A nice analysis of the trimethylation of histon 3 at lysine 4 (H3K4me3) appears in Cell this week (http://dx.doi.org/10.1016/j.cell.2014.06.027). Benayoun and Pollina et al. claim that this marker labels preferentially those proteins that are essential for the cell’s function. The marker has been found at the start of most transcribed genes, but Benayoun and Pollina argue that not its mere presence, but the intensity of its presence is a sign that this protein is relevant for lineage specifity. If this intensity is disturbed, that function is not maintained.
This is a metaanalysis of a very broad range including human, mammalian, protostomes, plants and fungi. Nicely done!
Epigenetic modification of DNA, mostly methylation, is the way which ensures lineage specity in mammalian organization and propagation of cell types. It is inherited while cells multiply.
In Nature this week (doi:10.1038/nature13648) Reik and Kelsey describe two article (et al. Nature 511, 606–610 (2014) and et al. Nature 511, 611–615 (2014)) where the methylation patterns in egg, sperm, fertilized eggs and blastocysts are analyzed. As has been found in mice before, blastocysts lose most of their methylation. Later in development the DNA gets remethylated again. This has been suggested but formal proof was lacking. The imprinting – methylated gene regions due to maternal or paternal origin – is not as much removed for maternal genes, but for paternal ones.
Whether these papers will improve human stem cell research is to be seen.