Project description:The Tcra/Tcrd locus undergoes V(D)J recombination in CD4−CD8− double-negative (DN) thymocytes and CD4+CD8+ double-positive (DP) thymocytes to generate diverse TCRδ and TCRα repertoires, respectively. Here we reveal a Tcra/Tcrd locus chromatin interaction network in DN thymocytes that is formed by interactions between CTCF-binding elements (CBEs). Disruption of a discrete chromatin loop encompassing the Dδ, Jδ and Cδ gene segments allows a single Vδ segment to frequently contact and rearrange to Dδ and Jδ segments and dominate the adult TCRδ repertoire. Disruption of this loop also narrows the TCRα repertoire, which, we believe, follows as a consequence of the restricted TCRδ repertoire. Hence, a single CTCF-mediated chromatin loop directly regulates TCRδ diversity and indirectly regulates TCRα diversity. Examination of chromatin loops by 4C-seq from 4 viewpoints in two lymphoid cell compartments: CD4-CD8- thymocytes and naïve B splenocytes.
Project description:The Tcra/Tcrd locus undergoes V(D)J recombination in CD4−CD8− double-negative (DN) thymocytes and CD4+CD8+ double-positive (DP) thymocytes to generate diverse TCRδ and TCRα repertoires, respectively. Here we reveal a Tcra/Tcrd locus chromatin interaction network in DN thymocytes that is formed by interactions between CTCF-binding elements (CBEs). Disruption of a discrete chromatin loop encompassing the Dδ, Jδ and Cδ gene segments allows a single Vδ segment to frequently contact and rearrange to Dδ and Jδ segments and dominate the adult TCRδ repertoire. Disruption of this loop also narrows the TCRα repertoire, which, we believe, follows as a consequence of the restricted TCRδ repertoire. Hence, a single CTCF-mediated chromatin loop directly regulates TCRδ diversity and indirectly regulates TCRα diversity.
Project description:In order to understand the molecular mechanisms of DN thymocyte development, it may be also of use to clarify how these developmental processes are regulated in terms of their entire gene expression, to which cell differentiation is ultimately ascribed. In the current study, we approached this issue by investigating gene expression profiles in discrete subsets of DN thymocytes under development, in which DN2, DN3, and DN4 thymocytes were sorted and subjected to expression profiling analysis with high-density oligonucleotide microarrays. Experiment Overall Design: The DN2, DN3, and DN4 populations were FACS-sorted from DN thymocytes harvested from four C57BL/6 mice and analyzed by Affymetrix® Mouse Genome 430 2.0 Array® for gene expression. Four independent experiments were performed using 16 mice.
Project description:In order to understand the molecular mechanisms of DN thymocyte development, it may be also of use to clarify how these developmental processes are regulated in terms of their entire gene expression, to which cell differentiation is ultimately ascribed. In the current study, we approached this issue by investigating gene expression profiles in discrete subsets of DN thymocytes under development, in which DN2, DN3, and DN4 thymocytes were sorted and subjected to expression profiling analysis with high-density oligonucleotide microarrays. Keywords: developmental stages
Project description:Insulators are DNA elements, which prevent inappropriate interactions between the neighboring regions of the genome. They can be functionally classified as either enhancer blockers or domain barriers. CTCF (CCCTC binding factor) is the only known major insulator binding protein in the vertebrates and has been shown to bind many enhancer-blocking elements. However, it is not clear whether it plays a role in chromatin domain barriers between active and repressive domains. Here, we used ChIP-Seq to map the genome-wide binding sites of CTCF in three cell types and identified significant binding of CTCF to the boundaries of repressive chromatin domains marked by H3K27me3. Although we find an extensive overlapping of CTCF binding sites across the three cell types, its association with the domain boundaries is cell type-specific. We further show that the nucleosomes flanking CTCF binding sites are well positioned and associated with histone H2AK5 acetylation (H2AK5ac). Interestingly, we found a complementary pattern between the repressive H3K27me3 and the active H2AK5ac regions, which are separated by CTCF. Our findings indicate that CTCF may play important roles in the barrier activity of insulators and provide a resource for further investigation of the CTCF function in organizing chromatin in the human genome. Examination of the role of CTCF in chromatin domain barrier function In addition to the ChIP-seq analysis, two replicates of HeLa expression data were studied.
Project description:Intragenic 5-methylcytosine and CTCF mediate opposing affects on pre-mRNA splicing: CTCF promotes inclusion of weak upstream exons through RNA polymerase II pausing, whereas 5-methylcytosine evicts CTCF, leading to exon exclusion. However, the mechanisms governing dynamic DNA methylation at CTCF binding sites were unclear. In this study, we identify the methylcytosine dioxygenases TET1 and TET2 as active regulators of CTCF-mediated alternative splicing through conversion of 5-methylcytosine to its oxidation derivatives. Transcriptional profiling of human T-lymphocytes in the naïve and activated states was performed by RNA-Seq. Methylation status (5mC and 5hmC) was assayed by medIP-Seq. CTCF binding sites were identified by ChIP-Seq.