Pre-implantation development Flashcards
State the stages between zygote and expanded blastocyst
zygote
2-cell
4-cell
8-cell
late morula
early blastocyst
expanded blastocyst
What surrounds the embryo at the 4-cell stage
the zona pellucida
At what stage does compaction occur
8-cell stage
When does zygotic genome activation occur both in mice and mammals?
mice = the 2-cell stage
mammals = the 2-4 cell stage
What is the success of artificial twinning dependent on
the number of cells that end up in the epiblast
What events occur during the 8-cell stage?
cells become polar and have an inside and outside. cells with a free surface (unattached to another cell) accumulate actin
cells become compacted
What stage does cavitation occur and what happens
the 16-cell stage
tight junctions seal off the membrane and make gaps so cells are impermeable to water and salts
the blastocyst cavity forms
How does the blastocyst form?
Na and Cl move into the blastocyst and water moves in. increase in osmotic pressure and blastocyst expands. a major energy-requiring process as Na is pumped
What substance can artificially induce compaction
PKC
What is aneuploidy
an abnormal number of chromosomes, normally leads to embryo arrest when implanted to the mother in IVF
What factors make an embryo in IVF more likely to be chosen for implantation
expanded blastocyst, more rapid cell divisions, even cleavage divisions
What is pre-implantation genetic testing for aneuploidy (PGT-A)?
at the 8-cell stage, one cell is removed and analysed using next generation sequencing to test for aneuploidy. as all 8 cells are identical, diagnosing one cell will diagnose all
What is embryo mosaicism?
cells in different regions of the embryo having different levels of aneuploidy - leads to risk of misdiagnosis
Why is there an increase in oxygen consumption at the blastocyst stage?
due to presence of Na pump and action of glycolysis and mitochondria
What environment should embryos be grown on a culture medium for optimum growth?
2 steps:
1 = treat with pyruvate
2 = treat with glucose
culture should have a low oxygen of 5%
What is the zona pelucida made up of? What does it do?
Glycoproteins of matrix of cell. Protects egg from poly-sperm
What occurs during the cleavage stage?
Increased embryo gene expression
What occurs during compaction?
Loss of blastomere definition- through increase cell adhesion and tight junction formation
WHAT OCCURS DURING CAVITATION?
Inner cell mass formation
Trophectoderm Na/ K -ATPase pump creates classical cavity- pump fluid- to generate fluid filled balls
What is the inner cell mass?
A mass of cells within the blastocysts in the early development of an embryo which neutrally gives rise to structures of the fetus
What does the Trophectoderm do?
Creates supporting tissues
What occurs during implantation?
Initiated by adhesion between Trophectoderm and uterine endometrium
What causes delayed implantation?
Through hormonal control- oestrogen determines blastocyst and uterine endometrium interaction- unfavourable conditions for pregnancy
What is the mechanisms of Trophectoderm and inner cell mass allocation?
- Establish polarity within cell - allows different communication lines
- This enables cell to organise polarity within the embryo and establish paths for intercellular communication
- Cell differentiation and allocation to different lineages involes estabilishing spatially restricted patters of gene expression
- Critical fate determining gene of important include:
Cdx2 a TF that signals for trophoblast
GATA4/6- primitive endoderm
Oct4/ nanos- inner cell mass
What genes give rise to the subcortical maternal complex?
Za1, mater, floped and padi6
What do outside cells activate and repress?
Activate Cdx2
Repress oct4/ Nanog
What do inside cells repress and activate?
Cdx2 repressed
Oct4/ Nanog activated
What specifies the Trophectoderm?
Cdx2
What specifies the inner cell mass?
Oct4 and Nanog
How is Cdx2 gene activated in outside cells repress?
Hippo activation of last that in turn regulates Yap- is controlled by the extent of cell-cell contact.
Lower cell-cell contact- causes Yap to bind to Tead4- turning Cdx2 on
What does high cell-cell contact lead to for Yap?
