DNA is unarguably the carrier of genetic information.However,DNA sequence alone cannot explain how hundreds of cell types in a complex multi-cellular organism,such as a human individual can possess distinct transcription programs,while sharing the same genetic information.This is believed to be achieved by fine-tuning our genetic information with a so-called "epigenetic" system.To fulfill the two basic tasks challenging the multi-cellular organisms,epigenetic system must simultaneously offer dual characteristics,"Plasticity & Inheritability".Plasticity allows the transformation of one genome into hundreds of epigenomes and transcriptomes,whereas inheritability permits the maintenance of every single epigenome and its corresponding transcriptome.