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Mechanisms of Animal Development II > Stem cells > Flashcards

Stem cells Flashcards

1
Q

What is a stem cell?

A

undifferentiated cells

have ability to self-renew and give rise to differentiated lineages

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2
Q

How is cell homeostasis maintained?

A

a) single cell asymmetry: when dividing, one progeny becomes commited cell, another one stays stem
b) population asymmetry: stem cells can also divide symmetrically, but then some give rise to commited cells only, other so stem only
c) adult stem cell lineage: commited stem cell can give rise to transit progenitor cell that will amplify and create differentiated cells

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3
Q

Stem cells can be discriminated by their source. Which 2 classes do we sort them into?

A

a) embryonic

b) adult

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4
Q

Describe embryonic stem cells.

A

derived from either inner cell mass of mammalian blastocyst or from fetal gamete progenitor cells (gametes)

capable of producing ALL cells of the embryo

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5
Q

Describe adult stem cells.

A

found in the tissue of organs once the organ has matured

maintain tissue homeostasis because they can form a subset of cell types

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6
Q

Stem cells can be discriminated by their potency (ability to generate different types of differentiated cells). Which 5 classes do we sort cells into?

A 
totipotent
pluripotent
multipotent
unipotent
progenitor cells
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7
Q

What are totipotent cells?

A

can form every cell in the embryo AND the trophoblast

the only totipotent cells are zygote & first 4-8 blastomeres

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8
Q

What are pluripotent cells?

A

can form all cell of the embryo (all 3 layers + germ cells), but not trophoblast
are derived from the inner cell mass of the blastocyst or from the primordial germ cells in the fetus

undifferentiated germ cells can also form pluripotent stem cells

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9
Q

What are multipotent cells?

A

can be found in embryo or adult

commitment is limited to a relatively small subset of possible cells in the body (e.g. HSC)

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10
Q

What are unipotent cells?

A

found in particular tissues, commited cells with restricted fate
involved in regenerating a particular cell type

e.g. spermatogonia -> sperm only

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11
Q

What are progenitor cells?

A

not capable of unlimited self-renewal (terminally differentiate after a certain number of divisions; only transit amplification)

usually divide while migrating away from the stem cells niche

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12
Q

How do you induce stem cell differentiation in the lab?

A

embryonic stem cells + fibroblast/platelet-derived GF -> glial stem cells

embryonic stem cells + RA -> neuronal stem cells

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13
Q

Which are the core pluripotency transcription factors?

A

Oct4
Sox2
Nanog

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14
Q

How do the transcription factors keep the pluripotent stem cell in this state?

A

individually, they are dispensable (redundant)
but they define and sustain the naive state collectively by cross-regulating each other

can be sorted into gene regulatory network with outer and inner circuit
if outer circuit collapses, cells undergo lineage commitment
(2i inhibitors prevent this)

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15
Q

In mice embryo, 2 phases of pluripotency can be observed. Which two? What is the difference?

A

ground and primed state

ground state = ESC in mice
primed state = mESCs differentiated into mEpiSCs = hESCs

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16
Q

What are induced pluripotent stem cells?

A

are pluripotent cells that are generated from terminally differentiated cells by reprogramming

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17
Q

What can iPSCs be used for?

A

disease study mechanism:

  • take skin fibroblasts and reprograme them to iPSCs
  • > can characterize them or differentiate them towards endodermal tissues to assess cell-type specific functions (e.g. model to test drugs against cystic fibrosis)

use in regenerative medicine: shown to correct sickle-cell anemia phenotype in mice (fibroblasts -> iPSCs -> correct mutation by gene targeting -> differentate into HSC -> transplant back into irradiated mouse)

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18
Q

Combination of which genes is used to induce iPSCs in mice and why?

A

Sox2 & Oct3/4: activate Nanog transcription

c-Myc: opens up the chromatin and makes genes accessible for Sox2, Nanog, Oct4

Klf4: prevents cell death

19
Q

What is natural stem cell therapy?

A

cooperation between fetus and mother: fetal stem cells have been found in the blood of pregnant mice and women

in humans: the cells leave the mother’s blood and integrate preferentially into damaged or diseased organs in the mother, stay even decades after pregnancy

20
Q

Adult stem cells can only give rise to a limited number of cell and tissue types and have a low proliferation rate. Nontheless, they exist. List some.

A 
hematopoietic
epidermal
neural
hair
melanocyte
mesenchymal
gut
germline
21
Q

Describe hematopoietic stem cells.

A

they generate cells of the blood throughout the entire life

in bone marrow, but kinda rare (1/15k)

22
Q

How were hematopoietic stem cells discovered?

A

In 1960s:

  • serial transplantation experiment: injected BM into lethally irradiated primary recipient mouse
  • some donor cells entered the spleen and formed colonies containing all types of blood cells (arose from single cells)
  • to show that they are stem: took these and inject them into another mouse, where the same thing happened

(marking these cells by specific radiation induced chromosomal breaks)

23
Q

What is a stem cell niche?

A

a privileged site that provides a milieu of ECM, juxtacrine and paracrine factors that allow cells residing there to remain undifferentiated, to self-renew and to control the differentiation of those progeny that do leave the niche

24
Q

Name a couple of high-turnover stem cell niches.

A 
mesenchymal
hematopoietic
intestinal
epidermal
hair follicle
sperm
25
Q

Name a couple of low turnover niches.

A

brain

skeletal muscle

26
Q

How is hematopoietic stem cell niche also called and where is it? How is hematopoiesis regulated there? Which stem cell populations do we find in the blood then?

