Mice

Question 1

In placental mammals there is an extra stage to development. What is it?

Answer 1

Implantation of the embryo to the uterus wall.

Question 2

Why are mammals difficult to study?

Answer 2

Development is internal, thus pre-implantation development is more widely studied.

Question 3

When does implantation occur?

Answer 3

Between blastulation and gastrulation.

Question 4

Why do scientists record the time as E0.5 at the start of development?

Answer 4

Mice mate during the night, thus 0.5 refers to the half day that has already passed when they are checked on in the morning.

Question 5

In mammals where is the egg fertilised?

Answer 5

Near the ovary in the oviduct.

Question 6

What is the zone pellucida?

Answer 6

A membrane that prevents ectopic pregnancy.

Question 7

Define the process of compaction.

Answer 7

When the blastula compacts to form the morula.

Question 8

Define the morula.

Answer 8

A solid ball of cells.

Question 9

What happens when the morula is formed?

Answer 9

The cells become polarised. Microvilli interdigitate and pull the cells together.

Question 10

The morula is still permeable to external fluid. True or false?

Answer 10

False - the morula is impermeable to external fluid.

Question 11

What happens during the process of cavitation?

Answer 11

Phenotypic differences appear in the inner and outer cells.

Question 12

During cavitation, describe the a) outer and b) inner cells.

Answer 12

a) larger and polarised

b) smaller and apolar

Question 13

What forms the blastocoel within the morula?

Answer 13

Transportation of vectorial fluid from the outside to the inside of the morula.

Question 14

What do the outer cells of the morula become?

Answer 14

Trophoectoderm (TE).

Question 15

What is the trophoectoderm fated to become?

Answer 15

Chorion, which in mammals contributes to the formation of the placenta.

Question 16

What do the inner cells become?

Answer 16

The inner cell mass (ICM)

Question 17

What is the ICM fated to become?

Answer 17

Amnion and embryo proper.

Question 18

What are the chorion and amnion important for?

Answer 18

Gas exchange.

Question 19

What 3 types of cell are born from the TE?

Answer 19

1. Trophoblast stem cells
2. Giant trophoblast cells
3. Placental cells

Question 20

The ICM is subdivided into what 2 things?

Answer 20

1. The outer ICM becomes the primitive endoderm (PrE)

2. The inner ICM becomes epiblasts (EBs)

Question 21

What does the PrE become?

Answer 21

Amnion

Question 22

What do the epiblasts give rise to?

Answer 22

The embryo proper.

Question 23

What 2 genes are expressed by the TE?

Answer 23

Eomesodermin and Cdx2

Question 24

What gene do all ICM cells express?

Answer 24

Oct4

Question 25

What is the function of Oct4?

Answer 25

It down-regulates Eomes and Cdx2, preventing ICM from becoming TE.

Question 26

What is the interaction of Oct4 and Eomes/Cdx2 described as?

Answer 26

Mutually repressive.

Question 27

What 3 genes are only expressed by PrE?

Answer 27

1. GATA6 2. GNCF 3. Sox17

Question 28

What 3 genes are only expressed by epiblasts?

Answer 28

1. nanog 2. Sox2 3. Stat3

Question 29

Epiblasts can give rise to any cell in the embryo. True or false?

Answer 29

False - they can give rise to any cell from the embryo proper but cannot form embryonic membranes.

Question 30

There are 2 theories for the formation of TE and ICM. What are they?

Answer 30

1. Polarisation theory | 2. Inside-out model

Question 31

There are 2 theories for the formation of TE and ICM. Explain the polarisation theory.

Answer 31

The polarisation that occurs during compaction alters the distribution of cytoplasmic determinants. The polarised outer cells become TE and the apolar inner cells become ICM.

Question 32

There are 2 theories for the formation of TE and ICM. Suggest support for the polarisation theory.

Answer 32

Division is asymmetrical.

Question 33

There are 2 theories for the formation of TE and ICM. Explain the inside-out model.

Answer 33

Compaction creates different microenvironments for the outer and inner cells, e.g. exposure to fluid (outer) or not (inner).

Question 34

What do TEAD4 mutants lack?

Answer 34

TEAD4 mutants lack Cdx2 activation and thus do not develop TE.

Question 35

What does TEAD4 require in order to activate Cdx2?

Answer 35

A co-factor called YAP

Question 36

How is Cdx2 activated?

Answer 36

By the translocation of TEAD4 and YAP to the nucleus.

Question 37

YAP and lats are involved in the Hippo signalling pathway. What is Hippo signalling for?

Answer 37

Tumour suppression.

Question 38

Briefly explain Hippo signalling.

Answer 38

1. Hippo is a transmembrane protein that activates lats 2. lats phosphorylates YAP 3. YAP degrades 4. TEAD4 cannot activate Cdx2 if YAP is degraded

Question 39

It is thought Hippo signalling occurs in the ICM. Why?

Answer 39

The physical contact of cells in the ICM creates enough critical mass to activate Hippo. This then inactivates Cdx2.

Question 40

Hippo signalling does not occur in the TE. Why?

Answer 40

The TE is on the outside and has reduced contact with other cells.

Question 41

There are 3 theories for the formation of PrE and EB from the ICM. What are they?

Answer 41

1. The positional model 2. Stochastic model 3. Time-outside/time-inside model

Question 42

There are 2 theories for the formation of PrE and EB from the ICM. Explain the positional model.

Answer 42

The different microenvironments in cavitation create different cell fates.

Question 43

There are 2 theories for the formation of PrE and EB from the ICM. What is a flaw in the positional model?

Answer 43

Early on in development all cells there is a homogenous distribution of cells and thus no variation in microenvironment.

Question 44

There are 2 theories for the formation of PrE and EB from the ICM. Explain the stochastic model.

Answer 44

The expression of PrE or EB markers overlap in the morula, which causes cellular migration.

Question 45

There are 2 theories for the formation of PrE and EB from the ICM. Explain the time-outside/time-inside model.

Answer 45

Developmental origin causes differentiation: the first cells to internalise are the EB and these express nanog. The last cells to internalise are the PrE and express GATA6.

Question 46

All the cells in a mouse embryo are totipotent up the 8-cell stage. True or false?

Answer 46

True.

Question 47

The totipotency of cells up to the 8-cell stage is responsible for identical sibs. True or false?

Answer 47

True.

Question 48

What does the fusion of two 8-cell mammalian embryos result in?

Answer 48

A normal chimera.

Question 49

Fusing 8-cell embryos from other species also forms chimeras. True or false?

Answer 49

False - only the fusion of 8-cell mammal embryos foms chimeras.

Question 50

What does GRN stand for?

Answer 50

Gene regulatory network.