scholarly journals A Two-Step, PU.1-Dependent Mechanism for Developmentally Regulated Chromatin Remodeling and Transcription of the c-fms Gene

2006 ◽  
Vol 27 (3) ◽  
pp. 878-887 ◽  
Author(s):  
Hanna Krysinska ◽  
Maarten Hoogenkamp ◽  
Richard Ingram ◽  
Nicola Wilson ◽  
Hiromi Tagoh ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Molecular Mechanisms ◽  
Regulatory Element ◽  
Gene Activation ◽  
Myeloid Cell ◽  
Developmentally Regulated ◽  
Enhancer Activity ◽  
Hematopoietic Stem ◽  
Multipotent Progenitors ◽  
Ets Family

ABSTRACT Hematopoietic stem cells and multipotent progenitors exhibit low-level transcription and partial chromatin reorganization of myeloid cell-specific genes including the c-fms (csf1R) locus. Expression of the c-fms gene is dependent on the Ets family transcription factor PU.1 and is upregulated during myeloid differentiation, enabling committed macrophage precursors to respond to colony-stimulating factor 1. To analyze molecular mechanisms underlying the transcriptional priming and developmental upregulation of the c-fms gene, we have utilized myeloid progenitors lacking the transcription factor PU.1. PU.1 can bind to sites in both the c-fms promoter and the c-fms intronic regulatory element (FIRE enhancer). Unlike wild-type progenitors, the PU.1−/− cells are unable to express c-fms or initiate macrophage differentiation. When PU.1 was reexpressed in mutant progenitors, the chromatin structure of the c-fms promoter was rapidly reorganized. In contrast, assembly of transcription factors at FIRE, acquisition of active histone marks, and high levels of c-fms transcription occurred with significantly slower kinetics. We demonstrate that the reason for this differential activation was that PU.1 was required to promote induction and binding of a secondary transcription factor, Egr-2, which is important for FIRE enhancer activity. These data suggest that the c-fms promoter is maintained in a primed state by PU.1 in progenitor cells and that at FIRE PU.1 functions with another transcription factor to direct full activation of the c-fms locus in differentiated myeloid cells. The two-step mechanism of developmental gene activation that we describe here may be utilized to regulate gene activity in a variety of developmental pathways.

scholarly journals The Pu.1 Locus Is Differentially Regulated at the Level of Chromatin Structure and Noncoding Transcription by Alternate Mechanisms at Distinct Developmental Stages of Hematopoiesis

2007 ◽  
Vol 27 (21) ◽  
pp. 7425-7438 ◽  
Author(s):  
Maarten Hoogenkamp ◽  
Hanna Krysinska ◽  
Richard Ingram ◽  
Gang Huang ◽  
Rachael Barlow ◽  
...  
Keyword(s):  
T Cells ◽  
Transcription Factor ◽  
Transcription Factors ◽  
B Cells ◽  
Regulatory Element ◽  
Precursor Cells ◽  
Hematopoietic Stem ◽  
Tissue Specific ◽  
Specific Regulation

ABSTRACT The Ets family transcription factor PU.1 is crucial for the regulation of hematopoietic development. Pu.1 is activated in hematopoietic stem cells and is expressed in mast cells, B cells, granulocytes, and macrophages but is switched off in T cells. Many of the transcription factors regulating Pu.1 have been identified, but little is known about how they organize Pu.1 chromatin in development. We analyzed the Pu.1 promoter and the upstream regulatory element (URE) using in vivo footprinting and chromatin immunoprecipitation assays. In B cells, Pu.1 was bound by a set of transcription factors different from that in myeloid cells and adopted alternative chromatin architectures. In T cells, Pu.1 chromatin at the URE was open and the same transcription factor binding sites were occupied as in B cells. The transcription factor RUNX1 was bound to the URE in precursor cells, but binding was down-regulated in maturing cells. In PU.1 knockout precursor cells, the Ets factor Fli-1 compensated for the lack of PU.1, and both proteins could occupy a subset of Pu.1 cis elements in PU.1-expressing cells. In addition, we identified novel URE-derived noncoding transcripts subject to tissue-specific regulation. Our results provide important insights into how overlapping, but different, sets of transcription factors program tissue-specific chromatin structures in the hematopoietic system.

