Epigenetic Reprogramming in Mammalian Development

During the mid-twentieth century Conrad Waddington proposed his ontogenic concept of canalization, and suggested that epigenetic mechanisms might serve as a means of metastable memory imposed on the genetic material during differentiation. Subsequently, Waddington's theories have received substantial acknowledgment during the first decade of the twenty-first century, with numerous studies unraveling the important contributions of epigenetic mechanisms and the epigenomic control of differentiation. The early embryogenesis and primordial germ cell development have received much attention as developmental stages with extensive epigenomic reprogramming. In both developmental phases, the epigenomic landscape of chromosomes is rapidly and dramatically altered, and this goes along with a substantial change in the developmental potential of cells. In this chapter, a summary is provided of the current knowledge of epigenetic reprogramming mechanisms. These are discussed in line with biological concepts, and with the role of DNA methylation in particular.