A

endosteum
in the hollow cavities of trabecular bones e.g. femur where the bone marrow is -> allows HSCs to be in close proximity to osteocytes and endothelial cells

hematopoiesis regulated by paracrine factors (Wnt, SCF, angiopoietin)
cell surface signals (Notch, integrin)
hormons
neurotrnasmitters
pressure from blood vessels

active vs quiescent cells

27
Q

Explain what’s happening in Drosophila’s testes germ stem cell niche (!).

A

germline stem cells are in the “hub” microenvironment:

  • cca 12 somatic testes Hub cells
  • cca 5-9 stem cells next to them

Stem cells divide (asymmetrically) and form:

  • another germline stem cell
  • gonialblast (-> will divide to form sperm precursors)

Asymmetry:
when the germ stem cell is dividing, one centrosome remains attached to the cortex at the contact site between the stem and hub cell; another one on the opposite side because of how mitotic spindle orients
–> when the cells are separated, the one further away becomes gonialblast:
- Hub cells secrete Unpaired -> activates Jak/STAT
pathway and specifies self-renewal
- cells that are too distant (=gonialblast) start to
differentiate

28
Q

The intestine is under constant mechanical and chemical stress, so it has to homeostatically renew. What is the turnover time in humans?

A

7-10 days

29
Q

Intestinal stem cells are found where in the intestine?
Why are the cells surrounding them important?
Which transcription factor is characteristic for them?

A

in the crypts, between Paneth cells
Paneth cells secrete Wnt3 and Dll1/4 and maintain the stem cell pool
- too far from the crypt bottom = less Wnt = signal for differentiation

Lgr5+

30
Q

If you genetically trace Lgr5+ stem cells in the intestine, what can you observe?

A
  1. present cells are progeny of the initially labelled cell (high turnover of intestinal cells!)
  2. when dividin asymmetrically: new ISCs are kept at the bottom of the crypt
  3. higher up the crypt, they divide symmetrically: either all the progeny becomes differentiated cells, or they colonize the crypt as stem cells again
31
Q

What do we mean by the term plasticity when talking about cells?

A

ability of cells to broaden their fate and differentiation potential
e.g. during tissue regeneration after wounding to ensure tissue homeostasis

unipotent precursors become multipotent
commited cell dedifferentiates to stem cell-like state

32
Q

What metabolic shift happens when cells go from stem cells to differentiated cells? Why?

A

from glycolysis and PPP to oxidative metabolism

differentiated cells do not replicate anymore (lower anabolic demands)
require large amounts of energy for specialized functions

33
Q

Which metabolic processes do embryonic stem cells depend on?

A

glycolysis for ATP production
pentose phosphate pathway for generation of biosynthetic substrates

partial breakdown of glucose -> intermediates for PPP

34
Q

On a mitochondial level, what marks stemness?

A

low mtDNA copy number

spartse mitochondrial infrastructure with immature cristae

35
Q

Switch from stem to differentiated cell is also marked on epigenetic level. Which 2 inputs influence it and why?

A

nutrient levels
cell metabolism

define how much substrates for chromatin remodelling complexes there are

36
Q

During HSC development, what segregates the development of myeloid and erythroid lineage?

A

metabolism (glutamine and glucose-dependent nucleotide synthesis)

37
Q

Define regeneration.

A

reactivation of development in postembryonic life to restore missing or damaged tissues

38
Q

List and describe 4 ways of how regeneration can happen.

A
  1. stem-cell mediated: stem cells allow an organism to regrow certain organs/tissues that have been lost (e.g. hairshafts, blood cells, flatworms)
  2. epimorphosis: adult structures -> dedifferentiation to form blastema-> redifferentiation (e.g. amphibian limbs)
  3. morphallaxis: repatterning of existing structures, almost no new growth (e.g. hydra)
  4. compensatory regeneration: differentiated cells divide, but maintain their differentiated functions (e.g. mammalian liver)
39
Q

How do planarian flatworms reproduce? At some point, they form neoblasts. What is their potency?

A

binary fission = they split from top to bottom and regenerate the missing left/right part

neoblasts are pluripotent and can form all 3 germ layers

40
Q

Reptilian limb regeneration is an example of epimorphic regeneration: cells dedifferentiate and form regeneration blastema. When doing that, do they retain their specification and how can you trace them?

A

specification is retained = blastema is heterogeneous assortment of restricted progenitors that are not fully dedifferentiated

transplant cartilage from GFP-expressing limb to WT animal -> amputation -> see where you find green cells after regeneration

41
Q

Which organism can regenerate in 2 different ways (mechanistically, not morphologically) when cut in different ways?

A

hydra:

cut it close to the head = morphallactic regeneration (no proliferation)

cut it close to the mid-gastric bisection = epimorphic regeneration (incudes new zone of proliferation below the zone of apoptosis)

42
Q

Mammalian liver can regenerate after partial hepatectomy (remaining lobes enlarge). By which mechanims of regeneration?

A

compensatory regeneration = differentiated cells divide to recover the structure and function of the damaged organ

it is combination of hypertrophy (enlargement of the cells) and proliferation (if really needed)

43
Q

Is declined stem cell activity during aging caused by declined function of the stem cells or by a declined ability of the stem cell niche to support the cells? Which experiment showed that?

A

PARABIOSIS EXPERIMENT
surgically joined circulatory system of a young and old mouse = share 1 blood supply

old mouse exposed to young blood: restored muscle and liver regeneration
young mouse exposed to old blood: restricted proliferation of neural stem cells -> decrease in learning and memory

Mechanisms of Animal Development II (11 decks)

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