What are stem cells?

One of the recent achievements in bioscience is the discovery of stem cells, which are cells at the earliest stage of cell development and differentiation. Stem cells are primitive cells without being specialized and they maintain the ability to renew themselves into a diverse range of specialized cell types. What makes the stem cells so unique? We all understand that each one of us starts out as just one cell, a single fertilized egg, which is made when an egg from the mother and a sperm from the father fuse together. The single fertilized egg divides to make two new cells, and then divides again to form four cells, and again to make eight. Different cell types containing genetic blueprint group together to form organs and organ systems that work together to form a living and functional organism. The majority of the cells that make up a human body will lose their ability to differentiate when an entire human body is formed.

Stem cells originate from a very early embryonic developmental stage. Cells that can be differentiated into other types of cells are called stem cells. For instance, a fertilized egg is a primitive stem cell that is able to divide and self-renew indefinitely into various types of fundamental cells that group together in the body to form tissues and organs such as heart, liver, brain, or lymphoid tissues (Figure 1). After a body is formed, some stem cells still have the ability to differentiate, and these cells become pluripotent (multipotent) stems cells or progenitor cells, which play an important role in the cell renewal, repair, and regeneration in human tissues and organs. For example, stem cells in the bone marrow are capable of developing into red blood cells, leucocytes, and other types of blood cells to build up our blood system; hence, the hematopoietic stem cell shows significant importance in bone-marrow transplant and recovery.

Medical researchers consider that since stem cells possess the potential ability to repair tissues and organs, there might be a way to cure many untreatable diseases. If scientists were able to control the differentiation process of stem cells, various kinds of dead cells could be replaced by the same new cells; for instance, pancreas cells could be given to patients with diabetes or brain cells could be used to treat patients with Parkinson disease. Thus, controlling the growth mechanism of the stem cells is seen as a decisive factor for the prevention and possible cure of many diseases.

Origin and Differentiation of Stem Cells