The image above shows the complete set of chromosomes in a 2-cell stage mouse embryo. DNA-packaging proteins called histones in the chromosomes have been tagged with chemicals that show up in different colours. The tag H3K27me3 (shown in green), can switch gene activity off. The tag H3K4me3 (shown in red) can turn gene activity on. White represents the chromosomes’ centromeres, and blue represents DNA.
In research published in Nature, Yi Zhang and colleagues at Harvard have discovered that modifying the H3K27 histone shuts down the activity of some genes in mice.
The researchers hope that this will offer insights into “imprinted” genes. These are genes that an organism possesses two copies of – one from each parent – but only one copy is active.