PU.1 and p53 Double Mutant Mice Develop Aggressive AML with Dysplastic Features

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 769-769
Author(s):  
Petra Vlckova ◽  
Libor Stanek ◽  
Pavel Burda ◽  
Karin Vargova ◽  
Filipp Savvulidi ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Transcription Factor ◽  
Progenitor Cells ◽  
Double Mutant ◽  
Molecular Mechanisms ◽  
Conflicts Of Interest ◽  
Regulatory Element ◽  
Tumour Suppressor ◽  
Mutant Mice ◽  
Stem And Progenitor Cells

Abstract Abstract 769 Introduction: Downregulation of tumour suppressor transcription factor PU.1 in haematopoietic stem and progenitor cells represents primary underlying mechanism for the development of acute myeloid leukaemia (AML) in mice with homozygous deletion of the upstream regulatory element (URE) of PU.1 gene. Human AML often display differences in aggressiveness that are associated with mutations of a well known tumour suppressor p53. We produced murine model carrying mutations of p53 and URE that develops highly aggressive AML and focused on molecular mechanisms that are responsible for AML aggressiveness. Mouse models: PU.1ure/ure (Rosenbauer F, et al. 2004) and p53−/− (Jacks T, et al. 1994) mice were used. Conditional deletion of the URE leads to downregulation of PU.1 and is marked by clonal accumulation of myeloid c-Kit+Mac-1low Gr-1low blast cells within bone marrow, spleen, and peripheral blood mirrored by lower numbers of lymphoid and erythroid cells. AML development in PU.1ure/ure mice involves a preleukaemic phase (at 2–3 months) marked by proliferation of myeloid c-Kit+Gr-1+ cells and splenomegaly. Interestingly, p53−/−mice do not develop AML, instead loss of p53 predisposes mice to solid tumours, mostly lymphomas, by 6 months of age. Results: Deletion of TP53 in the PU.1ure/ure mice (PU.1ure/ure p53−/−) results in more aggressive AML with significantly shortened overall survival, prominent hepatosplenomegaly and cachexia (wasting syndrome). Mild differences in cell surface phenotype of bone marrow derived cells were observed between PU.1ure/ure and PU.1ure/ure p53−/− mice by flow cytometry (these included: blasts expansion and lymphopenia). Next, the PU.1 expression was determined in all genotypes at progenitor and stem cell levels. PU.1 mRNA level in more aggressive PU.1ure/ure p53−/− murine AML is decreased in the entire c-Kit+tumour cell population compared to AML in PU.1ure/ure mice including haematopoietic stem and progenitor cells (HSPCs). Correspondingly to RNA level, in the PU.1ure/ure progenitors the PU.1 protein was decreased compared to p53−/− progenitors and is yet further reduced in the PU.1ure/ure p53−/− c-Kit+ Mac1+progenitors. p53−/− progenitors express similar level of PU.1 as wild type progenitors indicating that despite p53 can bind DNA as a transcription factor, it does not regulate PU.1 level directly. In addition to URE deletion we searched for other mechanisms that control PU.1 levels and found that PU.1-inhibiting microRNA miR-155 gene display altered chromatin structure and expression of both pri-miR-155 as well as its spliced mature form in the AML of PU.1ure/ure and (to higher extent in) PU.1ure/ure p53−/− murine progenitors. Upregulation of miR-155 coincides with upregulation of the Mir155hg activators: Myc and Myb. Finally, upon inhibition of either Myb or miR-155 in vitro the AML progenitors restore PU.1 levels and lose leukaemic cell growth. Conclusion: In summary, PU.1 and p53 double mutant mice develop aggressive AML with dysplastic features. Defective control of PU.1 levels in PU.1ure/ure and PU.1ure/ure p53−/−AML involves miR-155. Lastly, restored PU.1 level and cell differentiation capacity are achieved by inhibiting either Myb or miR-155 in the PU.1ure/ure p53−/− progenitors. (Grant support: P305/12/1033, UNCE 204021, PRVOUK-P24/LF1/3, SVV-2012-264507, P301/12/P380. MK was sponsored by GAUK 251070 45410, 251135 82210) Disclosures: No relevant conflicts of interest to declare.

