Early development Flashcards
What stage is compaction accomplished?
8/10 cell stage
At what cell stage is the ICM versus trophoblast decision made
16 cell stage/morula
At what stage is cavitation initiated at?
32 cell
At which stage does hatching from the Zona occur
107 cell/blastocyst
At what stage do zygotic cells activate?
Around eight cell
What are imprinted genes?
When only the maternal or paternal copy is expressed
What was observed in a zygote with two egg derived pronuclei
Nearly normal Embry
Small placenta
What was observed in a zygote with two sperm derived pronuclei?
Stunted embryo
Nearly normal placenta
In what type of vertebrates does imprinting occur in?
Mammals
How many imprint genes have been identified?
About 150
What is the first decision of the blastomere?
ICM versus trophoblast
What is the allantois?
Acts as waste storage, located at the posterior end of the embryo.
What is the purpose of the chorion?
Enables gas exchange.
What type of cleavage do mammalian embryos undergo?
Holoblastic cleavage.
What is holoblastic cleavage?
a type of embryonic cell division where the entire zygote (fertilized egg) divides into smaller cells called blastomeres, typically seen in eggs with moderate to sparse yolk.
Where is gastrulation initiated?
At the primitive streak.
What is the placenta?
An organ that contains tissues and blood vessels from both the embryo and the mother.
What processes is the placenta responsible for?
3
- Gas exchange
- Nutrient uptake
- Waste elimination
Why do mammalian embryos frequently contain odd numbers of cells instead of exponentially increasing?
Mammalian blastomeres do not all divide at the same time.
When are zygotic genes activated in humans?
Around the 8-cell stage.
What happens around the 8-cell stage that allows for compaction to occur?
Expression of cell adhesion proteins like E-cadherin.
What is produced by the division of the 8-cell embryo?
16-cell morula
Describe the composition of the morula.
Contains a small group of internal cells surrounded by a larger group of external cells.
What do the outer cells of the morula tend to give rise to?
Trophoblast (AKA trophectoderm) cells
What do the inner cells of the morula tend to give rise to?
Inner cell mass (ICM)
What does the ICM give rise to?
4
The embryo, yolk sac, allantois, amnion.
What is produced by trophoblast cells?
3
- Chorion tissue
- Extraembryonic membrane
- Portion of placenta that provides oxygen and nourishment to the fetus
Aside from gas exchange, what else is the chorion responsible for?
2
- Secretes hormones allowing the mother to retain the fetus
- Produces immune response regulators preventing rejection of the embryo
What are totipotent cells?
Cells capable of differentiating into any type of cell.
What are pluripotent cells?
Cells that can differentiate into any cell type, excluding extraembryonic tissues.
What type of cells are early blastomeres?
Totipotent
What type of cells are the cells of the ICM?
Pluripotent
True or false: Cells of the ICM can self-renew indefinitely in culture under appropriate conditions.
True
What two genes are involved in the first decision regarding ICM vs. trophoblast fate?
Oct4 and Cdx2
What is the relationship between Oct4 and Cdx2?
They reciprocally repress each other’s gene expression.
What two genes are involved in the second decision regarding ICM vs. trophoblast fate?
Nanog and Gata6
What does expression of Nanog mean for the ICM?
Means it retains its pluripotency.
What does expression of Gata6 mean for the ICM?
Cells will become primitive endoderm.
What three transcription factors maintain ICM pluripotency?
Oct4, Sox2, Nanog
What is the relationship between Oct4, Sox2 and Nanog?
When they bind to their own gene enhancers, they maintain their own expression while simultaneously activating the enhancers of the other TFs.
By what stage have the ICM and trophoblast become separate cell layers?
64-cell stage
gWhat is cavitation?
A process whereby the morula develops an internal cavity, called the blastocoel, which eventually gives rise to the blastocyst.
Describe how the blastocoel is formed.
Trophoblast cell membranes pump Na+ into the central cavity of the morula.
Accumulation of Na+ draws in water, creating and enlarging the blastocoel.
Describe the formation of the blastocyst.
As the blastocoel expands, the ICM becomes positioned on one side of the ring of trophoblast cells, producing the blastocyst.
What is the lower layer of the ICM that is contact with the blastocoel called?
Primitive endoderm
What is the upper layer of the ICM called
Epiblast
What forms the bilaminar germ disc?
The epiblast and primitive endoderm.
Where in the embryo does gastrulation begin?
At the posterior end where the primitive streak arises.
How are identical twins formed?
Dissociation of cells from a single embryo
Dissociation of which types of cells can lead to identical twins?
Separation of early blastomeres or separation of ICM into two regions.
What might be indicated by identical twins having two complete and separate chorions?
That separation could have occured prior to trophoblast formation.
What might be indicated by identical twins sharing one common chorion?
Separation may have occurred after trophoblast formation.
What could be indicated if identical twins share a chorion but have two separate amnions?
Separation could have occurred after trophoblast formation but prior to amnion formation.
What could be indicated by identical twins with one chorion and one amnion?
Separation occurred after amnion formation.
