The early-life social environment and DNA methylation.

DNA methylation is a chemical modification of DNA that confers, upon identical sequences, different identities that are reflected in different gene expression programming. DNA methylation has a well-established role in cellular differentiation by providing a mechanism for one genome to express multiple phenotypes in a multicellular organism. Recent data point however to the possibility that in addition to the innate process of cellular differentiation, DNA methylation can serve as a genome adaptation mechanism, adapting genome function to changing environmental contexts including social environments. A critical time point for this process is early life when cues from the social and physical environments define lifelong trajectories of physical and mental health. DNA methylation and additional epigenetic modifications could therefore serve as molecular links between 'nurture' and 'nature'. Data that are consistent with this new role for DNA methylation as a mechanism for conferring an 'environment' specific identity to DNA will be discussed.