After Midterm 1 - Blastulation, Gastrulation and Body-Axis Formation in the Chick Flashcards
In the chick, cell division occurs in a small island of cells in the animal pole, floating on top of the giant yolk, called the _________.
blastoderm or blastodisc
At the very beginning, the blastoderm of the chick is multi-layered. Then the inner layers shed off/die, leaving only a single layer called the ________
epiblast.
The space between the epiblast and the yolk, prior to the formation of the hypoblast, is referred to as the ____________
Subgerminal space
What is the area pellucida?
The portion of the blastoderm that contains the single-cell layer epiblast and is the inner portion of the blastoderm, if you’re looking down at the embryo as a circle.
What is the area opaca?
The cells surrounding the periphery of the area pellucida, which are several layers thick (the inner cells have not shed/died off), not one-cell layer thick like the area pellucida.
After the formation of the hypoblast, the space between the hypoblast and epiblast is the ________
blastocoel.
True or false. Before even gastrulation begins, the dorsal-ventral axis and the anterior-posterior axis of the chick is already established
True
Where is the posterior marginal zone (PMZ) of the chick blastoderm located?
It’s located in one place where the area opaca meets the area pellucida.
What is the koller’s sickle?
A structure that forms at the anterior-most edge of the posterior marginal zone.
The hypoblast is formed from two sources. Explain
The hypoblast is formed from primary and secondary hypoblast cells.
Primary hypoblast cells are epiblast cells that have delaminated and formed islands of cells called hypoblast islands.
Secondary hypoblast cells form and extend from the Koller’s sickle.
The hypoblast is formed as secondary hypoblast cells extending from the Koller’s sickle joins hypoblast islands together.
How do you know where is anterior and where is posterior of the chick embryo before gastrulation?
Where the Koller’s sickle forms is the posterior end, and the opposite end of the blastoderm is the anterior end.
Where is the wnt-signalling pathway, and therefore beta-catenin, localized in the chick embryo?
Localized in the Koller’s sickle.
Homologous in function to the micromeres in the sea urchin and the organizer/cells of the dorsal blastopore lip of the xenopus
What structure is it whose formation tells us that the chick embryo has begun gastrulation?
the primitive streak
How does the primitive streak form?
Cells at the Koller’s sickle, in between the epiblast and hypoblast layer, will begin to extend via convergent extension from posterior to anterior, and these cells extending in between the epiblast and hypoblast forms the primitive streak.
What’s the middle of the primitive streak called?
The primitive groove. The primitive streak is the whole structure, including the ridges around the primitive groove.
What happens at the primitive “groove”?
Epiblast cells begin to go through first a small invagination, following by those cells currently in the primitive groove undergoing ingression via EMT. These ingressing epiblast cells will travel into the blastocoel.
The cells that go through EMT in the chick embryo primitive groove are ______cells
epiblast cells
Does the primitive streak elongate across the entire area pellucida?
No, but it does extend along the majority of the area pellucida.
The primitive streak of the chick is analogous FUNCTIONALLY to the ________ in other model embryos, and STRUCTURALLY/MORPHOLOGICALLY to the _________ of the Xenopus embryo
Functionally, the primitive streak acts like the blastopore
Morphologically, the primitive STREAK is like an extended blastopore lip.
Is the process of EMT that happens in chick gastrulation similar to EMT in sea urchin PMCs?
No. Different proteins and receptors are involved, but the steps are the same (lose affinity to x, gain affinity for y).
What happens to the first set of epiblast cells that ingress into the blastocoel in the chick? I’m referring to the cells at the leading edge of the primitive groove? What germ layer do these cells become?
The cells that first ingress displace the hypoblast layer at the bottom of the blastocoel completely.
These cells become endoderm.
What happens to the rest of the epiblast cells (not at the leading edge) that ingress into the blastocoel of the chick? What germ layer do these cells become?
These cells stay in the blastocoel and give rise to mesoderm.
What happens to the epiblast cells that do not ingress/go into the primitive groove?
These cells undergo epiboly, and form the ectoderm of the chick
Describe the migration of cells in chick gastrulation after the formation of the primitive groove, in full.
The cells that first ingress/go through EMT from the primitive groove displace the hypoblast layer at the bottom of the blastocoel completely. These cells later become endoderm.
Cells that ingress/go through EMT afterwards remain in the blastocoel and give rise to mesoderm.
Cells that do not ingress/go through EMT via the primitive groove undergo epiboly and form the ectoderm of the embryo.