Phosphorylation of Yap= negatively regulates YAP - so cdx2 off
What happens in Nanog and oct4 mutant embryos?
Defective in ICM formation
What does the primitive endoderm differentiate to?
Extraembyonic endoderm- to make yolk sac and amnion
What is pluripotency?
Non-restricted potential to commit to all germ layers and differentiate to all cell types of body.
What did sir martin Evan’s do?
Isolated ICM - demonstrated self renewal
Name the stages from spermatogonia to spermatozoa?
Spermatogonia> primary spermatocytes> secondary spermatocytes> spermatids > spermatozoa
Name steps from oogonia to oocyte?
Oogonia> primary oocyte > oocyte
Where does the sperm mature in the testes?
Near the tail of the epididymis
Where is spermatozoa formed?
In seminiferous tubules
What is the role of follicular cells?
Support the oocyte
What is the difference between metaphase I and metaphase II in Oogenesis?
Metaphase I has one meiotic spindle whereas metaphase II has a secondary meiotic spindles
Where does fertilisation take place?
In the uterine tube
When does oocyte proliferation stop?
Before birth
When does the first meiotic division begin?
During puberty
When does the first polar body get emitted?
Before ovulation
When is the peak number of germ cells in humans?
4-6 months
When do the two polar bodies and two pro nuclei form?
After fertilisation
At what point does the fertillisation of a clam occur?
GV oocyte
At what point does the fertillisation of insects ascidians occur?
MI oocyte
What point do vertebrates become fertilised?
MII oocyte
At what point does the fertillisation of a a sea urchin and jellyfish occur?
Egg
At what point do gap junctions disappear?
When fertilised
What is the role of cortical granule exocytosis?
Form a thick barrier, called a fertilisation envelope, stops polyspermy
What does a positive Action potential do to fertilisation?
Blocks it
What does the acrosome reaction do?
Leads to Ca2+ influx
What does cortical granules do?
They undergo exocytosis, release Ovastacin and Zn2+, leading to proteolysis so zona hardening
How does mouse fertilisation occur?
Izumi bind juno receptor, leading to juno shedding
What is physiological polyspermy in newts, birds and reptiles?
Female pro nucleus, selects one male pro nucleus and others die. No cortical granules, no membrane depolarisation
During egg activation what events can calcium release trigger?
Completion o meiosis
Cortical granule exocytosis
Metabolic stimulation (e.g pH rise in sea urchins)
Changes in protein synthesis
Onset of mitotic cell cycles
Membrane potential changes
What causes a cortical flash? What does it prevent?
Due to action potentials. Prevents more than one sperm entering
What are protosomes?
The site of gastrulation is said to give rise to the mouth.
What are deuterostomes?
Forms the anus with the mouth arising from a second opening distant to the site of gastrulation is
What causes egg activation in drosophila?
Ovulation- in which ca2+ waves without a sperm, driven by a ca2+ influx
How does polyspermic fertilisation in newt eggs occur?
Many sperm fuse and release calcium but only has a limited calcium wave- so egg is activated by the summation of calcium waves- in which usually 10-20 sperm are needed
What is the mechanism of egg activation?
Ca2+ triggers CaMKII which phosphorylates EMI2 to APC which activate cycling/CDK1
What happens when EMI2 is blocked?
When destroyed it allows APC to break down cyclone/cdk1
What are the two proposed mechanisms of how calcium release is triggered?
Receptor mechanism or soluble sperm factor
What is the receptor mechanism?
A receptor in the egg is activated by the sperm bind which triggers a signaling pathway involving InsP3, leading to calcium release
What is the soluble sperm factor?
A Soluble actor from inside the sperm fuses with the membran- setting up a signalling pathway- releasing calcium but only
What is Phospholipase C (zeta)?
70kDa protein
That is sperm specific found in all mammals-
Associated with soluble sperm factor theory- So triggere InsP3 and so calcium relased
Where is PLC (zeta) localised?
The equatorial region of the sperm head
What happens if PLC zeta is knocked out in mice?
No oscillations occurs
