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lecture 17 Flashcards

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1
Q

what do we mean when we talk about stem cells

A

stuff that happens in fully developed organism (has completed embryonic development)

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2
Q

is adult body static or dynamic

A

not static; in dynamic EQ; new cells are being born, differentiating, dying

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3
Q

stem cell

A

undifferentiated cell, analogous to undifferentiated embryonic cell that can become anything

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4
Q

what do stem cells do

A

continue to divide indefinitely

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5
Q

what happens if a cell can’t continuously divide

A

it’s not a stem cell

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6
Q

what do stem cells produce

A

daughter cells that either remain a stem cell or differentiate into like muscle, fat, blood etc.

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7
Q

what is self renewal

A

remains stem cell, as cell divides it’s always gonna produce at least one more stem cell, so you maintain stem cells

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8
Q

where are stem cells found body? specific areas or just randomly throughout

A

specific locations known as stem cell niches

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9
Q

stem cell niches

A

special physical and chem envs. that control, regulate stem cell division and differentiation

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10
Q

example of a stem cell niche

A

bone marrow (where white blood cells are born and differentiated)

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11
Q

what did people use to think before

A

no more cell division in an adult; all the cells needed as an adult were produced within embryo

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12
Q

how was this modified as time went on

A

maybe differentiated cells were capable of replenishing themselves, like if u hurt muscle, cells could produce more muscle cells

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13
Q

main assumption in 1940s

A

but DNA and protein synthesis would be hard to detect because it’s so rare [basically all the cells, DNA, proteins we need are already produced]

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14
Q

how do we know this isn’t true (how do we know adult body isn’t static)

A

Charles LeBlond

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15
Q

what did Leblond show

A

you can detect new DNA and protein synthesis in adults, AND stem cells are major reason why that occurs

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16
Q

what method did LeBlond develop to detect new protein and DNA synthesis in living tissue

A

radioautography

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17
Q

describe radioautography experiment

A

fed animals radioactive phosphorus followed by normal food, give it some time and cross-section animal

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18
Q

what were results of radioautography experiment

A

radioactivity can cause a rxn on photographic film to render an image –> can see a dark signal of where the radioactive phosphorous is

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19
Q

conclusion of radioautography experiment

A

radioactive phosphorus stuck around and is incorporated into cells, DNA, protein b/c we can see it on film (means that there is new DNA protein synthesis going on, otherwise it would’ve just passed through the body)

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20
Q

what is being detected in this radioautograph experiment, where is it being detected, what does it tell us?

A

radioactive phosphorus is being detected in bone marrow of leg, shows us where stem cells would be located in that tissue

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21
Q

was LeBlond’s results universally accepted

A

no, especially when results came out he got a lot of pushback

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22
Q

what is next discovery of LeBlodn

A

stem cells

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23
Q

how did he approach this experiment of stem cells

A

knew that stem cell would have a capacity for self-renewal (as it divided, exact same cell type would be left behind while differentiating cells continued) –> used a histological approach

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24
Q

did LeBlond use antibody staining or fluorescent stuff to detect stem cells

A

no

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25
Q

specifically how did he detect stem cells

A

periodic acid-schiff technique: used chemical stain to give contrast to tissues

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26
Q

what did he do this stem cell experiment in

A

took sections of mouse testes, looking for stem cells that give rise to sperm, in gonads

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27
Q

what were results of stem cell experiment

A

cell A are stem cels because as they divide they persist but also give rise to much darker stained cells

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28
Q

what are darker stained cells

A

spermatocytes, initial steps toward differentiation into sperm cell

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29
Q

where are stem cells

A

in this case by edge of tissue where they’re generating the spermatocytes

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30
Q

what is a general principle of stem cell and differentiation

A

symmetric vs. asymmetric cell division

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31
Q

one way stem cell differentiation can happen

A

asymmetric cell division

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32
Q

what is asymmetric stem cell division

A

some factor (like protein, 2nd messenger) is concentrated on one side of cell, after division the factor is gonna be found on only one daughter cell (even tho DNA divides evenly)

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33
Q

what does this factor do

A

prevents differentiation, keeps stem cell as a stem cell

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34
Q

what happens to daughter cells without the factor (after divisiion)

A

will differentiate, because it doesn’t have that factor

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35
Q

so how is this asymmetric division

A

daughter cells are different; b/c of presence of factor one of them differentiates while other remains a stem cell

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36
Q

what is symmetric cell division

A

everything is uniformly mixed in cell, when it divides it is identical –> both stem cells

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37
Q

how does symmetric cell division give rise to differentiation

A

differing chemical environment

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38
Q

give an example of diff. chemical env. leading to differentiation

A

positions are different, maybe one cell is touching another cell that has some signaling molecules (other cell is not touching this) –> environmental change to cause differentiation event

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39
Q

what else did leBlond discover

A

stem cells in the gut

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40
Q

how did he discover stem cells in intestine

A

radioactive thymidine

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41
Q

describe gut/intestine

A

in mouse intestine, microvilli is reaching up to absorb nutrients from food, lined w/ intestinal epitheliumd

