Which cell movements really do occur in Avian's gastrulation?

Question

I thought it was Ingression, because the cells are migrating away from epiblast to form the primary hypoblast. But the key book said that it is supposed to be delamination. So can you explain why is it delamination?

Answer 1

During avian gastrulation, both ingression and delamination occur to form the primary hypoblast. Ingression involves the migration of cells from the epiblast into the space between the epiblast and hypoblast, which is known as the subgerminal cavity. This movement results in the formation of mesoderm and endoderm.

On the other hand, delamination involves the splitting of cells within the epiblast layer, resulting in the formation of a new cell layer, the hypoblast. The hypoblast layer forms by the separation of cells from the inner surface of the epiblast.

Therefore, both ingression and delamination occur during avian gastrulation to form the primary hypoblast. It is likely that the key book you mentioned was referring specifically to the process of hypoblast formation when it used the term "delamination."

Answer 2

1. Invagination: The primitive streak forms and cells at the anterior end of the streak invaginate into the blastocoel to form a structure called the mesodermal plate.
2. Epiboly: The mesodermal plate spreads laterally by epiboly to cover the entire surface of the yolk sac.
3. Delamination: The mesodermal plate splits into two layers, the dorsal and ventral mesoderm.
4. Ingression: Cells from the dorsal mesoderm ingress between the two mesoderm layers to form the notochord.
5. Convergence and Extension: The cells of the anterior and posterior primitive streaks converge and extend anteriorly to form the head process and posteriorly to form the tail bud.

So, invagination, epiboly, delamination, ingress, convergence, and extension are the cell movements that occur during avian gastrulation.