Over the past decade, stem cell biology has been an area that has caused much controversy. Stem cells have the ability to differentiate into many different types of cells and therefore, advocates of stem cell research argue that the cells have various medical applications. On the other hand, opponents of stem cell research denounce the use of human embryos for research purposes, claiming that the embryos represent human lives and that experimentation with them and subsequent annihilation of them is the same as killing a living human being. Nevertheless, the potential uses for stem cells are endless and stem cells have the ability to completely change modern medical practices.
Human embryonic stem cells (HESCs) are characterized by several fundamental attributes. As pluripotent cells, the embryonic stem cells live in an undifferentiated state and have the ability to differentiate into numerous cell types. Taken from the inner cell mass region in the embryo, human embryonic stem cells are selected from the early human blastocyst five days after fertilization. The human embryonic stem cells also have a normal karyotype and are able to survive and divide in vitro indefinitely under suitable culture conditions, allowing them to be a renewable resource for scientists to use in the laboratory environment. Furthermore, human embryonic stem cells can be frozen and unthawed successfully for storage purposes, and can differentiate into a variety of cell types both in vitro and in vivo. The human embryonic stem cells first differentiate to form the three major germ layers--ectoderm, mesoderm, and endoderm, and then further differentiates to form all of the major cell types in a complete human organism (Brivanlou et al. 2003).
In order to create the differentiated cells from human embryonic stem cells in laboratory cultures, the human embryonic stem cells must first be isolated and their pluripotent nature must be confirmed. Prior to 2001, the primary method used to isolate embryonic stem cell lines was to identify and segregate single colonies under a dissecting microscope. However, this process was time-consuming and costly and served to inhibit stem cell research. A new method has been developed that involves introducing a reporter gene into the embryonic stem cells and separating stem cell lines due to the gene's effects (Eiges et al. 2001).
The human embryonic stem cells were first transfected with enhanced green fluorescence protein (EGFP), under the control of the murine Rex-1 promoter. The cells with EGFP demonstrated high levels of GFP expression when in the undifferentiated state and therefore showed high levels of fluorescence. As the cells differentiated, the levels of GFP expression decrease along with the degree of fluorescence. The undifferentiated cells were then isolated from the culture using a Fluorescence Activated Cell Sorter (FACS) (Eiges et al. 2001).
Furthermore, the pluripotent nature of the human embryonic stem cells was...