T-Cell Factor 1 Is a Gatekeeper for T-Cell Specification in Response to Notch Signaling
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T-cell factor 1 is a gatekeeper for T-cell specification in response to Notch signaling Kristine Germara,b, Marei Dosea, Tassos Konstantinoua, Jiangwen Zhangc, Hongfang Wangd, Camille Lobrye, Kelly L. Arnettf, Stephen C. Blacklowf, Iannis Aifantise, Jon C. Asterd, and Fotini Gounaria,1 aKnapp Center for Lupus and Immunology Research, University of Chicago, Chicago, IL 60637; bGraduate Program in Immunology, Sackler School of Graduate Biomedical Sciences, Tufts University, Boston, MA 02111; cFaculty of Arts and Sciences, Research Computing, Harvard University, Cambridge, MA 02138; dDepartment of Pathology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02115; eHoward Hughes Medical Institute and Department of Pathology, NYU Cancer Institute, and Helen L. and Martin S. Kimmel Center for Stem Cell Biology, New York University School of Medicine, New York, NY 10016; and fDepartment of Cancer Biology, Dana-Farber Cancer Institute, and Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115 Edited* by Harvey Cantor, Dana-Farber Cancer Institute, Boston, MA, and approved October 19, 2011 (received for review June 27, 2011) Although transcriptional programs associated with T-cell specifica- function has not been linked with the up-regulation of T-lineage– tion and commitment have been described, the functional hierar- specific genes (16) or enhancement of T-cell development (17–19). chy and the roles of key regulators in structuring/orchestrating In this article, we establish that Tcf-1 is required in the earliest these programs remain unclear. Activation of Notch signaling in un- stages of T-cell specification. In the absence of Tcf-1, BM pro- committed precursors by the thymic stroma initiates the T-cell genitors entering the thymus fail to progress any further, and this differentiation program. One regulator first induced in these pre- effect is cell-intrinsic. The earliest defect detected in Tcf-1–de- fi cursors is the DNA-binding protein T-cell factor 1 (Tcf-1), a T-cell– cient thymocytes is the reduced expression of c-kit at the DN1 – fi specific mediator of Wnt signaling. However, the specific contri- stage of development. Tcf-1 de cient cells at this stage show increased apoptosis and have significantly reduced expression of bution of Tcf-1 to early T-cell development and the signals in- fi ducing it in these cells remain unclear. Here we assign functional genes involved in DNA metabolic processes, chromatin modi - significance to Tcf-1 as a gatekeeper of T-cell fate and show that cation, and response to damage compared with their WT coun- terparts. We further show that Notch binds the Tcf7 gene locus Tcf-1 is directly activated by Notch signals. Tcf-1 is required at the ∼ earliest phase of T-cell determinationforprogressionbeyondthe at a conserved element 31.5 kb upstream of the transcription start site, and ectopic expression of Notch1 leads to transcrip- early thymic progenitor stage. The global expression profile of tional up-regulation of Tcf-1. Thus, our data identify Tcf-1 as one Tcf-1–deficient progenitors indicates that basic processes of DNA of the earliest direct responders to Notch signaling in T-cell metabolism are down-regulated in its absence, and the blocked development. Tcf-1 is essential for thymic progenitors to proceed T-cell progenitors become abortive and die by apoptosis. Our through T-cell determination. data thus add an important functional relationship to the road- map of T-cell development. Results Tcf-1 Is Required for T-Cell Development Starting at the ETP Stage. cells are unique among hematopoietic cells because they need Earlier reports demonstrated that ablation of Tcf-1 causes an T a specialized organ, the thymus, to develop. Multipotent age-dependent degeneration of T-cell development (20). These progenitors (MPPs) migrating from the bone marrow (BM) studies showed that the DN1 population, thought at the time to through the blood stream seed the thymus (1, 2), whose micro- represent the earliest thymocyte subset, was abundantly present − − environment instructs them to lose stem cell properties and al- in Tcf-1 / mice, whereas the subsequent DN2, DN3, double- ternative developmental potentials and to differentiate along the positive, and single-positive populations were dramatically T-cell lineage (3). One important trigger for T-cell fate is the reduced. It is now understood that DN1 cells are highly het- activation of Notch signaling by Delta-like Notch ligands ex- erogeneous and can be subdivided into at least five subsets pressed on thymic stroma. Notch signaling induces the T-cell (DN1a–DN1e) (21). The c-kit–expressing DN1a and DN1b specification and commitment transcription programs (4). Com- subsets contain the most potent T-cell progenitors and are oth- mitment to the T-cell fate is endorsed as the cells progress from − − erwise