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Development > Mesoderm formation in Xenopus > Flashcards

Mesoderm formation in Xenopus Flashcards

1
Q

The genes bra, myf5, gsc and vent1 are only expressed in which tissue? When? Do the overlap?

A

In the mesoderm at early gastrula stage. They do not overlap.

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2
Q

What is bra?

A

Brachyury: a t-box transcription factor expressed pan-mesodermally.

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3
Q

Where is bra expressed?

A

Always around the blastopore and always in the notochord.

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4
Q

Without bra the notochord would not form correctly. True or false?

A

True.

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5
Q

As cells involute over the blastopore they maintain bra expression. True or false?

A

False: involuting cells lose bra expression.

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6
Q

a) What is gsc?

b? Where is it expressed?

A

a) Goosecoid: a homeobox TSF

b) Above the dorsal blastopore lip on the future dorsal side

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7
Q

Do bra and gsc overlap in expression?

A

No.

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8
Q

What is myf5 responsible for?

A

Myogenic factor 5, TSF responsible for muscle formation.

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9
Q

The expression of bra, gsc, myf5 and vent1 becomes more refined as development progresses. True or false?

A

True.

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10
Q

In specification map experiments…

a) What happens if you isolate the animal hemisphere?
b) What happens if you isolate the vegetal hemisphere?

A

a) It only forms epidermis
b) Will not form endoderm, although endoderm genes are being transcribed. Cannot form endoderm without supportive mesoderm.

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11
Q

In specification map experiments…

a) What happens if you isolate the animal hemisphere?
b) What happens if you isolate the vegetal hemisphere?

A

a) It only forms epidermis
b) Will not form endoderm, although endoderm genes are being transcribed. Cannot form endoderm without supportive mesoderm.

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12
Q

In specification map experiments…

a) What happens if you isolate the dorsal equatorial region?
b) What happens if you isolate the ventral equatorial region? Will they differentiate?

A

a) Neural tissue forms
b) Bags of blood form full of RBCs/mesenchyme etc. They are supposed to form somites but WILL NOT differentiate in isolation

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13
Q

From the specification map experiments we can see 2 types of mesoderm are set up. What are they and which genes are expressed there? What is expressed in the equatorial region?

A

Dorsal mesoderm (neural tissue) expresses bra.

Ventral mesoderm (blood) expresses gsc

Equatorial regions express myf5 and vent1.

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14
Q

Outline the experiments by Pieter Nieuwkoop in 1960.

A

He combined the animal and vegetal hemispheres from different axolotl embryos

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15
Q

In the experiments of Pieter Nieuwkoop in 1960, what happened when he recombined the hemispheres at the start of gastrulation?

A

Nothing, he just got ectoderm mixed with yolk.

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16
Q

In the experiments of Pieter Nieuwkoop in 1960, what happened when he recombined the hemispheres at mid-blastula stage?

A

He got endoderm, mesoderm and ectoderm.

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17
Q

How did Pieter Nieuwkoop discover that mesoderm was derived from the animal cap?

A

He used a normal and an albino embryo.

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18
Q

What was Pieter Nieuwkoop’s conclusion from his experiments?

A

Mesoderm formed from the animal cap under induction from the vegetal cap.

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19
Q

Describe what changes were made when Nieuwkoop’s experiments were repeated in Xenopus.

A

The animal cap was labelled with fluorescein. All mesodermal tissues thus expressed fluorescein.

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20
Q

The vegetal cap makes absolutely no physical contribution to the mesoderm. True or false?

A

True: only involved in signalling.

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21
Q

Nieuwkoop’s experiments only work at which stage of development?

A

Blastula stage.

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22
Q

What happened in experiments whereby individual blastomeres from the vegetal hemisphere were combined with the animal cap?

A

Ventral blastomeres induced ventral mesoderm and dorsal blastomeres induced dorsal mesoderm.

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23
Q

How can the ventral/dorsal blastomeres be identified?

A

They have slightly different pigmentation due to cortical rotation.

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24
Q

D1 is a blastomere that can induce a secondary dorsal axis if transplanted into D4 position. D1 did not physically contribute to this secondary axis. What is D1 known as? Where is it found?

A

The Nieuwkoop centre: it is a specialised inductive centre for dorsal mesoderm. It is found on the extreme dorsal side.

