- Specialized tissues can develop by cell differentiation in multicellular organisms.
- Differentiation involves the expression of some genes and not others in a cell’s genome.
- The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses.
Use of stem cells to treat Stargardt’s disease and one other named condition.
Ethics of the therapeutic use of stem cells from specially created embryos, from the umbilical cord blood of a new-born baby and from an adult’s own tissues.
Cell Differentiation
Imagine you and 6 of your schoolmates are assigned to finish an IB biology group project, you and your schoolmates will start dividing the job, each of you will have different tasks.
The cells in multicellular organisms are just like you and your schoolmates, the cells will differentiate, different cells take up different specific functions, so the organisms grow in complexity.
How do the cells “know” what duties they are assigned to?
All of the cells in multicellular organisms are derived from one cell, the zygote (formed once sperm and ovary combine). Hence, no matter our lung cell or nerve cell, they have the same genes.
However, different cells have different gene expression, resulting in each cell carries different functions.
e.g. the pancreatic cell expresses the gene for insulin production but the skin cell won't.
Emergent properties
Like in the group project, you have to communicate with your schoolmates for better cooperation, so the IB biology project gets a higher grade. If you work on your own, you won't achieve much. So do our cells!
Emergent properties = the function only exist in the collection of
That means, for example, the lungs expand and contract to pull or push the air in breathing, however, each individual lung cell cannot exert such function, only if they come together, they possess the function of lungs
The cells and organs communicate with each other to form a complex network for complex function.
Same type of cells gather --> Tissue --> Organs --> Organ systems --> cooperate with other organ system
e.g.: lung cells --> lung tissue --> lung --> respiratory system --> cooperate with cardiac system for oxygen supply
Stem Cells
Embryonic stem cell
As we have mentioned above, all cell in the multicellular organism comes from the zygote. The zygote keeps replicating and dividing itself, giving a ball of cells called blastocyst.
A blastocyst is known as embryonic stem cell, it is pluripotent.
Pluripotent = can differentiate into any type of body cell
e.g. nerve cell, pancreatic cell, skin cell etc. Finally, a baby is born!
Once it is differentiated, it cannot be reversed.
e.g. a nerve cell cannot go back to stem cell
Adult Stem cell
Stem cells do exist in adult! However, the differentiation potential is limited.
An adult stem cell is multipotent.
Multipotent = can differentiate, but it is much limited
e.g. the stem cell in bone marrow can differentiate into the blood cells but not into the nerve cell.
Same as embryonic stem cell, once it is differentiated, it cannot be reversed.
Characteristics of stem cells
- Unspecialized
- Can differentiate into different types of cell
- Can replicate and divide repeatedly to make plenty of specific type of cell
- Have a large nucleus relative to the volume of the cytoplasm
The choice of gene expression is not determined yet in stem cells
** Be reminded that, Plant also have stem cell! The tips of the stem and roots possess stem cells !
Ethical Issues
The source of stem cell is controversial.
An embryonic stem cell is most desirable because of its pluripotency. It has great potential to cure degenerative diseases. The source of embryonic stem cell is the discard embryo from in vitro fertilization. However, some view it is a kind of murdering, while some argue that it is worthy because it helps to cure millions of suffering patients.
An adult stem cell is much more acceptable because it involves no killing. It is common to see people donate their bone marrow to the leukaemia patient.
An umbilical cord stem cell is another trend of stem cell source. It can be found in the blood in the umbilical cord. You can see many companies provide the service of preserving the umbilical cord for the newborn baby. It is much less controversial as the umbilical cord belongs to the baby.
Therapeutic Use
As mentioned above, bone marrow stem cell cure leukaemia patient. But the use of stem cells is broad.
Umbilical cord stem cell
- Blood in the umbilical cord contains stem cell
- differentiate into any type of BLOOD cell.
- the amount of stem cell is limited, it supports the young children only
Therapeutic cloning
- altering the signalling pathway of stem cell to increase the no. of stem cell without losing its stem cell properties.
- Boost up the amount of umbilical cord stem cell to cure adult.
Stargardt’s Disease
- Inherited disease
- Destruction of retina cell in the eyes --> macular degeneration --> blind
- Embryonic stem cells --> Retinal stem cell --> inject to patient’s retina --> build up the retinal cell
- The patient visual performance improves
- Hopefully, it can cure age-related macular degeneration
In this IB biology topic, you have to
- remember the differences between embryonic and adult stem cells are their potency
- the dilemma and controversy of using stem cells
- the therapy use of stem cell, especially the Stargardt's Disease
That is the end of today topics~
Photo References:
1. Blastocyst Transfer. UNC Fertility. Retrieved URL from: https://uncfertility.com/treatment-options/in-vitro-fertilization/blastocyst-transfer/