Stem Cells - Rau's IAS

Undifferentiated cells are also called stem cells.
Further stem cells are classified into various types based on their potency to differentiate.

Types of Stem Cells

These are stem cells that are potent enough to differentiate into all types of cells.
In short, they can produce a clone of an entire organism.
Such cells are found in the embryo stage of human development. (inner mass cells)
Thus, they are also called embryonic stem cells.

Such cells have the potential to all types of cells associated with a particular organ or a tissue.
They help in repair, renew and maintenance of tissues or organs in an adult body. Thus, they are called adult stem cells.
Eg: Intestinal stem cells (renew every 45 days), cells in bone marrow etc.

Since all cells have the same DNA in their nucleus how is it that one is pluripotent another multi-potent and another has no ability to differentiate?
Answer lies in gene expression.
We now know that there are 4 transcription factors that are responsible for embryonic stem cells as compared to specialized adult cells. (details not important)
Thus, if we can somehow reprogram specialized cells (somatic cells) to tweak the transcriptional factors, it can reverse into embryonic stem cells.

Reprograming adult cells to become pluripotent was awarded Nobel prize in 2012.
Take any differentiated cell/somatic cell/adult cell (not adult stem cell) and induce the 4 transcription factors, it can reverse itself into an embryonic stem cell.
This reprogrammed cell is called induced-pluripotent stem cell (iPS cells) or human-induced pluripotent stem cells.
Once you get iPS cells you can culture them in-vitro and make them differentiate into different cell types like skin, neutrons, muscles etc.
iPS cells hold promise in both regenerative medicine (tissue engineering/ organ transplantation) and drug development.
Though at nascent stage, iPS cells are seen as the future of transplantation.
Living iPS are now used to see how they react to drugs thereby accelerating drug development.

Traditionally there was another way of growing an entire organism using the adult differentiated cell. It was called cloning.
Cloning involves 3 steps
Take any adult cell (skin, hair, nail etc.) and suck out its nucleus.
Take an egg cell from a donor and remove the nucleus from the egg/oocyte. (enucleated)
Inject the nucleus of the adult cell in the enucleated egg. You have an oocyte with somatic cell nucleus.
The oocyte cytoplasm reprograms the nucleus of the somatic cell and it makes embryonic stem cell.
The embryonic stem cell can then be grown into an organism identical to the person from whom adult cell was taken. (since it is the nuclear DNA that codes for proteins)
This is how dolly the sheep was cloned.

Disadvantage

The only problem is that reproductive cloning is very inefficient as the nucleus from somatic cell resists reprogramming.

Stem cell therapy is the use of stem cells to grow healthy adult cells in the lab to replace damaged, defective, or degraded adult cells in the body.
It is particularly useful in which
- cells are degraded as in case of neurological disorder where there is degeneration of neuron Alzheimer’s, Parkinson’s (motor neurons) etc. as neurons do not multiply
- damage of organ due to accident, old age etc.
- body produces defective cells as in case of blood related disorders like sickle cell anemia, beta thalassemia where regular blood transfusion is needed. In this case there are 3 ways
  - Stem cell transplantation of a healthy donor
  - Make iPS cells and grow healthy adult cells
  - Gene-edited stem cells from ones own body

Note: Stem cells from humans can be introduced in pigs to grow organs in them as they have a faster life cycle. (see CRISPR for details)