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BB20149 > Pre and post implantation mammalian development > Flashcards

Pre and post implantation mammalian development Flashcards

1
Q

What are the physical characteristics of mammalian embryos?

A

The egg is small and lacks yolk. The fertilisation and development is in the maternal environment.

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2
Q

What are the some of the developmental characteristics of mammalian embryos?

A

The early division is slow and cleavage leads to formation of equal blastomeres. Lineage commitment occurs early in development and the development is regulative.

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3
Q

What is the zona pellucida?

A

A translucent matrix of glycoproteins that surrounds the mammalian oocyte. It is critical to successful fertilisation.

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4
Q

What is the function of the zona pellucida?

A

It only allows species-species fertilisation, prevents polyspermy and enables the acrosome reaction for the successful adhesion and penetration of the sperm cell.

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5
Q

What are the major proteins of the zona pellucida and what are their roles in the mouse?

A

In general they bind to capacitated spermatozoa. ZP3 - allows species specific sperm binding, ZP2 - mediates subsequent sperm binding, ZP1 - cross-links ZP2 and ZP3.

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6
Q

What are the key goals for the early stages of mammalian development?

A

Conversion of the fertilized egg to a multicellular state, set aide the cells that form the embryo and those that will form the membranes surrounding the embryo (contributing to the placenta), and lead to the formation of the maternal foetal connection - the placenta which is essential for nurturing the embryo.

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7
Q

What do the different types of cleavage depend on?

A

The yolk content and the distribution of yolk.

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8
Q

What are the two cleavage planes?

A

The meridional plane and the equatorial plane.

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9
Q

What are the characteristics of cleavage in mice?

A

It is rotational and holoblastic (complete cleavage into separate blastomeres).

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10
Q

What potency do mice blastomeres have at the 2 and 4 cell stages?

A

Totipotent - can give rise to any cell type.

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11
Q

What are the key stages in mouse preimplantation development?

A

Cleavage to form blastomeres, compaction (with formation of morula), first differentiation and blasocyst stages, restriction of potency and hatching and implantation.

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12
Q

What is cleavage?

A

Cell division without intervening growth.

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13
Q

What are the stages of the embryo following the 2 cell stage?

A

4 cell stage and then the morula.

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14
Q

What is the morula?

A

Ball of cells following cleavage.

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15
Q

What occurs in compaction?

A

The cells change shape, gap junctions form between adjacent cells and outer cells become different from inner cells (different genes are expressed in outer and inner)>

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16
Q

What is the loose definition of compaction?

A

It is the critical first morphological event in the preimplantation development of the mammalian embryo. It is characterised by the transformation of the embryo from a loose cluster of spherical cells into a tightly packed mass.

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17
Q

What is compaction a key step in?

A

The establishment of the first tissue-like structures of the embryo.

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18
Q

What do the outer and inner cells of the morula form?

A

The outer cells form the trophectoderm and the inner cells form the inner cell mass.

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19
Q

What does the inner cell mass further differentiate into?

A

Primitive endoerm and the epiblast.

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20
Q

What is the inside-outside model of trophectoderm specification in the mouse embryo?

A

The cells on the inside and outside of the embryo receive different amounts of cell contact which is translated into differences in transcription factor expression.

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21
Q

What is the cell polarity model of trophectoderm development in the mouse embryo?

A

The presence or absence of an apical domain is translated into differences in transcription factor expression.

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22
Q

What is the final model of trophectoderm development in the mouse embryo?

A

LAts1/2 kinases phosphorylate Yap inside of the cells that prevent its movement into the nucleus. Without Yap, Tead4 cannot induce the expression of Cdx2. In outside cells, Lats1/2 are inactive and Yap can move into the nucleus and activate Cdx2. Increased cell-cell contact on the inside of the embryo may activate LAt1 and Lat2 via the hoppo signalling pathway, while some component of the apical domain may inhibit Hippo signalling and Lat1/2 activity in outside cells.

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23
Q

What is the first lineage segregation?

A

The trophectoderm (TE) vs the inner cell mass (ICM).

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24
Q

What is TE/ICM segregation initiated by?

A

Two rounds of asymmetric cell divisions that result in two spatially and molecularly distinct cell populations.

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25
Q

What is the first step in the TE/ICM segregation?

A

Cells acquire a unique inner or outer spatial localisation.

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26
Q

What is the second step in the TE/ICM segregation?

A

Asymmetric distribution of polarity RNA and proteins results in asymmetric inheritance of these factors by the daughter cells.

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27
Q

What does asymmetry depend on in TE/ICM segregation?

A

The orientation of the division plane relative to the polarity axes.

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28
Q

What are the two division planes that can occur in TE/ISM segregation?

A

A division plane parallel to the axes of polarity gives rise to two, outer polar daughter cells similar to the mother cell, whereas a division plane perpendicular to the axes of polarity results in one outer polar cell similar to the mother cell and one inner apolar cell that is different from the mother cell.

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29
Q

What are the two pathways important the TE/ICM segregation?

A

The hippo pathway and the Ras/MAPK pathway.

30
Q

What are CDx2 and Gata3?

A

TE-specifying genes.

31
Q

What is required for the expression of Cdx2 and Gata3 in outer cells?

A

The transcription factor Tead4 and the co-activator Yap.

32
Q

How is the hippo pathway activated in inner cells?

A

Increased cell-cell contact.

33
Q

What is the hippo pathway?

A

Phosphorylation of Yap by the protein kinase Lats1/2, exclusion of Yap from the nucleus and inhibition of Tead4 transcription.

34
Q

What happens in later stages of TE/ICM segregation?

