Stem Cells

Question 1

What are the 3 main features of stem cells?

Answer 1

Capable of dividing and renewing for long periods: long time renewal.
Unspecialised
Give rise to specialised cell types.

Question 2

What factors can drive stem cells to divide unsemetrically?

Answer 2

Environmental - messages sent from the environment that maintains one of the stem cells, cues to signal one of the daughter stem cells to terminally differentiate.

Divisional - A protein may be passed on to one of the daughter cells that prevents it from terminally specializing while the other does.

Question 3

How do cell fate determining cues contribute in symmetric vs asymmetric cell division?

Answer 3

During symmetric division, the 2 daughter cells will both inherit the cell fate determining cue, and thus have the same fate.

While during asymmetric division, only 1 daughter cell will inherit this cue, consequently these 2 cells will have different fates.

Question 4

What are the mitotic spindles like in unsymmetrical vs symmetrical division?

Answer 4

The mitotic spindles are evenly distributed between 2 daughter cells in symmetric division, while it’s unevenly distributed during asymmetric division.

Question 5

How does the inheritance of centrioles regulate assymetric division?

Answer 5

The cell that inherits te mother centrosome will remain undifferentiated while the other cell will differentiate.

Question 6

Describe the Immortal Cell Hypothesis.

Answer 6

In some tissues, stem cells segregate original DNA strands in one of 2 daughter cells. The cell that inherits this will remain a stem cell.

Question 7

What are committed transit amplifying cells?

Answer 7

Stem cells rarely divide. Therefore committed transit amplifying cells act as an intermediate population as they can divide many times before terminally differentiating in order to increase the cell population.

Question 8

Describe how stem cells maintain the epidermis.

Answer 8

Few and sparse stem cells sit on the basal layer of the epidermis. Maintenance of the epidermis relies on the transit amplifying cell, as it has a high turnover of cells as they are lost constantly.

Therefore stem cells infrequently divide and give rise to the transit amplifying cells which divide and specialise.

Question 9

Describe totipotent stem cells.

Answer 9

Can differentiate into cells and tissues of the embryo as well as the extraembryonic tissues that support the development of the embryo.

Question 10

Describe pluripotent stem cells.

Answer 10

Can differentiate into cells of the 3 germ layers of the embryo, slightly less potent, but still able to differentiate into cells of all tissues apart from embryonic tissues.

Question 11

Describe multipotent stem cells.

Answer 11

Can differentiate into cells of the same germ layer from which they’ve been isolated. E.g. Hematopoietic stem cells (HSCs) are the stem cells that give rise to other blood cells.

Question 12

Describe unipotent (tissue-specific) stem cells.

Answer 12

Can differentiate into only 1 type of cell. E.g. Stem cells of the epidermis.

Question 13

What are progenitor cells?

Answer 13

They are descended from stem cells but lose some differentiating abilities of stem cells, therefore are more limited than a stem cell.

Can differentiate to form one or any kinds of cells, but they can’t divide and reproduce indefinitely like stem cells.

Question 14

At which stage of embryonic development can totipotent cells be obtained?

Answer 14

Totipotent stem cells are the blastomeres of the early developing embryo. After fertilization, the zygote is formed and undergoes divisions. These divided cells, up to morula stage, have the ability to give rise to a new individual.

The cells can actually form clones, individuals which are genetically identical.

Question 15

At which stage of embryonic development can pluripotent cells be obtained?

Answer 15

After the morula stage, a process of compaction occurs which marks the limit for totipotent cells and only pluripotent cells can be obtained from further stages.

If we take out the ICM cells and put in culture, we can develop embryonic stem cells.

Question 16

Describe embryonic stem cells.

Answer 16

Comes from the ICM cells of blastocyst.

Pluripotent

Question 17

Describe embryonic germ cells.

Answer 17

Comes from primordial germ cells (precursors of differentiated gametes).
Pluripotent

Question 18

What type of stem cells are stem cells from fetal tissues (trophoblasts, umbilical cord..)?

Answer 18

multipotent

Question 19

What type of stem cells are adult stem cells?

Answer 19

uni-multi-potent

Question 20

State features of embryonic stem cells.

Answer 20

Generated from the blastocyst.
Able to proliferate long term.
Pluripotent (totipotent if came before morula)
Can contribute to all cells of an individual.
If transplanted in an adult, it can give rise to tumours.

Question 21

Describe the first types of stem cells obtains and their properties.

Answer 21

The first types of stem cells derived are mouse embryonic stem cells.

They can spontaneously differentiate in vitro, and can give rise to cells of all 3 germ layers. Under specific conditions, they can even be ‘pushed’ to differentiate into one layer over another.

Question 22

Describe limitations in the application of human embryonic stem cells to medicine.

Answer 22

Genomic instability and unpredictable long term differentiation, e.g. Tumours.

When differentiated in vitro, ES produces immunogenic molecules which raises the question of rejection.

Risk of recombination with pathogens.

Question 23

Describe how adult stem cells can be applied in medicine?

Answer 23

They are able to solve 2 limits of current transplantation technology - shortage of organs; rejection.

