Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

L3 Epigenetics > Epigenetic regulation of stem cell developmental potential > Flashcards

Epigenetic regulation of stem cell developmental potential Flashcards

1
Q

What are stem cells?

A

Undifferentiated proliferation-competent cells capable of both self-renewing and differentiating into multiple specialised cell-types

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is developmental potential?

A

The capacity for embryonic, foetal or adult stem cells to self-renew and/or commit to distinct programmes of cell differentiation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the 3 types of stem cell developmental potential?

A
  • Totipotency
  • Pluripotency
  • Multipotency
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the potency of a fertilised egg? (2)

A
  • Totipotent
  • Gives rise to all embryonic and extra-embryonic cell types
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the potency of embryonic stem cells? (2)

A
  • Pluripotent
  • Can self renew and give rise to all definitive embryonic cell types
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the potency of adult stem cells e.g. haematopoietic stem cells? (2)

A
  • Multipotent
  • Can self-renew and give rise to all haematopoietic cell types
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Where are pluripotent embryonic stem cells found? (2)

A
  • Inner Cell Mass of preimplantation stage embryo (blastocyst)
  • Gives rise to germ layers (endoderm, ectoderm, mesoderm)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What happens to CpG methylation upon zygote formation? (3)

A
  • Genome wide active CpG demethylation to erase epigenetic marks from gamete genomes
  • Persists into early preimplantation stages of development
  • Followed by de novo DNA methylation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are DMRs? (2)

A
  • Differentially methylated regions
  • Genomic regions with different methylation statuses among multiple samples (tissues, cells, individuals etc.)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the gamete-specific differences seen in de novo methylation? (3)

A
  • Oocyte contributed DMRs decrease and remain low/decline further
  • Sperm contributed DMRs decrease and then a subset are re-established during re-methylation
  • This is evidence that global DNA demethylation in the preimplantation blastocyst removes epigenetic barriers to acquisition of pluripotency
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the 2 types of enzymes involved in re-methylation?

A
  • De novo methylation done by DNA methyltransferases DNMT3A and DNMT3B
  • Long term persistence of methylation in dividing cell populations requires maintenance DNA methyltransferase DNMT1
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What happens to DNA methylation in dividing cells? (3)

A
  • Fully methylated DNA becomes hemi-methylated after DNA replication and cell division
  • DNMT1 converts hemi into fully methylated DNA (maintenance)
  • Methylation modifications would be diluted/lost passively in the absence of maintenance methyltransferases in proliferating cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How does active demethylation occur? (3)

A
  • TET demethylases do a series of oxidation reactions on 5-methylcytosine
  • Forms an intermediate recognised by thymine deglycosylase which removes the base from the DNA
  • Base excision repair (BER) process restores the double stranded DNA by replacing with a normal cytosine
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What does the blastocyst give rise to? (2)

A
  • Epiblast (pluripotent embryonic cells)
  • Trophectoderm (differentiating extraembryonic tissue)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the difference between day 6 and day 7 mouse blastocyst? (2)

A
  • Day 6 epiblast cells are pluripotent, best time to derive pluripotent stem cells
  • Day 7 egg cylinder cells are multipotent ectoderm, mesoderm and endoderm layers
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How do you get embryonic stem cells? (2)

A
  • Take cells from epiblast of preimplantation blastocyst and can maintain in 2i culture indefinitely
  • Get self-renewing pluripotent embryonic stem cells (ESCs)
17
Q

What is the definition of pluripotency?

A

Cells have the capacity to give rise to all differentiated cell types (ectoderm, mesoderm, endoderm, germline) when experimentally transplanted into a host embryo

18
Q

How are embryonic stem cells maintained in a state of pluripotency in vitro? (3)

A
  • Inhibition of FGF signalling via MEK inhibition (downstream of FGF)
  • Inhibition of GSK3 which is a negative regulator of wnt signalling
  • Results in inhibition of FGF signalling and potentiation of wnt signalling
19
Q

What are the OSN transcription factors? (2)

A
  • Oct4, Sox2 and Nanog
  • Required in ESCs to maintain pluripotency
20
Q

What is the difference in ESCs in 2i culture vs serum? (3)

A
  • Demethylation of Nanog in 2i culture compared to in serum
  • Better for maintaining pluripotency because demethylation allows expression of pluripotency genes such as Nanog
  • Presence of hydroxymethylcytosine in 2i culture ESCs is proof of active demethylation to maintain pluripotency
21
Q

What is the effect of forced expression of the OSKM group in fibroblasts?

