Chapter 10

Question 1

The pedigree of cells in the body of a worm.
C. elegans: 959 somatic cells
Complete cell lineage-some end abruptly: become post-mitotic or undergo apoptosis.

Answer 1

Cell Immortalization and Tumorigenesis

Question 2

Proliferative capacity of serially passaged human fibroblasts.
a.) Number of population cell doublings.
b.) Fibroblasts approximately 60 doublings.
c.) Then cell senescence
Metabolically inactive
Cannot re-enter cell cycle.

Answer 2

Cell-specific controls determine the number of cell generations through which a particular cell lineage can pass

Question 3

Upper, growing fibroblast.
Lower, senescent cells
Large cytoplasms(fried egg appearance)
Express acidic Beta-galactosidase enzyme.

Answer 3

Senescent cells in vitro and in vivo

Question 4

Age-dependent senescence
Number of population doublings is higher in tissues of
newborns.

Answer 4

Loss of Proliferative capacity depends on age, species and tissue source.

Question 5

Increased age=loss of skin stem cell proliferative capacity.
Tissue regeneration decline=thinning of keratinocyte layer of skin(epidermis).

Answer 5

Loss of proliferative capacity with age

Question 6

Possible explanations:
A.) Number of population doublings.
B.) Damage.
C.) Loss of metabolic function.

Answer 6

Loss of proliferative capacity with age

Question 7

Embryonal stem cells are immortal.
Cancer cell lines are also immortal.

Answer 7

Loss of proliferative capacity

Question 8

Generations of cells forming a tumor mass.
Tumor size vs. population doublings

Answer 8

Cancer cells need to become immortal in order to form tumors

Question 9

Model of exponential growth of a tumor

Answer 9

Relationships between population doublings and formation of a tumor mass.

Question 10

In reality, many cells of a tumor are lost to apoptosis.
Mouse mammary tumor in mouse carrying oncogenic
Wnt-1 transgene.
TUNEL, (brown spots)

Answer 10

Relations between population doublings and formation of tumor mass

Question 11

Result is 30-40 cell generations instead of 10.

Answer 11

Effect of cell loss on the cell generations required to form a tumor mass

Question 12

Memory is cell autonomous, ie intrinsic
Cells measure: Cumulative physiologic stress, number of generations, then “crisis”.

Answer 12

How do cells remember replicative history

Question 13

Influence of cell culture conditions on senescence.
Oxygen tension
3% is closer to normal.

Answer 13

cell-physiologic stresses impose a limitation on replication

Question 14

keratinocytes
on plastic:
p16(INK4A)
Less induction in presence of a feeder layer.

Answer 14

dependence of epithelial cells on stromal factors

Question 15

human fibroblasts, in vitro
p16(INK4A)
p21(Cip1)
Also, level of p53 increases 10-40 fold

Answer 15

induction of tumor suppressor proteins during in vitro culture

Question 16

Left, normal cells
small
few focal contacts(yl)
few actin fibers(org)
Mid, senescent cells
ectopic expression of p16(INK4A)
Right, normal cells with replicative senescence.

Answer 16

Normal versus senescent cells

Question 17

the effect is dependent on the ability of Large T to inactivate p53 and pRb.
May be a factor for cancer cells in vivo?

Answer 17

Role of large T antigen in circumventing senescence

Question 18

kidney tissue from rats at indicated age.
stained for Beta-galactosidase

Answer 18

Evidence of senescent cells in living tissues

Question 19

senescent human melanocytes within a dysplastic nevi(beta-gal)

Answer 19

evidence of senescent cells in living cells

Question 20

After replicative senescence, cells in culture will undergo “crisis”
Disintegrating cells(white, refractile)
A truly functioning counting device-telomere length

Answer 20

Apoptosis associated with cell population in crisis

Question 21

Telomere detected by FISH.
Each chromatid with a telomere at each end.
Cells deprived of TRF2(maintains telomere structure)
End-to-end fusion.
Chromosomes with two or more centromeres.

Answer 21

The proliferation of cultured cells is also limited by the telomeres of their chromosomes

Question 22

Human lymphocytes: telomere length decreases with population doubling.
Large TTAGGG repeats.
Immortal-just slightly longer that cells in crisis.

Answer 22

Shortening of telomere DNA and Cell proliferation

Question 23

telomeric DNA
body of chromosomal DNA
telomeric DNA
successive cell generations
Crisis

Answer 23

the shortening of telomeric DNA with cell division

Question 24

end-to-end fusion(occurs at G2 phase)
Breakage fusion cycles

Answer 24

Telomere shortening

Question 25

telomere erosion
unprotected chromatid ends
end-to-end fusion

Answer 25

telomere shortening

Question 26

During mitosis: dicentric chromatid, with two telomeres and two centromeres.

Answer 26

telomere shortening

Question 27

normal sister chromatids
mitosis
point of fusion
fused sister chromatids
mitosis

Answer 27

telomere shortening

Question 28

dicentric chromosomes cannot segregate properly
creates a cycle of fusion and breakage(breakage fusion bridge cycles(BFB cycles))

Answer 28

telomere shortening