Can be isolated and manipulated in vitro for replacement, reparation and regeneration of damaged tissues (cell therapy).

Tolerate the introduction of exogenous genes to replace defective or mutated genes (gene therapy).

Can be expanded and controlled in vitro before transplanting.

Question 24

Describe limitations for the application of adut stem cells to medicine.

Answer 24

Not easy to isolate adult SC, may be difficult to obtain the tissue.

Small number of stem cells in adult tissue, therefore needs to be expanded in vitro.

Question 25

What are the first adult stem cells to be isolated?

Answer 25

Hematopoietic stem cells are the first to be isolated, they were obtained from the bone marrow, which is a more accessible tissue.

Question 26

Describe how adult stem cells can be used in cellular therapy.

Answer 26

Transplanting stem cells derived from a specific tissue in damaged tissue in order to restore functionality.

Stem cell therapy has recently been proposed to restore the number of contractile cardiac cells, thus repairing the damage suffered by the myocardium.

Question 27

What are the applications of IPS to medicine?

Answer 27

The implication of this is that it would be possible to induce specialisation in IPS cells and use this in various therapeutic applications. E.g. Hanna J et al, used IPS cells to treat sickle cell anemia in a mouse model.

Question 28

Describe the general method of obtaining stem cells from cloning.

Answer 28

Isolate the nuclei from differentiated cells.
Transplant into enucleated oocyte.
Allow development up to blastocyst.
Make a NT-mouse and obtain NT embryonic stem cells.

Question 29

Describe Gurdon’s experiment of cloning.

Answer 29

The nucleus from the skin cell of frog B was transplanted into enucleated egg of A.

A tadpole which is a clone of B is formed.

Question 30

How did Gurdon ensure that the nucleus in the enucleated egg was killed?

Answer 30

He used different markers in order to ensure that the UV radiation killed the resident nucleus and that in fact a clone was made.

The nucleoli was used as a marker. He used a strain of amphibian with 2 nucleoli, if the transfer embryo contained 2 nuclei, then it shows that the UV radiation didn’t kill the resident nucleus.

Question 31

Describe the cardiomyocyte differentiation test that shows the differentiation ability of different stem cells.

Answer 31

This is done via the formation of embryonic bodies - drops of medium containing embryonic stem cells grown hanging on a lid of a culture plate.

After a few days it’s visibly seen that these stem cells have differentiated into contracting myocytes.

Question 32

What tumours can embryonic stem cells give rise to in adults? What do they contain?

Answer 32

When transplanted into adults, ES cells can give rise to tumours called teratomas or teratocarcinomas.

These contain undifferentiated cells, or cells differentiated in the 3 embryonic lines - ectoderm, mesoderm and endoderm.

Question 33

How can adult stem cells be isolated from the skin?

Answer 33

By taking a biopsy, dissociating the cells and putting them in culture, we can obtain 3 different types of clones: holoclone, meroclone and paraclone.

By looking at their proliferative and clonogenic ability, we can identify the holoclones as the stem cells of the skin.

Question 34

How was adult stem cells used to cure junctional epidermolysis bullosa?

Answer 34

The patient was heterozygous for a null and point mutation in a gene that codes for a molecule of the basement membrane(laminin), which is important for the adhesion of the epidermis to the underlying connective tissue. Therefore by lacking this gene, the patient had blistering skin.

Adult stem cells of patients not affected by the disease. These cells were cultured and transfused using antibodies against laminin. After growing in vitro, the cell was growing a layer and transplanted in the diseased portion of the patient’s skin. After a few months, the patient was cured.

Question 35

How are IPS cells made?

Answer 35

4 transcription factors were introduced into mouse cells, they were able to reprogramme the cell and take it back to an undifferentiated state.

Question 36

What applications can IPS cells have?

Answer 36

The implication of this is that it would be possible to induce specialisation in IPS cells and use this in various therapeutic applications. E.g. Hanna J et al, used IPS cells to treat sickle cell anemia in a mouse model.

Question 37

Describe the stem cell niche.

Answer 37

The stem cell needs a specific microenvironment called the stem cell niche in order to maintain homeostasis.

Question 38

Why is the interaction between stem cells and basement membrane so important?

Answer 38

Depending on the orientation of the mitotic spindle, the differentiation into progeny cells is defined.

If both daughter stem cells keep interaction with basement membrane, they will remain stem cells.

If one cell does not, then it will become a progenitor cell and eventually differentiat.

Question 39

Describe component of the stem cell niche.

Answer 39

Other cells
Components of the extracellular matrix.
Soluble factors released by other cells.
Neural interactions
Factors coming from the bloodstream.

Question 40

Provide some examples of stem cell niches.

Answer 40

Osteoblastic niche - hematopoietic stem cells reside here and make physical interaction with osteoblasts lining the endotherm.

At the intestinal criptae, stemnesss is maintained by exchanged signals between epithelial cells and connective tissues.

The ‘bulge’ in hair follicles responsible for maintaining and repairing hair and any injuries.

The abluminal compartment of the seminiferous epithelium where germline stem cells are stored (spermatogonia).