کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5533105 | 1550355 | 2017 | 9 صفحه PDF | دانلود رایگان |
- Importance of R-loops in isotype switching in B cells
- New transgenic mouse over-expressing RNase H1
- Decrease in R-loops does not alter frequency of switching.
- Somatic hypermutation increased on transcribed DNA strand.
R-loops, three-strand structures consisting of mRNA hybridized to the complementary DNA and a single-stranded DNA loop, are formed in switch regions on the heavy-chain immunoglobulin locus. To determine if R-loops have a direct effect on any of the steps involved in isotype switching, we generated a transgenic mouse that over-expressed RNase H1, an enzyme that cleaves the RNA of RNA/DNA hybrids in B cells. R-loops in the switch μ region were depleted by 70% in ex vivo activated splenic B cells. Frequencies of isotype switching to IgG1, IgG2b, IgG2c, and IgG3 were the same as C57BL/6 control cells. However, somatic hypermutation was increased specifically on the transcribed strand from μ-γ joins, indicating that R-loops limit activation-induced (cytosine) deaminase access to the transcribed DNA strand. Our data suggest that, in the normal G + C-rich context of mammalian class switch recombination regions, R-loops are obligatory intermediates. Processing of the R-loops is needed to remove RNA allowing activation-induced (cytosine) deaminase to promote somatic hypermutation on both DNA strands to generate double-strand DNA breaks for efficient class switch recombination. One of the two cellular RNases H may assist in this process.
Graphical Abstract152
Journal: Journal of Molecular Biology - Volume 429, Issue 21, 27 October 2017, Pages 3255-3263