Topic 7 - Stem Cells

Question 1

What is the endoderm? (Embryonic development)

Answer 1

Embryonic germ layer which will form cells of the gut and lungs, and cells lining the liver and pancreas.

Question 2

What is the mesoderm?

Answer 2

Embryonic germ layer which will form muscle and connective tissues including bone, cartilage, fat and blood.

Question 3

What is the ectoderm?

Answer 3

Embryonic germ layer which will form nervous system and skin.

Question 4

What is meant by the term ‘cellular differentiation’?

Answer 4

It is the process by which a less specialised cell becomes a more specialised cell type; for example, during the formation of specialised tissues and organs in the course of embryonic development.

Question 5

What are adult stem cells?

Answer 5

Undifferentiated cells found in various tissues throughout the body that divide to generate cells that repair and replace cells in that tissue.

Question 6

What are the forms of stem cell potency?

Answer 6

The range of commitment options available to a stem cell (of which there are four categories: totipotent, pluripotent, multipotent, unipotent).

Question 7

What are the characteristics of Totipotent stem cells?

Answer 7

Characterised by the greatest plasticity. Derived from fertilised eggs up to the 16-cell stage (the exact stage varies between different vertebrates). Able to form the entire organism. Able to differentiate into all the cells of the three germ layers of an embryo (endoderm, mesoderm and ectoderm), as well as embryo-derived extra-embryonic cells (called trophectoderm) that go on to form the amniotic sac and the fetal portion of the placenta. Plant meristem cells are totipotent; hence the ability to grow an entire plant from a cutting.

Question 8

What are the characteristics of Pluripotent stem cells?

Answer 8

Able to differentiate into all cell types of a particular organism, except the extra-embryonic lineages. These are embryonic stem cells (ESCs). Several differentiated adult cell types (e.g. skin fibroblasts) have been reprogrammed to a pluripotent state in culture to give induced pluripotent stem cells.

Question 9

What are the characteristics of Multipotent stem cells?

Answer 9

Capable of differentiating into diverse types of cells, but specific to the tissue they reside in. Examples include neural, mesenchymal and adipocyte stem cells.

Question 10

What are the characteristics of Unipotent stem cells?

Answer 10

Able to give rise to only one specialised cell type.

Examples include skin, muscle and spermatogonial stem cells.

Question 11

What are mesenchymal stem cells (MSCs)?

Answer 11

Mesoderm-derived multipotent stem cells found in bone marrow, connective tissue, adipose tissue and adult muscle that differentiate into these tissue specific cell types. In addition, given appropriate stimuli, MSCs can differentiate into some ectodermal cell types including nervous system and skin cells.

Question 12

What are the unusual properties of stem cells?

Answer 12

They remain undifferentiated.
They can divide asymmetrically.
They can protect themselves against metabolic stress.
They can protect themselves against environmental damage to their proteins and DNA.

Question 13

Recalling your earlier studies in this module, what is the molecular biology technique that can be used to identify transcription factor binding sites on specific genes?

Answer 13

The technique is chromatin immunoprecipitation, using an antibody directed against a specific transcription factor.

Question 14

What are six main signalling pathways involved in maintaining the balance between ESC self-renewal and the commitment to differentiation (note that these are not universally used in all stem cells)?

Answer 14

insulin-like growth factors (IGFs)
fibroblast growth factors (FGFs)
Wingless-related integration site (Wnt)
transforming growth factor beta (TGF-β) family
bone morphogenetic proteins (BMPs)
Delta/Notch.

Question 15

During a single round of mitosis, if the newly synthesised DNA was uniquely labelled in some way, what would be the relative distribution of labelling in the daughter cells and in their subsequent progeny?

Answer 15

There would be an equal distribution of newly synthesised labelled DNA between the two daughter cells. During subsequent rounds of cell division, the DNA label would similarly be divided equally between daughter cells, becoming more and more diluted with each round of cell division.

Question 16

In what phase of the cell cycle is new DNA synthesised?

Answer 16

DNA is synthesised during S phase.

Question 17

What is the advantage of the selective sorting of older DNA to the stem cell within the immortal strand hypothesis?

Answer 17

One benefit of non-random segregation of DNA is that it could help protect the stem cell against DNA replication-induced errors that might occur as this template is being copied during mitosis, since the stem cell always retains a relatively ‘pristine’ copy of the genome.

Question 18

Which stem cell transcription factor controls the ability of early transit-amplifying cells to revert to a stem cell?

Answer 18

Oct4. In ESCs, Oct4 inhibits commitment and allows stem cell daughters to progress in and out of the early specification stages while still self-renewing.

Question 19

What are clonogenic stem cells?

Answer 19

stem cells that are able to revert back to become a quiescent stem cell. Considered to be an intermediate stage between the stem cell and transit-amplifying cells.

Question 20

What are segregating determinants?

Answer 20

Proteins that become selectively concentrated on one side of a stem cell prior to cell division. Depending upon the axis of division, the determinants can become segregated into just one of the daughter cells (asymmetric cell division) or can be equally divided between the daughter cells (symmetric division).

Question 21

What is the ‘immortal’ strand of DNA?

Answer 21

Some stem cells retain an ‘immortal’ strand of DNA that is passed selectively from mother to daughter stem cells. This may reduce the chances of replication errors in the stem cell genome during mitosis.

Question 22

How can Differentiated cells can be induced to a stem cell state?

Answer 22

Differentiated cells can be induced to a stem cell state by nuclear reprogramming (transfer of a differentiated cell nucleus into an enucleated fertilised egg cell), or by the fusion of two different differentiated cells, or by reintroducing a key set of four stem cell transcription factors (the Yamanaka factors Klf4, Oct4, Sox2 and c-Myc).