Breaking Symmetry: The Asymmetries in Epigenetic Inheritance.

Symmetry and asymmetry are fundamental aspects of life. Most cells within a multicellular organism contain the same genetic information, passed on from one originating cell - the zygote; however, these cells can take on a variety of different identities, with diverse appearances and functions. A fundamental question in biology ponders how cells containing identical DNA content can take on different cell identities. Epigenetic mechanisms could be the symmetry breaking factor, as they are able to change gene expression in cells without changing the DNA sequence. While the process of duplication and segregation of DNA during cell division has been well studied, it is less understood how the epigenetic information is established and inherited in the cells within a multicellular organism. Studies of asymmetric stem cell division, where a stem cell division gives rise to a self-renewed stem cell and a differentiating daughter cell, provides a model to study how epigenetic information is maintained or changed to produce daughter cells with identical genetic information but distinct cell fates. Here, we discuss findings and ideas of how epigenetic information is maintained or changed during asymmetric cell division and the importance of this asymmetry in influencing cell fate.