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Vertebrate development > Gastrulation > Flashcards

Gastrulation Flashcards

1
Q

Gastrulation

- purpose

A

> generate basic body plan

> specify anterior and posterior of embryo

> generate 3 germ layers

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2
Q

Gastrulation

- involves 2 processes

A

Cell migration + movement

Changes in cell-cell interactions
- cell adhesion

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3
Q

5 basic movements associated with gastrulation

A 
>Epiboly 
>Intercalation 
>Convergent extension 
>Delamination + ingression 
>Involution
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4
Q

Epiboly

A

Cell flatter along apiece-basal axis

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5
Q

Intercalation

A

Double cell layer becomes a single layer

as cells make new contacts with each other

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6
Q

Convergent extension

A

Multilayered sheets of cells become narrower

as cells make new contacts

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7
Q

Delamination and ingression

A

Individual cells change shape + lose contact with their neighbours
- cells become bottle shaped

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8
Q

Involution

A

Epithelium turns around on itself and spreads in direction opposite to basal margin

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9
Q

Amphibian gastrulation

A

Initiated along future dorsal side of embryo (just below equator)
- in the marginal zone

Cells invaginate to form blastopore

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10
Q

Stabilisation of Beta-catenin by Dsh

A

Initially b-catenin present throughout egg

Later degraded by GSK3 mediated phosphorylation
- only in ventral cells

This is prevented in dorsal region by inactivation of GSK3 by Dsh

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11
Q

Dsh

  • name
  • role
A

Dishevelled

Transported to dorsal region from vegetal region by cortical rotation
Protects b-catenin from degradation

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12
Q

Events leading to induction of the organiser

A

Stabilisation of b-catenin on dorsal site

b-catenin translocates to nucleus + associates with Tcf3

-> activation of transcription of Siamois

Siamois + Xlmi1 activated by Vg1 + Nodal
- critical for expression of organiser specific genes
= e.g. goosecoid

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13
Q

Nieuwkoop Centre and the organiser

  • induced by…
  • then specifies…
A

Dorsal most vegetal cell of blastula
- capable of inducing the organiser

The Nieuwkoop Centre specifies the organiser

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14
Q

Candidate molecule responsible for formation of Nieuwkoop Centre

A

B-catenin
= multifunctional protein

Behaves as an anchor for cell-membrane catherine
Can behave as a TF

Component of the Wnt/wingless signalling pathway

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15
Q

Gastrulation in mouse + chick

A

> Origin of PS marks posterior of embryo
Opposite end marks anterior
Dorsal side is where cells migrate inwards
Groove marks left + right

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16
Q

Types of tissue in blastocyst + early post-implantation embryo

A

EPI = Epiblast

PE = parietal endoderm
- primitive endoderm-derived cell population

emVE = Embryonic visceral endoderm
- subset of visceral endoderm cells

DVE = Distal visceral endoderm

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17
Q

Apposition of tissues in blastocyst + early post-implantation embryo

A

EPI - 1 of 3 cell lineages of late blastocyst

PE - forms by EMT, migrates + finally lies next to mural trophectoderm

emVE - overly the epiblast
- contribute to endoderm layer of visceral yolk sac + embryonic gut

DVE - located at distal tip of embryos
- containing the precursors of some of the AVE

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18
Q

Cavitation of epiblast at early post-implantation

- interplay of which 2 signals?

A

promoting cell death vs promoting cell survival

19
Q

Cavitation of epiblast at early post-implantation

- 1st signal

A

= death signal
Produced by adjacent layer of visceral endoderm cells

Acts over short distances to create cavity
- by inducing apoptosis of internal epiblast cells

20
Q

Cavitation of epiblast at early post-implantation

- 2nd signal

A

= survival signal
Mediated through contact with basement membrane positioned at epiblast/visceral endoderm interface

Promotes survival of epiblast cells located adjacent to visceral endoderm

21
Q

Pre-gastrulation cell movement in VE

- general

A

Mesoderm that’s 1st formed migrates posteriorly + will for extra-embryonic mesoderm

