5. stem cell niches

Question 1

what are the three difference fates of a stem cell?

Answer 1

• self-renew
• differentiate
• remain quiescent

Question 2

what helps to regulate a stem cells function?

Answer 2

the stem cell niche

Question 3

why is it important for a stem cell to have a niche?

Answer 3

the niche incorporates lots of signals so that the stem cell knows what it needs to be going
e.g. if there is an injury, the stem cell will know to adjust its progeny production accordingly

Question 4

what is the stem cell niche?

Answer 4

a microenvironment where stem cells reside and receive stimuli to determine their fate

Question 5

name one role of the stem cell niche?

Answer 5

to keep stem cells protected

Question 6

what is an example of something that contributes to the niche but is not localised within the stem cell microenvironment?

Answer 6

hormones can regulate stem cell function but may be produced far away from the microenvironment

Question 7

what is the difference between the stem cell microenvironment and the niche?

Answer 7

• the microenvironment is small physical location where the stem cell resides e.g. neighbouring cells and ECM
• the niche is everything that regulates the stem cells function e.g. hormones and blood

Question 8

what occurs when adult stem cells are removed from their niche?

Answer 8

they differentiate

Question 9

what did Schofeild hypothesise in 1978?

Answer 9

• stem cells remain stem cells due to their locations and thus interactions made with other cells.
• when they produce progeny, unless they can occupy a similar stem cell niche they will proliferate and differentiate

Question 10

what is seen when HSC from BM are transplanted into mice? and what did this show?

Answer 10

• white patches of progenitors on the spleen.
• the number of patches corresponds to the number of HSC injected.
• these could not reconstitute an irradiated mouse’s BM
• this showed that there as something in the BM which allowed the HSC to remain HSC

Question 11

can the niche exist in the absence of the stem cell?

Answer 11

yes - it is an area that can host the stem cell

Question 12

what two contacts are essential in the niche?

Answer 12

cell to cell and cell to matrix contacts

Question 13

vasculature is often presents in niches - what sort of signals to these provide?

Answer 13

humoral signalling

Question 14

describe the gonads of C. elegans

Answer 14

• gonad germ stem cells are in contact with distal tip cells
• when they lose contact with this they start to proliferate and differentiate into germ cells

Question 15

describe drosophila testes

Answer 15

• somatic stem cells and germ stem cells both in contact with hub cells
• as they lose contact with hub cells they proliferate and differentiate
• somatic stem cells become somatic cyst cells
• germ stem cells become spermatogonia
• somatic cyst cells are vital for spermatogonia function and so both cells remain in contact throughout differentiation

Question 16

give an example of a system where the differentiation of two lineages occurs side by side?

Answer 16

in drosophila testes, the differentiation of somatic stem cells and germ stem cells occurs side by side

Question 17

where is the germ stem cell niche in Drosophila ovaries?

Answer 17

the germarium

Question 18

describe drosophila ovaries

Answer 18

• terminal filament and cap cells make contact with anterior of germ stem cells
• as contact with these cells is lost cells begin to differentiate into cytoblasts
• cytoblasts continue to divide until they are surrounded by somatic follicle cells

Question 19

what is Dpp?

Answer 19

Dpp is a highly localised niche signal that maintains germ stem cells by supressing Bam transcription (which is essential for GSC differentiation)

Question 20

when Dpp signalling is manipulated and reduced what will occur?

Answer 20

germ stem cells will differentiate

Question 21

describe the skeletal muscle niche

Answer 21

• stem cells are localised at the edge of muscle fibres
• they also make contact with the basal lamina
• the progeny of the stem cell become part of the niche (muscle fibres)

Question 22

what will happen to muscle stem cells in vitro by themselves? and the addition of what will stop them from doing this?

Answer 22

• muscle stem cells alone in vitro will differentiate

- the addition of muscle fibres will stop the differentiation and allow them to remain as stem cells

Question 23

where does hematopoietic stress shift the HSC niche to?

Answer 23

extramedullary sites outside the bone marrow

Question 24

perturbing and changing levels of something in the niche may have an affect or may not, why is this?

Answer 24

cells can contribute to the niche in a unique or redundant manner

Question 25

heterogeneity in HSC raised what idea?

Answer 25

distinct niches home different sub-populations of HSC

Question 26

determining what cells neighbour HSC in BM has been hard, why is this?

Answer 26

- it is hard to maintain integrity of BM during sectioning | - complexity of immunostaining method necessary to identify HSC

Question 27

isolation of HSC by flow cytometry is easy. why is identification of HSC within the tissue much harder?

Answer 27

- immunoflourescent markers used by flow cytometry are two complex for microscopy - less reliable marker with more specificity must therefore be used (BrdU/H2BGFP LRC)

Question 28

why is using label retention as a marker of HSC not very good?