A

Reverses differentiation and makes them induced pluripotent stem cells (iPSCs)

22
Q

What is the OSKM group? (2)

A
  • Pioneer transcription factors Oct4, Sox2, Klf4, Myc which are powerful regulators of phenotypic plasticity
  • Includes OSN factors Oct4 and Sox2
23
Q

How do the OSN factors maintain pluripotency in ESCs? (3)

A
  • Oct4, Sox2, Nanog form a complex at genes that are required to maintain pluripotency/undifferentiated cell state e.g. Jarid2 in ESCs
  • Recruit histone acetyltransferase p300/CBP which performs H3K27ac modifications to promote gene expression
  • H3K27ac prevents H3K27me by PRC2 at pluripotency genes
24
Q

Which residues do histone acetyltransferases target? (2)

A
  • Non-specific so will add acetyl groups to multiple lysines in the N-terminal tails of ALL core histones at transcriptionally active genes
  • H3K27 (methylation target of E(z)) acetylation by p300/CBP prevents H3K27 methylation
25
Q

What is the structure of p300/CBP? (4)

A
  • Histone acetyltransferase domain (‘writer’)
  • Bromodomain which binds acetylated histones (‘reader’)
  • Zinc finger domain which binds H3K4 methylation (trithorax target) which isn’t a silencing modification
  • Recognises and boosts local acetylation
26
Q

Which genes are frequently mutated by chromosomal translocation in leukaemia? (2)

A
  • CBP
  • Trithorax
27
Q

How are pluripotent embryonic stem cells poised for differentiation? (3)

A
  • A class of developmental regulatory gene promoters exhibit bivalent (opposing) H3 histone modifications in their promoters i.e. H3K4me and H3K27me
  • Genes that are poised for transcription but inactive
  • Many of these are transcription factor encoding
28
Q

What is a characteristic of the ES cell pluripotent state?

A

Bivalently modified transcriptionally silent genes

29
Q

Which genes are transcriptionally active when pluripotent cells are differentiating into neural cells? (3)

A
  • Nkx2.2
  • Sox21
  • Zfpm2
30
Q

What is associated with H3K4 methylation?

A

Gene activation

31
Q

What is associated with H3K27 methylation?

A

Gene repression

32
Q

What happens to methylation of regulatory gene promoters during differentiation into neural cells? (2)

A
  • Nkx2.2, Sox21, Zfpm2: retain H3K4 methylation and lose H3K27 methylation, transcriptional activation
  • The genes that aren’t required retain H3K27me and lose H3K4me, remain silent
33
Q

What is marked by bivalent histone modifications? (2)

A
  • Developmental regulatory genes that are required for differentiation
  • Contain opposing H3 modifications in the same stretch of chromatin (H3K4me and H3K27me) so are poised for activation by signals
34
Q

What is the location of bivalent modifications? (4)

A
  • H3K27me3 is either side of the TSS (adjacent nucleosomes)
  • H3K4me3 is directly on the TSS
  • They are on slightly different nucleosomes
  • RNA polymerase sits ready on the TSS until it gets the signal to start transcription
35
Q

What is a mammalian orthologue for trithorax? (2)

A
  • Mll2
  • Required for H3K4 methylation at bivalent promoters
36
Q

What is the function of PRC2 in ESCs?

A

Catalyses H3K27me2,3

37
Q

What is the effect of loss of PRC2 function in ESCs? (2)

A
  • Loss of H3K27me on differentiation genes
  • Induces spontaneous differentiation into meso-endodermal tissue
38
Q

What is the function of polycomb and trithorax proteins in differentiation genes? (2)

A
  • Functionally antagonistic
  • Polycomb repress (PRC2, H3K27me), trithorax activate (H3K4me)

L3 Epigenetics (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions