Mechanisms Of Gastrulatuon And Gene Regulatort Networks In Sea Urchins

Question 1

How are spicules formed? And what do they form?

Answer 1

Formed by primary mesenchyme cells.

Early formation of the skeleton

Question 2

See page 63 lecture 13

Answer 2

….

Question 3

What is the archenteron?

Answer 3

Larval gut, skeletogenic mesoderm, mouth etc.

Question 4

What is the fluid filled cavity in an embryo called?

Answer 4

Blastocoel

Question 5

What does the predictability of cell fate suggest?

Answer 5

Internal programming- mosaic development- has an input

Question 6

What does the unequal 4th cleavage form (right at the bottom of the vegetal pole)? What does this stage suggest?

Answer 6

Produces small micromeres (the cells above them are called macromeres). At this stage suggests we may be getting some internal signals

Question 7

What do animal half embryos give rise to?

Answer 7

Analyses embryos. Forms a ball of skin cells with cilia (normally form larvae that do not possess a gut)

Question 8

What is vegetal half embryos give rise to?

Answer 8

Vegetalised embryos- ball of gut with some skeleton structures present

Question 9

See isolated hemispheres page 65

Answer 9

…

Question 10

What is the combination that the archenteron normally forms in?

Answer 10

. 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

Question 11

What does animal 1 layer + 4 micromeres form?

Answer 11

Normal pluteus

Question 12

What does animal 2 layer + 4 micromeres form?

Answer 12

Vegetalised larva-archenteron over-expressed

Question 13

What does animal 2 layer + 2 micromeres form?

Answer 13

Normal larvae

Question 14

What does animal 2 layer + 1 micromere form?

Answer 14

Animalised larva, archenteron under-expresses, even permanent blastula (Dauer blastula)

Question 15

What do Lithium ions do to developing larvae?

Answer 15

Causes vegetalised larvae

Question 16

What do many dyes, and zinc ions do to developing larvae?

Answer 16

Causes animalised larvae (suggests chemical signals are important)

Question 17

What is gradient theory?

Answer 17

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

Question 18

Explain the gradient theory of sea urchin development

Answer 18

. 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

Question 19

Explain the french flag model

Answer 19

. 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

Question 20

What are gene regulatory networks?

Answer 20

On/off switches controlling development

Question 21

How is transcription regulated?

Answer 21

By binding of proteins to regulatory DNA elements- each cell will experience different combination depending on is location

Question 22

What do transcription factors influence and how?

Answer 22

They have a positive/enhancer or negative influence on the core element

Question 23

Middle of page 68

Answer 23

…

Question 24

Describe beta-catenin

Answer 24

. 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

Question 25

Top page 69

Answer 25

…

Question 26

How does the gene regulatory network m work for inhibition?

Answer 26

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)

Question 27

How does a gene regulatory network work in gene activation?

Answer 27

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