Diff5 - 36

Question 1

What causes different cytoplasmic determinants to sink in the egg?

Answer 1

Gravity in xenopus, placenta interaction in mammals

Question 2

What does cytoplasmic determinants sinking cause?

Answer 2

Cells in this region to be different - they then have specific transcription factors localised and activated

Question 3

What specific transcription factors are localised and activated in the Xenopus egg?

Answer 3

Vegetal portion - the heavy yolk - has VgT activated

Question 4

What is VgT?

Answer 4

T box transcription factor

Question 5

What does the vegetal section induce?

Answer 5

Dorsal and ventral mesoderm

Question 6

Example of dorsal mesoderm derivative

Answer 6

Notochord

Question 7

Example of ventral mesoderm derivative

Answer 7

Blood

Question 8

Why are two forms of mesoderm induced by vegetal section?

Answer 8

Differential gene expression

Question 9

What causes differential gene expression in the vegetal section?

Answer 9

Sperm induced cortical rotation

Question 10

What does sperm induced cortical rotation cause the expression of?

Answer 10

Wnt signalling from the dorsal side

Question 11

What does activation of Wnt signalling lead to?

Answer 11

The stabilisation of a factor called beta-catenin, which enters the nucleus and changes the transcriptional profile

Question 12

What does Wnt bind to?

Answer 12

Frizzled

Question 13

What does frizzled signal to?

Answer 13

Dishevelled

Question 14

What does dishevelled interact with?

Answer 14

Axin - to prevent GSK3 from degrading free beta-catenin

Question 15

How does Wnt induce a difference in vegetal cells?

Answer 15

Wnt on the dorsal side, VgT on vegetal = 3 dimensional gradient

Question 16

What is the region of Nodal and Wnt expression overlap called?

Answer 16

Nieuwkoop centre

Question 17

What is the name for Nieuwkoop progeny?

Answer 17

Organiser/Dorsal mesoderm

Question 18

Summarise early morphogenetic gradients in the Xenopus embryo

Answer 18

Question 19

Outline the properties of the organiser

Answer 19

Ability to self-differentiate into axial mesoderm, ability to dorsalise adjacent mesoderm, ability to induce adjacent extoderm to a neural fate

Question 20

What controls the properties of the organiser?

Answer 20

Siamois, then goosecoid later

Question 21

What is the axial mesoderm?

Answer 21

Rod of cells around which the future body’s axis forms

Question 22

How is the axial mesoderm created?

Answer 22

Convergent extension - cells in a circle or sheet, then all desperately want to be in the centre

Question 23

What three cell types form axial mesoderm?

Answer 23

Prechordal mesendoderm, prechordal mesoderm, notochord

Question 24

What form dorsal aspects of the axial mesoderm?

Answer 24

Prechordal mesendoderm, prechordal mesoderm

Question 25

What is important to note about Nodal expression in the Xenopus?

Answer 25

Doesn't differentiate all the way to the top of the animal hemisphere, only changes the fate of a band of animal hemisphere cells that areimmediately adjacent to the vegetal hemisphere.

Question 26

What does convergent extension cause in the developing embryo?

Answer 26

Complete change in shape - from sphere to larva-like shape

Question 27

Why does convergent extension cause a change in embryo shape?

Answer 27

The yolk from the yolky vegetal cells is being used, so they all but disappear; top animal cap cells now have the induced mesoderm cells arranged in rod-like sturcutres inside of them, running down the AP extent of the body

Question 28

What do the three main precursors form of the organiser region form?

Answer 28

Pharyngeal endoderm, prechordal mesoderm and notochord

Question 29

What does the rod follow during convergent extension?

Answer 29

Fibronectin rich pathways

Question 30

When does gastrulation occur in vertebrates?

Answer 30

Shortly after blastocyst stage, when the trophextoderm and inner cell masses have formed, and it has implanted into the uterine wall

Question 31

What causes gastrulation in vertebrates?

Answer 31

Signals coming from the developing placenta, forcing the ICM to start differentiating into hypoblast or epiblast

Question 32

What does epiblast go on to be?

Answer 32

Embryo proper - equivalent to Xenopus animal hemisphere

Question 33

What can the hypoblast be considered equivalent to?

Answer 33

Xenopus vegetal hemisphere

Question 34

Where does the vertebrate version of the Nieuwkoop centre form?

Answer 34

The hypoblast

Question 35

What does the organising part of the hypoblast induce?

Answer 35

Some epiblast cells to become mesoderm and definitive endoderm

Question 36

What occurs to the vertebrate organiser, and what does this form?

Answer 36

Moves from propective posterior to anterior, creating the primitive streak