Abstract
Ten-eleven translocation (TET) enzymes oxidize 5-methylcytosine, facilitating DNA demethylation and generating new epigenetic marks. Here we show that concomitant loss of Tet2 and Tet3 in mice at early B cell stage blocked the pro- to pre-B cell transition in the bone marrow, decreased Irf4 expression and impaired the germline transcription and rearrangement of the Igκ locus. Tet2/3-deficient pro-B cells showed increased CpG methylation at the Igκ 3' and distal enhancers that was mimicked by depletion of E2A or PU.1, as well as a global decrease in chromatin accessibility at enhancers. Importantly, re-expression of the Tet2 catalytic domain in Tet2/3-deficient B cells resulted in demethylation of the Igκ enhancers and restored their chromatin accessibility. Our data suggest that TET proteins and lineage-specific transcription factors cooperate to influence chromatin accessibility and Igκ enhancer function by modulating the modification status of DNA.
Highlights
Cell lineage specification is typically accompanied by changes in DNA cytosine methylation, most of which occur at CpG dinucleotides in somatic cells (Klose and Bird, 2006; Ooi et al, 2009)
Because B220 and CD43 are co-expressed on B cells and on plasmacytoid dendritic cells, we reanalyzed CD19+B220+ bone marrow cells based on c-kit and CD25 expression; this analysis confirmed that percentages and numbers of pre-B cell (IgM-CD19+B220+ckit–CD25+) were substantially reduced in Tet2/3 DKO mice (Figure 1E)
We have shown that mice with a germline deletion of Tet2 in conjunction with Mb1Cre-driven deletion of Tet3 display a block in B cell development at the pro-B to pre-B transition, reflective of decreased Igk rearrangement and expression
Summary
Cell lineage specification is typically accompanied by changes in DNA cytosine methylation, most of which occur at CpG dinucleotides in somatic cells (Klose and Bird, 2006; Ooi et al, 2009). DNA methyltransferases (DNMTs) convert cytosine to 5-methylcytosine (5mC)(Ziller et al, 2013); subsequently, proteins of the TET dioxygenase family oxidise 5mC to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC)(He et al, 2011; Ito et al, 2011; Pastor et al, 2013; Tahiliani et al, 2009). These modified bases, together termed oxidized methylcytosines (oxi-mC), facilitate DNA demethylation and are epigenetic marks in their own right (Mellen et al, 2012; Spruijt et al, 2013). 5fC and 5caC are substrates for excision by TDG and subsequent ’active’ demethylation
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