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Development and disease > Early cell fate decisions in the mammalian embryo > Flashcards

Early cell fate decisions in the mammalian embryo Flashcards

1
Q

When do inner cell mass and trophectoderm become morphologically apparent?

A

These cells become apparent morphologically at blastocyst stage(blastula), but molecular changes occur before this

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2
Q

What does the first cell fate decision seperate?

A

First cell fate decision separates the ICM and TE in the blastocyst

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3
Q

What does the second cell fate decision give rise to?

A

Second cell fate decision gives the rise of epiblast and hypoblast

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4
Q

What are inner cell mass and trophectoderm governed by?

A

-Trophectoderm and inner cell mass are governed by transcription factors and the expression of transcription

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5
Q

What are trophectoderm cells associated with the expression of?

A

-Trophectoderm cells are associated with the expression of the Tead4 and Cdx2 transcription factors

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6
Q

What are inner cell mass associated with the expression of?

A

-Inner cell mass cells are associated with the expression of Nanog, Oct4, Sox3, Sal4 transcription factors

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7
Q

What binary decision do the inner cell mass undergo?

A
  • Inner cell mass makes binary decision to give rise to epiblast(EPI) or primitive endoderm(PE)
    • GATA6 transcription factor is associated with the epiblast cell fate
      • Nanog transcription factors is associated with the primitive endoderm cell fate
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8
Q

What transcription factors are expressed in inner cell mass?

A

-Oct3/4, Sox3, Sal4, Nanog transcription factors are expressed in inner cell mass

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9
Q

What transcription factors are expressed in trophectoderm?

A

-Cdx2, Gata4 expressed in Trophectoderm

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10
Q

What are the 2 possible mechanisms for the generation of multiple cell types and polarity?

A
  1. Localised maternal determinant

2. No localised maternal determinant

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11
Q

Localised maternal determinant

A
  • Something passed down the mother
  • The polarity within the embryo is set aside
  • Early polarisation may lead to early asymmetric inheritance
  • The asymmetric inheritance is the reinforced to give rise to 2 different cell types
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12
Q

No localised maternal determinant

A

-External influences can determine polarity of embryo

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13
Q

What does it mean by cells being equivalent up until the 8-16 cell stage?

A
  • Up until the 8-16 cell stage the embryo cells are equivalent
  • This means that if you remove a single cell, it has the ability to give rise to a normal embryo
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14
Q

How are initial differences established between cells?

A
  • It is possible that early asymmetry to occur and early cells aren’t homogeneous
    • This early asymmetry may be provided by the polar bodies
    • As those cells begin to divide, some cells will end up towards the outside of the embryo and some cells will end up towards the inside of the cluster of cells
    • Some cells are partly dependent on position and divide in different ways.
      • Some divide symmetrically and become equivalent
      • Some divide asymmetrically and the cell may take up a different fate.
    • During the 16 cell phase, the outside cells will develop polarity and epithelium phenotype
      • As the blastocyst is formed, there’s differences within the inner cell mass. Some may be lying closer to the blastocoel and may receive signals from the blastocoel.
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15
Q

How is Cdx2 mRNA distributed?

A

-Cdx2 messenger RNA isn’t distributed equally in the embryo.

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16
Q

Where is Cdx2 mRNA more concentrated?

A

Cdx2 mRNA is more concentrated on the polarised outer edges of the embryo

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17
Q

What happens to the concentration of the inherited Cdx2 mRNA when the cells of the outside embryo undergo symmetrical division?

A

-If the cells of the outside undergo symmetrical division, both cells will inherit the same concentration of Cdx2 mRNA

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18
Q

What happens to the concentration of the inherited Cdx2 mRNA when the cells of the outside embryo undergo asymmetrical division?

A

-If the cells divide asymmetrically, the one cell will inherit a greater concentration of Cdx2 mRNA than the other cell.

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19
Q

What is expression of Cdx2 party established by?

A

-Expression of Cdx2 is partly established by cell polarity

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20
Q

What does Cdx2 promote differentiation of cells into?

A

-Cdx2 promotes differentiation of cells into trophectoderm

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21
Q

What transcription factors does Csx2 inhibit?

A

-Cdx2 inhibits NANOG and OCT4 transcription factors

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22
Q

What does Nanog increase expression of?

A

-NANOG increases expression of OCT4

23
Q

What is required for the expression of cdx2?

A

-TEAD4 is required for the expression of Cdx2

24
Q

What formation is tead4 a regulator for?

A

-Tead4 is a regulator for trophectoderm formation

25
Q

What is tead4 required for the expression of?

A

-Tead4 is required for the expression of Cdx2

26
Q

What is Tead4 expressed throughout and where is it activated?

A

Tead4 is expressed throughout the embryo, however only activated in outer cells of embryo

27
Q

What pathway is Tead4 expression controlled by?

A

Controlled by a hippo signalling pathway

28
Q

What does the hippo signalling pathway mediate?