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42
Q

describe radioactive thymidine experiment

A

after 8 hrs it is concentrated at bottom of microvilli (where new cells are being created)

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43
Q

where are new cells being created

A

bottom of microvillli

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44
Q

what happens after 72 hrs

A

through staining we see radioactive thymidine positive cells all along microvilli, b/c we see where the cells go not just where they are being created

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45
Q

explain this idea of stem cells in gut

A

stem cells are created at base of microvilli, as cell division continues it’s like a conveyor belt of cells just continuously pushed up to tip of vili

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46
Q

what happens as cells are pushed up to tip of villi

A

shed into lumen of gut

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47
Q

what are the stem cells doing to gut

A

constant renewal of intestinal epithelium

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48
Q

where are these stem cells located

A

stem cell crypts

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49
Q

how is lining of small intestine continually renewed

A

through cell proliferation in crypts

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50
Q

where are stem cells located

A

in crypt

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51
Q

what happens as the stem cells divide and differentiate

A

move up along crypt and epithelial villie

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52
Q

what happens as these stem cells move up

A

they are able to differentiate into diff cell types

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53
Q

describe stem cells at crypt base

A

multipotent; give rise to full range of differentiated intestinal cell types

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54
Q

describe pulse chase experiment for microvilli stem cells

A

at first, just the stem cell is blue; after 5 days and 60 days, progeny of those stem cells are also blue (extends up along microvilli)

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55
Q

does this microvilli pulse chase exp. have same results as radioactive thymidine

A

yes; shows stem cells in crypts at base of microvilli, as they differentiate progeny are pushed up along microvilliw

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56
Q

what ultimately happens to stem cell progeny as they are pushed up along microvilli

A

they are shed at tips

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57
Q

what are 4 major differentiated cells in intestines

A

absorptive cells, goblet cells, paneth cells, entereoendocrine cell

58
Q

what is absorptive cell

A

most popular; responsible for absorbing nutrients from lumen of intestine

59
Q

where do absorptive cells absorb nutrients from

A

lumen of intestine

60
Q

what are goblet cells

A

secrete mucus to protect epithelium and smooth passage of food along cavity

61
Q

what are paneth cells

A

help w/ immune functions, also in crypt they prevent stem cells from differentiating

62
Q

who prevents stem cells from differentiating

A

paneth cells

63
Q

what are enteroendocrine cells

A

hella rare; secrete hormones to control cell proliferation, digestion, growth

64
Q

what does Wnt signaling do in the gut

A

maintains gut stem-cell compartment

65
Q

what is critical in molecular pathways controlling differentiation of stem cells in the gut

A

Wnt

66
Q

what is APC

A

turns off Wnt signaling

67
Q

what happens when they experimentally knocked out APC in mouse intestines

A

saw formation of tumors/adenomas that are just basically out of control stem cells

68
Q

what does Wnt signaling do

A

increases stem cell proliferation, triggers tumor formation

69
Q

what does APC do

A

turns OFF Wnt signaling, prevents like out of control stem cell proliferation and cancer

70
Q

what does loss of APC function lead to

A

hyperactivation of Wnt signaling

71
Q

what does notch signaling do in gut

A

controls gut cell diversification and helsp maintain stem cell state

72
Q

what does Wnt signaling lead to in crypts

A

expression of notch and delta

73
Q

what do paneth cells express

A

delta

74
Q

what happens when delta binds notch

A

notch is expressed on stem cells

75
Q

what happens after delta binds notch

A

causes signaling that prevents stem cell from differentiating

76
Q

what does that stem cell do

A

divides, symmetric cell division

77
Q

what happens after that symmetric cell division

A

they differentiate

78
Q

how do stem cells differentiate after symmetric cell division

A

lateral inhibition

79
Q

what does lateral inhibition lead to

A

causes 2 symmetric daughter cells to become asymmetric, differentiate into diff fates

80
Q

what happens to daughter cells after lateral inhibition

A

one daughter cell expresses delta other expresses notch

81
Q

what is fate of daughter cell that expresses delta

A

fated to become secretory cells on the villi, secretes mucus

82
Q

what is fate of daughter cell expressing notch

A

becomes absorptive cell

83
Q

describe lateral inhibition

A

cells 1 and 2 both express protein X that is trying to turn off X in the other cell

one cell wins by random chance, end up with protein X in one cell and it turns off on the other cell

84
Q

what happens to cause one cell to have protein X and other cell to not have it

A

gene regulation; X is massively transcribed in cell 1, degraded in cell 2

85
Q

describe delta and notch

A

transmembrane proteins that bind each other

86
Q

what happens when notch is activated

A

releases trans regulator that enters nucleus

87
Q

what does notch’s transcriptional regulator do

A

in nucleus, causes changes to gene regulation (turn off delta expression)

88
Q

what does notch do when activated

A

prevents cell from differentiating, actively tries to downregulate delta

89
Q

why does notch prevent cell from differentiating

A

so it remains a stem cell (when ontch is active)

90
Q

describe both stem cells in terms of notch and delta

A

gut stem cell divided into 2, identical; cell is expressing delta and activating notch

