Pluripotent stem cells
Pluripotent stem cells are the undifferentiated cells that are the precursors of specialized cells. Unlike the differentiated cells of the human body the stem cells are capable to replicate themselves almost endlessly and give rise to the specialized cells. It is considered that in the stem cell population some of the cells self replicate, whereas the other differentiate. This process is called asymmetric differentiation.
Types of stem cells, according to the potency
Potency is the potential of the stem cell to differentiate into specialized cells.
There are several types of stem cells, according to their ability to produce specific cells:
- Totipotent/omnipotent stem cells are able to create a complete new individual by forming both extraembryonic and embryonic cells. Totipotent stem cells are called blastomeres;
- Pluripotent stem cells are able to differentiate into the germ layers of the embryo – mesoderm, endoderm and ectoderm, but cannot form the extraembryonal cells;
- Multipotent stem cells can differentiate into the different cells, which are related to each other (derive from one germ layer);
- Oligopotent stem cells have the ability to differentiate into a few types of cells;
- Unipotent cells are able only to reproduce themselves;
Pluripotent stem cells are the following:
|Name of the stem cell||Origin|
|Embryonic stem cell (ESC)||Epiblast of late-blastocyst|
|Embryonic stem cell (ESC)||Primordial germ cells from extraembryonic mesoderm and early genital ridge|
|Epiblast stem cell (EpiSC)||Epiblast of early postimplntation embryo|
|Spermatogonial stem cells||Spermatogonia from postnatal testis|
Embryonic stem cells
Every embryo consists of pluripotent stem cells, which produce all the tissues of the human body. Approximately 50-150 of these cells may be seen in the embryo 4-5 days after the conception. ESC give rise to three germ layers.
|Ectoderm||the brain and spinal cord; the peripheral nervous system; the sensory epithelia of the eye, ear, and nose; the epidermis, the nails and hair; the mammary glands; the enamel of the teeth|
|Mesoderm||connective tissue, cartilage, and bone; striated and smooth muscles; the heart walls, blood and lymph vessels and cells; the kidneys; ovaries and testes; the spleen; the adrenal gland|
|Endoderm||the tonsils, the liver, the thymus, the thyroid, the parathyroids, and the pancreas; the epithelial lining of the internal organs|
It is supposed that the expression of the transcription factor Oct4 is the main feature of these cells that keeps them undifferentiated. Another transcription factor called Nanog was discovered in mice ESCs.
Researchers are currently working with these cells, as they hope to use their properties to investigate and treat various diseases and disorders (Parkinson’s disease, various genetic conditions, infertility), to restore the damaged organs and tissues after the injuries, produce organs for transplantation, and explore the methods of DNA repair.
Human embryonic stem cells may be received from the embryos, which were formed via in vitro fertilization (IVF). IVF is a procedure during which the egg is fertilized by sperm outside of the body – in vitro.
The researches which involve the human embryos are highly ambiguous, as there are a lot of ethical and moral issues in embryonic stem cell research.
Induced pluripotent stem cells
Unlike embryonic stem cells, adult stem cells are not pluripotent and they are not able to give rise to whatever tissue. Adult stem cells renew themselves, but not produce another type of cells. However, the researchers can reprogram these cells to pluripotent state by the means of genetic engineering.
Oct-3/4 and some factors from the Sox gene family are influenced to create pluripotent cells.
These “artificially produced” pluripotent cells are called induced pluripotent stem cells (iPSCs). This technology was invented in 2006 by Shinya Yamanaka’s in Japan. In 2012 the researcher was awarded the Nobel Prize for his discovery.
This invention is especially significant as there is no moral and ethical issues regarding the usage of these cells and the person can become a donor for him/herself, so the immune rejection may be avoided.