15 Flashcards
What are the differences between the Nieuwkoop centre and organizer in amphibians and in fish?
They have similar roles, but the fish organizer is called the embryonic shield and the Nieuwkoop centre is the yolk syncitial layer below the shield.
How does B-catenin act in organizer formation in zebrafish verus in amphibians?
Similarly. B-catenin accumulates in the Nieuwkoop centre and just above it (which is where the embryonic shield/organizer will be located). B-catenin activates squint (nodal-like) and bozozok (siamois ortholog) which activate chordino, noggin, goosecoid, and dickkopf (BMP and Wnt inhibitors)
Where is Hensen’s Node? What is its role?
It is the site of the amniote organizer (though it’s just called the node in mammals) and is at the anterior end of the primitive streak. It expresses BMP inhibitors.
What are the extraembryonic membranes and their functions?
Yolk sac: nutrition
Chorion: gas exchange
Allantois: waste
Amnion: protection
How does cleavage in the chick occur?
There’s a lot of yolk cleavage prior to laying, then the MZT occurs at 128 cells, then the subgerminal cavity forms, lots of the epiblast cells slough off and die, and the inner area pellucida is formed which is the epiblast from which the body of the embryo develops.
What is the role of the primitive streak in chick development?
It’s where gastrulation occurs. The streak extends posterior->anterior until about 18-20 hours, at which point Hensen’s node is formed and gastrulation starts, then the streak shortens and allows ant->post development to occur. Eventually the streak disappears. Cells undergo EMT to enter through the streak, no involution.
How can you predict the fate of cells entering the primitive streak?
Based on time and location. Earlier cells tend to form more anterior structures, and more anterior entry cells tend to form more dorsal structures.
Where is noggin expressed at this stage?
In the epiblast, it does not ingress. It blocks BMP expression and activity around the anterior primitive streak, all BMP expressing cells are endo or meso.
