Inheritance of epigenetic transcriptional memory through read-write replication of a histone modification.

Epigenetic transcriptional regulation frequently requires histone modifications. Some, but not all, of these modifications are able to template their own inheritance. Here, I discuss the molecular mechanisms by which histone modifications can be inherited and relate these ideas to new results about epigenetic transcriptional memory, a phenomenon that poises recently repressed genes for faster reactivation and has been observed in diverse organisms. Recently, we found that the histone H3 lysine 4 dimethylation that is associated with this phenomenon plays a critical role in sustaining memory and, when factors critical for the establishment of memory are inactivated, can be stably maintained through multiple mitoses. This chromatin-mediated inheritance mechanism may involve a physical interaction between an H3K4me2 reader, SET3C, and an H3K4me2 writer, Spp1 - COMPASS. This is the first example of a chromatin-mediated inheritance of a mark that promotes transcription.