Chapter 5: Stem Cell Niches II

Question 1

HSCs (hematopoeitic stem cells) are located near ___, __ cells and __ cells

Answer 1

osteocytes, endothelial and stromal cells.

Question 2

Outline and name the process that allows for the deposition of HSCs into the bone marrow.

Answer 2

in embryo, HSCs are actually found in the liver and in the blood vessels. When bone starts forming vascularization, HSCs get deposited in the middle of the bone in the marrow.

This is known as HOMING. Ability for HSCs to migrate through the circulatory system and find their tissue-specific destination.

Question 3

What is the mechanism of homing

Answer 3

HSCs have a CXCL4 receptor that senses CXCL12 chemokine expressed by osteoblasts and stromal cells of the marrow. Adhestion proteins like E-selectins and Vcam1 support HSC homing into the bones.

Question 4

HSCs have a ___ receptor that senses ___ chemokine expressed by osteoblasts and stromal cells of the marrow. Adhestion proteins like E-___ and ___ support HSC homing into the bones.

Answer 4

HSCs have a CXCL4 receptor that senses CXCL12 chemokine expressed by osteoblasts and stromal cells of the marrow. Adhestion proteins like E-selectins and Vcam1 support HSC homing into the bones.

Question 5

2 niches of HSC

Answer 5

1) endosteal niche

2) perivascular niche

Question 6

in the endosteal niche, the HSCs have direct contact with ___. What “type” of HScs does this niche contain/

Answer 6

direct contact with HScs. contains quiescent HSCs– they have a long term ability to self renew and maintain stem cell population

Question 7

How is the endosteal niche regulated?

Answer 7

the number of osteoblasts directly corerlate with the number of quiescnet HSCs in the endosteal niche.

Osteoblasts secrete angiopoietin-1 and thrombopoietin which promotes the cells to remain in quiescent state for a long period of time.

Question 8

in the endosteal niche that isn’t super super vascularized, how do HSCs get enough oxygen?

Answer 8

the endosteal niche contains microvessels. HSCs can detect changes in O2 content and uses it as a cue for assessing where blood vessels are.

Question 9

in the perivascular nich, the HSCs have direct contact with ___ and __ cells in blood vessels. What “type “ of HScs does this niche contain?

Answer 9

direct contact with stomal and endothelial cells of blood vessels.
contains active HSCs that divide rapidly and holds more progenitor cells.

Question 10

in the perivascular niche, ___ is expressed by both endothelial and stomal cells, as well as __ cells and ___ cells. This chemokine is bound by HSCs at the ___ receptor and maintains quiesence and retains HSCs in the perivascular region.

Answer 10

in the perivascular niche, CXCL12 is expressed by both endothelial and stomal cells, as well as CAR cells and MESENCHYME cells. This chemokine is bound by HSCs at the CXCL4 receptor and maintains quiesence and retains HSCs in the perivascular region.

Question 11

To retain HSCs in the perivascular region, the surrounding cells secrete CXCL12. When this compound is downregulated, what happens?

Answer 11

loss of CXCL12 in MSCs resuces the number of HSCs. When Carcells/ Mesenchyme cells don’t produce CXCL12, the stem cell enters into the blodo and leaves the bone, often as progenitor cells –> where they further differentiate.

Question 12

How is CXCL12 secretion by cells in the perivascular niche regulated by the circadian rhythym.

Answer 12

There is more division and maintenance of HSCs at night, indicating that there is more CXCL12 being produced by CAR/endothelial/stromal/mesenchyme cells in the perivascular region at night.

• there is more migration of progenitor cells at the day. This indicates that there is less CXCL12 being produced in the day since the HSCs can enter the blood and leave the bone/differentiate.
• this is due to NE innervation. NE increases= CXCL12 down regulation, allowing HSC progenitor cells to circulate. too much stress = les and less CXCL12 = less stem cell proliferation.

Question 13

WHat neurotransmitter is responsible for CXCL12 downregulation

Answer 13

NE. more NE = more CXCL12

Question 14

Mesenchymal stem cells (MSCs) are aka

Answer 14

bone marrow-derived stem cells (BMDCs)

Question 15

BMDCs, aka MSCs, resemble ___ morphologically

Answer 15

resemble fibroblasts.

