Apoptosis in Embryos Flashcards Preview

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Flashcards in Apoptosis in Embryos Deck (36)
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1
Q

What are four differences between apoptosis and necrosis?

A
  1. Necrosis involves disruption of organelles whereas apoptosis involves preservation of organelles.
  2. Necrosis results from lack of oxygen (causing swelling/bursting) whereas apoptosis involves rapid engulfment by neighboring cells to prevent inflammation.
  3. Necrosis damages neighboring cells.
  4. Hallmark of apoptosis is DNA fragmentation (chromatin condenses and cell shrinks; plasma and nuclear membrane “blebs”).
2
Q

What are seven morphological features indicating apoptosis of a cell is occurring?

A
  1. Scattered single cells
  2. Chromatin condensation
  3. Indentation of nuclear membrane
  4. Cytoplasmic vacuoles
  5. Nuclear fragmentation
  6. Cytoplasmic fragmentation and apoptotic body formation
  7. Phagocytosis or extraction and secondary necrosis
3
Q

What are six biochemical features indicating apoptosis of a cell is occurring?

A
  1. Separation of cell from neighbors
  2. Increased endonucleases
  3. Lamin disassembly
  4. Caspase activation
  5. Lamin disassembly
  6. Expression of surface triggers of phagocytosis
4
Q

What are six diseases related to decreased rates of apoptosis?

A
  1. Cancer (follicular lymphomas, carcinomas with p53 mutations)
  2. Breast cancer
  3. Prostate cancer
  4. Ovarian cancer
  5. Autoimmune disorders (mixed increase and decrease)
  6. Viral infections
5
Q

What are three types of diseases/injuries related to increased rates of apoptosis?

A
  1. AIDS (non-infected cells increase apoptosis)
  2. Neurodenerative disorders (Alzheimer’s, Parkinson’s, Ischemic injury, Toxin-induced liver disease)
  3. Other conditions (sarcopenia, atrophy, fiber loss, myocyte loss?)
6
Q

How was apoptosis discovered and in what creature was it originally found?

A

In nematode worms exactly 1090 somatic cells were formed during development, of which 131 undergo programmed death during embryogenesis and larval development (leaving exactly 959 cells).

7
Q

What are four important nematode genes involved in apoptosis and why are they important?

A
  1. Ced-9 “life gene” prevents apoptosis in certain cells (countering ced-3 and ced-4).
  2. Caspases ced-3 and ced-4 “death genes” downstream of ced-9 (when they lose function, 131 cells remain living).
  3. Ced-1 and ced-2 control engulfment of the dead cell by a neighbor.
  4. Nuc-1 codes for a DNA endonuclease to digest the dead cell nucleus.
8
Q

What three mammal genes homologous to nematode genes involved in apoptosis have been discovered?

A
  1. Human bcl-9 (oncogene - can mutate and cause cancer) homologous to nematode ced-9.
  2. IL-1 converting enzyme or “ICE” or “caspase-1” in mammals homologous to nematode ced-3.
  3. Apaf-1 in mammals is a regulator that is homologous to nematode ced-4 (facilitates caspase activation).
9
Q

What does the earliest event of apoptosis in human embryos appear in the form of?

A

Membrane changes; apoptotic cell rounds up and separates from neighboring cells.

10
Q

Cells that are excluded between other blastomeres and the zona pellucida in a human embryo (with poor gap junctions) indicate what?

A

Apoptosis.

11
Q

What are two ways to mark early evidence of apoptosis in human embryos?

A
  1. Phosphatidylserine in apoptotic cells is not in the inner membrane leaflet like in healthy cells–it’s found on the outside of the cell membrane.
  2. Anticoagulant protein annexin V binds to phosphatidylserine in apoptotic cells but not in healthy cells with full membrane integrity.
    NOTE: Some studies showed no labeling of annexin V (conflict in results).
12
Q

What is one common feature of pre-implantation human embryos that also may indicate the presence of apoptosis?

A
  1. Vacuoles (transluscent cytoplasmic vacuoles in apoptotic cells).
13
Q

How is chromatin condensation observed in apoptotic embryos?

A

By staining with DNA dyes.

14
Q

Chromatin condensation and nuclear fragmentation have been detected in apoptotic embryos of what stages?

A

Cleavage stage embryos and blastocysts.

15
Q

What is considered to be the hallmark of apoptosis?

A

DNA degradation into oligonucleosomal fragments.

16
Q

How can DNA fragmentation be examined in apoptotic human embryos?

A

Using terminal deoxynucleotidyl transferase mediated dUTP nick-end label (TUNEL).

17
Q

What does TUNEL labeling show in apoptotic human embryos?

A

Highlights a fragmented nucleus with its stain/dye.

18
Q

What percentage of arrested human embryos showed apoptosis through TUNEL labeling?

A

~30% of the embryos.

19
Q

Prolonged culture of arrested embryos (up to 72 hours) changed TUNEL labeling percentages in what way?

A

Increase of TUNEL labeled and fragmented nuclei.

20
Q

Was TUNEL labeling also found in fragmented unarrested human embryos?

A

Yes; mainly in the compaction stages.

21
Q

What percentage of IVF embryos show some degree of fragmentation?

A

~75%

22
Q

Is fragmentation of embryos an in vitro artifact? Why or why not?

A

No, because fragmented embryos have been found in vivo as well.

23
Q

What do fragmented embryos indicate?

A

Presence of chromosomal abnormalities.

24
Q

Is cytoplasmic fragmentation in embryos an indicator of apoptosis (why or why not)?

A

Not necessarily because it was not always found in apoptotic bodies and the majority of fragmented embryos didn’t show either TUEL or annexing labeling.

25
Q

Phagocytosis was shown in apoptotic blastocysts of what two species?

A

Humans and monkeys.

26
Q

How do some blastomeres escape phagocytosis following apoptosis and what happens to those cells?

A

By escaping into the lumen from the (single-layered) epithelia; they wind up possibly undergoing necrosis instead?

27
Q

Explain the roles of BAX and BCL-2 in apoptotic human embryos.

A
  1. Both exist in varying concentrations.
  2. When BAX concentration is higher, cell undergoes apoptosis.
  3. When BCL-2 concentration is higher, cell remains alive.
28
Q

Cells with good morphology have higher concentrations of what apoptotic-related gene?

A

BCL-2 (NOT BAX!)

29
Q

Increased BAX expression in embryos was associated with what (that leads to apoptosis)?

A

Increased fragmentation.

30
Q

When does apoptosis usually appear in embryos?

A

After compaction and blastocyst formation.

31
Q

Does minor fragmentation affect human embryos?

A

Not usually.

32
Q

Major cytoplasmic fragmentation is frequently followed by what phenomenon in an embryo?

A

Embryo arrest.

33
Q

What is observed 24 hours after embryo arrest (at any stage)?

A

Nuclear and DNA fragmentation.

34
Q

Can suboptimal in vitro culture medium affect cell death?

A

Yes, apoptosis can increase.

35
Q

What two growth factors improve the quality of embryos?

A
  1. TGF-alpha

2. Insulin like growth factor I

36
Q

What are two important biological roles of apoptosis in embryos?

A
  1. Eliminate cells with chromosomal abnormalities.

2. Eliminate inner cell mass cells with inappropriate developmental potential.