Amphibian Gastrulation And Primary Embryonic Induction Flashcards
See page 92!
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Explain what the Distal-less (DII) gene is responsible for in drosophila larvae and where it is expressed/ inhibited
In drosophila Distal-less (DII) gene is critical for forming proximal-distal axis of appendages (drosophila larvae do not have any appendages themselves).
Expressed in head and thorax, inhibited by Abd-A and Ubx in abdomen-linked yo presence of appendages (none in abdomen)
Unlike Drosophila butterfly larvae have prolegs on their abdomen. Why is this?
Abd-A, Ubx and DII expression (identical in drosophila but in butterflies in some regions these are not being switched on) similar between Drosophila and butterfly early in development, but Abd-Ab and Ubx expression is later in development, but Abd-A and Ubx expression is later inhibited in patches of the abdomen in buttery only- allowing expression of DII and development of prolegs
Ultrabithorax (Ubx) is expressed throughout the imaginal discs in which segment?
The third thoracic segment
Butterflies have hindwings however flies have what?
Halteres
What is the difference in general pattern of Hox gene expression in flies and butterflies?
There is no difference
See middle page 93. Sentence beginning many of the genes…
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In vertebrates which side of the animal does the central nervous system run down?
The dorsal side
What gives rise to internal organs In gastrulation in amphibians?
Future Endodermal and mesodermal cells move from the outer surface of the embryo to the inside, where they give rise to internal organs
Where do the future mesoderm and ectoderm lie?
In the marginal zone immediately below the animal pole
Give an overview at gastrulation
. Begins with bottle cells forming in the blastopore region followed by involutuon if mesoderm at dorsal lip and under the ectoderm
. Marginal zone endoderm moves onwards under the mesoderm, forming roof of anchenton
. Ectoderm cells spread out (epiboly), from animal pole, eventually covering embryo
. Mesoderm cells move under ectoderm (convergent extension)
. Tissue movements create a new body cavity, the archenteron, which will become the gut
. The blastocoel reduces in size and blastopore surrounds a yolk plug
. (The cells in the vegetal poles of amphibians are larger than in the animal pole because they have more yolk in them)
. (The bottle cells move onwards and start forming the tube that will later form into the gut but this occurs in one of the lateral sides of the embryo, so it actually occurs at the side of the embryo forming the dorsal lip- and what starts to happen is that these cells will start to thicken and move onwards and you get a tube surrounded by ectoderm that moves up this side and moves into the top of the embryo forming the gut. The cells that form the mesoderm they also move onwards and follow the extension of the developing ectoderm cells and become parallel to the ectoderm, forming a sort of sandwich look and they actually move inside that whole the is formed by the dorsal lip. This forms a displacement and shiftsbthe blastocoel to the side, so the gut forms here
What does the archenteron become in gastrulation?
The gut
How is the roof of the archenteron formed?
Marginal cone endoderm moves inwards under the mesoderm
How does gastrulation begin?
With bottle cells forming in the blastopore region followed by involution of mesoderm at dorsal lip and under the ectoderm
What are the cells in vegetal poles of amphibians larger than in the animal pole?
Because they have more yolk in them
In neurulation what does the midline notochord form?
The vertebral column
In neurulation what does the dorsal-lateral the somites form?
Vertebrae, ribs, muscle and skin
What are cells that overlie the mesoderm cells destined to become?
The nervous tissues of the brain and spinal cord (the neurectoderm)
What is the tissue of the brain and spinal cord called?
Neurectoderm
What is the inner lining of the gut formed by?
The ectoderm
What does the mesoderm go on to form?
The notochord- which will later turn into the vertical column running down the dorsal surface of the animal
Ectoderm cells roll up and form a tube which is? What is this called?
The spinal cord and in the anterior the brain- neurolation
How is the neural tube formed?
. Inwardly migrating cells form the roof of the archenteron
. These cells will form the dorsal mesoderm:
- in the midline notochord
- dorso-lateral the s’mores. Cells that overlie these mesoderm cells are destined to form the nervous tissue of he brain and spinal cord
. The neuroectoderm
. First they form the neural plate
. Then the plate forms a neural groove
. And finally a neural tube
The role of the underlying mesoderm in specifying the fate of the overlying ectoderm was discovered early in the 20th century by the embryologist Hans Spermann and his collaborators. What was this proceeds termed?