A novel Sp1-relatedciselement involved in intestinal alkaline phosphatase gene transcription

1999 ◽  
Vol 276 (4) ◽  
pp. G800-G807 ◽  
Author(s):  
Jeong H. Kim ◽  
Shufen Meng ◽  
Amy Shei ◽  
Richard A. Hodin
Keyword(s):  
Alkaline Phosphatase ◽  
Transcriptional Activation ◽  
Molecular Mechanisms ◽  
Regulatory Element ◽  
Gene Activation ◽  
Regulatory Region ◽  
Intestinal Alkaline Phosphatase ◽  
Mobility Shift ◽  
Sv40 Promoter

We have used sodium butyrate-treated HT-29 cells as an in vitro model system to study the molecular mechanisms underlying intestinal alkaline phosphatase (IAP) gene activation. Transient transfection assays using human IAP-CAT reporter genes along with DNase I footprinting were used to localize a critical cis element (IF-III) corresponding to the sequence 5′-GACTGGGCGGGGTCAAGATGGA-3′. Deletion of the IF-III element resulted in a dramatic reduction in reporter gene activity, and IF-III was shown to function in the context of a heterologous (SV40) promoter in a cell type-specific manner, further supporting its functional role in IAP transactivation. Electrophoretic mobility shift assays revealed that IF-III binds Sp1 and Sp3, but these factors comprise only a portion of the total nuclear binding and appear to mediate only a small portion of its transcriptional activity. IF-III does not correspond to any previously characterized regulatory region from other intestine-specific genes. We have thus identified a novel, Sp1-related cis-regulatory element in the human IAP gene that appears to play a role in its transcriptional activation during differentiation in vitro.

Autoregulation of the Transcription Factor PU.1 Via Its Evolutionarily Conserved Upstream Regulatory Element Is Critical in Adult Mouse Hematopoiesis.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 1468-1468
Author(s):  
Philipp B. Staber ◽  
Pu Zhang ◽  
Min Ye ◽  
Gang Huang ◽  
Boris Bartholdy ◽  
...  
Keyword(s):  
Transcription Factor ◽  
B Cells ◽  
Regulatory Element ◽  
Hematopoietic Differentiation ◽  
Targeted Disruption ◽  
Hematopoietic Stem ◽  
Evolutionarily Conserved ◽  
Upstream Regulatory Element

Abstract Abstract 1468 Poster Board I-491 Background: Levels of the Ets transcription factor PU.1 control normal hematopoietic differentiation and even modest alterations can lead to leukemia and lymphoma. Regulation of PU.1 levels at different stages of hematopoiesis requires multiple interactions between several regulatory elements and transcription factors. Our previous studies identified a potential autoregulatory mechanism of the PU.1 gene through the combined activity of the proximal promoter and an evolutionarily conserved upstream regulatory element (URE), located at –14 kb relative to the transcription start site in mice. PU.1 binds to a conserved PU.1 site in the PU.1 URE both in vitro and in vivo. Approach: To ask at which stages of hematopoietic differentiation autoregulation of PU.1 via binding to its URE might play a role, we developed a mouse model with targeted disruption of the PU.1 binding site in the PU.1 URE. Results: Targeted mutation of the PU.1 autoregulatory site in PU.1 URE abolished PU.1 binding as verified by Chromatin Immuno-precipitation (ChIP). PU.1 URE activity was manifestly reduced resulting in a variety of lineage-specific abnormalities. As shown here in adult mice, the absence of the autoregulatory PU.1 site affected PU.1 expression in a lineage dependent manner. PU.1 expression was markedly decreased in phenotypic long term hematopoietic stem cells (LT-HSC: CD150+/CD48−/ c-kit+/sca-1+/lin−) and short term HSCs (ST-HSCs: CD150−/CD48+/ c-kit+/sca-1+/lin−) and, to a lesser extent, in Common Myeloid Progenitors (CMPs: lin−/c-kit+/Sca-1−/CD34+/FcrRlow), and Megakaryocyte/Erythrocyte Progenitors (MEPs: lin−/c-kit+/Sca-1−/CD34−/FcrRhigh). Within the lymphoid linage, PU.1 levels were unchanged in Common Lymphoid Progenitors (CLPs: lin−/c-kitlow/Sca-1low /IL-7Ra+/Thy1.1−) and pre-B-cells (B220+/ CD43−), up in pro-B-cells (B220+/CD43+), and down in mature B cells. Myeloid cells appeared to be unaffected. Interestingly, while PU.1 levels were decreased in LT- and ST-HSC populations, only phenotypic LT-HSCs were reduced in number. To further analyze HSC function of PU.1 site mutated mice we performed limiting dilution transplantation assays and measured the frequency of competitive repopulation units (CRU) using the congenic Ly5.1/Ly5.2 system. Our preliminary data indicated a decrease of LT-HSC function in PU.1 site mutated mice, although their homing and engraftment functions were not affected. This was also observed in mice with targeted disruption of all three AML-1 sites that are in close proximity of the PU.1 site at the PU.1 URE. While AML-1 itself appeared not to influence LT-HSC function (M. Ichikawa, T. Asai et al. Nature Medicine, 2004), we found that the conformational changes of the URE present in mice with disrupted AML-1 binding sites, as measured by Quantitative Chromosome Conformation Capture, impede PU.1 binding to its autoregulatory site. Conclusion: PU.1 indeed autoregulates its expression via binding to the -14kb URE in a lineage specific manner in vivo. Our data point to a critical role of PU.1 autoregulation especially for long-term hematopoietic stem cell function. Disclosures: No relevant conflicts of interest to declare.

