Pre-implantation development

Question 1

State the stages between zygote and expanded blastocyst

Answer 1

zygote
2-cell
4-cell
8-cell
late morula
early blastocyst
expanded blastocyst

Question 2

What surrounds the embryo at the 4-cell stage

Answer 2

the zona pellucida

Question 3

At what stage does compaction occur

Answer 3

8-cell stage

Question 4

When does zygotic genome activation occur both in mice and mammals?

Answer 4

mice = the 2-cell stage
mammals = the 2-4 cell stage

Question 5

What is the success of artificial twinning dependent on

Answer 5

the number of cells that end up in the epiblast

Question 6

What events occur during the 8-cell stage?

Answer 6

cells become polar and have an inside and outside. cells with a free surface (unattached to another cell) accumulate actin
cells become compacted

Question 7

What stage does cavitation occur and what happens

Answer 7

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

Question 8

How does the blastocyst form?

Answer 8

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

Question 9

What substance can artificially induce compaction

Answer 9

PKC

Question 10

What is aneuploidy

Answer 10

an abnormal number of chromosomes, normally leads to embryo arrest when implanted to the mother in IVF

Question 11

What factors make an embryo in IVF more likely to be chosen for implantation

Answer 11

expanded blastocyst, more rapid cell divisions, even cleavage divisions

Question 12

What is pre-implantation genetic testing for aneuploidy (PGT-A)?

Answer 12

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

Question 13

What is embryo mosaicism?

Answer 13

cells in different regions of the embryo having different levels of aneuploidy - leads to risk of misdiagnosis

Question 14

Why is there an increase in oxygen consumption at the blastocyst stage?

Answer 14

due to presence of Na pump and action of glycolysis and mitochondria

Question 15

What environment should embryos be grown on a culture medium for optimum growth?

Answer 15

2 steps:
1 = treat with pyruvate
2 = treat with glucose
culture should have a low oxygen of 5%