title: Foxn1 regulates lineage progression in cortical and medullary thymic epithelial cells but is dispensable for medullary sublineage divergence.
abstract: The forkhead transcription factor Foxn1 is indispensable for thymus development, but the mechanisms by which it mediates thymic epithelial cell (TEC) development are poorly understood. To examine the cellular and molecular basis of Foxn1 function, we generated a novel and revertible hypomorphic allele of Foxn1. By varying levels of its expression, we identified a number of features of the Foxn1 system. Here we show that Foxn1 is a powerful regulator of TEC differentiation that is required at multiple intermediate stages of TE lineage development in the fetal and adult thymus. We find no evidence for a role for Foxn1 in TEC fate-choice. Rather, we show it is required for stable entry into both the cortical and medullary TEC differentiation programmes and subsequently is needed at increasing dosage for progression through successive differentiation states in both cortical and medullary TEC. We further demonstrate regulation by Foxn1 of a suite of genes with diverse roles in thymus development and/or function, suggesting it acts as a master regulator of the core thymic epithelial programme rather than regulating a particular aspect of TEC biology. Overall, our data establish a genetics-based model of cellular hierarchies in the TE lineage and provide mechanistic insight relating titration of a single transcription factor to control of lineage progression. Our novel revertible hypomorph system may be similarly applied to analyzing other regulators of development.
authors.affiliation: MRC Centre for Regenerative Medicine, Institute for Stem Cell Research, School of Biological Sciences, University of Edinburgh, Edinburgh, UK.
authors.forename: Craig S
authors.initials: CS
authors.lastname: Nowell
authors.forename: Nicholas
authors.initials: N
authors.lastname: Bredenkamp
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Tetélin
authors.forename: Xin
authors.initials: X
authors.lastname: Jin
authors.forename: Christin
authors.initials: C
authors.lastname: Tischner
authors.forename: Harsh
authors.initials: H
authors.lastname: Vaidya
authors.forename: Julie M
authors.initials: JM
authors.lastname: Sheridan
authors.forename: Frances Hogg
authors.initials: FH
authors.lastname: Stenhouse
authors.forename: Raphaela
authors.initials: R
authors.lastname: Heussen
authors.forename: Andrew J H
authors.initials: AJ
authors.lastname: Smith
authors.forename: C Clare
authors.initials: CC
authors.lastname: Blackburn
mesh_terms: D000313:Adrenal Medulla / Q000166:cytology* / Q000378:metabolism; D000483:Alleles; D000818:Animals; D002454:Cell Differentiation / Q000235:genetics*; D019070:Cell Lineage / Q000235:genetics*; D047108:Embryonic Development / Q000235:genetics*; D004847:Epithelial Cells / Q000378:metabolism / Q000502:physiology; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D019426:Integrases / Q000737:chemistry / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D013629:Tamoxifen / Q000737:chemistry; D013950:Thymus Gland / Q000254:growth & development*
chemical_list: D051858:Forkhead Transcription Factors; C090140:Whn protein; D013629:Tamoxifen; C045073:Cre recombinase; D019426:Integrases
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