  • also moves around laterally + contributes to embryonic mesoderm
22
Q

Pattern of cell movement during embryogenesis

  • Pre-Gastrulation
  • step 1
A

DVE cells move to prospective anterior side of embryo

-> forms AVE

23
Q

Pattern of cell movement during embryogenesis

  • Pre-Gastrulation
  • step 2
A

Lateral movement of AVE after leading population reaches border of epiblast + the extra embryonic ectoderm

24
Q

Pattern of cell movement during embryogenesis

  • Pre-Gastrulation
  • step 3
A

Distribution of VE cell clones that’re derived from ICM of blastocyst

25
Q

Remodelling of the conceptus simultaneous with the onset of gastrulation

A

Thickening of the epiblast
- marks posterior of embryo

Cells from epiblast delaminate + ingress through the streak forming the mesoderm

Anterior most part of primitive streak forms different things in different species

26
Q

What does the anterior most part of the primitive streak form in mice, chicks and amphibians?

A

Mice = Node

Chick = Hensen’s node

Amphibians = Spemann organiser

27
Q

Early gastrulation cell movement

- general

A

Mesoderm in extra embryonic region develop intercellular lacunae
- which then rise to form exocoelom

Formation of amniotic folds

28
Q

Early gastrulation cell movement

- step 1

A

Movement of endoderm accomplished by coordination of movement of AVE to extra embryonic yolk sac

29
Q

Early gastrulation cell movement

- step 2

A

Anterior-proximal movement of more distally located VE

30
Q

Early gastrulation cell movement

- step 3

A

Anterior displacement of definitive endoderm

31
Q

Early gastrulation cell movement

- step 4

A

Movement of mesoderm commences with ingression of progenitor cells through the primitive streak

32
Q

Early gastrulation cell movement

- step 5

A

Anterior spreading of the tissue sheet

33
Q

Morphogenesis of mesoderm and endoderm

A

At the primitive streak
- cells under EMT, ingress + migrate away to form mesoderm

Cells fated to form the definitive endoderm undergo MET + egress into epithelium of emVE

34
Q

Node

- what is it?

A

Group of (~200) specialised cells located at most anterior aspect of PS

Equivalent of the organiser

35
Q

Node

- what does it do?

A

Can induce additional anterior structures when transplanted into ventral side of Xenopus embryo

Causes duplication of digits in developing avian embryo

36
Q

Node

- heterotopic grafting

A

To a posterolateral position of the node

-> leads to induction of a 2nd neural axis

37
Q

Network of signalling activity leading to patterning of the VE
- step 1

A

In ExE
- nodal precursor protein
(produced by epiblast)
acts by active receptors 1B + 2A to activate transcription of Furin + Pcsk6

38
Q

Network of signalling activity leading to patterning of the VE
- step 2

A

ExE secretes convertase enzymes encoded by Fruin + Pcsk6

39
Q

Network of signalling activity leading to patterning of the VE
- step 3

A

Convertase enzymes cleave the nodal precursor to processed Nodal

40
Q

Network of signalling activity leading to patterning of the VE
- step 4

A

Nodal signals from epiblast repress genes e.g. Hnf4, Gata4, Ttr + Furin
- which are normally expressed in the ExVE after the DVE stage

41
Q

Network of signalling activity leading to patterning of the VE
- step 5

A

Simultaneously

nodal signals maintain expression of EmVE genes e.g. Lhx1, Fgf5…

42
Q

Network of signalling activity leading to patterning of the VE
- step 6

A

Nodal + GDF3 working with cripto (a co-receptor)
- generate a proximal-distal gradient of signalling activity in the embryo

= crucial for specification of DVE

43
Q

2 signalling centres in mammals

A

Node
- responsible for creation of body axis

AVE

  • Node with signalling from AVE responsible for creation of anterior structures
44
Q

Patterning of the anterior-posterior axis

- FGFs + RA

A

Expression of Nodal + gradients of Wnts, BMP + FGFs in the posterior part of the primitive streak

FGF8 necessary for ingression of mesodermal cells through primitive streak

RA gradient + FGF8 regulates AP patterning regulating the Hox through the Cdx genes

Vertebrate development (12 decks)

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