Gastrulation PLS FINISH Flashcards
What is gastrulation?
The formation of a gastrula - word comes from gaster (meaning to have a stomach)
What is the purpose of gastrulation?
Generate the basic body plan which serves as the blueprint for the subsequent development of the embryo. It specifies the anterior and posterior of the embryo and generates the three germ layers.
What are the three germ layers?
The ectoderm, mesoderm and the endoderm.
What are the two bilayers before gastrulation?
The intracellular matrix and the trophectoderm. This is the blastocyst stage. (ectoderm and endoderm)
What does gastrulation involve?
Cell migration and movement, changes in cell-cell interactions in cell adhesion.
What are the cell movements associated with gastrulation?
Epiboly, intercalation, convergent extension, delamination and ingression, involution.
What is epiboly?
The cells flatten along their apico basal axis.
What is intercalation?
When a double cell layer becomes a single layer as cells make new contacts with each other. (the two layers “flatten” into each other)
What is convergent extension?
When a multilayered sheet of cells become narrower as cells make new contacts - similar process to intercalation.
What is delamination and ingression?
Individual epithelial cells change shape and lose contact with their neighbours. The cells become bottle shaped. In delamination a curve can be formed in the cells with the “curved” cells being bottle shaped.
What is involution?
The epithelium turns around on itself and spreads in the direction opposite to its basal margin.
Where is gastrulation initiated in amphibians?
Along the future dorsal side of the embryo just below the equator - this is the marginal zone.
What is the first stage in gastrulation?
A group of cells migrate to form the presumptive epidermis.
Where the sperm enters the egg cell, what will this form?
This will form the ventral side and the opposite side will be the dorsal side.
What is the second stage in gasrtrulation?
Cells invaginate to form a slit like opening called the blastopore.
When does differentiation between animal and vegetal pole occur?
Before fertilisation.
What are the differences between the animal and vegetal pole?
Animal pole is highly pigmented and has rapidly dividing cells, vegetal pole is yolky.
What is the blastocoel cavity displaced with?
Ectoderm and endoderm - mesoderm.
Where is the dorsal lip blastopore formed?
The opposite side to sperm entry.
What experiments did Spemann and Mangold do?
They took cells from the dorsal blastopore lip from a donor and transferred to a donor blastopore lip. It was found that the embryo where the embryo took place gave rise to an embryo with two axes.
What happens to b-catenin throughout gastrulation?
It is degraded by GSK3 mediated phosphorylation in the ventral cells.
How is phosphorylation of b-catenin prevented in the dorsal region?
Inactivation of GSK3 by dishevelled (Dsh).
How does Dsh get to the dorsal region?
It is transported from the ventral region by cortical rotation. This protects the b-catenin from degradation.
What are the events leading up to the induction of the organizer?
There is stabilisation of beta-catenin on the dorsal side which then translocates to the nucleus and associates with Tcf3. This leads to the activation of transcription of Siamois, which together with Xlim1 (activated by Vg1 and Nodal) is critical for the expression of organizer specific genes such as goosecoid.
What were experiments that showed the vegetal cells initiate gastrulation?
Ventral cell transplanted into irradiated amphibian embryo. If allowed to develop this occurred normally. If it wasn’t transported, only a ventral piece formed. If a ventral cell was transported to a normal recipient, two axes were formed.
