Mechanisms Of Gastrulatuon And Gene Regulatort Networks In Sea Urchins Flashcards
How are spicules formed? And what do they form?
Formed by primary mesenchyme cells.
Early formation of the skeleton
See page 63 lecture 13
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What is the archenteron?
Larval gut, skeletogenic mesoderm, mouth etc.
What is the fluid filled cavity in an embryo called?
Blastocoel
What does the predictability of cell fate suggest?
Internal programming- mosaic development- has an input
What does the unequal 4th cleavage form (right at the bottom of the vegetal pole)? What does this stage suggest?
Produces small micromeres (the cells above them are called macromeres). At this stage suggests we may be getting some internal signals
What do animal half embryos give rise to?
Analyses embryos. Forms a ball of skin cells with cilia (normally form larvae that do not possess a gut)
What is vegetal half embryos give rise to?
Vegetalised embryos- ball of gut with some skeleton structures present
See isolated hemispheres page 65
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What is the combination that the archenteron normally forms in?
. The archenteron is formed from cells of the Veg2 layer in intact embryos- but these are not present in manipulated embryos
. The micromeres therefore appear to exert an important regulatory influence (can change the fate of the cells above)
. The Veg2/ bottom micromere layers tell the layers above them, Veg1, what to develop into, so when you take out Veg 1 they are powerful enough to change what the fate of the animal cells/ what they become
What does animal 1 layer + 4 micromeres form?
Normal pluteus
What does animal 2 layer + 4 micromeres form?
Vegetalised larva-archenteron over-expressed
What does animal 2 layer + 2 micromeres form?
Normal larvae
What does animal 2 layer + 1 micromere form?
Animalised larva, archenteron under-expresses, even permanent blastula (Dauer blastula)
What do Lithium ions do to developing larvae?
Causes vegetalised larvae
What do many dyes, and zinc ions do to developing larvae?
Causes animalised larvae (suggests chemical signals are important)
What is gradient theory?
Positional status of a cell may be defined in relation to 2 gradients of influence- animalising gradient and vegetalised gradient. Chemical gradient could tell cell where they are in the embryo
Explain the gradient theory of sea urchin development
. A complete embryo can be formed by combining cells from animal and vegetal poles
. Certain ‘vital dyes’ (colour living cells) reveal centres of metabolic activity at the animal and vegetal poles
. Possible to imagine a gradient of a ‘morphogen’ produced by the most animal pole cells
. And another produced by the most vegetal pole cells
. Lowest amount of chemical at the pole it is not produced
Explain the french flag model
. Developed by Lewis Wolpert in 1969s
. Each cell has potential to develop as ‘blue’, ‘white’ or ‘red’
. White develops at the interface between blue and red
. In a cell the concentration of chemical/ morphogen determines what they will turn into
What are gene regulatory networks?
On/off switches controlling development
How is transcription regulated?
By binding of proteins to regulatory DNA elements- each cell will experience different combination depending on is location
What do transcription factors influence and how?
They have a positive/enhancer or negative influence on the core element
Middle of page 68
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Describe beta-catenin
. Is a transcription factor, binds to regulatory regions of the DNA
. Derived from maternal RNA deposited in the egg (produced by the mum)
. Accumulated in micromere and Veg2 cell nuclei
Beta-catenin staining in embryo: fluorescent-tagged antibody
Top page 69
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How does the gene regulatory network m work for inhibition?
The events of gastrulation are inhibited by a repressor gene beta-catenin (and Otx) stimulates expression of the Pmar1 gene which switches off the repressor and promotes development of the skeleton (the cells below the repressor have been switched off)
How does a gene regulatory network work in gene activation?
Pmar1 protein activates gene providing an ‘early signal’ to vegetal cell layers promoting differentiation into endoderm and mesoderm. The protein binds to the repressor and deactivates it and also binds to early which tells the cells in the vegetal pole to start differentiating