LSD1 Plays an Important Role in GATA Switch during Erythroid Differentiation

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 4846-4846
Author(s):  
Yue Jin ◽  
Yidi Guo ◽  
Dongxue Liang ◽  
Yue Li ◽  
Zhe Li ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Conflicts Of Interest ◽  
Es Cells ◽  
Regulatory Element ◽  
Erythroid Differentiation ◽  
Erythroid Cell ◽  
Erythroid Cells ◽  
Hematopoietic Stem ◽  
Mouse Es Cells ◽  
Murine Erythroleukemia

Abstract GATA factors play important role in hematopoiesis. In particular, GATA2 is critical for maintenance of hematopoietic stem and progenitor cells (HS/PCs) and GATA1 is required for erythropoiesis. GATA1 and GATA2 are expressed in reciprocal patterns during erythroid differentiation. It was shown that GATA1 occupied the -2.8Kb regulatory element and mediated repression of the GATA2 promoter in terminally differentiating erythroid cells. However, the detailed molecular mechanisms that control the enhancer/promoter activities of the GATA2 gene remain to be elucidated. In this report, we found that LSD1 and TAL1 co-localize at GATA2 1S promoter through ChIP and double-ChIP assays in murine erythroleukemia (MEL) cells. To further test whether LSD1 and its mediated H3K4 demethylation is important for repression of the GATA2 gene during erythroid differentiation, we silenced LSD1 expression in both MEL cells and mouse ES cells using retrovirus mediated shRNA knockdown and induced them to differentiate into erythroid cells with DMSO and EPO, respectively. GATA2 expression was elevated while the level of GATA1 was repressed by RT-qPCR. Furthermore, consistent with the GATA witch hypothesis, ChIP analysis revealed that the levels of H3K4me2 were increased at the GATA2 1S promoter.  In addition, knock-down of LSD1 in MEL cells results in inhibition of erythroid cell differenciation and attenuation of MEL cell proliferation and survival. Thus, our data reveal that LSD1 involved in control of terminal erythroid differentiation by regulating GATA switch. The LSD1 histone demethylase complex may be recruited to the GATA2 1S promoter by interacting with TAL1. The H3K4 demethylation activity of LSD1 leads to downregulation of the active H3K4m2 mark at the GATA2 promoter that alters chromatin structure and represses transcription of the GATA2 genes. Disclosures: No relevant conflicts of interest to declare.

Novel nuclear target for thrombin: activation of the Elk1 transcription factor leads to chemokine gene expression

Blood ◽  
2000 ◽  
Vol 96 (12) ◽  
pp. 3696-3706 ◽  
Author(s):  
Qi-Jing Li ◽  
Sucheta Vaingankar ◽  
Frances M. Sladek ◽  
Manuela Martins-Green
Keyword(s):  
Transcription Factor ◽  
Molecular Mechanisms ◽  
Inflammatory Responses ◽  
Gene Activation ◽  
Tumor Development ◽  
Growth Factor Receptor ◽  
Early Response ◽  
Transcriptional Level ◽  
Binding Domains ◽  
Thrombin Activation

Thrombin is primarily known for its role in homeostasis and thrombosis. However, this enzyme also plays important roles in wound healing and pathologic situations such as inflammation and tumorigenesis. Among the molecules stimulated by thrombin in these latter processes are the stress response proteins, chemokines. Chemokines are also known for their roles in inflammatory responses and tumor development. These correlative observations strongly suggest that chemokines may be mediators of some of thrombin's functions in these processes. Elucidation of the molecular mechanisms of stimulation of chemokines by thrombin may help to unravel the ways in which their expression can be modulated. Up-regulation of the chemokine 9E3/cCAF by thrombin occurs via its proteolytically activated receptor with subsequent transactivation of the epidermal growth factor receptor tyrosine kinase. This study shows that stimulation by thrombin very rapidly activates this chemokine at the transcriptional level, that 2 Elk1 binding elements located between −534 and −483 bp of the promoter are major thrombin response elements, that activation occurs via the Elk1 transcription factor, and that the latter is directly activated by MEK1/ERK2. The common occurrence of Elk1 binding domains in the promoters of immediate early response genes suggests that it may be characteristically involved in gene activation by stress-inducing agents.