Question 16

list 3 paracrine factors that can aid in the regulation/differentiation of MSCs

Answer 16

1) Platelet derived growth factor (PDGF): involved in FAT and CHONDROCYTE formation
2) TGFBeta: also required for chondrogenesis
3) Fibroblast growth factor (FGF): involved in bone cell differentiation.

therefore, paracrine factors appear to detect development of the MSC into specific lineages.

Question 17

2 broad factors that aid in MSC regulation

Answer 17

1) paracrine factors

2) ECM/environmental factors.

Question 18

how does ECM/envrionmental factors influence MSC differentiation.

Answer 18

through Laminin: (big proteoglycan of the basal lamina). Keeps MSCs in a state of undifferentiated stemness.

• dif ECM components cause differentiation of MSCs into dif cells
• if grown on soft ECM with lots of collagen, MSCs become neurons
• if grown on medium ECM with medium amount of collagen, MSCs become muscle
• if grown on hard ECM, MSCs become bone cells.

Question 19

adult NSC’s retain characteristics of __ ___ cells, which are actually embryonic progenitor cells.

Answer 19

adult NSC’s retain characteristics of EMBRYONIC PROGENITOR cells, which are actually embryonic progenitor cells.

Question 20

How are adult NSCs polarized

Answer 20

there is an apicobasal axis

Question 21

2 niches of neural stem cells

Answer 21

1) subgranular zone of HC

2) Ventricular-subventricular zone of the lateral ventricles.

Question 22

NSC’s in the ____ maintains contact with the cereberal spinal fluid

Answer 22

VSVZ

Question 23

during development of VSVZ, radial glia NSCs transition into type ___ cells, which form specific neurons in the ___ ___ and the ___ structures.

Answer 23

during development of VSVZ, radial glia NSCs transition into type B cells, which form specific neurons in the OLFACTORY BULB and the STRIATUM structures.

Question 24

B cells project cilium into ____ from the ___ surface, and their ___ ____ makes contact with blood vessels.

Answer 24

B cells project cilium into CSF from the APICAL surface, and their BASAL ENDFOOT makes contact with blood vessels.

-B CELLS ARE POLARIZED STEM CELLS

Question 25

4 Fundamental cell constituents of VSVZ Niche

Answer 25

1) E cells: ciliated
2) B cells
3) C cells (progenitor cells)
4) A cells: neuroblasts.

Question 26

3 subtypes of B cells

Answer 26

B1: quiescnet cell. When they divide, 1 remains pluripotent while the others differentiate into older stages

B2 and B3: actively proliferating neural stem cells.

Question 27

B cell clusters are surrounded by ___ cells in the VSVZ to form a ___ pinwheel

Answer 27

E cells in the VSVZ to form a Rosette pinwheel.

Question 28

Cell production in VSVZ begins with a ___ cell at the CENTER of the Rosette pinwheel creating a ___ cell. These (progenitor) ___ cells proliferate ___ times to form a type __ cell precursor. __ Cell precursors move into ___ ___ where final differentaition occurs.

Answer 28

Cell production in VSVZ begins with a B3 cell at the CENTER of the Rosette pinwheel creating a C cell. These (progenitor) cells proliferate 3 times to form a type A cell precursor. A Cell precursors move into OLFACTORY BULB where final differentiation occurs.

Question 29

2 main juxtacrine signals that help maintain the NSC pool

Answer 29

1) VCAM 1

2) Notch

Question 30

Role of VCAM1 to maintain NSC pool

Answer 30

VCAM1: found in B cell on ciliated side (apical surface facing CSF). Adhesion of VCAM maintains the Rosette Pinwheel structure.

• in the pinwheel, B cells that are closer to E cells are quiescnet (B1).
• B cells further from E cells /n the middle of the VSVZ are actively proliferating B2/B3 cells. Inhibition of VCAM 1 disrupts the pinwheel pattern and causes NSC to LOSE QUIESENCE while promoting differentiation of progenitors.

