Making embryos Flashcards
What are the three steps of fertilization?
Penetration through the cumulus cell matrix
Penetration through the zona pellucida
Fusion with the egg plasma membrane
How is the cumulus cell matrix tightly bound?
Cell adhesion proteins and hyaluronic acid
What triggers the release of EGF receptor ligands by mural granulosa cells?
LH
How is hyaluronic acid released?
Pro-factors and ligands upregulate the transcription of genes
What is the role of sperm-specific hyaluronidases?
They surround the surface of the sperm and digest the hyaluronic acid, allowing the sperm to get through the matrix
How many proteins are found in the zona pellucida in primates?
Four
Deletion of which zp proteins prevents assembly of zona?
zp2 and zp3
What test can be done to observe the role of zp2 in fertilization?
Replace mouse zp gene by human homologue; mix transgenic mouse egg with human sperm -> sperm doesn’t stick to the zona of mouse egg BUT sticks to zp2 of human egg
What sperm membrane protein is required for sperm-egg fusion?
Izumo
Izumo gene activation leads to _____________ males and _____________ females
Infertile; fertile
True or false: Izumo knockout leads to the inability for sperm to stick to the membrane
False, it disables sperm from fusing into the membrane while still being able to stick to the membrane
What egg membrane protein is required for sperm-egg fusion?
Juno
Juno binds to ___________
Izumo
Fluorescent Izumo no longer binds to __________ because anti-_____________ antibody covers ____________
Juno; Juno; Juno
Deleting Juno from males led to no _____________ and deleting Juno from females led to no _______________
Effect; fertilization
What is another membrane protein required for sperm-egg fusion?
CD9
CD9 is a member of ________________ cell surface protein family
Tetraspanin
CD9 gene inactivation leads to ____________ males and severely sub-fertile _______________
Fertile; females
What is the role of CD9 in fertilization?
CD9 aggregates Juno proteins on the cell surface for easier targeting of Izumo on the sperm
Which of the following is part of the activation of the egg?
a) Initiation of mitotic cell cycles of embryo
b) Completion of the first meiotic division
a)
How is the increase of intracellular calcium linked to the mechanism of activation?
Sperm penetration induces repetitive release of calcium ions
Parthenogenetic stimuli induce calcium release
Inhibiting release of calcium prevents activation of the egg
How does the sperm trigger calcium release in the egg?
Sperm acts as a ligand to activate intracellular signaling pathway
Sperm component enters oocyte cytoplasm, triggers calcium release
How are G-protein coupled receptors and phospholipase C linked to calcium release?
G-protein binds to GPCR and triggers phospholipase C to break down PIP3 into IP3 and diacylglycerol
IP3 triggers the calcium release
True or false: Sperm specific phospholipase C is required for release in the egg
True
Is sperm release linked to GPCR?
No, sperm releases its own phospholipase C
Where can polyspermic fertilization be blocked?
Zona pellucida and membrane of egg
Calcium released at fertilization triggers cortical granule _______________
Exocytosis
Cortical granules are responsible for modifying _________ so that sperm can no longer bind to the zona
zp2
What protein cleaves zp2 at the disulfide bonds and modifies the zona pellucida?
Ovastacin
When does meiosis II occur in the egg?
After fertilization
How many polar bodies are formed after fertilization?
Two
At which phases of meiosis is cohesin degraded?
Anaphase I and II
How is separase activated?
CDC20 and APC form a complex that activates separase by separating it from securin
What inhibits the CDC20/APC complex in the first meiotic division?
Spindle assembly checkpoint
What inhibits the CDC20/APC complex in the second meiotic division?
EMI2
What causes the degradation of EMI2?
Calcium
During the first period of DNA replication, chromosomes from egg and sperm are _____________ in the oocyte
Separate
Histones replace ______________ in sperm chromatin __________ fertilization
Protamines; after
The period of development before implantation into the uterus lasts _______ days
Five
Cleavage divisions produce an embryo containing ____________ cells
50-100
What is morula?
Cells are flattened against each other to increase surface area
When does activation of embryonic transcription occur in humans and in mouse?
Major activation occurs at 2-cell stage in mouse, 4-cell stage in humans
Which cells form the blastocyst?
Epiblast (primitive ectoderm) and primitive endoderm (inner cell mass) + trophectoderm
The primitive ectoderm gives rise to which cell types?
All tissues of the embryo, amnion, allantois, yolk sac mesoderm
The primitive endoderm gives rise to which cell type?
Yolk sac endoderm
The trophectoderm gives rise to which cell type?
Fetal portion of placenta
What are the two models that determine the fate of inner and outer cells?
Inside-outside model where fate is determined by position
Polarity model where differential inheritance of polarity domains determine cell fate
What is the Hippo signaling pathway?
Mob1 and LATS1/2 is activated when MST1/2 and SAV1 are phosphorylated and ubiquitinates YAP/TAZ complex for degradation
When the hippo signaling pathway is off, the YAP/TAZ complex is ______________
Activated
If Hippo is off and YAP is stabilized, which cell type is formed?
Trophectoderm
If Hippo is on and YAP is degraded, which cell type is formed?
Inner cell mass
AMOT cannot recruit the machinery that phosphorylates YAP in the _____________ domain
Apical
AMOT can recruit the machinery that phosphorylates YAP in the _________________ domain
Basolateral
FGF signaling differentiates primitive ectoderm and primitive ______________
Endoderm
The epiblast expresses ___________ while the primitive endoderm expresses ________________
Nanog; Gata6
Why is X-chromosome inactivated?
To equalize the gene dosage
One X-chr becomes inactivated in _________ and a single X-chr remains active in ____________
Females; males
What is the mechanism of X-chr inactivation?
Xist RNA is expressed from one X-chromosome
Xist RNA coats that X-chr
Xist-coated X is transcriptionally inactive
When does X-chr inactivation occur?
After implantation
Some genes are ___________ and escape inactivation
Conserved