L6 The stem cell niche

Question 1

Where are adult stem cells generally found in?

Answer 1

They are found in special micro environments called niches.

Question 2

What type of cells does the embryo start off as?

Answer 2

A clump of totipotent stem cells (embryonic stem cells).

Question 3

What are the different distinct stem cells in the adult?

Answer 3

• Mesenchymal stem cells: Bone cells (osteoblasts), cartilage cells (chondrocytes) and fat cells (adipocytes)
• Blood stem cells: red blood cells, platelets and white blood cells
• Satellite stem cells: muscle
• Germ cells: oocytes and sperm

Question 4

How long would RBC, white blood cells, skin, colon, sperm and brain cells last for?

Answer 4

Red blood cells live for about four months

White blood cells more than a year

Skin cells two or three weeks

Colon cells about four days

Sperm cells about three days

Many brain cells can last an entire lifetime

Question 5

Why is stem cell maintenance so important?

Answer 5

Stem cell maintenance is a tightly regulated process that ensures the long-term survival and functionality of these essential cells

Question 6

Explain the division of stem cells

Answer 6

1. There are three sorts of division.
2. Division rates must be balanced so as to keep stem cell population constant

Question 7

Explain the ‘classical’ stem-cell division

Answer 7

Stem cell produces 2 daughter cells:
- One is a replacement stem cell
- One goes down the differentiation route

Question 8

Does the epidermis needs to be continually renewed?

Answer 8

Yes

Question 9

What are the three main layers of the skin?

Answer 9

• Epidermis - Made up of keratinocytes
• Dermis - Contains fibroblast and blood vessels.
• Subcutis

Question 10

What stimulates keratinocyte proliferation?

Answer 10

Signals from the dermis and basement membrane stimulate keratinocyte proliferation.

Question 11

Which layer of the skin is a stem cell niche?

Answer 11

The basal layer of the epidermis is a stem cell niche

Basal cell layer contains stem cells that proliferate (basal keratinocytes)

Question 12

What is produced that provides strength to the skin and moves towards the surface?

Answer 12

• Cells produce high levels of the fibrous protein keratin that provides strength to the skin

Question 13

What inhibits differentiation and maintains the stem cell population?

Answer 13

Wnt signals from the dermis inhibits differentiation (maintains stem cell population).

Question 14

What is the role of integrin?

Answer 14

Integrins (adhesion molecules) hold cells to the basement membrane (maintains stem cell population).

Question 15

What inhibits integrins?

Answer 15

Notch signals in maturing keratinocytes inhibit integrins.

Which allows differentiation if integrins are inhibited

Question 16

What inhibits Notch activity?

Answer 16

EGF inhibits notch

Question 17

How does Egf maintain stem cell maintenance?

Answer 17

Egf inhibits Notch activity, which inhibits integrins, (double negative) which are responsible for holding cells to the basement membrane which ultimately increases stem cell population

Question 18

What is the stem cell niche in the epidermis?

Answer 18

The basal layer of the epidermis is a stem cell niche

Question 19

What is the stem cell niche called in the hair follicle?

Answer 19

There is another stem cell niche in the hair follicle called the bulge.

Question 20

What forms the follicles?

Answer 20

The stem cells from the bulge forms the follicles.

Question 21

What happens when the skin is badly damaged and needs replacement?

Answer 21

When skin is badly damaged, there is a greater need for replacement cells. In this situation, bulge cells can also contribute to epidermis and sebaceous glands.

Question 22

What happens if there is a large areas of tissue needed for restoration?

Answer 22

Different stem cell niches may be able to provide cells

Question 23

What is the third stem cell niche of the epidermis?

Answer 23

A third stem cell niche is in the area of the dermal papilla

Question 24

What is JEB?

Answer 24

Junctional epidermolysis bullosa

Question 25

What is Junctional epidermolysis bullosa (JEB)?

Answer 25

This is a disorder in the epidermis where adhesion between the dermis and epidermis is impaired, patients have a muation in adhesion genes eg. LAMB3.

Question 26

What regenerative medicine ways are being used to treat JEB?

Answer 26

* Skin epidermis (basal keratinocytes) can be cultured to replace skin in burn patients * Scientists are now culturing cells from JEB patients, replacing the damaged gene in cell culture, then growing it to replace the skin in the patient. * Inactivated viruses (viral vectors) can be used to introduce DNA into cells.

Question 27

Is our gut lining continuously replinished?

Answer 27

Yes.

Question 28

Why does the gut lining needs to be replinished? (2)

Answer 28

* The contents of the gut create a very harsh environment where cells need to be continuously replenished. * Villi increase the surface area of the intestine to aid in absorption. Cells at the ends of the villi are continuously shed

Question 29

What are the cells of the small intestine and their functions? (6)

Answer 29

* Enterocyte – absorption * Goblet cells – secrete mucus * Enteroendocrine cells – secrete peptide hormones * Paneth cells – secrete anti-microbial peptides * Stem cells * Submucosa cells – help to maintain the stem cell

Question 30

Where and how does the stem cells of the small intestine proliferate?

Answer 30

* Stem cells at the base of the crypt proliferate, in mouse each crypt produces 12 cells per hour. Each crypt is made up of about 250 cells. * This produces a conveyor belt of cells

Question 31

What are the two types of gene markers expressed?

Answer 31

- Slow dividing stem cells express Bim1 - Fast dividing stem cells express Lgr5 These genes are markers for stem cells

Question 32

How do we know if Lgr5 positive cells are stem cells?

Answer 32

1. Lineage tracing allows us to determine the fate of a cell. 2. Transgenes can be made that cause single cells to express a marker. In this case the transgene is controlled by the promoter for Lgr5. 3. And the marker is a bacterial gene called beta galactosidase which can be used to turn cells blue. 4. The marker is expressed in the cell and in all of its offspring permanently.

Question 33

Where can embyronic stem cells be isolated from?

Answer 33

Embryonic stem cells can be isolated from the epiblast and grown in cell culture.

Question 34

How are stem cells maintained?

Answer 34

Specially defined conditions maintain them in the pluripotent state (BMP and LIF). This replaces the stem cell niche found in vivo.

Question 35

What does removal of BMP/LIF cause in stem cells?

Answer 35

Removal of BMP/LIF causes the cells to differentiate into different cell types. Each cell type needs a specific set of conditions

Question 36

What is the difference between mouse ES (Embryonic stem cells) and human ES?

Answer 36

- Mouse ES requires BMP + LIF - Human ES requires FGF + activin

Question 37

What are the different assays for pluripotency?

Answer 37

* Expression of epiblast markers: e.g. Nanog, Oct4, Sox2, Klf4 * Chimeras are made when you mix ES cells in with a normal embryo and the ES cells contribute to different tissues in the adult. * Teratomas are benign tumours that contain differentiated tissues. * Direct the ESCs to adopt cell fates in vitro

Question 38

How do maintenance conditions block differentiation?

Answer 38

Epiblast markers are used to maintain the pluripotent state within cells - Nanog Oct3/4 Sox2 Esrrb Klf4

Question 39

What happens if we activate epiblast marker expression in differentiated cells?

Answer 39

The cells dedifferentiate and become stem cells

Question 40

What role does yamanaka factors do in formation of induced ploripotent stem cells (iPS cells)?

Answer 40

Yamanaka factors - Oct3/4 Sox2 Klf4 + c-Myc Differentiate and produce induced pluripotent stem cells (iPS). | This approach means that we do not have to obtain ES cells difficultly.