Embryonic stem cells have been the cell model for our understanding of the mechanisms regulating cell differentiation. As discussed in Module One, stem cells have two basic properties:
  1. The capacity for self renewal of their stem cell state and
  2. The ability to differentiate into a wide variety of specialized cell types.

Maintaining the balance specifically between stability and plasticity has been a major challenge for stem cell scientists. Over the past several years, extensive studies have been conducted that focus on understanding the contributions of transcription factors and epigenetic enzymes to the "stemness" properties of these cells. Identifying the molecular switches that regulate ES cell self-renewal versus differentiation could provide insight into the nature of the pluripotent state while also enhancing the potential use of these cells in therapeutic applications.

How do epigenetic processes, such as transcription factors and DNA modification regulate the activity of genes in the cell?

There are several ways in which the cell can regulate which genes are turned on (to synthesize a specific protein that is involved in the cellular activities) and which genes are turned off (silenced). One pathway involves transcription factors and the other pathway involves chemical modifications of either DNA or the proteins associated with DNA, i.e., histones (Hanna, Saha et al. 2010). The processes we mention are part of epigenetics which we describe below.

Clearly, the properties of different specialized cells depends on which genes are turned off or on in the cells. Thus, a muscle cell will have a different array of genes turned on or turned off that will dictate its capacity to function as a muscle cell. Similarly, a white blood cell will have a different array of genes to enable it to serve as an immune cell.

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