91
Q

what are both cells trying to do

A

both trying to remain stem cells, both trying to turn off delta in the other one

92
Q

what ends up happening in lateral inhibition

A

cell that has a little more delta than the other cell wins, continues to express delta while other cell turns off

93
Q

what does the cell that wins do to other cell

A

activates notch in other cell to prevent cell specialization (remains stem cell)

94
Q

what does winning stem cell do

A

differentiates (expresses delta, so no notch, meaning nothing preventing it from differentiating)

95
Q

what happens to losing cell

A

remains a stem cell, turns off delta all the way; activates notch to prevent specialization

96
Q

what does lateral inhibition do in terms of symmetric cell division

A

lateral inhibition is environmental factor that allowed one cell to differentiate and other to maintain its stemness

97
Q

where are paneth cells

A

at base of crypt

98
Q

what do paneth cells do

A

keeps initial stem cell a stem cell

99
Q

what happens once stem cell symmetrically divides

A

lateral inhibition takes over

100
Q

what does paneth cell express

A

expresses delta, keeps cells from differentiating; after division lateral inhibition takes over

101
Q

what does notch activation do

A

maintains stemness at base of crypt (no specialization)

102
Q

what are ultimate fates of losing cell (notch cell)

A

absorptive cells

103
Q

what is ultimate fate of winning cell (delta cell)

A

secretory cells (goblet)

104
Q

what happens if you get rid of APC

A

cell population expands massively

105
Q

what is Wnt signaling pathway important for

A

controlling stem cell numbers

106
Q

what happens in crypt:

A

bottom of crypt, Paneth cells maintain stem cell population, symmetric division, lateral inhibition (ultiately absorptive cells and goblet cells)

107
Q

what is needed for lateral inhibition to work

A

symmetric daughter cells

108
Q

what would happen if this was the only thing going on in the cell

A

stem cells would be depleted

109
Q

what else is happening in the backgroudn

A

self-renewal, stem cell divides and always remains a stem cell

110
Q

what does epidermal stem-cell system maintain

A

self-renewing waterproof barrier of dead skin cells

111
Q

where can we find other stem cell populations in bodies

A

dermis/skin

112
Q

why are we always shedding dead skin

A

b/c dermal stem cells are right against basement membrane, as they are displaced by further cell divisions you get movement from bottom (basement membrane) to top, which is skin surface

113
Q

what happens as dermal cells move to top

A

differentiate and die, filled w/ keratin, hydrophobic barrier

114
Q

what are stem cells of connective tissue

A

bone marrow stromal cells

115
Q

what are mesenchymal stem cells

A

bone cells, fibroblasts, cartilage, fat cells, smooth muscle cells

116
Q

where do mesenchymal cells reside

A

bone marrow

117
Q

how are bones continuously remodeled

A

osteoclasts and osteoblasts

118
Q

osteocytes

A

cells that can create bone

119
Q

where do osteocytes come from

A

mesenchymal stem cells

120
Q

osteoblasts

A

cells that can create new bone, allow it to heal

121
Q

osteoclasts

A

remove bone, help remodel it

122
Q

are muscle fibers renewed or static

A

constantly renewed

123
Q

what do myoblasts do

A

fuse to form new skeletal muscle fibers

124
Q

what happens to other myoblasts

A

not all of them fuse, some end up as satellite cells on surface of muscle fibers

125
Q

what are satellite cells

A

stem cell population that generates muscle progenitors that can fuse & regenerate muscle fibers

126
Q

what are satellite cells activated in response to

A

injury; create muscle progenitor cells –> help form /regenerate muscle

127
Q

basically what/where are satellite cells

A

in muscle; stem cell population, response to injury they divide and create new muscle progenitors to make muscle

128
Q

what lines all blood vessels and lymphatics

A

endothelial cells

129
Q

what do endothelial cells do

A

respond to signals in environment to create new endothelial cells

130
Q

is endothelial cell a stem cell

A

not really, but it shows how dynamic it is

131
Q

what happens when we need to form a new blood vessel

A

endothelial cells react w/ signals in env. to change gene transc. to create new cytoskeletal structures

132
Q

what do endothelial cells do in response to signals

A

form pseudopodial processes;

133
Q

what do pseudopodial (protrusion) processes allow them to do

A

navigate to source of signals and create new blood vessel (like a pathfinder)

134
Q

what happens if you have a region of tissue hella low in oxygen

A

you want to deliver oxygenated blood thru new blood vessel

135
Q

describe cells/tissue w/ low oxigen

A

high HIF1a

136
Q

what does HIF1a do

A

transcriptional regulator than causes cells to secrete VegF

137
Q

what does VegF do

A

diffuses to nearest capillary, sends a signals saying it needs a blood vesel over here

138
Q

what does VegF activate

A

activates nearest endothelial cell, causes it to form pesudopodia and form new blood vessel where it’s needed

139
Q

what do tissues requiring a blood supply release

A

release VegF

140
Q

what are required to maintain stem cell populations

A

self-renewal and asymmetric cell division

141
Q

what do stem cells generate

A

diverse cell populations required to maintain gut, bone, muscles, blood vessels

bio 211 (18 decks)

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