A

Specific transcriptional networks are established to reinforce cell fate decision.

35
Q

What factors are important to maintain the TE?

A

Cdx2, Eomes and Gata3. They function by inducing each other and repressing ICM genes.

36
Q

What factors are important in the ICM?

A

OCt4, Nanog, Sox2, Sall4. They repress TE-specifying genes in these cells.

37
Q

What are the transcription factors important for the generation of the first three lineages in the blastocyst?

A

Oct4, Cdx2, Naog, Gata6.

38
Q

What is Oct4?

A

A protein observed in all blastomeres throughout early cleavage stages due to maternally encoded protein.

39
Q

What happens to Oct4 at the blastocyst stage?

A

It is gradually downregulated in the outer trophectoderm cells by Cdx2 through direct physical interaction and transcriptional regulation.

40
Q

What is Cdx2?

A

A protein detected beginning at the 8-16 cell stage. Its initial expression is random. By early morula to early blasocyst stages the expression is ubiquitous but higher in outer, apically polarized cells.

41
Q

What are Nanog and Gata6?

A

They are detected from the 8-cell stage and are both proteins expressed uniformly in all cells until the early blasocyst stage. The expression of Nanog is downregulated in outer cells by Cdx2 and in a subpopulation of the ICM. Gata6 expression is maintained by Grb2-dependent signalling. THe subpopulation o Nanog in the ICM is due to Grb2-dependent signalling.

42
Q

What happens in terms of Nanog and Gata6 in the late blastocyst stage?

A

ICM cells express Nanog or Gata6 exclusively.

43
Q

What happens in blastocyst formation?

A

Epithelialization of outer layer of cells and establishment of polarity. There is vectorial fluid transport.

44
Q

PE

A

Primitive endoderm

45
Q

EPI

A

Epiblast

46
Q

What is the second lineage segregation?

A

The ICM to the Primitive endoderm and the epiblast (PE/EPI).

47
Q

What initiates the second lineage segregation (1)?

A

Differential expression of Gata6 and Nanog.

48
Q

What do Gata6 cells form?(1)

A

The primitive endoderm.

49
Q

What do Nanog expressing cells form?(1)

A

The epiblast.

50
Q

What is the salt and pepper organisation?(1)

A

Random distribution between eachother.

51
Q

What happens to the PE and EPI progenitors distribution?(1)

A

They sort into two organised layers.

52
Q

How is sorting of the progenitors for the PE and EPI carried out?(1)

A

Differential adhesion and signals coming from either the TE or blastocoel and forces exerted by the blastocoels or the TE.

53
Q

How are the progenitors for PE/EPI achieved?(1)

A

Forces exerted by the blastocoels or the TE.

54
Q

What determines the differential expression of Nanog and Gata6?(2)

A

FGF signalling.

55
Q

What do ICM cells express initially?(2).

A

Both the growth factor Fgf4 and the receptor Fgfr2.

56
Q

What does Fgfr2 do? (2)

A

It activates the expression of Gata6 that antagonizes Nanog. Nanog cells later on upregulate Fgf4 but lose Fgfr2 - this is required for the reinforcement of Gata6 transcription.

57
Q

What leads to complete loss og Gata6 in the EPI?(2)

A

Nanog expressing cells losing Fgfr2 (required for the reinforcement of Gata6 transcription), and with the Nanog inhibition of Gata6 - leads to the complete loss of Gata6 in the EPI.

58
Q

What do Gata6 expressing cells retain?(2)

A

The expression of Fgfr2 which is activated by Fgf4 secreted from EPI cells.

59
Q

What is nanog inhibited by?(2)

A

Fgfr2 and Gata6 - whereas Gata6 enhances its own expression.

60
Q

What are some PE-specifying genes?(2)

A

Sox17, Gata4.

61
Q

What is the regulatory loop formed and what is it made up of?(2)

A

It is made up of Fgfr2, Gata6, Sox17 and Gata4. It is required to maintain the PE identity.

62
Q

What is blastocyst hatching essential for?

A

Implantation of mammalian embryos.

63
Q

What is blastocyst hatching?

A

Emerging out of the zona pellucida.

64
Q

What is important in blastocyst hatching?

A

Mechanical and enzymatic factors.

65
Q

Why does hydrostatic pressure increase within the blastocoel?

A

Volume of the blastocyst increases 2-3 fold due to intake of fluid.

66
Q

What happens to the trophoblast epithelum during hatching of the blastocyst?

A

It stretches due to the intake of fluid.

67
Q

What is believed about an enzyme in blastocyst hatching?

A

It is believed that a protease-like enzyme is involved in the hatching that is released by the blastocyst or the endometrium.

68
Q

What are the stages from one cell stage to early egg cylinder?

A

1 cell, 2 cell, 8 cell, early morula, late morula, blastocyst, late blastocyst, early egg cylinder.

69
Q

What happens in the formation of the early egg cylinder?

A

There is tilting o the ectoplacental cone away from the proximodistal axis.

70
Q

What are the characteristic features of the early blastocyst?

A

Fluid-filled cavity, blastocoel.

71
Q

How is development different in humans compared to mouse?

A

Similar but compaction occurs at the 16-cell stage and the mutually exclusive expression patterns of Cdx2 and Oct4 are not established intil the late blastocyst stage. The expression of Nanog and Gata6 in human development haven’t been characterised yet.

72
Q

What are the important implications from understanding early mouse development?

A

Similar in humans, greater understanding of similarities and differences - improved reproductive technologies and for deriving ES cells, helped development of methods for culture and preimplantation embryos, prenatal diagnosis, transgenic and kmockout mice.

BB20149 (16 decks)

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