(Multi／Pluri／Toti) Potential Stem Cells

Stem Cell Types

Stem Cells: From Zygote to Adult

1. Sperm fertilizes an egg and forms a single cell called a zygote
2. The zygote undergoes a process known as mitosis, in which it replicates its chromosomes (which carry each parent’s DNA) and then divides, resulting in two identical cells. These cells are called totipotent and have the ability to develop into a new organism. The zygote repeats the process of mitosis for about 5 or 6 days creating a small ball of a few hundred cells called a blastocyst.
3. The blastocyst has an outer-layer of cells called the trophoblast, which will eventually form the protective placenta. Inside the trophoblast is a group of cells called the inner cell mass. The organism in a stage between zygote to fetus is called an embryo* and the cells are called embryonic stem cells.
4. At this point embryonic stem cells have the ability to become a cell for any part of the body (nerve, muscle, blood, etc.). This ability to become any type of cell in the body is called pluripotent. The difference between totipotent and pluripotent cells is only that totipotent cells can give rise to both the placenta and the embryo.
5. As the embryo grows these pluripotent cells develop into specialized, multipotent stem cells. Multipotent stem cells have the ability to develop specific types of cells (terminally differentiated cells). For example a blood stem cell (Multipotent Hematopoietic Stem Cell) can develop into a red blood cell, white blood cell or platelets (all specialized cells). There are multipotent stem cells for all of the different types of tissue in the body.