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Vertebrate development Flashcards

(48 cards)

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1
Q

What are the 3 germ layers that form

A

Ectoderm - Skin
Mesoderm - Muscle, skeleton, blood
Endoderm, gut

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2
Q

What are the advantages of using Xenopus to look at early embryo processes

A

Large abundant eggs
Develop externally
Easy to inject with dyes and other stuff
Micro surgery possible
Conserved Structure with Humans

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3
Q

Describe the structure of a fertilised Egg

A

Animal pole - EPIBLAST
Vegetal pole - HYPOBLAST

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4
Q

What does the vegetal pole contain

A

Maternal genes that pattern the animal pole

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5
Q

What maternal genes pattern the animal pole

A

T-box genes - VegT –> Nodal morphogen expression in Veg pole cells

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6
Q

What is Nodal and how does it act

A

A TGF-B morphogen
High nodal-> Endoderm fate
Low nodal -> Mesoderm fate
No nodal -> Ectoderm fate

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7
Q

What germ layers arise from where as a result of Nodal signalling

A

Vegetal pole becomes Endoderm
Animal pole border cells become Mesoderm
Rest of animal pole becomes Ectoderm

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8
Q

What cells give rise to the organiser (hensons node)

A

Nieukoop center cells

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9
Q

Name a symmetry breaking event why

A

Fertilisation as it causes shifts in cytoplasmic contents

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10
Q

What happens during fertilisation that leads to creation of the organiser

A

Sperm entry causes a cortical rotation in the egg cell that positions Dorsalising factors to the opposite end of the cell to where sperm entered.
In Xenopus this is a 30 degree rotation

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11
Q

What are the doralising factors and how do they pattern the nieukoop center

A

They are Wnt and Dishevelled - Visualised using B-catenine
Expression of both Wnt and Nodal in the now Dorsal part of the vegetal hemisphere leads to organiser fate

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12
Q

How do Nodal and Wnt act on the genome to activate organiser fate

A

Nodal is a distal enhancer that allows the proximal binding of B-catenine to proximal enhancer of genes

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13
Q

How is nodal activated and used to bind to enhancers

A

Via binding of SMAD2

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14
Q

What are the genes that specify organiser fate

A

Goosecoid
Samoins
Not1
Lim1

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15
Q

What TF is expressed throughout the mesoderm before gastrulation

A

Brachyury

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16
Q

How is gastrulation initiated

A

The combination of gene targets from Brachyury and organiser TF induces dorsal axial mesoderm which then starts gastrulation

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17
Q

How does gastrulation ‘move’

A

Using convergent extension which patterns cells posteriorly at first and then moves anteriorly

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18
Q

How does involution occur during gastrulation

A

Bottle cells create a dorsal lip that follows underneath extending organiser.

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19
Q

What cavity grows during gastrulation

A

The archenteron

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20
Q

What does the archenteron form and how so?

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A

Forms the gut as it is lined with endodermal cells

21
Q

Which cavity shrinks during gastrulation

22
Q

What do Ectodermal cells do during gastrulation

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A

Spread around the gastrula surface - EPIBOLY

23
Q

What mammalian structure is analogous to the dorsal blastopore lip in Xenopus

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A

The primitive streak

24
Q

At what point in a Human embryo do we see formation of ‘animal and vegetal poles’

25
Overall what Axes are formed during gastrulation
The anterior posterior axis and Dorsal Ventral Axis
26
The organiser comprises of..
Mesodermal progenitor cells
27
What 3 cell types does the organiser give rise to
Anterior endoderm pre-chordal mesoderm notochord
28
How was the organiser discovered
Spemann and Mangold cut out and provided ectopic dorsal mesoderm cells before gastrulation to a different egg. created a A-P axis
29
Does the organiser change the signals it sends out over time
YES
30
What signals does the early organiser express
Cerberus - Wnt and Bmp antagonist Other bmp and wnt antagonists
31
What signals does mid organiser express
Same as early but no cerberus
32
What signals does late organiser express
Only BMP antagonists
33
What are the positions of the stages of the organiser
Late organiser is posteriorly located as the organiser originated posteriorly Early organiser is found anteriorly as it is newly created as the organiser convergently extends anteriorly
34
What antagonists from the organiser form the head and brain
Wnt and BMP antagonists as they are present in early organiser
35
As a result of antagonist action what signal will be present in the posterior organiser
Wnt due to lack of Wnt antagonists
36
What signals from the organiser pattern the neural plate
BMP antagonist chordin, Noggin and cerberus
37
Why is cerberus important in head induction
It is only expressed anteriorly in early organiser. It inhibits wnt8 and bmp4 allowing for a separate identity to the rest of the neural tube
38
How does the organiser pattern dorso-ventrally
Creates gradient of BMP activity, highest away from organiser (ventrally)
39
How does the organiser pattern Anterior-Posteriorly
Wnt activity gradient, highest posteriorly
40
What promotes spinal chord fate
BMP inhibition without Wnt inhibition
41
How are different spinal chord fates determined
At first all neural tissue was induced by cerberus expression in early extending organiser. Mid and late organiser don't express Wnt antagonist as highly (or at all). Posterior now exposed to Wnt and retanoic acid and FGF gradients which patterns it posteriorly, removing anterior forebrain fate.
42
Overall what induces neural tube fate
Bmp antagonists
43
What patterns neural tube A-P axis
anterior expression BMP antagonists, Wnts, FGFs and RA which increase posteriorly differential expression of this activates HOX genes
44
What specifically induces expression of HOX genes in the neural tube
Retanoic acid conc gradient
45
The order of Hox genes expressed A-P and the regions they give rise to
hox5 - Neck hox6 + hox9 - thoracic region hox9 + hox10 - Lumbar Hox10 +hox11 - Sacral hox11 - Caudal (tail)
46
Neurulation
Plate folds in half, with most distal cells becoming Roof plate and Neural crest cells, which escape and form other structures
47
D-V patterning of neural tube
BMPs from roof plate create differential expression patterns with the distances they travel Shh expressed in notochord induces Shh in neural tube floor plate cells which the pattern the ventral tube using morphogen gradient
48
What Tfs are expressed as a result of Shh signalling in the neural tube?
Pax7, Pax6 and Nkx6.1 Low shh<-------high shh

Advanced Development (8 decks)

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