Novel Epigenetic Markings

Epigenetic markings are changes to DNA or its packaging components that alter gene expression, effectively turning gene transcription on and off, and that are inherited by daughter cells. Commonly studied epigenetic modifications are CpG dinucleotide methylation, which are often concentrated at Alu and SVA sequences (one estimate asserts that over 30% of all CpG sites are within Alu sequences), and modifications of histones. While research examining these patterns of epigenetic modifications has found that patterns are largely conserved across species, human-specific alterations have also been found. Studies have found that methylation patterns vary between humans and non-human primates both at the global and individual gene level, and that these patterns correlation to species-specific gene expression. Additionally, differences between species exist in histone modification patterns, which again corresponds to changes in expression. While estimates of the degree to which these modifications are responsible for species-specific expression patterns are low (~ 10% of the variance explained), these epigenetic modifications have the potential to explain some of the human phenotypic uniqueness that cannot be attributed to changes in DNA sequence.