Dnmt3b recruitment through E2F6 transcriptional repressor mediates germ-line gene silencing in murine somatic tissues

Abstract

Methylation of cytosine residues within the CpG dinucleotide in mammalian cells is an important mediator of gene expression, genome stability, X-chromosome inactivation, genomic imprinting, chromatin structure, and embryonic development. The majority of CpG sites in mammalian cells is methylated in a nonrandom fashion, raising the question of how DNA methylation is distributed along the genome. Here, we focused on the functions of DNA methyltransferase-3b (Dnmt3b), of which deregulated activity is linked to several human pathologies. We generated Dnmt3b hypomorphic mutant mice with reduced catalytic activity, which first revealed a deregulation of Hox genes expression, consistent with the observed homeotic transformations of the posterior axis. In addition, analysis of deregulated expression programs in Dnmt3b mutant embryos, using DNA microarrays, highlighted illegitimate activation of several germ-line genes in somatic tissues that appeared to be linked directly to their hypomethylation in mutant embryos. We provide evidence that these genes are direct targets of Dnmt3b. Moreover, the recruitment of Dnmt3b to their proximal promoter is dependant on the binding of the E2F6 transcriptional repressor, which emerges as a common hallmark in the promoters of genes found to be up-regulated as a consequence of impaired Dnmt3b activity. Therefore, our results unraveled a coordinated regulation of genes involved in meiosis, through E2F6-dependant methylation and transcriptional silencing in somatic tissues.DNA methylation | immunodeficiency | centromeric instability | facial anomalies | E2F family | hypomorphic mutation | hox genes

Stable Methylation at Promoters Distinguishes Epiblast Stem Cells from Embryonic Stem Cells and the In Vivo Epiblasts

“…We show that Dnmt3b is more abundant in EpiSCs compared with ESCs, which in particular could explain the increased deposition of methylation at promoters of germline genes [53]. The expression of the two main Tet enzymes involved in active demethylation and present in ESCs, Tet1 and Tet2, are largely downregulated in EpiSCs.…”

DNA replication is altered in Immunodeficiency Centromeric instability Facial anomalies (ICF) cells carrying DNMT3B mutations

“…ICF-specific changes in RNA levels of genes critical for immune function, development, and neurogenesis were identified through the analysis of global expression profiles. [13][14][15][16] Finally, various late-replicating sequences (ie, satellite 2, telomeric repeats, and genes in F-heterochromatin) replicate earlier in ICF than in control cells. 9,11,17 In female ICF cells, genes located in F-heterochromatin lose DNA methylation and escape silencing, and this activation process is associated with a change in their replication timing from late to an earlier stage in the Sphase.…”

Promoter DNA methylation couples genome-defence mechanisms to epigenetic reprogramming in the mouse germline

“…Moreover, DNA methylation at low CpG-density promoters is readily bypassed by activating signals, whereas CpGdense promoters, for which DNA methylation is correlated with significant transcriptional silencing, are rarely methylated in vivo (Metivier et al, 2008;Meissner et al, 2008;Weber et al, 2007). Nonetheless, two recent genome-wide studies have identified genes that rely on DNA methylation for transcriptional silencing in either early embryos or embryonic fibroblasts, and these gene sets are enriched for germline-specific genes (Borgel et al, 2010;Velasco et al, 2010). This observation is consistent with DNA methylation regulating the expression of the germline-specific genes Dazl, Mvh (Ddx4 -Mouse Genome Informatics) and Sycp3 as loss of DNA methylation at these promoters is associated with their transcriptional activation in the developing germline (Maatouk et al, 2006).…”