Animal development 3 Flashcards
What is gastrulation?
The formation of the hut and main body plan
Describe echinoderm gastrulation
The vegetal pole of the blastula flattens
Some cells change shape and move inwards to form the archenteron
Other cells break free and become the primary mesenchyme
More cells break free and become the secondary mesenchyme
Thin extensions of these cells (filopodia) attach to the overlying ectoderm
The archenteron is elongated by contraction of the mesenchymal filopodia and cell rearrangement
The mouth will form where the archenteron meets the ectoderm
The blastopore will form the anus
Describe radial cleavage
Animal cells from the ectoderm
Vegetal cells from the endoderm and mesoderm
Unequal 4th cleavage forms small micromeres at the 16th cell stage
What happens if the cells are separated at the 4 cell stage?
There is complete developmental flexibility at the 4 cell stage if the cells are separated
The animal half embryos give rise to ‘animalised’ embryos
The vegetal half embryos give rise to ‘vegetalised’ embryos
What happens to animal half embryos if they grow?
Form larvae that do not possess a gut
What happens if the animal half embryo is combined with 4 micromeres?
Forms a normal ‘pluteus’ larva
The archenteron forms normally but is usually formed from cells of the Veg2 layer in intact embryos
Thus micromeres can exert regulatory influence
What does the Ani1 layer and 4 micromeres produce?
Normal pluteus
What does the Ani2 layer and 4 micromeres produce?
Vegetalised larva as the archenteron is over-expressed
What does the Ani2 layer and 2 micromeres produce?
Normal larva
What does the Ani2 layer and 1 micromere produce?
Animalised larva where the archenteron is under-expressed and gives a permanent blastula (Dauer blastula)
What is gradient theory?
The positional status of a cell may be defined in relation to the concentration gradients of chemical signals or morphogens
What is the French flag model?
Each cell has the potential to develop into white, red, or blue
However white will have to develop at the interface of the red and blue
Explain the importance of β-catenin
Is a transcription factor derived from maternal RNA deposited in the egg
Accumulates in the micromere and Veg2 cell nuclei (binds to DNA)
What does LiCl treatment do to β-catenin?
Causes it to accumulate in the cell nuclei all over the blastula causing a vegetalised larva
What does treatment preventing β-catenin from entering the nuclei do?
Produces animalised larva
