title: Epigenetic memories: structural marks or active circuits?
abstract: A hallmark of living systems is the management and the storage of information through genetic and epigenetic mechanisms. Although the notion of epigenetics was originally given to any regulation beyond DNA sequence, it has often been restricted to chromatin modifications, supposed to behave as cis-markers, specifying the sets of genes to be expressed or repressed. This definition does not take into account the initial view of epigenetics, based on nonlinear interaction networks whose "attractors" can remain stable without need for any chromatin mark. In addition, most chromatin modifications are the steady state resultants of highly dynamic modification and de-modification activities and, as such, seem poorly appropriate to work as long-term memory keepers. Instead, the basic support of epigenetic memory could remain the attractors, to which chromatin modifications belong as do many other components. The influence of chromatin modifications in memory is highly questionable when envisioned as static structural marks, but can be recovered under the dynamic circuitry perspective, thanks to their self-templating properties. Beside their standard repressive or permissive functions, chromatin modifications can also influence transcription in multiple ways such as: (1) by randomizing or inversely stabilizing gene expression, (2) by mediating cooperativity between pioneer and secondary transcription factors, and (3) in the hysteresis and the ultrasensitivity of gene expression switches, allowing the cells to take unambiguous transcriptional decisions.
authors.affiliation: Université de Rennes1, Irset. IFR-GFAS Campus de Beaulieu, Rennes cedex, France.
authors.forename: Floriane
authors.initials: F
authors.lastname: Nicol-Benoît
authors.forename: Pascale
authors.initials: P
authors.lastname: Le-Goff
authors.forename: Yves
authors.initials: Y
authors.lastname: Le-Dréan
authors.forename: Florence
authors.initials: F
authors.lastname: Demay
authors.forename: Farzad
authors.initials: F
authors.lastname: Pakdel
authors.forename: Gilles
authors.initials: G
authors.lastname: Flouriot
authors.forename: Denis
authors.initials: D
authors.lastname: Michel
mesh_terms: D005075:Biological Evolution; D042002:Chromatin Assembly and Disassembly / Q000502:physiology*; D003491:Cybernetics; D044127:Epigenesis, Genetic / Q000502:physiology*; D005786:Gene Expression Regulation / Q000502:physiology*; D053263:Gene Regulatory Networks / Q000502:physiology*; D008957:Models, Genetic