosomal recessive FOXN1 mutations result in a nude and severe combined immunodeficiency phenotype, the impact of single-allelic or compound heterozygous FOXN1 mutations is less well-defined. OBJECTIVE With more than 400 FOXN1 mutations reported, their impact on protein function and thymopoiesis remains unclear for most variants. We developed a systematic approach to delineate the functional impact of diverse FOXN1 variants. METHODS Selected FOXN1 variants were tested with transcriptional reporter assays and imaging studies. Thymopoiesis was assessed in mouse lines genocopying several human FOXN1 variants. Reaggregate thymus organ cultures were used to compare the thymopoietic potential of the FOXN1 variants. RESULTS FOXN1 variants were categorized into benign, loss- or gain-of-function, and/or dominant-negatives. Dominant negative activities mapped to frameshift variants impacting the transactivation domain. A nuclear localization signal was mapped within the DNA binding domain. Thymopoiesis analyses with mouse models and reaggregate thymus organ cultures revealed distinct consequences of particular Foxn1 variants on T-cell development. CONCLUSIONS The potential effect of a FOXN1 variant on T-cell output from the thymus may relate to its effects on transcriptional activity, nuclear localization, and/or dominant negative functions. A combination of functional assays and thymopoiesis comparisons enabled a categorization of diverse FOXN1 variants and their potential impact on T-cell output from the thymus.
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Affiliation(s)
- Angela Moses
- Department of Immunology, University of Texas Southwestern Medical Center, Dallas, Tex
| | - Pratibha Bhalla
- Department of Immunology, University of Texas Southwestern Medical Center, Dallas, Tex
| | - Austin Thompson
- Department of Immunology, University of Texas Southwestern Medical Center, Dallas, Tex
| | - Laijun Lai
- Department of Allied Health Sciences, University of Connecticut, Storrs, Conn
| | - Fatma S Coskun
- Department of Immunology, University of Texas Southwestern Medical Center, Dallas, Tex
| | - Christine M Seroogy
- the Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, Wis
| | - Maria Teresa de la Morena
- the Department of Pediatrics, University of Washington and Seattle Children's Hospital, Seattle, Wash
| | - Christian A Wysocki
- Departments of Pediatrics, University of Texas Southwestern Medical Center, Dallas, Tex; Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Tex
| | - Nicolai S C van Oers
- Department of Immunology, University of Texas Southwestern Medical Center, Dallas, Tex; Departments of Pediatrics, University of Texas Southwestern Medical Center, Dallas, Tex; Microbiology, University of Texas Southwestern Medical Center, Dallas, Tex.
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Kadouri N, Givony T, Nevo S, Hey J, Ben Dor S, Damari G, Dassa B, Dobes J, Weichenhan D, Bähr M, Paulsen M, Haffner-Krausz R, Mall MA, Plass C, Goldfarb Y, Abramson J. Transcriptional regulation of the thymus master regulator Foxn1. Sci Immunol 2022; 7:eabn8144. [PMID: 36026441 DOI: 10.1126/sciimmunol.abn8144] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
FOXN1 is a transcription factor critical for the development of both thymic epithelial cell (TEC) and hair follicle cell (HFC) compartments. However, mechanisms controlling its expression remain poorly understood. To address this question, we performed thorough analyses of the evolutionary conservation and chromatin status of the Foxn1 locus in different tissues and states and identified several putative cis-regulatory regions unique to TECs versus HFCs. Furthermore, experiments using genetically modified mice with specific deletions in the Foxn1 locus and additional bioinformatic analyses helped us identify key regions and transcription factors involved in either positive or negative regulation of Foxn1 in both TECs and HFCs. Specifically, we identified SIX1 and FOXN1 itself as key factors inducing Foxn1 expression in embryonic and neonatal TECs. Together, our data provide important mechanistic insights into the transcriptional regulation of the Foxn1 gene in TEC versus HFC and highlight the role of FOXN1 in its autoregulation.