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25
Q

Name 2 maternal TSFs.

A

VegT and beta-catenin.

26
Q

Where is VegT found?

A

Throughout the vegetal hemisphere.

27
Q

Where is beta-catenin found?

A

On the dorsal side of the embryo.

28
Q

Where is the part of the embryo that vegT and beta-catenin overlap?

A

The Nieuwkoop centre.

29
Q

Combining antisense oligonucleotides to prevent mRNA translation with grafting experiments showed that a) vegt and b) beta-catenin are essential for what?

A

a) Necessary for both dorsal and ventral mesoderm (vegT depleted embryo did not develop mesoderm)
b) Necessary for dorsal mesoderm induction (beta-cat depleted embryos did not develop dorsal mesoderm)

30
Q

VegT and beta-cat are maternal TSFs. Can they initiate mesoderm formation directly?

A

No: they must activate zygotic TSFs

31
Q

How was it proved that the molecules that induce mesoderm are diffusible proteins?

A

In grafting experiments a membrane was put between the animal and vegetal caps. Cells could not pass through it but signalling molecules could. Mesoderm still formed.

32
Q

What does MIF stand for?

A

Mesoderm Inducing Factor.

33
Q

What is activin?

A

A protein that induces notochord formation.

34
Q

Why does activin cause the animal cap to change shape?

A

The animal cap forms ectoderm. The notochord is ectoderm. Activin causes it to elongate in convergent extension, thus changing the shape of the animal cap.

35
Q

All mesoderm inducing factors produce various shape changes. True or false?

A

True.

36
Q

What is TGFβ?

A

Transforming growth factor beta: a family of growth factor proteins.

37
Q

What is activin’s homologue in mammals?

A

GDF3

38
Q

What is FGF?

A

Fibroblast growth factor: a family of growth factor proteins.

39
Q

All MIFs identified have been from either TGFβ or FGF. True or false?

A

True.

40
Q

Is activin a MIF?

A

Yes.

41
Q

Activin has differential effects depending on concentration. True or false?

A

True.

42
Q

What effect does activin have in a) high and b) low concentration?

A

a) Dorsal mesoderm

b) Ventral mesoderm

43
Q

If high activin induces dorsal mesoderm, what does super high activin induce?

A

Endoderm…

44
Q

What is nodal?

A

Another MIF

45
Q

What is bmp?

A

An MIF that only induces ventral mesoderm

46
Q

All the TGFβ proteins appear to act in the same way. How?

A

High concentration produces dorsal mesoderm.

47
Q

All the FGF proteins appear to act in the same way. How?

A

They induce ventral mesoderm EXCEPT in super high concentrations they will induce dorsal mesoderm.

48
Q

All the TGFβ proteins appear to act in the same way. How?

A

High concentration produces dorsal mesoderm.

49
Q

What kind of receptors do TGFβ have?

A

STK1 and 2: these bind to serine kinase 1 and 2

50
Q

Why must STK1 and 2 be bound together by a TGFβ member?

A

STK1 is inactive without STK2.

51
Q

What do bound STK1 and STK2 do?

A

Activate SMAD proteins the regulate gene transcription, e.g. bra.

52
Q

Without STK1/2 signalling, what happens to embryos?

A

They are just balls of epidermis.

53
Q

What is nodal?

A

A zygotic MIF

54
Q

What was used to help deduce the role of nodal?

A

Cer-S: Cerberus short is a mutant version of Cerberus (a secreted binding protein). Cer-S targets nodal proteins and stops them binding their targets, thus can see what happens.

55
Q

What happened in grafting experiments with Cer-S injected into the vegetal cap? What does this tell us?

A

The animal cap failed to produce mesoderm. Nodal is necessary for mesoderm induction.

56
Q

Approx. how many nodal genes are there in xenopus?

A

6, there is only 1 in mammals.

57
Q

How does a) vegT and b) vegT combined with beta-cat affect nodal transcription?

A

a) VegT alone causes low level transcription of nodal

b) Where vegT and beta-cat overlap in the Nieuwkoop centre, high level transcription of nodal is activated

58
Q

Cells with beta-catenin are more sensitive to nodal. True or false?

A

True.

59
Q

VegT is specific to anurans. True or false?

A

True.

60
Q

What kind of receptors do FGFs have?

A

Receptor tyrosine kinase.

Development (18 decks)

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