Mesoderm formation in Xenopus Flashcards
(60 cards)
The genes bra, myf5, gsc and vent1 are only expressed in which tissue? When? Do the overlap?
In the mesoderm at early gastrula stage. They do not overlap.
What is bra?
Brachyury: a t-box transcription factor expressed pan-mesodermally.
Where is bra expressed?
Always around the blastopore and always in the notochord.
Without bra the notochord would not form correctly. True or false?
True.
As cells involute over the blastopore they maintain bra expression. True or false?
False: involuting cells lose bra expression.
a) What is gsc?
b? Where is it expressed?
a) Goosecoid: a homeobox TSF
b) Above the dorsal blastopore lip on the future dorsal side
Do bra and gsc overlap in expression?
No.
What is myf5 responsible for?
Myogenic factor 5, TSF responsible for muscle formation.
The expression of bra, gsc, myf5 and vent1 becomes more refined as development progresses. True or false?
True.
In specification map experiments…
a) What happens if you isolate the animal hemisphere?
b) What happens if you isolate the vegetal hemisphere?
a) It only forms epidermis
b) Will not form endoderm, although endoderm genes are being transcribed. Cannot form endoderm without supportive mesoderm.
In specification map experiments…
a) What happens if you isolate the animal hemisphere?
b) What happens if you isolate the vegetal hemisphere?
a) It only forms epidermis
b) Will not form endoderm, although endoderm genes are being transcribed. Cannot form endoderm without supportive mesoderm.
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) 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
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?
Dorsal mesoderm (neural tissue) expresses bra.
Ventral mesoderm (blood) expresses gsc
Equatorial regions express myf5 and vent1.
Outline the experiments by Pieter Nieuwkoop in 1960.
He combined the animal and vegetal hemispheres from different axolotl embryos
In the experiments of Pieter Nieuwkoop in 1960, what happened when he recombined the hemispheres at the start of gastrulation?
Nothing, he just got ectoderm mixed with yolk.
In the experiments of Pieter Nieuwkoop in 1960, what happened when he recombined the hemispheres at mid-blastula stage?
He got endoderm, mesoderm and ectoderm.
How did Pieter Nieuwkoop discover that mesoderm was derived from the animal cap?
He used a normal and an albino embryo.
What was Pieter Nieuwkoop’s conclusion from his experiments?
Mesoderm formed from the animal cap under induction from the vegetal cap.
Describe what changes were made when Nieuwkoop’s experiments were repeated in Xenopus.
The animal cap was labelled with fluorescein. All mesodermal tissues thus expressed fluorescein.
The vegetal cap makes absolutely no physical contribution to the mesoderm. True or false?
True: only involved in signalling.
Nieuwkoop’s experiments only work at which stage of development?
Blastula stage.
What happened in experiments whereby individual blastomeres from the vegetal hemisphere were combined with the animal cap?
Ventral blastomeres induced ventral mesoderm and dorsal blastomeres induced dorsal mesoderm.
How can the ventral/dorsal blastomeres be identified?
They have slightly different pigmentation due to cortical rotation.
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?
The Nieuwkoop centre: it is a specialised inductive centre for dorsal mesoderm. It is found on the extreme dorsal side.
