Mechanisms of epigenetic inheritance

The mechanisms by which stable gene expression patterns are inherited during cell division are not well understood. Chromatin is subject to a number of covalent modifications and it is generally believed that the transfer of these modifications between cell generations plays a critical role in inheritance, though how this occurs is a matter of debate. In one proposed model, replication of chromatin in a semi-conservative fashion would allow ‘template reading’ and ‘writing’ mechanisms to copy modifications from old histones to new histones. Conversely, if chromatin is replicated in a conservative fashion, then other mechanisms, such as the replacement and/or modification of histones during transcription, may mediate the replication of these modifications. Finally, several recent studies suggest that the faithful replication of DNA methylation patterns may be used to propagate histone modifications associated with gene silencing.