Embryonic Stem Cells (ESC) are one type of stem cell that can be found in the early stages of embryonic development. They are generally derived from a structure called the inner cell mass of the blastocyst for research use and have the ability to become any type of body cell when exposed to certain molecules or environments. This ability to become any type of cell is called pluripotency.

 

ESCs have 3 basic characteristics:

1. Pluripotency

2. Self-renewal

3. Differentiation

 

Embryonic Stem Cells undergo two different types of division. In asymmetric division, one ESC divides into one identical copy of itself and another cell whose function is more specialized or more differentiated. In symmetric division (also called mitosis), one ESC divides into two identical copies of itself. When given proper conditions, ESCs will remain immortal in vitro (“in the lab”) without undergoing apoptosis, a fancy word for programmed cell death.

 

 

 

 

 

 

 

 

 

 

 

 

​Let’s go over the growth process of the embryo. The first step is fertilization, where sperm from the male combines with an egg from the female. In order to arrive at the final destination, a sperm must go through various biological barriers within the female reproductive system and compete against millions of counterparts to win the only chance to meet and combine with the egg. When combined, the nuclei of the sperm and the egg break and integrate with each other to form a new nucleus which includes all the parental genes. When the new nucleus is formed, the fertilization step is complete. After a series of chain reactions inside the fertilized egg, or zygote, the single egg cell divides, or proliferates, into 2 identical copies. This identical division repeats until you’ve gone from a simple mixture of cells to a more compacted and structured body called the blastocyst, containing about 50-150 cells. The blastocyst takes the shape of a ball comprised of several smaller balls, but the outer ball is not filled by the smaller ball aggregate. The “smaller ball aggregate” is called the inner cell mass (ICM), and that’s where we collect and isolate ESCs.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The blastocyst is usually fully formed by the fourth or fifth day after fertilization. Pluripotency of ESCs is first demonstrated when they develop into the 3 germ layers. The 3 germ layers are called the endoderm, the mesoderm, and the ectoderm, respectively. These 3 germ layers can differentiate into corresponding body tissues and organs via a process named organogenesis. However, when in the lab, they can differentiate into any type of body cells when inducing molecules in charge of gene expression are added. Embryonic Stem Cells have often been the subject of ethical debates because isolating them for research requires the destruction of a developing embryo. Such problems won’t exist for other types of stem cells discussed in the following chapters.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What makes ESCs important, despite its short existing time in the human body? Since they can turn into any type of body cell, they may provide a deep insight into how we develop from a single cell into an organism of billions of different cells with corresponded functions. Secondly, ESCs are easy to isolate from the inner cell mass of the blastocyst, which is of crucial value for preclinical research and potential clinical usage. Finally, since ESCs are immortal when given proper cultivating conditions, they can provide an indefinite source for research on other types of cells (for example, adult stem cells or somatic cells).