known as ETPs (22). However, T cells can also be derived the early thymic progenitor (ETP; Lin CD44+c-kit+CD25 ), the from the atypical DN1c–DN1e subsets, although inefficiently most immature recognizable thymocyte, to the double-negative 3 (21). In light of these recent findings, we reanalyzed the earliest − − − − (DN3; Lin CD25+CD44 )stage.Aspartofthisprocess,co- thymic subpopulations in Tcf-1 / mice, including the classical − − − ordinated changes in the transcription profiles of these progeni- DN1 (Lin CD25 CD44+) (Fig. 1A), the ETP (Lin CD44+c- − tors gradually restrict their ability to become B, myeloid, dendritic, kit+CD25 ) (Fig. 1B), and the DN1a–DN1e subsets (Fig. 1C). − − and natural killer cells. Sustained Notch signaling is required Surprisingly, these analyses showed that Tcf-1 / thymi had during T-cell specification and commitment; however, Notch a previously unappreciated 100-fold reduction in absolute DN1 needs to collaborate with numerous other regulators in these numbers and a dramatic 300-fold reduction in ETPs compared − − − processes (5). Final commitment to the T-cell fate at the late DN2 with Tcf-1+/ or wt controls (Fig. 1D). Tcf-1 / DN1 cells had stage is marked by Bcl11b-mediated down-regulation of stem and reduced levels of surface c-kit (Fig. 1E), and an increased fraction progenitor cell transcriptional regulators (6–8). Thymus-like organs are present in all animals with adaptive immune systems, further emphasizing the specialized need for this organ (9, 10). Author contributions: K.G., M.D., T.K., H.W., and C.L. performed research; I.A., J.C.A., and Tcf-1 (product of the Tcf7 gene, referred to as Tcf-1 through- F.G. designed research; K.L.A., S.C.B., and J.C.A. contributed new reagents/analytic tools; out this article), is a T-lineage–specific, high-mobility group K.G., M.D., J.Z., H.W., and C.L. analyzed data; and K.G. and F.G. wrote the paper. (HMG) box-containing, DNA-binding protein. Tcf-1, like the The authors declare no conflict of interest. other T-cell factor/lymphoid enhancer-binding factor (Tcf/Lef) *This Direct Submission article had a prearranged editor. factors, mediates transcriptional activation when bound by Data deposition: The data reported in this paper have been deposited in the Gene Ex- β-catenin in response to Wnt signals or transcriptional repression pression Omnibus (GEO) database, www.ncbi.nlm.nih.gov/geo (accession no. GSE33513). when bound by Groucho (11). It has been well established that 1To whom correspondence should be addressed. E-mail: [email protected]. Tcf-1 is required in multiple stages of thymic and peripheral This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. T-cell development (12–15). However, Tcf/β-catenin gain of 1073/pnas.1110230108/-/DCSupplemental. 20060–20065 | PNAS | December 13, 2011 | vol. 108 | no. 50 www.pnas.org/cgi/doi/10.1073/pnas.1110230108 Downloaded by guest on September 29, 2021 − − Fig. 1. Early thymocyte development in Tcf-1 / mice. Pro- − − − files of gated Tcf-1 / and control Lin DN thymocytes are shown. (A) CD44 versus CD25 profiles. The DN1–DN4 subsets are indicated. Numbers indicate the frequencies of each subset. (BLeft) CD44 versus c-kit profiles show the electronic gating for pro-T cells. (Right) c-kit versus CD25 profiles of gated pro-T cells define the ETP, DN2a, and DN2b subsets as − − indicated. (C) Analysis of the DN1 subsets in Tcf-1 / and control mice. (Left) CD44 versus CD25 profiles show the gating of DN1 prothymocytes. (Right) CD24 versus c-kit profiles of gated DN1 cells define the DN1a (c-kit+CD24−), DN1b (c-kit+CD24+), DN1c (c-kitloCD24+), DN1d (c-kit−CD24+), − − and DN1e (c-kit CD24 ) subsets. (D) Bar histograms of cell − − − numbers in the indicated subsets of Tcf-1 / and Tcf-1+/ mice (n =4–6). (E) Histogram overlay of c-kit levels in gated DN1 thymocytes from the indicated mice. MFI, mean fluo- rescence intensity of c-kit. − − of cells expressed intermediate levels of CD25 (Fig. 1 A and C). In (Fig. 2E). Thus, Tcf-1 / progenitors are able to migrate agreement with earlier reports, DN2 cells and all subsequent through the bloodstream. thymic subsets were dramatically reduced. Thus, Tcf-1 is re- − − quired earlier than previously described: at, or before, thymic Tcf-1 / Progenitors Are Cell-Intrinsically Defective in T-Cell entry of uncommitted thymus-seeding progenitors. Although the Specification. The normal distribution of BM and blood progen- − − − − profile of early thymocytes in Tcf-1 / mice resembled that of itors compared with the reduced presence of Tcf-1 / ETPs fl fl fl Notch1-deficient, Notch2-haploinsufficient (MxCreN1 / N2 /+) suggests a functional inability to progress along the T-cell line- thymocytes (Fig. S1), no accumulation of B cells or macrophages age. To address this possibility, we examined the T-cell potential −/− was observed (Fig. S2), indicating that Tcf-1 may not be involved of hematopoietic progenitors from Tcf-1 mice in cocultures in the suppression of B-cell fate.