samenvatting H4: gastrulation van prof Zwijsen

H4 : GASTRULATION
A. ZWIJSEN




Inhoudsopgave
4.1 INTRODUCTION OF GASTRULATION......................................................................1
4.2 GERM LAYERS..................................................................................................... 3
4.3 EMT: EPITHELIAL-TO-MESENCHYMAL TRANSITION AND MET: MESENCHYMAL-TO-
EPITHELIAL TRANSITION............................................................................................ 4
4.4 GASTRULATION IN FROG......................................................................................6
4.4.1 EPIBOLY, INVOLUTION, EMT....................................................................................................... 7
4.4.2 BLASTULA TO GASTRULA............................................................................................................ 8
4.4.3 FATE MAP............................................................................................................................... 8
4.4.4 SIGNALS FOR MESODERM FORMATION......................................................................................... 10
4.5 GASTRULATION IN ZEBRAFISH...........................................................................14
4.6 GASTRULATION IN CHICKEN...............................................................................17
4.7 GASTRULATION IN MOUSE.................................................................................18
4.7.1 PRIMITIVE STREAK: EMT........................................................................................................... 21
4.7.2 FIRST MOLECULAR APPEARANCE OF A-P AXIS PRECEDES GASTRULATION.............................................22

4.8 GASTRULATION IN HUMAN.................................................................................23
4.8.1 HUMAN VS MOUSE EMBRYO...................................................................................................... 26

4.9 MODELLING GASTRULATION...............................................................................26
4.9.1 EMBRYO DEVELOPMENT IN A DISH: EMBRYOIDS.............................................................................26

4.10 PHYSIOLOGICAL EMT.......................................................................................28
4.11 PATHOLOGICAL EMT........................................................................................29
4.12 CONCLUSIONS................................................................................................. 31




4.1 INTRODUCTION OF GASTRULATION


1

,Memo: body axes:




Goals of this lecture:

 Comprehension of concepts like:
o Organizer
o Gastrulation
o EMT
o MET
o convergent extension
 Comprehension of features of gastrulation stages of embryos
 Comprehension of cues that trigger gastrulation
 Detecting (dis)similarities in gastrulation processes between species
 Linking gastrulation with other EMT processes, with pathology

The developing:

1) Fertilization
2) Cleavage → blastula
 Hallow ball with clump of cells
 2 germ layers:
o Endoderm
o Ectoderm
3) Gastrulation → gastrula
 Because of migration: cells are given new positions and neighbors with transformation
of epithelial cells into mesenchymal cells (EMT) and endodermal cells.
 Gastrulation results in formation of the third germ layers. The 3 embryonic germ
layers are:
o Ectoderm
o Mesoderm (is formed in this stage)
o Endoderm
 during gastrulation: the germ layers become more districted
 It goes from: Bilaminar  trilaminar  multilayered organism
 Body axis formation
 Internalization of mesodermal and endodermal tissues and organs so formation of a
primitive body plan

4) Folding – neurulation (formation of nerve station) – gastrointestinal track
5) Organogenesis
Themes/questions:

 Changes in cell shape and migration
 Germ layer formation: ectoderm, mesoderm, endoderm
o differentiation: pluripotency ® all major embryonic lineages

2

, o EMT - MET
 What signalling events coordinate gastrulation? Where?
 How are body axes & primitive body plan established?
 How to study (human) gastrulation in vitro?
 Are there other gastrulation-like processes during development?
 What is the link between gastrulation and pathology?


The grey line is the scale bar to show
the difference in size and shape.

What do we see?

 Frog and zebrafish: a ball of cells.
 Chicken: at stage of blastula is the
embryo a disk sheet consists of 2
cell layers
 Mouse: ball with fluid cavity and a
clump of cells, cup shaped
 Human: resembles little bit a
chicken because it is also a 2-layer
disk



After process of gastrulation looks the embryos very similar. Gastrulation stops when the
organism gets the form of a shrimp.



4.2 GERM LAYERS

There are 3 germ layers. They are represented by 3 colors. Ectoderm (blue), mesoderm (red) and
endoderm (yellow). All the cells in our body comes out of one of these 3 layers.




The 3 germ layers:

Ectoderm:

 Columnar cells that are clewed together
 Polar cells
3

,  Tight layer, the tissue is tightly sealed together
 Becomes:
o Nervous system
o Neural crest cells

Mesoderm:

 Loose cells with little connections with each other
 Apolar cells
 Becomes:
o Skeleton-muscular system
o Connective tissue
o Blood
o Cardiovascular system
o Urogenital system

Endoderm:

 Tightly sealed
 Polar cells
 Becomes:
o Gastro-intestional system
o Associated organs (bv: lungs, liver, pancreas,…)

Ecto- and endoderm are sheet like structures = epithelium  they are polar cells (top and bottom
orientation).

Epithelial vs mesenchymal cells:

 Epithelial cell types:
o Sheet of cells
o Tightly bound by adhesive cell junctions
o Basement membrane

 Mesenchymal cell types:
o Loose cells
o Migratory cells (individually)

Mesoderm cells are often mesenchymal. Mesoderm cells can also condensate into epithelial cells.




4.3 EMT: EPITHELIAL-TO-MESENCHYMAL TRANSITION AND MET:
MESENCHYMAL-TO-EPITHELIAL TRANSITION

Important mechanisms.




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