Orientation-specific RAG activity in chromosomal loop domain contribute to Tcrd V(D)J recombination during T cell development
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ABSTRACT:
ORGANISM(S): Mus musculus
SUBMITTER: Lijuan Zhao
PROVIDER: E-GEOD-79892 | biostudies-arrayexpress |
REPOSITORIES: biostudies-arrayexpress
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Project description:T cell antigen receptor δ (Tcrd) variable region exons are assembled by RAG-initiated V(D)J recombination. Here, we employ a high throughput method to map hundreds of thousands of RAG-initiated Tcrd D segment (Trdd1 and Trdd2) rearrangements in developing thymocytes. We find that Trdd2 joins directly to Trdv, Trdd1, and Trdj segments, but Trdd1 joining is ordered with joining to Trdd2 a prerequisite for further rearrangement. We also find frequent, previously unappreciated Trdd1 and Trdd2 rearrangements that inactivate Tcrd. Moreover, we find numerous RAG off-targets that are generated via unidirectional RAG tracking across the loop-domain containing Trdd1, Trdd2 and Trdj. Correspondingly, disruption of the upstream domain boundary causes spreading of on- and off-target RAG activity to the proximal Trdv domain.
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Project description:Chromatin looping mediated by the CCCTC binding factor CTCF regulates V(D)J recombination at antigen receptor loci. CTCF-mediated looping can influence recombination signal sequence accessibility by regulating enhancer activation of germline promoters. CTCF-mediated looping has also been shown to limit directional tracking of the RAG recombinase along chromatin, and to regulate through-space interactions between recombination signal sequences, independent of the RAG recombinase. However, in all prior instances in which CTCF-mediated looping was shown to influence V(D)J recombination, it was not possible to fully resolve the relative contributions to the V(D)J recombination phenotype of changes in accessibility, RAG-tracking, and RAG-independent long-distance interactions. Here, to assess mechanisms by which CTCF-mediated looping can impact V(D)J recombination, we introduced an ectopic CTCF binding element (CBE) immediately downstream of Eδ in the murine Tcra-Tcrd locus. The ectopic CBE impaired inversional rearrangement of Trdv5 in the absence of measurable effects on Trdv5 transcription and chromatin accessibility. Moreover, although the ectopic CBE limited directional RAG tracking from the Tcrd recombination center, such tracking cannot account for Trdv5-to-Trdd2 inversional rearrangement. Rather, the defect in Trdv5 rearrangement could only be attributed to a reconfigured chromatin loop organization that limited RAG-independent through-space interactions between the Trdv5 and Trdd2 RSSs. We conclude that CTCF can regulate V(D)J recombination by segregating RSSs into distinct loop domains and inhibiting RSS synapsis, independent of any effects on transcription, RSS accessibility and RAG tracking. RAG-initiatd Tcrd D segment rearrangements in developing thymocytes were generated by deep sequencing using illumine Miseq
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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.
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Project description:In developing B lymphocytes, V(D)J recombination assembles IgH and Igk variable region exons from hundreds of gene segments clustered across mega-base Igh and Igk loci. V, D, and J segments are flanked by conserved recombination signal sequences (RSSs) that target RAG endonuclease. RAG orchestrates Igh V(D)J recombination upon capturing a JH-RSS within the JH-RSS-based recombination center (RC). JH-RSS orientation programs RAG to scan upstream D- and VH-containing chromatin linearly presented by cohesin-mediated loop extrusion. During Igh scanning, RAG robustly utilizes only D- or VH-RSSs in convergent ("deletional") orientation with JH-RSSs. However, for Vk-to-Jk joining, RAG utilizes Vk-RSSs from deletional- and inversional-oriented clusters, inconsistent with linear scanning. Here, we elucidate the Vk-to-Jk joining mechanism. Igk undergoes robust primary and secondary rearrangements, which confounds scanning assays. Thus, we engineered cells to undergo only primary Vk-to-Jk rearrangements and found that RAG-scanning from the primary Jk-RC terminates just 8kb upstream within the CTCF-Site-based Sis element. While Sis and the Jk-RC barely interacted with the Vk locus, the CTCF-site-based Cer element, 4kb upstream of Sis, interacted with various loop-extrusion impediments across the locus. Like VH-locus inversion, DJH inversion abrogated VH-to-DJH joining; yet Vk-locus or Jk inversion allowed robust Vk-to-Jk joining. Together, these experiments implicated loop extrusion in bringing Vks near Cer for short-range diffusion-mediated capture by RC-based RAG. To elucidate key mechanistic elements for diffusional V(D)J recombination in Igk versus Igh, we assayed Vk-to-JH and D-to-Jk rearrangements in hybrid Igh-Igk loci generated by targeted chromosomal translocations, and pinpointed remarkably strong Vk and Jk RSSs. Indeed, RSS replacements in hybrid or normal Igk and Igh loci confirmed ability of Igk versus Igh RSSs to promote robust diffusional joining. We propose that Igk evolved strong RSSs to mediate diffusional Vk-to-Jk joining; while Igh evolved weaker RSSs requisite for modulating VH joining by RAG scanning impediments.
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Project description:In developing B lymphocytes, V(D)J recombination assembles IgH and Igk variable region exons from hundreds of gene segments clustered across mega-base Igh and Igk loci. V, D, and J segments are flanked by conserved recombination signal sequences (RSSs) that target RAG endonuclease. RAG orchestrates Igh V(D)J recombination upon capturing a JH-RSS within the JH-RSS-based recombination center (RC). JH-RSS orientation programs RAG to scan upstream D- and VH-containing chromatin linearly presented by cohesin-mediated loop extrusion. During Igh scanning, RAG robustly utilizes only D- or VH-RSSs in convergent ("deletional") orientation with JH-RSSs. However, for Vk-to-Jk joining, RAG utilizes Vk-RSSs from deletional- and inversional-oriented clusters, inconsistent with linear scanning. Here, we elucidate the Vk-to-Jk joining mechanism. Igk undergoes robust primary and secondary rearrangements, which confounds scanning assays. Thus, we engineered cells to undergo only primary Vk-to-Jk rearrangements and found that RAG-scanning from the primary Jk-RC terminates just 8kb upstream within the CTCF-Site-based Sis element. While Sis and the Jk-RC barely interacted with the Vk locus, the CTCF-site-based Cer element, 4kb upstream of Sis, interacted with various loop-extrusion impediments across the locus. Like VH-locus inversion, DJH inversion abrogated VH-to-DJH joining; yet Vk-locus or Jk inversion allowed robust Vk-to-Jk joining. Together, these experiments implicated loop extrusion in bringing Vks near Cer for short-range diffusion-mediated capture by RC-based RAG. To elucidate key mechanistic elements for diffusional V(D)J recombination in Igk versus Igh, we assayed Vk-to-JH and D-to-Jk rearrangements in hybrid Igh-Igk loci generated by targeted chromosomal translocations, and pinpointed remarkably strong Vk and Jk RSSs. Indeed, RSS replacements in hybrid or normal Igk and Igh loci confirmed ability of Igk versus Igh RSSs to promote robust diffusional joining. We propose that Igk evolved strong RSSs to mediate diffusional Vk-to-Jk joining; while Igh evolved weaker RSSs requisite for modulating VH joining by RAG scanning impediments.
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2015-08-26 | E-GEOD-71005 | biostudies-arrayexpress
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.
2015-08-10 | GSE67442 | GEO