21. Cell Differentiation and Gene Expression

Question 1

Describe cell differentiation (2pt)

Answer 1

• Cell differentiation is the process through which a cell undergoes changes in gene expression and gene activity to specialise and take on specific roles in an organism.
• Irreversible process

Question 2

Describe what happens as we approach maturity?

Answer 2

The proportion of dividing cells fall as we approach maturity. In adults the majority of the cells are terminally differentiated which means they cannot divide any more. Only a small minority of cells are capable of cell division.

Question 3

Describe a stem cell

Answer 3

Undifferentiated and unspecialised cells of the human body

Question 4

Describe a totipotent stem cell

Answer 4

Can differentiate into every cell type. It has the ability to develop into a total individual.

Question 5

Describe a pluripotent stem cell?

Answer 5

Can differentiate into all cell types except placental cells.

Question 6

Describe a multipoint stem cell?

Answer 6

Can differentiate into a limited number of cell types e.g hemaotpoetic stem cells.

Question 7

Describe a unipotent stem cell?

Answer 7

Can form one type of differentiated cell only e.g dermatocytes.

Question 8

Describe Asymmetric Division? (2pts)

Answer 8

1. State that a stem cell produces one stem cell and one differentiated stem cell.
2. A fate regulator e.g polarity protein distributes unequally in the daughter cells.

Question 9

Describe Symmetric division?

Answer 9

A stem cell produced two differentiated cells or two stem cells

Question 10

Describe embryonic stem cells? (2pts)

Answer 10

1. Pluripotent

2. Derived from a blastocyst

Question 11

Describe adult stem cells? (5pts)

Answer 11

1. Multipotent
2. Typically gives rise to various types of differentiated cells within the tissue they reside in as they are tissue specific stem cells.
3. Their function is dead cell replacement.
4. Low number in tissues where there is a low rate of cell turnover.
5. Abundant in tissues such as intestine epithelium and blood cells.

Question 12

Describe adult stem cells? (5pts)

Answer 12

1. Multipotent
2. Typically gives rise to various types of differentiated cells within the tissue they reside in as they are tissue specific stem cells.
3. Their function is dead cell replacement.
4. Low number in tissues where there is a low rate of cell turnover.
5. Abundant in tissues such as intestine epithelium and blood cells.

Question 13

Describe stem cell niches?

Answer 13

1. Tissue specific stem cells are maintained in an environment called stem cell niches.
2. These consist of:
3. Supporting ECM
4. Neighbouring niches cells
5. Secreted soluble signalling factors such as growth factors and cytokines.
6. Physical parameters such as sheer stress, tissue stiffness and topography
7. Environmental signals- metabolites, hypoxia and inflammation.

Question 14

Describe bone marrow stem cells?

Answer 14

From foetal week 20 blood cells are produced from the bone marrow. There are two types- Hematopoetic stem cells and Mesenchymal stem cells (MSC).

Question 15

Describe a Hematopoetic stem cell? (4pts)

Answer 15

1. Multipotent stem cells anchored to fibro-blast like osteoblasts of the marrow of long bones
2. Produce all blood cells and some immune system cells.
3. Regular self renewal
4. Can replicate indefinitely

Question 16

Describe Mesenchymal stem cells (MSCs)? (5pts)

Answer 16

1. Stromal cells found in the bone marrow and other organs.
2. Poorly defined and heterogenous
3. Do not self renew very regularly
4. Multipotent
5. Give rise to cartilage, bone, muscle cells and adipocytes.

Question 17

Describe Progenitor cells?

Answer 17

Progenitor cells can only divide a limited number of times and can only differentiate into one type of linage unlike stem cells which can divide indefinitely.

Question 18

How can we determine how a cell differentiates?

Answer 18

The types and number of proteins a cell generates helps to determine how a cell differentiates.

Question 19

How can we analyse the transcription profile of each cell?

Answer 19

RNA sequencing and microarrays assay allow to analyse the transcription profile of each cell.

Question 20

Describe regulatory transcription factors? (3pts)

Answer 20

1. Transcription factors bind to regulatory regions of a gene and affect its expression by switching it on and off.
2. Certain transcription factors are tissue specific and different transcription factors are associated with differentiation of stem cells into different tissues.
3. Specific transcription factors ensure the genes are expressed in the right cell at the right time and at the right amount.

Question 21

Describe regulatory transcription factors? (3pts)

Answer 21

1. Transcription factors bind to regulatory regions of a gene and affect its expression by switching it on and off.
2. Certain transcription factors are tissue specific and different transcription factors are associated with differentiation of stem cells into different tissues.
3. Specific transcription factors ensure the genes are expressed in the right cell at the right time and at the right amount.

Question 22

Describe transcriptional factors? (3pts)

Answer 22

1. Different genes are activated by different transcription factors according to the binding elements in their promoters and enhancers
2. Each cell type transcribes a different set of genes
3. For transcription to occur RNA polymerase must have access to chromatin.

Question 23

Describe House-keeping genes?

Answer 23

Genes are transcribed in all cell types e.g basic metabolic enzymes.

Question 24

Describe Luxury genes?

Answer 24

Specialised genes expressed in only some type of cells e.g haemoglobin gene in red blood cells.

Question 25

Describe Pioneer factors? (3pts)

Answer 25

1. Transcription factors that can bind closed chromatin, remodel it and imitate cell-fate and differentiation. 2. Highly expressed in embryonic stem cells and needed to maintain their pluripotency. 3. Can activate or inhibit gene expression via histone modification and DNA methylation blockage.

Question 26

Describe DNA methylation? (4pts)

Answer 26

1. DNA methylation is the addition of a methyl group to DNA. 2. Heritable and reversible changes in gene expression which do not involve a change in the DNA sequence. 3. Results from external or environmental factors or as part of a development program. 4. The DNA methylation pattern is inherited and remembered in daughter cells.

Question 27

Describe DNA methylation in Cytosine? (4pts)

Answer 27

1. Covalent addition of the methyl group at the 5-carbon of the cytosine ring results in 5-methylctyosine(5-mC) 2. In somatic cells, 5-mC occurs on CPG sites. 3. During differentation unmehtylated CpG pairs can become methylated by a de nova methyltransferase. 4. It is copied to the opposite strand by a maintenance methyltrasnferase.

Question 28

Describe the consequences of DNA methylation? (3pts)

Answer 28

1. DNA methylation increases folding (hterochromatin) and silences transcription. 2. DNA methylation means the gene is switched off and transcription does not occur. 3. Developmentally regulated: 1. In embryonic stem cells the majority of Cpg sites are unmethylated. 2. Globin genes are expressed in the red blood cell lineage but not elsewhere. Their promoters are methylated in other cell types. 3. In sperm genes are silenced by methylation. DNA is very heterochromatic.

Question 29

Describe Somatic cell nuclear transfer? (3pts)

Answer 29

1. Artificial removal of the nucleus of a differentiated somatic cell and its placement in a denucleated egg cell. 2. Introduced nucleus is reprogrammed by factors in the egg cytoplasm. 3. The new egg behaved like a zygote (totipotent) - challenging and time consuming. e.g dolly the sheep

Question 30

Describe induced pluripotent stem cells? (4pts)

Answer 30

1. Pluripotent stem cells artificially produced from somatic cells. 2. Can potentially produce all cells of the organism. 3. Cells exposed to only 4 transcription factors. 4. Induced pluripotent stem cells have many applications as they have the capacity to keep dividing and differentiating cell types ion the body. Used in gene therapy, regenerative medicine and model disease and drugs screening.