A

Mediates cell differentiation

29
Q

Hippo signalling pathway

A
  1. Outer cells are polarised and effect the actin cytoskeleton
  2. In the absence of hippo signalling, the YAP molecule it moves from the cytoplasm to the nucleus where it acts in concert with Tead4 to turn on the trophectoderm specific genes such as Cdx2
  3. In the inner cell mass, as they don’t have the polarity, hippo signalling is activated. This activates the Lats kinase which phosphorylates Yap molecule, preventing YAP from moving into the nucleus and therefore unable to activate trophectoderm specific genes
30
Q

What is Oct4 associated with?

A

-Oct4 is associated with inner cell mass differentiation

31
Q

What can we add to Oct4 and measure?

A

-Nuclear fluorescence can be added to the nucleus and can measure decay

32
Q

Slow Oct4 kinetics properties

A
  • Low kout
  • Low kin
  • High immobile fraction
33
Q

What is the inference of slow Oct4 kinetics?

A

-Inference is that more accessible Oct4 sites on genomic DNA so more binding therefore lost more slowly

34
Q

What is the fate of slow oct4 kinetics?

A

-Fate of slow oct4 kinetics is that it gives rise to asymmetrical division therefore giving rise to 1 trophectoderm and 1 inner mass cell

35
Q

Fast Oct4 kinetics properties

A
  • High kout
  • High kin
  • Low immobile fraction
36
Q

What is the inference of fast Oct4 kinetics?

A

-Inference is that there are less accessible Oct4 sites on genomic DNA so less binding therefore lost faster

37
Q

What is the fate of fast oct4 kinetics?

A

-Fate of fast oct4 kinetics is that it gives rise to symmetrical division therefore gives rise to 2 trophectoderm cells

38
Q

The methylation of what histone leads to more accessibility for Oct4 binding site and Sox2 binding site on genomic DNA? And what cells does this give rise to?

A
  • Methylation of H3 Arginine 26 is linked with more accessibility for Oct4 binding site and Sox2 binding site on genomic DNA
    - Therefore those cells are more likely to give rise to inner cell mass
39
Q

What does the lack of methylation of H3 arginine 26 linked to and what cell does this give rise to?

A
  • Whereas lack of methylation of H3 Arginine 26 is linked with tighter winding of DNA around Oct4 and Sox2 binding sites
    - Therefore those cells are more likely to give rise to trophectoderm cells
40
Q

Where is DNA methylation most heavily seen?

A

-DNA methylation are seen most heavily in ICM

41
Q

What region of the Elf5 gene is there DNA methylation?

A

There’s DNA methylation of promoter region of Elf5 gene

42
Q

What is the Elf5 gene associated in the acquisition of?

A

-Elf5 is associated in the acquisition of the cell fate of trophectoderm

43
Q

What does the methylation of the promoter region of Elf5 gene prevent the expression of?

A

-Methylation prevents expression of elf5 in the ICM

44
Q

What gene does the Elf5 gene activate?

A

-Elf5 gene activates Cdx2 gene and vice versa, forming a loop

45
Q

What are Elf5 genes modified by and what do they promote in trophectoderm cells?

A

Elf5 gene in trophectoderm cells are modified by acetylation and histone methylation which promotes binding of elf5 and activation of Cdx2

46
Q

Model A of the epiblast and primitive endoderm segregation

A
  • Its possible that there are inductive signals from blastocoel that cause those primitive endoderm cells to be induced just towards the blastocoel side
  • Its possible that there’s also cell sorting so that the primitive endoderm cells end up towards the blastocoel side
  • A combination of both induction and sorting occurs leading to a nicely organised late blastocyst
47
Q

Model B of the epiblast and primitive endoderm segregation

A
  • Waves of symmetric and asymmetric division may play a role in epiblast primitive endoderm division
  • In early waves of asymmetric division gives rise to epiblast progenitors
  • In a second slightly later wave of asymmetric division gives rise to primitive endoderm progenitors
48
Q

What is the acquisition of primitive endoderm cell fate versus epiblast cell fate governed by?

A

The acquisition of primitive endoderm cell fate versus epiblast cell fate is governed by transcription factors Nanog and Gata6

49
Q

What are high levels of nanog expression associated with?

A

-High levels of Nanog expression are associated with epiblast cell fate

50
Q

What are high levels of Gata6 expression associated with?

A

-High levels of Gata6 expression are associated with primitive endoderm cell fate

51
Q

What is communication between both primitive endoderm and epiblast done by?

A

Communication between both primitive endoderm and epiblast is by a secreted growth factor Fgf4

52
Q

What is Fgf4 secreted by and what transcription factor at high levels does it require?

A

-Fgf4 is secreted by epiblast cells and requires high levels of Nanog

53
Q

What does Fgf4 bind to and do?

A

-Fgf4 binds to Fgf4 receptor on Primitive endoderm, activating signalling pathway which leads to the elevation of the Gata6 transcription factor

Development and disease (20 decks)

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