Gastrulation Flashcards
Describe the cell movement extension/epiboly
sheet of cells expands in some way to cover a greater surface area. Can be done many ways - maybe cell shape changes and flattens (sea urchin ectoderm), or maybe they go through radial intercalation (Xenopus ectoderm), which is where multiple cell layers fuse to form fewer layers that are more spread out and covering a larger SA.
What is radial intercalation ?
A type of epiboly where multiple overlying cell layers fuse to form fewer layers that are more spread out and covering a larger SA.
Name, don’t describe, the three forms of internalization cell movement?
- involution
- ingression
- invagination
What is…
- invagination
- ingression
- involution
- infolding a layer of cells into the interior of an embryo, like pushing a finger into a balloon
- Internalization of individual cells into the interior of an embryo, they are loosely organized with one another
- Outer cell layers migrate inward but stay close to the basal lamina of the epithelial cells that are the exterior of the embryo
What is convergent extension/mediolateral intercalation/
cells fuse together in the same plane, so that the sheet of cells extends in a certain direction perpendicular to the fusing of cells.
What is delamination?
The splitting of one layer of cells, into two layers of cells
In the 60 cell stage of the sea urchin embryo, what structures do the different tiers of cells eventually become?
the animal tiers form ectoderm/epidermis
The yellow forms the gut
The macromeres (large red, non-micromere parts) become non-skeletogenic mesenchyme
The micromeres become skeletogenic mesenchyme, eventually forming the skeletal rods of the sea urchin embryo.
Can cell movements be independent of one another?
No, many forms often work in tandem. For example, if invagination is happening at the vegetal pole, epiboly/extension needs to happen at the animal pole to maintain the shape of the embryo.
What are the four cell movements that drive gastrulation in the sea urchin?
- ingression of micromeres to give rise to skeletogenic mesenchyme/primary mesenchyme
- Invagination of the endomesodermal cells of the vegetal tier.
- epiboly of ectodermal cells to maintain shape of embryo after invagination and to cover whole embryo’s exterior
- convergent extension - archenteron extending from the vegetal pole to the animal pole.
What lines the blastocoel in the sea urchin?
The basal lamina of epithelial cells, and extracellular matrix (ECM). Stella uses these terms interchangeably to refer to extracellular matrix.
True or false, the extracellular matrix lining the blastocoel consists of many structural proteins
true.
In the sea urchin, how do micromeres become primary mesenchymal cells/skeletogenic mesenchymal cells?
Do the cells undergo ingression before or after this process?
Through a process called EMT (Epithelial-Mesenchymal Transition).
The mesenchymal cells will undergo ingression after this.
What causes EMT to happen to micromeres, triggering the early gastrulation phase in sea urchins?
It is believed beta-catenin localization, and associating gene regulation, is responsible for triggering EMT and gastrulation in the sea urchin.
What four processes must occur for after EMT for the primary mesenchymal cells (PMCs) to undergo ingression in the sea urchin?
- The PMCs must lose affinity with the hyaline layer of the embryo - reduce expression of hyaline receptors.
- The PMCs must lose affinity with neighbouring cells - expression of tight junctions and adherens junctions must be reduced.
- The PMCs must gain affinity for the basal lamina/ECM - increase expression of the receptor “integrin” to increase interaction with a protein found in the ECM; laminin.
- The PMCs need a way to increase motility - form filopedia.
When PMCs undergo ingression, where do they specifically move INITIALLY? And why?
They initially move to the vegetal-lateral walls of the blastocoel. They move there because filopedia can sense and make contact with the ECM and cell membrane of epithelial cells in that region.
