Epigenetic responses to environmental change and their evolutionary implications

摘要

Chromatin is a complex of DNA, RNA, histones and non-histone proteins and provides the plat-form on which the transcriptional machinery operates in eukaryotes. The structure andconfiguration of chromatin are manipulated by families of enzymes, some catalysing the dynamicaddition and removal of chemical ligands to selected protein amino acids and some directly alteringor displacing the basic structural units. The activities of many of these enzymes are sensitive toenvironmental and metabolic agents and can thereby serve as sensors through which environmentalagents can alter gene expression. Such changes can, in turn, precipitate either local or cell-widechanges as the initial effect spreads through multiple interactive networks. This review discussesthe increasingly well-understood mechanisms through which these enzymes alter chromatin func-tion. In some cases at least, it seems that the effects on gene expression may persist even afterthe removal of the inducing agent, and can be passed on, through mitosis, to subsequent cellgenerations, constituting a heritable, epigenetic change. If such changes occur in germ cells ortheir precursors, then they may be passed on to subsequent generations. Mechanisms are nowknown to exist through which an epigenetic change might give rise to a localized change in DNAsequence exerting the same functional effect, thereby converting an epigenetic to a geneticchange. If the induced genetic change has phenotypic effects on which selection can act, thenthis hypothetical chain of events constitutes a potential route through which the environmentmight directly influence evolution.