RT Journal Article
SR Electronic
T1 Immunoglobulin enhancers increase RNA polymerase 2 stalling at somatic hypermutation target sequences
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2021.09.16.460442
DO 10.1101/2021.09.16.460442
A1 Alina Tarsalainen
A1 Yaakov Maman
A1 Fei-Long Meng
A1 Minna K. Kyläniemi
A1 Anni Soikkeli
A1 Paulina Budzynska
A1 Jessica J. McDonald
A1 Filip Šenigl
A1 Frederic W. Alt
A1 David G. Schatz
A1 Jukka Alinikula
YR 2021
UL http://biorxiv.org/content/early/2021/09/17/2021.09.16.460442.abstract
AB Somatic hypermutation (SHM) drives the genetic diversity of immunoglobulin (Ig) genes in activated B cells and supports the generation of antibodies with increased affinity for antigen. SHM is targeted to Ig genes by their enhancers (DIVACs; diversification activators), but how the enhancers mediate this activity is unknown. We show using chicken DT40 B cells that highly active DIVACs increase the phosphorylation of RNA polymerase 2 (Pol2) and Pol2 occupancy in the mutating gene with little or no accompanying increase in elongation-competent Pol2 or production of full-length transcripts, indicating accumulation of stalled Pol2. DIVAC has similar effect also in human Ramos Burkitt lymphoma cells. The DIVAC-induced stalling is weakly associated with an increase in the detection of single-stranded DNA bubbles in the mutating target gene. We did not find evidence for antisense transcription, or that DIVAC functions by altering levels of H3K27ac or the histone variant H3.3 in the mutating gene. These findings argue for a connection between Pol2 stalling and cis-acting targeting elements in the context of SHM and thus define a mechanistic basis for locus-specific targeting of SHM in the genome. Our results suggest that DIVAC elements render the target gene a suitable platform for AID-mediated mutation without a requirement for increasing transcriptional output.Competing Interest StatementThe authors have declared no competing interest.