Answer 28

vast majority for BM cells that retain their label are not HSC

Question 29

what can be used in combination of label retention to identify HSC?

Answer 29

positive and negative staining for CD (cluster of differentiation) proteins

Question 30

give an example of three factors that contribute to the HSC niche?

Answer 30

blood vessels, osteoblasts and mesenchymal stromal cells

Question 31

what three factors ensure HSC are localised to the niche?

Answer 31

- SDF1 produced by osteoblasts binds chemokine receptor on HSC - calcium released by osteoclasts binds G coupled protein receptor of HSC - VCAM expressed on surface of endothelial cells and osteoblast alpha-4-beta-1-intergrin on HSC

Question 32

interactions with what cell type maintain HSC quiescence?

Answer 32

osteoblasts

Question 33

what will the over expression of Dkk1 by osteoblast lead to?

Answer 33

HSC self-renewal impairment

Question 34

describe the process by which HSC can be found in peripheral blood

Answer 34

- HSC are trafficked in and out of the bone marrow | - they stay in the blood for about 3 minutes

Question 35

what does the short time that HSC are found in the blood suggest?

Answer 35

that they are maintained as HSC in the BM

Question 36

what regulates the different number of HSC found in the blood at morning and evening?

Answer 36

circadian rhythm

Question 37

what happens to HSC injected into blood?

Answer 37

they will home to the BM

Question 38

what do HSC use to extravasate from the BM?

Answer 38

- they roll along the endothelium - adhere to the endothelium, mediated by VCAM and selectins - migrate through the endothelium

Question 39

the mechanism that HSC use to extravasate the BM is a similar mechanism employed by what other cell type?

Answer 39

lymphocytes

Question 40

what mediates homing of HSC back to the BM?

Answer 40

- SDF1 produced by osteoblasts and bone marrow stroma cells is a chemokine which is produced in high levels in the BM - SDF1 binds to HSC chemokine receptor CXCR4

Question 41

what treatment can cause HSC mobilisation into the blood?

Answer 41

G-CSF treatment

Question 42

how does G-CSF work?

Answer 42

G-CSF binds receptors on monocytes | when this occurs, monocytes supress osteoblasts and so reduce localisation signals to HSC

Question 43

the sympathetic nervous system has what affect of HSC niche?

Answer 43

it has been shown to regulate the attraction of HSC to their niche

Question 44

in combination with G-CSF, what has been shown in increase HSC mobilisation?

Answer 44

b2 adrenergic agonists i.e. something that stimulate adrenergic neurons

Question 45

how does stimulating adrenergic neurons increase HSC mobilisation?

Answer 45

they release norepinephrine which supresses osteoblasts

Question 46

it is possible that G-CSF may also act directly on adrenergic neurons?

Answer 46

yes - this stimulates the production of norepinephrine - neurotransmitters may also potentially regulate HSC mobilisation

Question 47

why is G-CSF given after chemotherapy?

Answer 47

- chemotherapy reduces bodies ability to make white blood cells and so makes patient more susceptible to infection. - G-CSF strengthens the immune system by mobilising HSC

Question 48

give an example of how the progeny of HSC are part of the niche?

Answer 48

regulatory T cell, macrophages and megakaryocytes are in the vicinity of HSC and have been shown to effect their localisation and function

Question 49

what is the difference between the inter-follicular epidermis of mouse and humans

Answer 49

humans have a thicker inter-follicular epidermis as we don't have hair as an additional protective barrier

Question 50

what is anagen?

Answer 50

the growing phase of the hair follicle | here the dermal papilla is at maximal size

Question 51

what is the resting phase of a hair follicle called?

Answer 51

telogen | the hair follicle is smallest at this point

Question 52

what is the hair follicle bulge and what is it composed of?

Answer 52

the bulge is the stem cell niche that is composed of dermal cells

Question 53

what does the dermal sheath do?

Answer 53

the dermal sheath surrounds the hair follicle | and contains progenitor cells which are recruited during anagen

Question 54

what is the function of the dermal papilla?

Answer 54

it regulates hair follicle development and growth

Question 55

where is the reservoir of multipotent stem cells in the hair follicle located?

Answer 55

the dermal papilla

Question 56

which glands release their content into the hair follicle?

Answer 56

apocrine gland

Question 57

when stem cells in the hair follicle proliferate where do they move?

Answer 57

- they move downwards towards the bottom of the hair follicle of the growing hair - as they differentiate they move upwards out the follicle

Question 58

what are the three phases that the postnatal follicle undergo?

Answer 58

catagen, telogen and anogen

Question 59

what happens in catagen?

Answer 59

this is the regression phase where the hair follicle shinks which is mediated by apoptosis

Question 60

where are stem cells found in the intestine? and where is it located?

Answer 60

the crypt | the base of the vili