Early Embryo Metabolism Flashcards
In what region of the female reproductive tract does fertilisation occur?
Ampulla region of the fallopian tube
At what stage is the embryo first known as a zygote
2 cell stage
At what stage does compaction occur?
16-32 cell stage
How long does compaction last?
3 to 4 days
When does the embryo become a blastocyst?
Following compaction, when the morula is released in to the uterus.
What cell changes define blastocyst stage of embryo development?
At blastocyst stage, cells gain developmental competence - stat to form crude cell lineages
What is the cell fate of outer cells in blastocyst?
trophectoderm, due to be placenta
What is the cell fate of inner cells in blastocyst?
Inner cell mass, due to be fetus
Which cellular interaction increases at compaction?
cell to cell adhesion
What is the main mediator molecule of increased cell adhesion at compaction?
E-cadherin
What dependency do outer cells gain during polarisation at compaction stage?
Calcium dependency
In absence of calcium - will compaction occur?
no
What secondary protein allows the binding of e-cadherin to actin cytoskeleten in blastomers?
Alpha and beta catenins
At what stage of embryo development is e-cadherin expressed?
expressed from early cleavage, but loacalised to regions of cell to cell contact at compaction.
What is theory for relocalisation of e-cadherin
Driven by PKc (protein kinase C)
What do E-cadherin knockouts, alpha catenin knockouts and embryos treated with e-cadherin antibodies all have in common?
They will fail at compaction stage
What is an occludin?
transmembrane protein involved in embryo development
What further proteins exist in occludin complexes?
ZO-1, ZO-2 and cingulin
At what cell stage does the biogenesis of tight junctional proteins occur?
beginning at 6 - 8 cell stage, up until blastocyst formation
Where are TJPs polarised to?
Apical face of cells.
What allows embryos to go from permeable to sealed?
formation of tight junctions between cells.
What is the blastoceole?
Area of water (and some other factors) found in the middle of the blastocyst
Via what mechanism does the blastoceole increase in size?
Due to a sodium gradient, water flows in to the embryo.
Synonymously, tight junctions are being formed, and water is retained in the embryo. Cells become impermeable
What are the two main hypotheses for cell polarization in early embryo development?
Inside/Outside hypothesis and Cell Polarity hypothesis
What is the main difference between the 2 hypotheses for cell polarisation in early embryo development?
Inside/outside hypothesis assumes that cell division determines the cell fate. Cell Polarity hypothesis assumes that cell fate determines the direction of cell division.
Where can Oct4 be found in the blastocyst
Inner cell mass
How is Oct4 localised?
Oct4 expression is repressed by Cdx2, found localised to trophectoderm
What about the location where Cdx2 is found is special?
At the apical domain of cells where Cdx2 is found, there are exposed cell faces. In all other cells in the blastocyst, there is isometric binding - connected at all faces.
Where can Nanog be found in the blastocyst
salt and peppered in Inner cell mass
Where can Gata6 be found in the blastocyst?
Salt and peppered in inner cell mass (not in same cells as nanog)
How does Grb2 regulate Nanog and Gata6?
Grb2 inhibits Nanog expression and promotes Gata6 expression.
In early cleavage embryo, what is the main energy substrate?
pyruvate
Up until compaction, what is the main mechanism for energy production in the embryo?
TCA cycle (Krebs cycle)
During and after compaction, what is the main mechanism for energy production in the embryo?
glycolysis
At what point of embryo development would you expect to see lactate production increase?
compaction
what mechanism do cumulus cells utilise to provide energy substrate for the oocyte?
glycolysis (to produce pyruvate)
What is the main product of the PPP pathway in cumulus cells?
NADPH
What is the main effect of the accumulation of ATP in early embryo? (other than use for energy)
Disrupts the ATP:ADP ratio having a negative impact on the production of phosphofructokinase (PFK), so glycolysis cannot occur.
How is the ATP:ADP ratio restored?
use of ATP for high energy processes eg compaction
Other than glycolysis, what is glucose used for in the embryo?
basic material required for nucleic acid synthesis, required for phospholipid and non essential amino acid biosynthesis.
What are glucose transporter proteins known as?
GLUT
When is GLUT4 expressed?
Only expressed from blastocyst stage onwards
When is GLUT5 expressed?
GLUT5 expression begins at 8 cell stage
Are embryos that have high glucose uptake more or less likely to be viable?
More likely
Are embryos that have high rates of glycolysis more or less likely to be viable?
Less
what effect does culturing embryos in high oxygen concentration have?
toxic
High production of alanine at early embryo stages can be an indicator of what?
embryo arrest
What will happen to embryos which have high metabolic activity and use of amino acids at very early stages?
they will fail :( (metabolic stress)
