Lecture 37

Question 1

List the characteristics of Stem Cells

Answer 1

Not terminally differentiated

Can divide without limit

Ability to renew themselves

When they divide, each new cell has the ability to remain a stem cell OR become a different cell type

They undergo slow division

Question 2

Compare the characteristics of Totipotent cells, Pluripotent cells, and Multipotent cells. (include examples of all 3 types of cells)

Answer 2

Totipotency: ability of a cell to give rise to all cells of an organism, including embryonic and all extra-embryonic tissues ex. zygote

Pluripotency: ability of a cell to give rise to all cells of the embryo and subsequently adult tissues (NOT able to become extra-embryonic cells) ex. embryonic stem cells

Multipotency: ability of a cell to give rise to different cell types of a given lineage ex. adult stem cells

Question 3

Compare the definitions of Asymmetric division and Independent choice. what are these concepts?

Answer 3

Asymmetric division: creates 2 cells, one with stem cell characteristics and another with the ability to differentiate

Independent choice: Division makes 2 identical cells but the outcome is stochastic (random) and/or influenced by the environment

Both of these are hypotheses as to how stem cells proliferate

Question 4

State a drawback of the asymmetric division theory and an advantage of the Independent choice theory.

Answer 4

the asymmetric division theory cannot explain how existing stem cells rapidly increase their numbers

the independent choice theory is more flexible and explains the sharp increase in stem cell numbers when they are needed for repair (this theory is more backed by evidence)

Question 5

describe the number and characteristics of founder cells of a specific organ/tissue. State how these characteristics are controlled.

Answer 5

each organ/tissue has a fixed number of founder cell populations that are programmed to have a fixed number of divisions.

this is controlled by short range signals that operate to define the size of final structures

Question 6

describe what transit amplifier cells are. describe their programming

Answer 6

they are a type of “intermediate cell” that occurs between founder cells dividing (also giving rise to one daughter cell that remains a stem cell) and that cell becoming a terminally differentiated cell.

they are programmed to undergo a limited number of times

Question 7

adult stem cells are ____ _____.

Answer 7

tissue specific

multipotent

Question 8

what do adult stem cells require in order to stay a stem cell? what type of factors regulate them?

Answer 8

they need a specialized environment (niche)

intrinsic and extrinsic factors regulate them

Question 9

what role do adult stem cells play in damaged tissues?

Answer 9

they serve as an internal repair system (dividing without limit to replenish cells that were damaged)

Question 10

Compare the epidermis, dermis, and hypodermis

Answer 10

epidermis: epithelial cells that form the outermost covering of the skin. Creates a water barrier and is continuously replaced

Dermis: second layer, rich in collagen and provides toughness

Hypodermis: fatty subcutaneous layer

Question 11

In the skin, what secretes the extracellular matrix to provide mechanical support? what provides nutrients? what 2 cells provide defense? what about immune response? lastly, what provides sensory information?

Answer 11

fibroblasts

blood vessels lined with endothelial cells

Macrophages and dendritic cells

lymphocytes

Nerve fibers

Question 12

The epidermis is a _____ layer, make of _____.

Answer 12

stratified

keratinocytes (have keratin intermediate filaments)

Question 13

What are the only dividing cells in the epidermis? how much time does it take for the entire epidermis to be completely replaced? what type of process is this?

Answer 13

the basal cell layer

about a month

the renewal of the epidermis is a self-renewing process

Question 14

State the order of the layers of the epidermis (5 layers)

Answer 14

Basal lamina

Basal cell layer

prickle cell layers

Granular cell layer

keratinized squame

(flaking off squame)

Question 15

which epidermal layer has numerous desmosomes? what do these desmosomes attach to?

Answer 15

the prickle cell layer

they attach to the tufts of keratin filaments

Question 16

Which layer of the epidermis serves as the boundary between active and dead cells? state the most prominent characteristic of this layer

Answer 16

the granular cell layer

this is a waterproof layer

Question 17

as a basal cell moves towards the surface, what occurs at each step of differentiation? state the term that describes the mechanism these cells undergo as they move towards the surface of the epidermis and what type of activation is occurring.

Answer 17

a change in gene expression (allows it to aquire the appropriate phenotype for the layer it is in)

cells undergo partial degradation, which is dependent on partial activation of apoptosis

Question 18

What controls the number of stem cells in the basal cell layer? what if this does not occur or stops occurring?

Answer 18

contact with the basal lamina

loss of contact triggers terminal differentiation of that cell

Question 19

what is the proliferative potential of stem cells directly correlated with?

Answer 19

the expression of the beta1 subunit of integrin

Question 20

what is the proliferative potential of stem cells directly correlated with? what does this mechanism help control?

Answer 20

the expression of the beta1 subunit of integrin

it helps control the size of the stem cell population

Question 21

State the 4 factors that govern the renewal of the epidermis

Answer 21

the rate of stem cell division

The probability that one of the daughter cells will remain a stem cell

the rate of division of transit amplifying cells

the timing of exit from the basal layer and the time the cell takes to differentiate and be sloughed away from the surface

Question 22

What happens if there is a perturbation of one or more of the various signaling pathways?

Answer 22

epidermal cancers

Question 23

What happens if the hedgehog pathway is over activated? what if there is a deficit of the hedgehog signal?

Answer 23

too much = it makes cells continue to divide even after they exit the basal layer

too little = loss of sebaceous glands

Question 24

What happens if the Wnt signaling is up-regulated? what if there is a loss of this signaling?

Answer 24

up-regulation = it causes extra hair follicles to develop (give rise to tumors)

loss = failure of hair follicle development (bald)

Question 25

What is the function of the Notch signaling pathway? how does this pathway achieve that?

Answer 25

notch signaling restricts the size of the stem cell population

it achieves this by lateral inhibition (causes neighbors of stem cells to become transmit-amplifying cells)

Question 26

What plays a key role in the repair of skin wounds? what role does it play?

Answer 26

TGFbeta: repairs skin wounds by promoting the formation of collagen-rich scar tissue

Question 27

True or False: as epidermal cells undergo partial degradation, they begin to lose their nucleus and mitochondria. explain

Answer 27

False (kind of)

as epidermal cells undergo partial degradation, they begin to lose their nucleus and other organelles (not just mito)

Question 28

Clusters of cells with high levels of _____ are found near the basal lamina and in the bulge of ____ _____. (fill in the blanks and explain why the word in the first blank is associated with stem cells)

Answer 28

integrin

hair follicles

integrin is associated with stem cells because it is a proteins that helps stem cells stay in contact with the basal lamina (effectively maintaining their status as a stem cell)