Lec 29: Limb Development and Malformations

Question 1

What gives rise to limb connective tissue (skeleton and tendons) and limb muscles?

Answer 1

Connective tissues = lateral mesoderm

Muscles = somites

Question 2

What is syndactyly? Polydactyly? Brachydactyly?

Answer 2

Syndactyly = fused digits
Polydactyly = extra digits
Brachydactyly = shortened digits

Question 3

What is phocomelia? Amelia? Clubfoot?

Answer 3

Phocomelia = missing proximal elements
Amelia = absent limb
Clubfoot = foot is turned inward and downward

Question 4

What signaling molecule determines where along the AP axis of embryo the limb buds form?

Answer 4

Hox

Question 5

What molecule defines forelimb identity? Hindlimb identity?

Answer 5

Forelimb = Tbx5
Hindlimb = Pitx1 -> Tb4

Question 6

What molecule controls outgrowth of limb bud, and what is its source?

Answer 6

FGFs from the apical ectodermal ridge

Question 7

What molecule plays a role in definition of PD limb regions?

Answer 7

Hox (different Hox genes expressed all along limb)

Question 8

What is critical for AP patterning of the limb and formation of digits, and what is its source?

Answer 8

Shh from the zone of proliferating activity

Question 9

What are 2 roles of Shh in the limbs?

Answer 9

Promotes mesenchyme proliferation and promotes AP differentiation
-also regulates Hox in distal limb regions

Question 10

What molecule mediates interdigital cell apoptosis?

Answer 10

BMPs

Question 11

What does thalidomide exposure reduce limb levels of?

Answer 11

FGFs, leading to less outgrowth

Question 12

What results if there is a mutation in Gli3 or ciliary proteins?

Answer 12

Polydactyly