Differences in the chromatin structure and cis-element organization of the human and mouse GATA1 loci: implications for cis-element identification

Blood ◽  
2004 ◽  
Vol 104 (10) ◽  
pp. 3106-3116 ◽  
Author(s):  
Veronica Valverde-Garduno ◽  
Boris Guyot ◽  
Eduardo Anguita ◽  
Isla Hamlett ◽  
Catherine Porcher ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Transcription Factors ◽  
Sequence Comparison ◽  
Regulatory Element ◽  
Cis Elements ◽  
Enhancer Activity ◽  
Cis Element ◽  
Human Sequence ◽  
Human And Mouse

Abstract Cis-element identification is a prerequisite to understand transcriptional regulation of gene loci. From analysis of a limited number of conserved gene loci, sequence comparison has proved a robust and efficient way to locate cis-elements. Human and mouse GATA1 genes encode a critical hematopoietic transcription factor conserved in expression and function. Proper control of GATA1 transcription is critical in regulating myeloid lineage specification and maturation. Here, we compared sequence and systematically mapped position of DNase I hypersensitive sites, acetylation status of histone H3/H4, and in vivo binding of transcription factors over approximately 120 kilobases flanking the human GATA1 gene and the corresponding region in mice. Despite lying in approximately 10 megabase (Mb) conserved syntenic segment, the chromatin structures of the 2 homologous loci are strikingly different. The 2 previously unidentified hematopoietic cis-elements, one in each species, are not conserved in position and sequence and have enhancer activity in erythroid cells. In vivo, they both bind the transcription factors GATA1, SCL, LMO2, and Ldb1. More broadly, there are both species- and regulatory element–specific patterns of transcription factor binding. These findings suggest that some cis-elements regulating human and mouse GATA1 genes differ. More generally, mouse human sequence comparison may fail to identify all cis-elements.

AML1/RUNX1 point mutation possibly promotes leukemic transformation in myeloproliferative neoplasms

Blood ◽  
2009 ◽  
Vol 114 (25) ◽  
pp. 5201-5205 ◽  
Author(s):  
Ye Ding ◽  
Yuka Harada ◽  
Jun Imagawa ◽  
Akiro Kimura ◽  
Hironori Harada
Keyword(s):  
Molecular Mechanisms ◽  
Myeloproliferative Neoplasms ◽  
Point Mutations ◽  
Chronic Phase ◽  
Myeloid Cell ◽  
Leukemic Transformation ◽  
Hematopoietic Stem ◽  
Cd34 Cells ◽  
Immature Myeloid Cells ◽  
Gene Alterations

Abstract Myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem cell disorders characterized by proliferation of one or more myeloid cell lineages. Some patients exhibit leukemic transformation (LT) by unknown mechanisms, and chemotherapy may increase the risk of LT. To clarify the molecular mechanisms of LT, gene alterations involved in LT from patients in the chronic phase (CP) of MPNs were identified. Among 18 patients who progressed to leukemia, AML1/RUNX1 mutations were detected in 5 patients at the LT but in none at the CP. To investigate the leukemogenic effect of AML1/RUNX1 mutants, the AML1D171N mutant was transduced into CD34+ cells from patients in the CP of MPNs. The D171N transduction resulted in proliferation of immature myeloid cells, enhanced self-renewal capacity, and proliferation of primitive progenitors. Taken together, these results indicate that AML1/RUNX1 point mutations may have a leukemogenic potential in MPN stem cells, and they may promote leukemic transformation in MPN.

scholarly journals A class I odorant receptor enhancer shares a functional motif with class II enhancers

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tetsuo Iwata ◽  
Satoshi Tomeoka ◽  
Junji Hirota
Keyword(s):  
Molecular Mechanisms ◽  
Odorant Receptor ◽  
Regulatory Element ◽  
Mammalian Species ◽  
Class Ii ◽  
Class I ◽  
Enhancer Activity ◽  
Functional Motif ◽  
Functional Region ◽  
Or Genes

