[Fundamentals of epigenetics].
The genetic code cannot alone explain the diversity of cellular and individual phenotypes. Epigenetics provides an additional level of information that is not encoded in the DNA molecule but nonetheless influences its activity in a stable and heritable manner through cell divisions. This effect on gene expression results from variations in chromatin states and is induced by biochemical modifications targeting the DNA molecule or associated histone proteins. Epigenetic regulation can convert a developmental or transient environmental signal into a stable transcriptional response, which will then be perpetuated even in the absence of the original stimulus. Epigenetic regulation explains how, starting from a unique genome, the pluripotent embryo can generate a variety of tissues and maintain their identity throughout development. Epigenetics has a broad impact on development, by controlling pluripotent and differentiated states. An increasing number of pathological situations are being attributed to abnormal establishment or maintenance of epigenetic patterns. Given the mitotic heritability of epigenetic states, a key question is whether epigenetic information can also be transmitted through generations.