Tissue renewal and stem cells

Question 1

tissue maintenance

Answer 1

involves molecular turnover and cellular turnover (involves cell division and cell death)

Question 2

where do new cells come from

Answer 2

stem cell division (often)
differentiated cell division (sometimes)
- liver hepatocytes
- pancreatic beta cells

Question 3

when do we have rapid cellular turnover

Answer 3

typically cells exposed to harsh
environments or activities (e.g. skin cells, cells lining the
gut lumen, blood cells)

Question 4

what cell types cannot be renewed

Answer 4

Often sensory cells with specialized architecture
* Photoreceptor cells in eyes for vision
* Auditory hair cells in the inner ear for hearing
* When these cells are lost, they cannot be replaced
* Loss of these cells can lead to vision and hearing defects with age, disease, or damage

Question 4

when do we have no cellular turnover

Answer 4

typically cells with highly specialized
structure and function (e.g. auditory hair cells, photoreceptor cells)

Question 5

how do we see that non renewable cells undergo molecular turnover
pulse-chase experiment

Answer 5

1. A “pulse” of radiolabeled leucine is
   supplied to photoreceptor cells
2. The labeled leucine is
   incorporated into new proteins in
   a new photoreceptive disc
3. More new proteins are made (with
   non-labeled leucine) and new
   discs move into the outer segment
4. The labeled proteins are pushed
   up the outer segment
5. At the end of their life, the labeled
   proteins are removed from the cell
   BIO230 Lecture 2-6 10

Question 6

cell turnover in healthy tissues

Answer 6

Cell turnover can be
stem cell dependent or
independent
* Stem cells must be
highly regulated by
specific mechanisms

Question 7

stem cells

Answer 7

1. Can divide indefinitely
2. Are not terminally differentiated
3. Can self-renew: child cell can remain
   a stem cell
4. Can differentiate: child cell can
   become a differentiated cell

Question 8

how are internal stem cell fate determinants partitioned between child cells

Answer 8

stem cells undergo either symmetric or asymmetric division
One child cell inherits all of the stem cell fate determinants and remains a stem cell. The other child
differentiates.
Both child cells inherit some
stem cell fate determinant and
both remain stem cells

Question 9

how can stem cell fate be determined by external factors

Answer 9

stem cells undergo symmetric division
Differences in the environment of the child cells determines whether they remain as stem cells or differentiate
* Flexible: both child cells can take on the same fate if they experience the same environment

Question 9

what does slow division protect stem cells from

Answer 9

• Random mutations from DNA replication
• Telomere depletion

Question 10

how can stem cell niche be defined

Answer 10

1. secreted signals
2. direct cell-cell contact
   if a stem cell leaves the niche it will differentiate
   stem niches also promote self renewal

Question 11

transmit amplifying cells

Answer 11

after stem cells divide, Transit-amplifying cells divide rapidly to increase cell numbers before final
differentiation

Question 12

progenitor cells

Answer 12

undergo stepwise differentiation, more differentiated cells have fewer cell fate options

Question 13

unipotent stem cells

Answer 13

can produce only one cell type

Question 14

terminally differentiated

Answer 14

fully differentiated and will usually not divide again

Question 15

stem cell concepts in the epidermis

Answer 15

basal lamina provides a stem cell niche
stem cells divide via symmetric divisions in the basal layer
transit amplifying cells undergo many divisions and migrate into the prickle cell layer
cells differentiate further into lateral layers
dead cells flake off from surface

Question 16

how do transplantation experiments identify hematopoietic stem cells

Answer 16

• x-irradiation halts blood production and mice will die without blood cell renewal
• Different cells were transplanted into mice to see whether they could recover
• Only 1/100,000 cells is a multipotent blood stem cell
• Transplant of 1 multipotent stem cell can restore all blood cell types, including stem cells
• This is the basis of bone marrow transplants to treat leukemia

a subpopulation of cells can be used in transplant experiments

Question 17

how do embryonic cells have full developmental potential

Answer 17

cells of inner mass are pluripotent cells
they can be cultured indefinitely and then factors can be added to change them into diff cells

Question 18

somatic cell nuclear transfer

Answer 18

cultured ES cells can be created without a fertilized embryo
donor cell placed next to enucleated egg, electric pulses causes donor cell to fuse with enucleated egg, cell division, embryo placed in foster mother, birth of child

Question 19

how can induced pluripotent cells be made from adult cells

Answer 19

through OSKM (Yamanaka) transcription factors
Oct4, Sox2, Klf4, Myc

Question 20

what type of cells are plant cells

Answer 20

totipotent