Implantation (wk 3)

Question 1

What are the 6 names of the stages of implantation?

Answer 1

Transport
Orientation
Hatching
Apposition
Attachment
Invasion

Question 2

Why is implantation necesssary?

Answer 2

Uterine secretions bathe the blastocyst (provides oxygen and metabolites necessary for growth/survival)

Important for the blastocyst to generate its own blood supply

Question 3

What are the two main requirements for implantation?

Answer 3

Involves SYNCHRONISATION between the blastocyst and uterine wall
Uterine wall needs to become receptive and the blastocyst needs to acquire implantation competancy

Relies one ovarian hormones (estrogen and progesterone) and locally produced signalling molecules

Question 4

What are the three stages of receptivity of the uterus to blastocyst?

Answer 4

Pre-receptive phase

• Epithelium has long apical microvillis, thick glycocalyx, negative charge
• impairs attachment

Receptive phase

• Apical protusions absorb volume and decrease volume in the uterine cavity
• Loss of negative charge
• Microvilli shorten, glycocalyx thins
• Attachment is ready

Refractory phase

• Goes back to a structure similar to pre-receptive phase
• Resists attachment

Question 5

T/F: during the pre-receptive phase, the uterine wall has a positive charge

Answer 5

False: negative charge

Question 6

T/F: the terminal web disappears during the receptive phase

Answer 6

True

Question 7

T/F: the focal adhesions remain during the receptive phase

Answer 7

False: they disappear to enable implantation

Question 8

Where do oestrogen and progesterone come from?

Answer 8

The ovaries

Question 9

T/F: oestrogen and progesterone levels are low during the pre-receptive phase

Answer 9

True

Question 10

Describe the levels of oestrogen and progesterone during the receptive phase

Answer 10

Elevated

Their peaks are critical to drive the receptive phase

Question 11

Describe the glandular epithelium during the pre-receptive phase

Answer 11

Increases in secretory function

Drives the epithelial mesenchyme transition

Question 12

Are tight junctions lost or kept during uterine receptivity?

Answer 12

Lost

Question 13

What happens to the glycocalyx proteins during uterine receptivity?

Answer 13

Uterus and embryo secrete enzymes to cause post-translational modifications
(chop them up)

Question 14

What is the role of focal adhesions?

Answer 14

Provide a structural link between the ECM and cytoskeleton

Question 15

Explain the role of osteopontin in terms of blastocyst adhesion competancy

Answer 15

Ovary secretes oestrogen
Then uterus secretes osteopontin
Osteopontin binds to integrin receptors on blastocyst which makes them activated and they aggregate together
Assists the blastocyst for adherance

Question 16

Explain the role of oestrogen in terms of endometrium receptivity

Answer 16

Oestrogen is secreted by ovary and acts on uterus
Endometrial glands secrete LIF (leukaemia inhibitory factor)
LIF receptors are on the epithelium and stroma
Makes endometrium receptive to attachment

Question 17

Explain the role of EGF

Answer 17

Blastocyst secretes a factor that acts on epithelial cells of the uterus
Uterus epithelial cells secrete and express heparin binding RGF
EGF has autocrine functions on blastocyst and uterus
Helps with the hatching process

Question 18

List the funcitons of the zona pellucida during early pregnancy

Answer 18

Prevents polyspermy
Prevents premature implantation
Prevents two zygotes from sticking together
Keeps blastomeres together until compaction

Question 19

Describe the two hatching mechanisms of the ZP

Answer 19

Rupture:
Mechanical= increase in cell numbers, ZP stretches and thins due to the pressure
Chemical= blastocyst secretes proteases to form a hole in ZP

Escape:
Embryo expands and contracts the cavity (pulsing movements), escapes through the hole in ZP

Question 20

Which cells become quite close to the endometrium

Answer 20

Trophoblast

Close apposition and adherance of trophoblast cells to endometrium

Question 21

What role do uterodomes play?

Answer 21

Involved in initial attachment
Flatten down when the blastocyst is brought onto the endothelial cells
Proteins on the surface of the uterodomes interact with the blastocyst

Question 22

Explain how integrins and ECM proteins play a role during cel-cell attachment

Answer 22

Integrins on uterus and blastocyst bind to ECM proteins and use it as a glud

Question 23

List some methods used for studying implantation

Answer 23

Co culture
Multilayer culture
Migration assay
Transwell migration assay
Invasion assay
Multilayer invasion assay

Question 24

Describe the stages of implantation

Answer 24

First: cell-cell contact (attachment)

Second: invasion by trophoblast cells through the epithelium and basement membrane

Third: decidualisation of stromal cells (so blood can come into close contact with the embryo)

Question 25

What is the major cause of IVF failure?

Answer 25

Implantation failure

Question 26

At what developmental stage is the embryo delivered back to the woman during IVF?

Answer 26

Blastocyst stage

Question 27

T/F: during TVF, the ovaries are stimulated to produce one egg

Answer 27

False

They are stimulated to produce multiple eggs

Question 28

How can the ZP be hatched during IVF?

Answer 28

Make a small hole
Thin the ZP by shining a laser
Use pippetes to squirt chemical reagents to break down ZP

Crucial for implantation

Question 29

T/F: serum is aded to culture during IVF

Answer 29

False
no serum, simple medium maternal growth factors are absent

large volume of fluid means the autocrine growth factors are diluted

Question 30

What is the difference between low and high density in IVF

Answer 30

Low density= one embryo, large volume of fluid, growth factors are diluted, poor development

High density= groups of embryos, small volume of fluid, growth factors are more concentrated, improved development, increased hatching

Question 31

Does the addition of IGF1 assist blastocyst development during IVF?

Answer 31

Yes

Inhibits apoptosis, stimulates hatching, helps development, increased attachment and invasion

Question 32

What is the main mechanism that allows addition of IGF1 assist attachment during IVF?

Answer 32

It increases the amounts of fibronectin (ECM protein)

This allows the integrins to bind to the ECM as a glue, critical for attachment process