Contribution of the IGCR1 regulatory element and the 3 & PRIME;Igh CTCF- binding elements to regulation of Igh V(D)J recombination
Proceedings of the National Academy of Sciences of the United States of America(2023)
摘要
Immunoglobulin heavy chain variable region exons are assembled in progenitor -B cells, from VH, D, and JH gene segments located in separate clusters across the Igh locus. RAG endonuclease initiates V(D)J recombination from a JH- based recombination center (RC). Cohesin-mediated extrusion of upstream chromatin past RC -bound RAG presents Ds for joining to JHs to form a DJH-RC. Igh has a provocative number and organization of CTCF-binding elements (CBEs) that can impede loop extrusion. Thus, Igh has two divergently oriented CBEs (CBE1 and CBE2) in the IGCR1 element between the VH and D/JH domains, over 100 CBEs across the VH domain convergent to CBE1, and 10 clustered 3 & PRIME;Igh- CBEs convergent to CBE2 and VH CBEs. IGCR1 CBEs seg-regate D/JH and VH domains by impeding loop extrusion-mediated RAG-scanning. Downregulation of WAPL, a cohesin unloader, in progenitor -B cells neutralizes CBEs, allowing DJH- RC- bound RAG to scan the VH domain and perform VH-to-DJH rearrange-ments. To elucidate potential roles of IGCR1- based CBEs and 3 & PRIME;Igh- CBEs in regulating RAG-scanning and elucidate the mechanism of the ordered transition from D- to- JH to VH-to-DJH recombination, we tested effects of inverting and/or deleting IGCR1 or 3 & PRIME;Igh- CBEs in mice and/or progenitor -B cell lines. These studies revealed that nor-mal IGCR1 CBE orientation augments RAG-scanning impediment activity and suggest that 3 & PRIME;Igh- CBEs reinforce ability of the RC to function as a dynamic loop extrusion impediment to promote optimal RAG scanning activity. Finally, our findings indicate that ordered V(D)J recombination can be explained by a gradual WAPL downregulation mechanism in progenitor -B cells as opposed to a strict developmental switch.
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关键词
V(D)J recombination, CTCF-binding elements (CBEs), CTCF, antibody repertoires, chromatin 3D structure
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