Primary embryonic induction
What is the primary embryonic induction process?
Mesoderm cells signal to the ectoderm cells above them to turn into the nervous system
Typically the mesoderm will cause ectoderm to form what?
Neurectoderm
What does implanted mesoderm beneath presumptive ectoderm cause?
The formation of neural structures
If the gray crescent is not present what structures don’t develop?
No dorsal structures develop- the nervous system, notochord, somites)
What does the gray crescent region give rise to?
Cells that form the dorsal lip of the blastopore
They did an experiment where they cut the embryo so only one side had the grey crescent region in it. What happened to the side with no grey crescent region?
The part of the embryo that didn’t have the grey crescent region only developed the ventral structures- the gut
Fate of dorsal lip is established early in development and is capable of what?
Capable of inducing host embryo cells to change their fate
Dorsal lip cells and their derivatives were termed what?
An organiser
The induction of the dorsal axis and neural tube is termed what?
Primary embryonic induction
What was the experiment Spemann and Mangold did and what happened?
They transplanted the dorsal lip in early stages into a different region and the embryo developed two nervous systems- two heads, backbones etc.- organiser cells)
Define determination
A stable change in the internal state of a cell such that its fate is now fixed, or determined
Define induction
The process whereby one group of cells signals to another group of cells in the embryo and so influences how they will develop
Define primary embryonic induction
The induction of the whole body/ dorsal axis
Define organiser
A signalling centre that directs the development of the whole embryo or part of the embryo, such as a limb (in amphibians, dorsal lip known as ‘Spemann organiser’)
Goosecoid protein activates genes in the organiser important instructing what?
The nervous system to form
Siamois protein interacts with what to control what?
With transforming growth factor- beta proteins to control goosecoid transcription(turns it on)
Beta-catenin activates expression of what gene in which part of the embryo?
Expression of the siamois gene in future dorsal half
The siamois gene is normally repressed by which transcription factor? In which part of the embryo does this take place?
. The Tcf-3 transcription factor
. The future ventral half of embryo
What is the Neiuwkoop centre?
Induction by organiser signalled by cells in the Nieuwkoop centre- where beta- catenin and TGF-beta proteins overlap
Experimental inactivation of GSK-3 allows accumulation of what? In which region? What is formed?
Accumulation of beta-catenin in ventral region- 2 dorsal aces formed
Where is beta-catenin mostly found?
On the future dorsal surface
Where is beta-catenin initially synthesised?
Throughout the embryo from maternal mRNA
Where is the Dishevelled, Dsh, protein found?
In the vegetal pole, occurs in the same region as the dorsal lip when the embryo has rotated and the grey crescent region has formed
After fertilisation what happens to Dsh protein?
It is transported by microtubules along cortical cytoplasm to future dorsal region (gray crescent)
What does glycogen synthase kinase 3, GSK-3, normally do?
Degrades beta-catenin
What does Dsh do to GSK-3 in the future dorsal region? what does this mean for the nuclei in the future dorsal and ventral regions?
Dsh blocks GSK-3 in future dorsal region- so protects beta-catenin in this region.
So future dorsal nuclei receive beta-catenin, but future central do not
See pages 99 and 100
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Recombinant DNA technology enable mRNA to be extracted from blastopore lip to make what?
cDNA clones
Sequence cDNA clones to identify what?
Genes and test effects of mRNA and encodes proteins
See page 101: molecular biology of the organiser
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What does bone morphogenetic protein 4 (BMP4) do?
. Inhibits cells from forming neural tissues
. Promoted formation of ventral structures, it’s absence promotes dorsal structures
How is BMP4 expressed during gastrulation?
Expressed ventrally
What suppress BMP4 signalling in the dorsal region?
Several genes expressed by the organiser
What allows dorsal mesoderm structures to form?
Genes associated with the formation of ventral structures are inhibited by the molecules secreted by organiser cells, allowing dorsal mesoderm structures to form
The organiser-specific proteins block what? Allowing what?
Block the BMP4 and allow the region to be dorsal
BMP4 (Dpp)/ chordin (Sog) interaction is an evolutionary ancient way of instructing the development of what?
A nervous system (difference in where BMP4 and Dpp are expressed accounts for dorsal or ventral localisation)
See page 101
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