Mammals Flashcards
Why is it difficult to study development in mammals?
Completely internal
Where does fertilization occur?
Oviduct
Where do the early stages of development occur?
Fallopian tubes
What type of yolk distribution is seen in mammals?
Isolecithal
What type of cleavage is seen in mammals?
Holoblastic, rotational
How does a morula become a blastocyst?
Compaction of cells
How does compaction occur to form a blastocyst?
Changes in cell adhesion through E-caderins, which increase the contact area between cells and causes really tight packing, and from cytoskeletal rearrangements
What are the two cell types in a blastocyst?
Trophoblast and ICM
At what cell stage do the trophoblast and ICM become specified?
32 cells
What are the 2 transcription factors that specify if a cell will become part of the trophoblast or part of the ICM?
Oct4 and Cdx2
What does the trophoblast become?
Extra-embryonic tissue. It becomes the chorion
What does the ICM become?
The embryo and the amnion
Which transcription factor specifies trophoblast?
Cdx2
Which transcription factor specifies ICM?
Oct4
What does Cdx2 do?
Inhibits Oct4 to specify cells to become trophoblast cells
What does Oct4 do?
Inhibits Cdx2 and turns on Sox2 to specify ICM cells
What does Sox2 do?
Promotes its own activity and the activity of Oct4. Turns on Nanog transcription
What does Nanog do?
Promotes activity of Oct4, Sox2 and itself
How does implantation of the blastocyst in the uterus occur?
Cell adhesion. First through labile interactions then through permanent interactions
What creates the labile interactions that lead to implantation?
Sulfated polysaccharides on the endometrium bind to L-secretin on the blastocyst
What creates the permanent interactions that lead to implantation?
P-cadherin is expressed by both the blastocyst and the endometrium
What cell movement splits the ICM into 2 layers?
Delamination
What are the 2 layers formed when the ICM splits into 2 layers? What do they become?
Hypoblast forms the yolk sac and epiblast forms the amnion and embryo
In mammals, the positioning of the germ layers and the cell movements are very similar to which animal?
Chickens
Which germ layer ends up in the original place of the hypoblast?
Endoderm
Which germ layer ends up in the original place of the epiblast?
Ectoderm
What are the 2 cell layers that make up the placenta?
Cytotrophoblast and syncytiotrophoblast
What is the cytotrophoblast?
A single layer of cells around the embryo
What is the syncytiotrophoblast?
A large network of cytoplasm that forms extracellular spaces in the growing tissue
How is the umbilical chord formed?
Differentiation of fetal blood vessels that connect with the mother’s vessels in the placenta
What are the 3 types of twins?
Monozygotic, dizygotic, conjoined
How genetically similar are identical twins?
Identical genetic makeup
How many amnions and chorions would be created for a set of monozygotic twins that had the zygote split very early on?
2 amnions and 2 chorions. Early splits form two blastocysts that both implant and each one has tissues specified into trophoblast and ICM
How many amnions and chorions would be created for a set of monozygotic twins that had the ICM split?
Two amnions and 1 chorion. The trophoblast and ICM are already specified, so each embryo still has its own amnion but they share trophoblast tissue
How many amnions and chorions would be created for a set of monozygotic twins that had the zygote split very late?
1 amnion and 1 chorion. The embryo would have split after some of the ICM branched off into the amnion, so the embryos share an amnion
How do dizygotic twins occur? How genetically similar are they?
Two eggs get ovulated and they both get fertilized and implanted. They are no more similar to each other than regular siblings
What are conjoined twins?
Twins that share some organs and tissues
What are 3 possible causes for conjoined twins?
- A second organizer is created and creates a new body axis
- Trauma that splits the epiblast
- Confused Nodal