AbstractIn the mouse, 129 functional class I odorant receptor (OR) genes reside in a ~ 3 megabase huge gene cluster on chromosome 7. The J element, a long-range cis-regulatory element governs the singular expression of class I OR genes by exerting its effect over the whole cluster. To elucidate the molecular mechanisms underlying class I-specific enhancer activity of the J element, we analyzed the J element sequence to determine the functional region and essential motif. The 430-bp core J element, that is highly conserved in mammalian species from the platypus to humans, contains a class I-specific conserved motif of AAACTTTTC, multiple homeodomain sites, and a neighboring O/E-like site, as in class II OR-enhancers. A series of transgenic reporter assays demonstrated that the class I-specific motif is not essential, but the 330-bp core J-H/O containing the homeodomain and O/E-like sites is necessary and sufficient for class I-specific enhancer activity. Further motif analysis revealed that one of homeodomain sequence is the Greek Islands composite motif of the adjacent homeodomain and O/E-like sequences, and mutations in the composite motif abolished or severely reduced class I-enhancer activity. Our results demonstrate that class I and class II enhancers share a functional motif for their enhancer activity.

scholarly journals Histone Acetylation Mediated by Brd1 Is Crucial for Cd8 Gene Activation during Early Thymocyte Development

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 1576-1576
Author(s):  
Yuta Mishima ◽  
Changshan Wang ◽  
Satoru Miyagi ◽  
Atsunori Saraya ◽  
Hiroyuki Hosokawa ◽  
...  
Keyword(s):  
T Cells ◽  
Expression Profile ◽  
Molecular Mechanisms ◽  
Conflicts Of Interest ◽  
Gene Activation ◽  
Epigenetic Mark ◽  
Thymocyte Development ◽  
Double Positive ◽  
Enhancer Activity ◽  
Retroviral Transduction

Abstract During T cell development, Cd8 expression is controlled via dynamic regulation of its cis-regulatory enhancer elements. Insufficient enhancer activity during initial Cd8 activation is known to cause a variegated CD8 expression, thereby generating a CD4+CD8-TCRb-/low population that should appear as CD4+CD8+ double-positive (DP) thymocytes. However, epigenetic and molecular mechanisms involved in initial Cd8 gene activation remain elusive. We previously reported that Brd1, also known as Brpf2, is responsible for the global acetylation of H3K14 as a subunit of the Hbo1 histone acetyltransferase (HAT) complex. In this study, we generated conditional Brd1 knockout mice (Tie2-Cre;Brd1fl/fl mice), in which Brd1 is inactivated in all hematopoietic cells. Although Tie2-Cre;Brd1fl/fl mice were born and grew normally, detailed analysis revealed an abnormal thymocyte differentiation. Deletion of Brd1 resulted in the appearance of CD4+CD8-TCRβ-/low thymocytes that was indistinguishable from DP thymocytes in their properties. Hierarchical clustering of gene expression profile showed that Brd1Δ/Δ CD4+CD8-TCRβ-/low thymocytes retain an expression profile nearly identical to one observed in DP thymocytes. These results indicate that Brd1Δ/Δ CD4+CD8-TCRβ-/low thymocytes correspond to immature thymocytes that would normally appear as CD4+CD8+ DP thymocytes, and was generated because of a variegated activation of Cd8 gene. Importantly, in the gut intraepithelial lymphocyte (IEL) compartment, the population of CD4+CD8aa+ aβT cells, whose generation requires Cd8 gene reactivation in CD4+CD8− helper T cells, were significantly decreased in Tie2-Cre;Brd1fl/fl mice compared to the Tie2-Cre control mice. In addition, the percentage of CD8aa expressing gdT cells was significantly reduced. These findings suggest that Brd1 is also required to initiate Cd8a activation in gdT cells as well as Cd8 reactivation in CD4+T cells. We further conducted retroviral transduction of Brd1 into Brd1Δ/Δ DN3 cells that were flowed by culture on TSt-4/DLL stromal cells. Upon exogenous Brd1 expression, CD8 expression was completely restored and thereby Brd1Δ/Δ DN3 cells differentiated into DP cells. ChIP analysis demonstrated that Brd1 and Hbo1 co-localize at the known enhancers in the Cd8 locus and that their bindings are responsible for acetylation at H3K14. Biochemical results confirmed a presence of Brd1 in Hbo1 HAT complexes. These findings indicate that the Brd1-mediated HAT activity is crucial for efficient activation of Cd8 expression via acetylation at H3K14, which would serve as an epigenetic mark that promotes the recruitment of transcription machineries to the Cd8 enhancers. Disclosures No relevant conflicts of interest to declare.

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