Signalling 3 - Intermediate Range Signalling

Question 1

How many cells does paracrine signalling act over?

Answer 1

1-100 cells

Question 2

When have most of the structures of an embryo formed?

Answer 2

• 8 weeks
• they then grow later

Question 3

explain early limb development in chicks, mice and humans

Answer 3

• highly conserved
• different later on in development

Question 4

Why would you study development in a chick embryo?

Answer 4

• develops in egg and not womb
• remove sections of shell and put in incubator - windowing

Question 5

What do mature wings develop from?

Answer 5

limb buds

Question 6

when does limb formation in a chick start?

Answer 6

around 3 days after fertilisation

Question 7

Explain the limb axes

Answer 7

proximo-distal
- proximal - close to body
- distal - distant from body

anterio-posterior
- thumb - digit 1 - anterior
- pinkie - digit 5 - posterior

Question 8

What is the distal end of the limb?

Answer 8

away from the body

Question 9

What is the proximal end of the body?

Answer 9

close to the body

Question 10

What is the anterior part of the arm?

Answer 10

thumb - digit 1

Question 11

What is the posterior part of the body?

Answer 11

little finger - digit 5

Question 12

What is the dorsal-ventral axis?

Answer 12

top of body to Bottom
- top - knuckles = dorsal
- bottom - palm = ventral

Question 13

What are the digits in the chick wing?

Answer 13

• 1
• 3
• 4

Question 14

What is the AER?

Answer 14

• apical ectodermal ridge
• structure at the tip of limb bud

Question 15

What happens if you remove the AER?

Answer 15

• development disrupted along proximal-distal axis
• the earlier AER is removed, the less wing that forms
• suggests important over a period

Question 16

What happens if you replace the AER with a supply of FGF4 signalling molecule soaked beads?

Answer 16

Wing formation is restored

Question 17

What is a morphogen?

Answer 17

a substance active in pattern formation whose special concentration varies and to which cells respond differently at different threshold concentrations

Question 18

What is the French flag model?

Answer 18

• morphogen is present at different concentrations at different positions
• cells respond to different concentrations by going a different colour in this model

Question 19

What is the ZPA?

Answer 19

• zone of polarising action
• at posterior end of limb bud
• secretes SHH
• an organiser

Question 20

what happens if you graft the ZPA onto the anterior end of the wing?

Answer 20

• the wing will create a mirror image of the other side and be symmetrical

Question 21

what happens if you graft SHH producing cells on the anterior axis?

Answer 21

• wing develops as a mirror image of itself and has a line of symmetry

Question 22

What is an organiser?

Answer 22

• signalling centre that directs the development of the whole embryo or part of the embryo