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Affiliation(s)
- Noam Kadouri
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Tal Givony
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Shir Nevo
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Joschka Hey
- Division of Cancer Epigenomics, German Cancer Research Center (DKFZ), Heidelberg, Germany.,Ruprecht Karl University of Heidelberg, Heidelberg, Germany
| | - Shifra Ben Dor
- Bioinformatics Unit, Weizmann Institute of Science, Rehovot, Israel
| | - Golda Damari
- Department of Veterinary Resources, Weizmann Institute of Science, Rehovot, Israel
| | - Bareket Dassa
- Bioinformatics Unit, Weizmann Institute of Science, Rehovot, Israel
| | - Jan Dobes
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Dieter Weichenhan
- Division of Cancer Epigenomics, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Marion Bähr
- Division of Cancer Epigenomics, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Michelle Paulsen
- Translational Lung Research Center Heidelberg (TLRC), German Center for Lung Research (DZL), Heidelberg, Germany.,Department of Translational Pulmonology, University of Heidelberg, Heidelberg, Germany
| | | | - Marcus A Mall
- Translational Lung Research Center Heidelberg (TLRC), German Center for Lung Research (DZL), Heidelberg, Germany.,Department of Translational Pulmonology, University of Heidelberg, Heidelberg, Germany.,Charité-Universitätsmedizin Berlin, Berlin, Germany
| | - Christoph Plass
- Division of Cancer Epigenomics, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Yael Goldfarb
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Jakub Abramson
- Department of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot, Israel
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Bhalla P, Su DM, van Oers NSC. Thymus Functionality Needs More Than a Few TECs. Front Immunol 2022; 13:864777. [PMID: 35757725 PMCID: PMC9229346 DOI: 10.3389/fimmu.2022.864777] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Accepted: 05/03/2022] [Indexed: 12/18/2022] Open
Abstract
The thymus, a primary lymphoid organ, produces the T cells of the immune system. Originating from the 3rd pharyngeal pouch during embryogenesis, this organ functions throughout life. Yet, thymopoiesis can be transiently or permanently damaged contingent on the types of systemic stresses encountered. The thymus also undergoes a functional decline during aging, resulting in a progressive reduction in naïve T cell output. This atrophy is evidenced by a deteriorating thymic microenvironment, including, but not limited, epithelial-to-mesenchymal transitions, fibrosis and adipogenesis. An exploration of cellular changes in the thymus at various stages of life, including mouse models of in-born errors of immunity and with single cell RNA sequencing, is revealing an expanding number of distinct cell types influencing thymus functions. The thymus microenvironment, established through interactions between immature and mature thymocytes with thymus epithelial cells (TEC), is well known. Less well appreciated are the contributions of neural crest cell-derived mesenchymal cells, endothelial cells, diverse hematopoietic cell populations, adipocytes, and fibroblasts in the thymic microenvironment. In the current review, we will explore the contributions of the many stromal cell types participating in the formation, expansion, and contraction of the thymus under normal and pathophysiological processes. Such information will better inform approaches for restoring thymus functionality, including thymus organoid technologies, beneficial when an individuals’ own tissue is congenitally, clinically, or accidentally rendered non-functional.
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Affiliation(s)
- Pratibha Bhalla
- Department of Immunology, The University of Texas Southwestern Medical Center, Dallas, TX, United States
| | - Dong-Ming Su
- Department of Microbiology, Immunology & Genetics, The University of North Texas Health Sciences Center, Fort Worth, TX, United States
| | - Nicolai S C van Oers
- Department of Immunology, The University of Texas Southwestern Medical Center, Dallas, TX, United States.,Department of Microbiology, The University of Texas Southwestern Medical Center, Dallas, TX, United States.,Department of Pediatrics, The University of Texas Southwestern Medical Center, Dallas, TX, United States
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Bhalla P, Wysocki CA, van Oers NSC. Molecular Insights Into the Causes of Human Thymic Hypoplasia With Animal Models. Front Immunol 2020; 11:830. [PMID: 32431714 PMCID: PMC7214791 DOI: 10.3389/fimmu.2020.00830] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Accepted: 04/14/2020] [Indexed: 12/30/2022] Open
Abstract
22q11.2 deletion syndrome (DiGeorge), CHARGE syndrome, Nude/SCID and otofaciocervical syndrome type 2 (OTFCS2) are distinct clinical conditions in humans that can result in hypoplasia and occasionally, aplasia of the thymus. Thymic hypoplasia/aplasia is first suggested by absence or significantly reduced numbers of recent thymic emigrants, revealed in standard-of-care newborn screens for T cell receptor excision circles (TRECs). Subsequent clinical assessments will often indicate whether genetic mutations are causal to the low T cell output from the thymus. However, the molecular mechanisms leading to the thymic hypoplasia/aplasia in diverse human syndromes are not fully understood, partly because the problems of the thymus originate during embryogenesis. Rodent and Zebrafish models of these clinical syndromes have been used to better define the underlying basis of the clinical presentations. Results from these animal models are uncovering contributions of different cell types in the specification, differentiation, and expansion of the thymus. Cell populations such as epithelial cells, mesenchymal cells, endothelial cells, and thymocytes are variably affected depending on the human syndrome responsible for the thymic hypoplasia. In the current review, findings from the diverse animal models will be described in relation to the clinical phenotypes. Importantly, these results are suggesting new strategies for regenerating thymic tissue in patients with distinct congenital disorders.
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Affiliation(s)
- Pratibha Bhalla
- Department of Immunology, The University of Texas Southwestern Medical Center, Dallas, TX, United States
| | - Christian A Wysocki
- Department of Pediatrics, The University of Texas Southwestern Medical Center, Dallas, TX, United States
| | - Nicolai S C van Oers
- Department of Immunology, The University of Texas Southwestern Medical Center, Dallas, TX, United States.,Department of Pediatrics, The University of Texas Southwestern Medical Center, Dallas, TX, United States.,Department of Microbiology, The University of Texas Southwestern Medical Center, Dallas, TX, United States
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