Cellular Differentiation, Stem Cells & Modern Medicine

Question 1

Describe how cells become more specialises and less flexible during development

Answer 1

• An embryo begins as a small number of naive, totipotent cells
• Embryonic stem cells can give rise to all cell types except trophectoderm (pluripotent)
• A cell’s fate is progressively limited until it becomes terminally differentiated and can only give rise to the same type of cell

Development process is: 8-cell stage to cell polarisation, to compaction, to inner, apolar cells cut off, to trophectoderm fully formed (formally polar) and embryo (in the middle).

Exception: stem cells, germ cells (eggs and sperm)

Question 2

Describe the three steps a cell takes to get from an embryonic precursor cell to different parts of a muscle fibre?

Answer 2

1. embryonic cells are not differentiated (embryonic precursor cell)
   - At this stage in development the cell could become any type of differentiated cell
   - Muscle specific genes are not being transcribed
2. Then their fate becomes determined (myoblast - determined)
   - The cell must now develop into a muscle cell
   - Certain control genes which code for transcription factors become activated
   (MyoD protein is a transcription factor)
3. Finally, the cell is terminally differentiated, playing a functional role in the organism (part of a muscle fibre - fully differentiated cell)
   - A different transcription factor binds to the genes in different places and other proteins are formed (that help the cell do its particular functions)

Question 3

What is genomic equivalence?

Answer 3

Differentiated cells contain all the DNA required to build an entire new organism

Question 4

What did John B. Gurdon and Shinya Yamanaka do?

Answer 4

Took a frog embryo and a nucleus from one of them, and transferred it into an empty egg (an egg that had been radiated by UV light so it was sterile)

Question 5

Describe how Embryonic Stem Cells are harvested and what they do

Answer 5

• These are ‘harvested’ from the inner cell mass (future embryo) of mammalian blastocyst embryos.
• Human embryonic stem cells are pluripotent: they can develop into any of the 200 or so types of cell in our bodies given the right conditions
• The cells derived from these ESCs are genetically indentical to the embryo donor

Question 6

Describe Induced Pluripotent Stem (iPS) Cells

Answer 6

• iPS cells are made by reprogramming adult skin cells
• iPS cells can be made from anyone, and are genetically identical to the source skin cells. As they are also pluripotent, they can generate any cell type

Question 7

Describe Adult (Tissue) Stem Cells

Answer 7

• Stem cells can divide without limit
• They are undifferentiated, multipotent cells
• They can divide and give rise to both stem cells and cells which will go on to differentiate into one or more (but not all) types of functional tissue cells

Question 8

Describe Umbilical Cord Stem Cells

Answer 8

• Cord blood banking is now common practice in some countries
• Stem cells from blood isolated from he umbilical cord of newborn babies are kept frozen (banked)
• The stem cells are multipotent, as they are immature blood stem cells. They are less restricted than blood stem cells from adults
• Can be used to treat leukaemia and many other blood diseases

Question 9

Describe the renewal tissues in Adult Stem Cells

Answer 9

• Stem cells are important for tissues such as blood and skin which need constant renewing
• Blood stem cells or haematopoietic stem cells are found in the bone marrow and can be used for transplants

Question 10

Describe the differences between Adult and Embryonic Stem Cells

Answer 10

Embryonic Stem Cells:
- A fertilised egg is totipotent, able to give rise to all cell types via cell division
- Embryonic stem cells are pluripotent, and can become all/any cells of the body

Adult Stem Cells:
- Adult Stem cells such as bone marrow cells usually only give rise to one or a few cell types: multipotent

Different culture conditions are used to persuade stem cells to develop into different kinds of differentiated cells

Question 11

What is the importance of Stem Cells in Modern Medicine?

Answer 11

• Integrative gene therapy is based on the idea that it may be possible to alter the genetic code of an individual’s cells
• It is proposed as a way of correcting single gene disorders
• A normal allele could be inserted into the cells of the affected tissue
• A virus can deliver genetic material into human cells
• CRISPR editing may also be used

Question 12

What is the importance of Stem cells in Modern Medicine in terms of regenerative medicine?

Answer 12

• Regenerative medicine is based on the idea that pluripotent stem cells can be used to repair or replace damaged organs or tissues
• Pluripotent stem cells can be made from skin cells or blood cells from a patient (genetically identical) or matched donors, or from embryos
• These stem cells can be encouraged to differentiate into specific cell types such as neurons, or retinal cells
• The different cells can be transplanted into patients
• Example: iPSC-derived corneal transplants

Question 13

Totipotent, vs Pluripotent, vs Multipotent

Answer 13

Totipotent:
- able to give rise to all cell types via cell division
- has the potential to divide until it creates an entire, complete organism

Pluripotent:
- able to give rise to most/all cells of the body
- canNOT develop into a complete organism on its own

Multipotent:
- able to give rise to only one or a few cell types