Published online by Cambridge University Press: 08 August 2009
Introduction
There is a growing awareness that whether or not a gene is actively expressed within a particular cell is determined not only by the primary nucleotide sequence of the gene and its regulatory elements, but also by changes in the way the DNA is modified and packaged within the nucleus. This non-sequence-based information is termed epigenetic. Epigenetic changes include methylation of the DNA itself, and modifications of the histone proteins that package the DNA within chromosomes. The pattern of epigenetic information varies from cell type to cell type and is reflected by the cell-specific profile of gene expression. Once established in a differentiated cell type, these epigenetic signals are stably inherited through mitosis, and are essential to maintain the correct gene expression profile within cells of that type for the life of the organism. The acquisition and maintenance of the correct epigenetic profile is therefore essential for normal development. The past decade has witnessed an explosion in our understanding of so-called ‘epigenetic diseases’, where the disruption of an epigenetic signal results in the inappropriate expression or silencing of one or more genes, giving rise to the disease phenotype. The aims of this chapter are to introduce the chemical nature of the major epigenetic signals, to discuss epigenetic processes which take place during normal development, and to briefly review some of the important examples of human diseases arising due to breakdowns in epigenetic processes.
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