Evolutionary Biology 5: embryogenesis functionality

Question 1

Functions of hedgehog signalling

Answer 1

Controls a wide range of animal developmental processes

Necessary for cell patterning and differentiation, producing arrays of complex cell types in different locations

Question 2

Function of hedgehog paracrine factor diffusion gradient

Answer 2

Concentration within the gradient determines the identity the differentiating cells will take on

i.e
High conc. First type of cell
Med conc. Second type
Low conc. Third type

Question 3

What are Wnts?

Answer 3

Wnts are ligands for frizzled receptors

Frizzled receptors are g-protein coupled receptors

Frizzled receptors signal through ‘canonical’ and ‘non-canonical’ pathways

• Canonical, mediated by beta-catenin signalling
• Non-canonical, mediated by Rac/Rho signalling

Question 4

Functions of Wnt signalling?

Answer 4

Cell

• proliferation
• fate determination
• polarity

Question 5

Describe Wnt signalling control of body axis formation (canonical)

Answer 5

• Wnts generate a posteriorising signal
• During vertebrate development, Wnt ligands establish and conc. gradient
• Wnt low in future anterior region, hign in future posterior region
• Disruption of this gradient disrupts anterior-posterior patterning

Question 6

Evidence - how globular embryo initiate cotyledons and become bilaterally symmetric?

Answer 6

Auxin

1 - all embryos synthesise auxins - bean to pine
2 - IAA transport -> along apical-basal axis
- basipetal - from shoot meristem to root tip
3- Chemical inhibitors that block polar transport of auxin -> collar ring