Abstract
A fertilized totipotent cell possesses the potential to become all the adult cell types and extra-embryonic tissues that are needed for embryo development. As it progresses along the development pathway, cell differentiations take place, giving rise to distinct cell types. It is now clear that regulation of expression of genes is the key to understanding how cell differentiation occurs in early developmental stages, as also in other stages of development. In this chapter, we have attempted to elucidate some aspects of two most important elements of gene regulation, gene regulatory networks and epigenetic modifications, in early development. We discuss the concept of master regulatory transcription factors in cell fate decisions and the dynamics of chromatin as it moves from a state of totipotency to more differentiated states. We also discuss master regulators involved in differentiation of the trophectoderm and the inner cell mass, which are incompletely known and similar is the situation for chromatin modifiers involved in these steps. Similarly, we also describe the master regulators that control the cell fate decisions that give rise to the epiblast and the primitive endoderm from the inner cell mass.