6. Gastrulation
Blastomeres are given new positions and neihbors (migration), resulting in the formation of the 3
germ layers of the embryo: ectoderm, mesoderm, endoderm.
Bilaminar trilaminar multi-layered organism. Body axis formation. Internalization of
mesodermal and endodermal tissue and organs.
Cells that neighbour will communicate with one and other and will make a body and will migrate.
Migration, cells come in contact with different cells thereby giving different signals to the cells.
further differentiation.
Overview
- Introduction of gastrulation Themes/questions
- Germ layers, epithelium and mesenchyme EMT
- Gastrulation in:
o Xenopus, Zebrafish, Chicken, Mouse, and Human
- Example Modeling gastrulation
o Physiological EMT
o Pathological EMT
- Example conjoined twins
- Conclusions
Memo: body axes
Goals
1
,Gastrulation gastrula
Themes/questions
- Changes in cell shape and migration
- Germ layer formation: ectoderm, mesoderm, endoderm
o differentiation: pluripotency ® all major embryonic lineages
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 top row is the fertilized egg of
different species. The egg of human
and mice is really small.
Blastula stage:
- Mouse = cup shape
- Human = bilayer
- Frog = ball of cells –
different organization to
the rest
Gastrulation stops when the
organism gets the form of a shrimp.
3 embryonic germ layers
3 germ layers: All the cells in the body are
derived from one of these layers. The
ectoderm is a tight layer, mesoderm is
loose and the endoderm is an epithelial
layer.
Epithelium vs. mesenchyme
Epithelial cell types Mesenchymal cell types
A sheet of cells, tightly bound by adhesive cell Loose cells
junctions. Basement membrane. Migratory cells (individually)
2
, Polar cells top and bottom orientation Apolar no orientation
Migrate as a sheet Mesoderm!
Endo- and ectoderm!
Epithelial-to-Mesenchymal Transition = EMT
Through gastrulation EMT occurs, very important mechanism!!!
Epithelial cells
convert to
mesenchymal cells.
EMT =
Epithelial-to-
mesenchymal transition / MET = Mesenchymal-to-epithelial
transition
TXN-factors (TFs) are gatekeepers of the mesenchymal development.
In the embryo, the ectoderm is epithelial. In the specific sites in the embryo is the gastrulation, the
epithelial will loose the cell junctions and the basal polarity, they acquire features of mesenchymal
cells. They change their transcriptome. The transcriptome of mesenchymal cells is different!
Epithelial cells come loose and they acquire mesenchymal features, they become more migratory.
Epithelial cells are tightly connected and work together.
Black cresent appears, in this location
is where EMT will first take place.
3
Blastomeres are given new positions and neihbors (migration), resulting in the formation of the 3
germ layers of the embryo: ectoderm, mesoderm, endoderm.
Bilaminar trilaminar multi-layered organism. Body axis formation. Internalization of
mesodermal and endodermal tissue and organs.
Cells that neighbour will communicate with one and other and will make a body and will migrate.
Migration, cells come in contact with different cells thereby giving different signals to the cells.
further differentiation.
Overview
- Introduction of gastrulation Themes/questions
- Germ layers, epithelium and mesenchyme EMT
- Gastrulation in:
o Xenopus, Zebrafish, Chicken, Mouse, and Human
- Example Modeling gastrulation
o Physiological EMT
o Pathological EMT
- Example conjoined twins
- Conclusions
Memo: body axes
Goals
1
,Gastrulation gastrula
Themes/questions
- Changes in cell shape and migration
- Germ layer formation: ectoderm, mesoderm, endoderm
o differentiation: pluripotency ® all major embryonic lineages
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 top row is the fertilized egg of
different species. The egg of human
and mice is really small.
Blastula stage:
- Mouse = cup shape
- Human = bilayer
- Frog = ball of cells –
different organization to
the rest
Gastrulation stops when the
organism gets the form of a shrimp.
3 embryonic germ layers
3 germ layers: All the cells in the body are
derived from one of these layers. The
ectoderm is a tight layer, mesoderm is
loose and the endoderm is an epithelial
layer.
Epithelium vs. mesenchyme
Epithelial cell types Mesenchymal cell types
A sheet of cells, tightly bound by adhesive cell Loose cells
junctions. Basement membrane. Migratory cells (individually)
2
, Polar cells top and bottom orientation Apolar no orientation
Migrate as a sheet Mesoderm!
Endo- and ectoderm!
Epithelial-to-Mesenchymal Transition = EMT
Through gastrulation EMT occurs, very important mechanism!!!
Epithelial cells
convert to
mesenchymal cells.
EMT =
Epithelial-to-
mesenchymal transition / MET = Mesenchymal-to-epithelial
transition
TXN-factors (TFs) are gatekeepers of the mesenchymal development.
In the embryo, the ectoderm is epithelial. In the specific sites in the embryo is the gastrulation, the
epithelial will loose the cell junctions and the basal polarity, they acquire features of mesenchymal
cells. They change their transcriptome. The transcriptome of mesenchymal cells is different!
Epithelial cells come loose and they acquire mesenchymal features, they become more migratory.
Epithelial cells are tightly connected and work together.
Black cresent appears, in this location
is where EMT will first take place.
3
