The nomenclature of chromatin containing the H3 family of histones, the amino acid lysine (K), at amino acid residue position 4 (counting from the N-terminus), having three methyl groups added (m3) is abbreviated “H3K4me3”. The attached paper tracks the distribution of bivalent H3K4me3/H3K27me3 chromatin in male germ cells (primordial cells from which sperm will arise) from six vertebrate species. These results have big implications for understanding the mechanisms that specify animal development.
Changes in gene regulation frequently underlie changes in morphology during evolution, and differences in the state of chromatin have been linked with changes in anatomical structure and gene expression across evolutionary time. Authors [attached paper] assess the relationship between evolution of the chromatin state in germ cells and evolution of the gene regulatory programs governing somatic development. They examined the poised (H3K4me3/H3K27me3 bivalent) epigenetic state in male germ cells from five mammalian and one avian species.
They discovered that core genes poised in germ cells from multiple amniote species (i.e. those having an embryo developing within a set of protective extra-embryonic members––the amnion, chorion and allantois) … are ancient regulators of morphogenesis that sit at the top of transcriptional hierarchies controlling somatic tissue development. In contrast, genes that gain epigenetic poising in germ cells from individual species act downstream of core poised genes during development in a species-specific fashion. Authors propose that critical regulators of animal development gained an epigenetically privileged state in germ cells, manifested in amniotes by H3K4me3/H3K27me3 poising, early in metazoan evolution (i.e. all animals having the body composed of cells differentiated into tissues and organs).
Nature Genetics Aug 2o16; 48: 888–894 & News-n-Views pp 822–823