Mechanisms of gastrulation

Question 1

Animal half embryos give rise to…

Answer 1

animalised embryos.
Vegetal half embryos give rise to vegetalised embryos
This suggests embryos can change their development in response to environmental signals- developmental flexibility is associated with REGULATIVE DEVELOPMENT.

Question 2

What is powerful micromeres?

Answer 2

An animal half embryo combined with 4 micromeres gives rise to a normal pluteus.

Question 3

What is the archenteron?

Answer 3

It is formed from cells of the veg2 layer in intact embryos- not present in manipulated embryos.
THEREFORE MICROMERES ARE IMPORTANT REGULATORY INFLUENCE

Question 4

How many micromeres are needed?

Answer 4

Animal 1 layer + 4 micromeres :normal pluteus
Animal 2 layer + 4 micromeres :vegetalised larva
Animal 2 layer + 2 micromeres :normal larva
Animal 2 layer + 1 micromere: animalised larva

Question 5

Larva can be animalised or vegetalised by exposure to what?

Answer 5

Lithium ions - vegetalised

Zinc ions- animalised

Question 6

The positional status may be defined in relation to what two gradients of influence

Answer 6

animalising gradient and vegetalising gradient

Question 7

Lewis Wolpert (1960)
FRENCH FLAG MODEL

Answer 7

Each cell has potential to develop as red, white, blue.

Question 8

B-catenin specifies..

Answer 8

Micromeres.
B-catenin is a transcription factor derived from maternal RNA deposited in the egg. Accumulates in micromere and veg2 cell nuclei,

Question 9

What does B-catenin do?

Answer 9

.Stimulates expression of pmar1gene
.Switches off repressor
.Promotes development of endoderm, mesoderm and skeleton.