Lecture 5 - early embryo metabolism Flashcards
What is cleavage?
Asynchronous division of cells. No net growth
When does compaction occur?
16-32 cell stage in humans
What happens after the morula is compacted?
Blastocyst forms. Trophectoderm and ICM, results in big change in metabolism
What is the maternal to zygotic transition?
The period where zygotic genes are activated and maternal genes are cleared. It is critical for cell survival
How is the blastocyst formed?
During compaction (ca dependent):
- increased cell:cell adhesion
- outer cells polarised - trophectoderm
What is the role of E-cad in compaction?
Extracell comp binds other e-cad
Intracell comp binds actin cytoskel via a and b catenin
Relocated to regions of cell-cell contact at time of compaction
What other molecules are needed for compaction?
Occludin, ZO1, ZO2 and cingulin
What happens as the the embryo progresses to blastocyst?
Increase number of tight junctions and embryo becomes sealed
What happens at blastulation?
Formation of blastocyst and blastocoel cavity
Max activity of TJ
How does the blastocoel form?
Na moves into embryo via Na/K ATPase. H20 follows the Na through AQP channels. TJ seal to prevent fluid loss
How does energy metabolism change?
Switch from TCA (pyruvate) to glycolysis (glucose) as main energy source around compaction
What are the mechanisms of early embryo metabolism?
Cumulus cells secrete lots of pyruvate - increased ATP
High ATP:ADP ratio blocks PFK function therefore TCA dependent
What happens at cleavage?
More ATP is used therefore lower ATP:ADP ratio. PFK is expressed and glycolysis takes over
What two transporters are important?
Glut4 and Glut5 in blasto - important for glucose uptake
What can glucose uptake measure?
Viability of the embryo
What is the role of oxygen?
Glycolysis required more oxygen however embryo must be cultured in 5% oxygen and 20% is toxic as the uterus is a hypoxic environment
What is the effect of increased oxygen?
Altered aa turnover and decreased glucose uptake - bad
What are the roles of aa?
Pt synth and cell function
Many used as energy source by early embryo
Why are aa marker for a viable embryo?
Can be used to look at the turnover to indicate if the embryo is using enough/too many aa
What happens with aa in the developing embryo?
Steady increase in aa utilisation
What happens to an embryo that uses too many aa early on?
Arrest in development
What is fragmentation?
Damaged DNA
How do they assess embryo quality?
- Ratio of ICM:TE (0.3/0.4 is good)
- TUNEL staining
- Time-lapse microscopy
- Metabolomic analysis e.g. NMR and mass spec
