Epigenetics and Development

Abstract

The term epigenetics was originally coined to understand how genes control phenotypic outcomes. In today’s definition of the term, it refers to any mechanism beyond genes that can be inherited through cell divisions. Proper development of the embryo involves a multilayer regulation of gene expression to ensure proper temporal and spatial control of expression of genes. This precise control of gene expression translates to initiation and maintenance of cell-type-specific developmental programs and proper formation of tissue types. In order to achieve the robustness in developmental programming, not only do cells in the embryo need to be able to turn on and off genes precisely, they also need to have mechanisms to dynamically respond and adapt to the environment that provides signals for fine-tuning the developmental processes. Taken together, there is an inherent need for both robustness and plasticity in the cells to give rise to proper tissues in the embryo. The key features mentioned above are imparted by epigenetic mechanisms that exist in the embryo. There are three major epigenetic mechanisms that cells use to establish and maintain their epigenetic states, namely, a specific structure and chemically modified forms of their chromatin via histone proteins, modifications of the histone proteins, methylation states of their promoters, and lastly expression levels of genes regulated by noncoding RNA-based mechanisms. Given the need for highly precise regulation, in many cases, there is a cross talk between the different mechanisms, leading to a very tightly controlled regulation. Genetic analyses in model organisms as well as occurrence of human diseases shine light toward the importance of these mechanisms both in the specification and morphogenetic events in the embryo. Having realized the potential of epigenetic mechanisms in regulating developmental processes, recent efforts have been revealing the distinct epigenetic states that exist and change during developmental transitions, and a whole field has evolved around that to try and harness the potential of altering epigenetic mechanisms to regulate cell lineages. Taken together, understanding epigenetic mechanisms of development will allow for a better understanding of how they may contribute to human disease.