Chromosomal elements conferring epigenetic inheritance.

Epigenetic regulation of transcription can lead to a stable differential expression of identical genetic information in the same cell or cell population. There is increasing evidence that higher order chromatin structures, involving specific multiprotein complexes, constitute one device to establish and maintain epigenetic marks. In addition, defined chromosomal elements conferring epigenetic inheritance of transcriptional expression states have recently been identified. During the period where the difference in expression of identical genes is established, these sequences appear to be used as switch elements by both negative and positive regulators. Once the epigenetic mark is "set", the elements maintain either the silenced or the activated expression state over many cell generations. Here we review recent data obtained from analyzing epigenetic gene regulation in different organisms and show that similarities in the underlying mechanisms appear to exist.