Limb development question

Question 1

Explain the role of the apical ectodermal ridge:

Answer 1

Sustains growth and development of limbs
- Maintains outgrowth of limb bud
- Keeps cells in PZ in undifferentiated states
- Tells mesenchyme cells to continue making FGF

Question 2

If AER is removed:

Answer 2

Limb development ceases

Question 3

If AER is extra:

Answer 3

Duplication of limb

Question 4

Explain the role of progress zone:

Answer 4

The progress zone is the sub-AER mesoderm
- Region of mitosis responsible for limb bud elongation
- PZ mesenchyme specifies skeletal identities along P-D axis

Question 5

Explain the role of ZPA:

Answer 5

Patterns the AP axis
- Grafting of ZPA to anterior limb bud mesoderm will duplicate digits

Question 6

Specific role of FGF in initiating limb-bud formation bilaterally along the anterior-posterior axis

Answer 6

FGF signals in lateral plate mesoderm will determine where limbs will forms

Question 7

Discuss the specific transcription factors involved in the identity (fore versus hind limb) of the limb along the A-P axis

Answer 7

• Forelimb: FGF expression near Tbx5 in the forelimb
• Hindlimb: FGF expression near Tbx4 in the hindlimb