Fundamentals of DNA methylation in development.

DNA methyation is critical to regulation of gene expression especially during developmentally dynamic changes. A large proportion occurs at CpG (a cytosine followed by a guanine nucleotide) sites and impacts gene expression based on location, timing and level of DNA methylation. The spectrum of effects produced by DNA methylation ranges from inhibition to enhancement of gene expression. Here basic terms and concepts in the study of DNA methylation are introduced. In addition, some of the commonly used techniques to assay DNA methylation are explained. New methods that allow the precise addition and removal of DNA methylation at specific sites will likely enhance our understanding of DNA methylation in development and may even lead to long-lasting therapeutic strategies to cure diseases. IMPACT: Fundamentals of DNA methylation including its significance are made accessible to a broad audience. Common assays for detecting DNA methylation are explained succinctly. Developmental patterns of DNA methylation detected in commonly used animal models are discussed and explained. Novel methodologies to investigate consequences of DNA methylation and demethylation are introduced.