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summary H4: gastrulation by prof. Zwijsen
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summary of the course concepts of developmental biology. chapter 4: gastrulation by prof An Zwijsen
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H4 : GASTRULATIONA. 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.
4
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