Transcription and histone methylation changes correlate with imprint acquisition in male germ cells.

Genomic imprinting in mammals is controlled by DNA methylation imprints that are acquired in the gametes, at essential sequence elements called 'imprinting control regions' (ICRs). What signals paternal imprint acquisition in male germ cells remains unknown. To address this question, we explored histone methylation at ICRs in mouse primordial germ cells (PGCs).

Genome-wide identification of new imprinted genes.

In the mid-1980s, elegant studies on mouse embryos revealed that both parental genomes are required for normal development leading to the discovery of genomic imprinting. Imprinting is a parent-of-origin-dependent epigenetic mechanism whereby a subset of autosomal genes is expressed from only one of the parental alleles. Imprinting control involves both DNA- and histone-methylation, which differentially mark the parental alleles.

Histone methylation is mechanistically linked to DNA methylation at imprinting control regions in mammals.

Mono-allelic expression of imprinted genes from either the paternal or the maternal allele is mediated by imprinting control regions (ICRs), which are epigenetically marked in an allele-specific fashion. Although, in somatic cells, these epigenetic marks comprise both DNA methylation and histone methylation, the relationship between these two modifications in imprint acquisition and maintenance remains unclear. To address this important question, we analyzed histone modifications at ICRs in mid-gestation embryos that were obtained from Dnmt3L(-/-) females, in which DNA methylation imprints at ICRs are not established during oogenesis.

[Differential epigenetic marking on imprinted genes and consequences in human diseases].

At the time of fertilisation, the parental genomes have a strikingly different organisation. Sperm DNA is packaged globally with protamines, whereas the oocyte's genome is wrapped around nucleosomes. The maternal and paternal genomes are functionally different as well, and are both required for normal uterine and postnatal development.

A mono-allelic bivalent chromatin domain controls tissue-specific imprinting at Grb10.

Genomic imprinting is a developmental mechanism that mediates parent-of-origin-specific expression in a subset of genes. How the tissue specificity of imprinted gene expression is controlled remains poorly understood. As a model to address this question, we studied Grb10, a gene that displays brain-specific expression from the paternal chromosome.

G9a histone methyltransferase contributes to imprinting in the mouse placenta.

Whereas DNA methylation is essential for genomic imprinting, the importance of histone methylation in the allelic expression of imprinted genes is unclear. Imprinting control regions (ICRs), however, are marked by histone H3-K9 methylation on their DNA-methylated allele. In the placenta, the paternal silencing along the Kcnq1 domain on distal chromosome 7 also correlates with the presence of H3-K9 methylation, but imprinted repression at these genes is maintained independently of DNA methylation.

Early mouse embryo development: could epigenetics influence cell fate determination?

It is generally assumed that the developmental program of embryogenesis relies on epigenetic mechanisms. However, a mechanistic link between epigenetic marks and cell fate decisions had not been established so far. In a recent article, Torres-Padilla and colleagues show that epigenetic information and, more precisely, histone arginine methylation mediated by CARM1 could contribute to cell fate decisions in the mouse 4-cell-stage embryo.