Gastrulation

Question 1

After the ICM and blastocoel and Trophectoderm are produced, which cavity forms next?

Answer 1

Amniotic cavity above the epiblast.

Question 2

How does the primitive streak form?

Answer 2

Cells on the surface of the epiblast involute inwards to form the start of the primitive streak. These cells undergo an epithelial to mesenchymal transition to delaminate and be able to migrate.

Question 3

Where do the three germ layers originate from?

Answer 3

Ectoderm = Cells remaining in the epiblast or cells between the amnion and epiblast
Mesoderm = Cells which have involuted through the primitive streak and move between epiblast and hypoblast
Endoderm = Hypoblast

Question 4

How is the bilaminar disc converted to a trilaminar disc?

Answer 4

The cells within the center of the primitive streak ingress/involute downwards to form a layer between the epiblast (ectoderm) and hypoblast (endoderm) to form the mesoderm. A body axis is created.

Question 5

What is the next stage?

Answer 5

Formation of the notochord within the midline of the mesoderm. It signals cells within ectoderm to form the neural plate.

Question 6

How does Drop-seq work for identifying the cells and what mRNA they produce for determining their role in forming the three germ layers?

Answer 6

1. Each cell (from heterogenous population of cells) joins with a barcoded bead in an oil droplet
2. Cell’s mRNA is captured by barcoded primers on the bead
3. Reverse transcribe the mRNA into cDNA
4. Beads are pooled together and the cDNA is amplified
5. High throughput sequencing of cDNA derived from individual cells and determine gene expression profile for each cell

Question 7

Will show specific markers for cell types across the three germ layers. Can construct a cell-type map which indicates the different tissues.