An Introduction to Epigenetic Mechanisms.

The astonishing array of cellular phenotypes required to make a complex organism such as a human is generated from an identical genetic sequence in the nucleus of each cell. The central nervous system is a highly ordered, complex system composed of multiple neuronal and glial cell types. Both neurons and glia are derived from neural stem/precursor cells (NPCs) in a temporally and spatially patterned process of cellular division and differentiation, migration, maturation and the establishment of neuronal connectivity. In part, this is testament to the power and flexibility of epigenetic mechanisms to direct transcription, producing a myriad of outcomes. The progressive restriction of developmental potential involves the acquisition of a hierarchy of epigenetic regulation which restricts and directs the developmental program of gene expression. Differentiation into each cell type is associated with the acquisition of a distinct epigenetic profile. The importance of epigenetic mechanisms for neurodevelopment is exemplified by the many neurodevelopmental disorders caused by the genetic disruption of epigenetic readers, writers or modifiers. In this chapter I will introduce the different classes of epigenetic mechanisms, and I will briefly discuss some of the known neurodevelopmental disorders caused by genetic disruption of these pathways to illustrate the importance of epigenetic processes in brain development and function.