Question 31

Role of Notch as a Juxtacrine molecule to maintain NSC pool

Answer 31

NOTCH maintains B cells. recall: when it binds to delta, a protease cleaves the intracellular domain, which can move into the nucleus and induce gene expression.

For NSCs (b1) , Notch intracellular domain (NCID) gets cleaved when Jag 1 from endothelial cell binds to Notch receptor on B1 cells and released to act as a TF that PREVENTS pro-neural gene expression.

There is another Notch pathway that binds to delta and results in Hes gene expression, which is involved in neurogenesis.

Question 32

increased NICD = stem cell ____, whereas decreased NICD =

Answer 32

increased NICD = stem cell QUIESCENCE, whereas decreased NICD = progenitor proliferation and maturation toward neural fates

Question 33

Other than NICD, explain how else Notch is implicated in NSC maintenance and regulation.

Answer 33

Notch 1 found in all stem cells (B1/B2/B3/A/C). Notch-delta signalling and its Hes gene target causes OSCILLATING expression patterns through NEGATIVE Feedback loops. Notch-Delta signalling = Hes-Mediated repression of Notch.

• therefore, constant activity of Notch signalling promote quiescence, whereas oscillating expression of Hes genes and consequently the anti-oscillation periods of PRO NEURAL genes like (Ascl1/Mash) supports proliferative states until proneural gene expression is sustained and the cell differentiates.

Question 34

While VCAM and Notch juxtacrine factors maintain the NSC pool, what two factors promote VSVZ DIFFERENTIATION

Answer 34

1) Epidermal growth factor

2) bone morphogenic protein.

Question 35

while quiescence is encouraged in B1 cells by NOTCH/ NCID signalling by repressing pro-neural gene expression and represses differentiation, how is neurogenesis promoted? In what cells? By what mechanism?

Answer 35

Notch activity is oscillated by TYPE C progenitor cells, which repress NOTCH by expressing EGF. (epidermal growth factor)

EGF= increased NUMB = Decreased NCID. Poromotes differentiation from C cells to A cells for neurogenesis.

-EGF signalling promotes the use of the stem cell pool for neurogenesis by counterbalancing Notch signalling.

Question 36

BMP promotes ____of neural stem cells

Answer 36

gliogenesis (type of differentiation ) of neural stem cells.

Question 37

In NSCs. BMP is secreted by ____ cells. It is kept in high concentrations at the ___ side of the niche. How is it prevented from moving to the opposite side of the niche?

Answer 37

In NSCs. BMP is secreted by ENDOTHELIAL cells. It is kept in high concentrations at the BASAL side of the niche.
ITS PREVENTED from moving to the Apical side of the niche where the E cells and B1 cells are because the E cells secrete Noggin, which is a BMP inhibitor

As B3 cells transition into type C-progenitor cells and then move cloesr to the basal border of the niche, they leave the reach of Noggin/BMP inhibitors in E cells and experience increased levels of BMP, which promotes neurogenesis with a preference towards glial cells.

Question 38

How does Neural activity modulate NSC proliferation?

Answer 38

migrating neural precursors secrete GABA to REDUCE the rate of proliferation in progenitor cells. To counteract GABA, B1 cells secrete GABA inhibitors to INCREASE B1 proliferation. They express 5HT receptors that activate 5HT pathway in B1 cells to increase proliferation

Question 39

How does Sonic HH signalling in the NSC niche modulate NSC proliferation?

Answer 39

SHH has a gradient from high at apical (CSF) to low at basal (vascular). LOW SHH REDUCES the number of apically-derived olfactory neurons. NSC clusters in more apical positions of the niche will adopt different neuron fates compared to cells derived from NSCS in more basal positions based on differences in SHH signalling.

Question 40

How does vasculature communication modulate NSC proliferation?

Answer 40

Recall: B cells basal end feet directly contact vasculature. Notch receptor in end feet bind to JAG 1 transmembrane receptor in endothelial cells.
- Notch becomes NCID: maintains B1 cell quiescence. As B2/B3 cell transition into C progenitor cells, their basal connections with endothelial cells are lost. NCID is reduced, enabling the progenitor cells to mature.

Question 41

What glycoprotein is responsible for keeping MSCs in undifferentiated state?

Answer 41

Laminin found in basal lamina