What are stem cells

Stem cells are cells found in almost all multicellular organisms. Their main characteristic is that they are able to renew themselves through a process called mitotic cell division and change into various specific cell types.

The term „stem cells“ was proposed by a histologist A. Maksimov in 1908. Another important date was when McCulloch and Till found that self-renewable cells are present in bone marrow.

There are two main types of stem cells: embryonic stem cells and adult stem cells. Embryonic stem cells are located in blastocysts and adult stem cells are located in adult tissues.

Two types of stem cells

The main difference between embryonic stem cells and adult stem cells is the potency. Embryonic stem cells are pluripotent and they can become any cell type. Adult stem cells are basically limited and can only differentiate into cell types of their original tissue. During treatment, patient’s own stem cells can be used. The main advantage of this way is that the new grown cells won’t be rejected by the immune system.

Since stem cells can grow and differentiate themselves into specific cell types which build certain tissues such as nerves or muscles through cell culture, their use in medicine became very significant.

On the image below you can see the stem cells hierarchy:

Stem cells hierarchy

Every stem cell has two main characteristics: it’s self-renewable, which means that it can go through many cell division process and still remain in the same state. The second characteristic is potency, which means that it is capable of differentiating into various specific cell types. Therefore, stem cells can be totipotent (they are produced by the fusion of an egg and sperm) and pluripotent (they are totipotent cells’ descendants). They can also be unipotent (can make only one cell type) and pluripotent (can make numerous cell types).

In order to ensure it’s self-renewal, a stem cell goes through two types of cell division. Symmetric division produces two identical daughter cells (with full stem cell characteristics), while the asimmetric division produces just one stem cells which self-renewal is limited.

Many researchers believe that the further development of stem cells with change the way diseases are treated nowdays. Many adult stem cells researches are being already done (for example, bone marrow transplants are used to treat leukemia). Scientists hope that in the future diseases such as Parkinson’s disease or cancer will be possible to treat.

Ever since there was embryonic stem cells, there was controversy surrounding them. Pluripotent, embryonic stem cells are obtained from tissues which have been removed during terminated pregnancies and such. Each cell group is called a cell line.
The controversy is present because the stem cells are obtained from embryos (the concerns are similar to those about abortion). There is also a possibility to clone embryos in order to get new stem cells, which is a big ethical dilemma.