Tissue Stem Cells

Question 1

How many pluripotent cells does the adult have?

Answer 1

None, they are lost early in development as the cells specialise

Question 2

What are multipotent progenitors?

Answer 2

Present near the end of gastrulation in mice. They are lineage restricted eg. pancreatic progenitors that arise from gut endoderm in E9, giving rise to all endocrine, exocrine, and ductal pancreatic cells. Progenitors are highly proliferative but not immortal. On receiving signals from surrounding tissues, they differentiate into more progenitors or terminally differentiated cells

Question 3

What are adult (tissue) stem cells?

Answer 3

Adult tissues don’t rely on progenitors, but adult stem cells which are thought to develop in organogenesis. It’s unknown when progenitors switch to stem cells.

Question 4

What is the main function of adult (tissue) stem cells?

Answer 4

Homeostasis and repair. They replace cells lost through normal wear and tear. Often multipotent.

Question 5

What are fetal stem cells?

Answer 5

Sparse cells that begin to appear in fetal tissues, sharing gene expression patterns of adult stem cells. Highly proliferative in order to meet the demands of growing organs.

Question 6

How do adult stem cells relate to fetal stem cells?

Answer 6

After birth, tissue stem cells take over from fetal stem cells because the demand on the cells change. Growth is redcued, and the main function required is repair and homeostasis. It is unknown if the fetal stem cells become adult stem cells or if the adult stem cells develop separately around the time of birth

Question 7

How were HSCs discovered?

Answer 7

After Hiroshima and Nagasaki people got radiation sickness, led to investigations. Lethally irradiated mice survived after BM transplants. HSCs particularly sensitive to radiation.

Question 8

What evidence shows that the pancreas doesn’t have resident stem cells?

Answer 8

On injury there’s no compensatory proliferation or repair, as evidenced in Type I diabetes (B cells attacked).

Question 9

What evidence shows that the brain doesn’t have resident stem cells?

Answer 9

Neurodegenerative diseases result in a loss of brain function.

Question 10

What is regenerative medicine?

Answer 10

Replacement cell types derived in a dish that can be transplanted to replace damaged tissues eg in the brain or pancreas

Question 11

Which stem cells proliferate slowly?

Answer 11

Intrafollicular epidermis stem cells, neural stem cells in subventricular zone and dentate gyrus, satellite cells in the muscle. They cycle slowly and often on demand ie. in the place of an injury.

Question 12

Explain how slowly proliferating cells can be identified

Answer 12

Label-retaining assays. The cells are given a dose of a labelled nucleotide analogue which incorporates into the DNA of all proliferating cells. If the cell retains the label it is a slow cycling cell.

Question 13

Describe the proliferation of cells in the small intestine

Answer 13

The stem cells in the small intestine rapidly and continuously give rise to highly proliferative transit-amplifying cells which turn into differentiated subtypes. Paneth cells are label retaining cells that support the stem cells. In this way, the Paneth cells are slowly proliferating, and the stem cells are constantly turned over

Question 14

What is the stem cell niche?

Answer 14

A specific microenvironment - the ECM and various support cells - which provides the right biochemical and physical properties to maintain undifferentiated stem cells. It can also signal the cell to proliferate/differentiate.

Question 15

Explain the role of the stem cell niche in the small intestine crypt

Answer 15

Paneth cells, fibroblast, myofibroblast, smooth muscle, endothelial cells etc. surround the crypt, producing signalling molecules that activate WNT and inhibit BMP signalling. As the cells move away from the crypt, this process reverses, leading the cells to differentiate.

Question 16

What happens if there is dysregulation in the niche/signals from it?

Answer 16

Could lead to pathological expansion of the stem cell compartment. Mutations in the negative regulators of WNT pathway results in expansion of the stem cells at the base of the crypt, leading to a neoplasm, that could cause cancer.

Question 17

How are stem and progenitor cells usually captured in vitro?

Answer 17

Oncogene expression is forced or the cells are taken from a tumour. Epiblast stem cells and embryonic stem cells are examples of progenitors captured as stem cells. Also neuroepithelium and neural stem cells.

Question 18

Explain the concept of the label-retaining assay

Answer 18

Slow proliferating cells will be retained over long periods of time. Therefore, the incorporated nucleotide won’t be diluted much due to the slow proliferation rate. However, if the cell is so slowly proliferating, it is hard to identify in the first place. Also, the technique tells us nothing about cell potency.

Question 19

Explain the concept of lineage tracing

Answer 19

Involves labelling a cell and after a period of time determining what cell types are produced from that cell

Question 20

Explain the concept of cell isolation and serial transplantation

Answer 20

HSCs are extracted from bone marrow and purified by a combination of cell surface markers. A true HSC can reconstitute an entire blood lineage of a lethally irradiated individual. Serial transplantations prove self renewal.

Question 21

How can we molecularly profile stem cells?

Answer 21

Sequencing mRNA allows us to understand the genes expressed. This will allow us to design strategies to locate the cells within tissues and mRNA sequencing niche cells allows us to investigate the signals required.