Dit is een samenvatting van het COO over gastrulatie. Hij is met name in het Engels, omdat ik veel zaken geknipt en geplakt heb. Onderwerpen die hierin aan bod komen, zijn: gastrulatie, mesoderm, epiboly, invaginatie, involutie, delaminatie, ingressie, convergente extensie, radiaal, medio-lateraal,...
COO gastrulatie
• “Gastrulation is the process of highly coordinated cell and tissue movement, whereby the
cells of the blastula are dramatically rearranged” (Gilbert).
• “Gastrulation is the process, whereby endoderm and mesoderm move from the outside to
the inside of the embryo, giving rise to internal organs” (Wolpert).
At the end of gastrulation:
- mesoderm and endoderm are located inside the embryo.
- ectoderm is completely covering the outside of the embryo.
- endoderm and mesoderm give rise to internal organs.
Mesoderm, bij sommige dieren (Xenopus) is het al voor de gastrulatie gevormd en bij andere wordt
het tijdens gastrulatie gevormd (Zee-egel).
Gastrulatie beweging, er zijn 5 gastrulatie bewegingen die voor kunnen komen:
- Epiboly, extension of a sheet of cells causing movement of this sheet over presumptive
deeper layers.
- Invagination, indentation of a region of cells resulting in the formation of a 'dimple'.
- Involution, inward movement of a layer of cells.
- Delamination, splitting of a tissue into 2 or more parallel cellular layers.
- Ingression, migration of individual cells from a surface layer to the blastocoel.
Convergent extension, in most species very extensive cell movements take place during
gastrulation. Often cells 'crawl' in-between each other (intercalate) and elongate (extend). This
process is called convergent extension. Two types of convergent extension are known:
- Radial, a double (or multiple) layer of cells
intercalate in such a way that a single layer
of cells is formed. As a result, the surface of
the layer of cells is enlarged. Occurs in for
example embolic movements in the ectoderm (e.g. in Xenopus, Zebrafish).
- Medio-lateral, cells of a single layer intercalate
medio-laterally. Due to this type of
intercalation, the cells form an elongated
structure. Occurs in for example the notochord.
Zee-egel (echinoderm)
De cellen van het blastoderm zijn aan elkaar
gebonden d.m.v. tight junctions. Alle cellen
hebben extern cilia en maken het mogelijk
om de embryo te draaien. De buitenkant is
ook bedekt in een hyaline laag, dat is een
laag extracellulaire matrix eiwitten. Aan de
binnenkant zijn de cellen bedekt met een
basale lamina laag.
, Vegetal plate, after the formation of a blastocoel, the cells at the vegetal side elongate
and form a ‘thick’ layer of cells. This layer is called the vegetal plate.
Apical tuft, At the animal pole, some cells developed very long cilia.
This group of cilia is called the apical tuft.
Mesoderm, the cells that will later form the mesoderm are all
derivatives (descendents) of the micromeres. In Sea Urchin embryos
the micromeres are located at the vegetal pole.
Gastrulatie, in the sea urchin
gastrulation starts in the vegetal
plate in individual cells:
1. Some cells of the vegetal
plate lose their affinity
for their neighbouring
cells and for the hyalin
layer. Moreover, their
affinity for the basal
lamina is increased.
2. These cells change shape...
3. and form filopodia.
4. Finally, these cells leave their epithelial
configuration...
5. ...and migrate into the blastocoel. This process is called ingression.
6. After ingression, the cells that migrated into the blastocoel are
called primary mesenchyme cells (PMC). All PMCs are derivatives
of the micromeres.
Filopodia, zijn dunne dynamische cel extensies van lange actine filamenten die bedekt zijn met
celmembraan. Ze kunnen snel van lengte veranderen en interacteren met andere cellen.
ECM, antibodies against ECM molecules block migration of PMC. The antibodies do not affect
ingression of PMC since the antibodies cannot affect the changes in affinity of the presumptive PCM
cells to the neighbouring cells and it cannot effect the ECM of the hyaline layer (outside the embryo).
Ventro-lateral regions, after ingression, the
primary mesenchyme cells (PMCs) move to
two ventro-lateral regions in the blastocoel.
Here they form calcium carbonate spicules
(spines). Two clusters remain connected by a
small row of primary mesenchyme cells, called
dorsal and ventral chain respectively. The
primary mesenchyme cells form filopodia with
which they 'probe' the surrounding cells and
the extracellular matrix (ECM).
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