Embryo Skeletogenesis

Question 1

What initiates limb outgrowth?

Answer 1

TBX5-forearm & FGF10 TBX4-Hind limb & FGF10

Question 2

1. ZPA stands for________
2. ZPA Produces_____
3. ZPA directs _____
4. Misexpression of ZPA products results in _____ _____
5. ZPA determines ____ & _____ axes

Answer 2

1. ZPA=Zone of Polarizing Activity
2. Produces - Retinoic Acid which initiates SHH expression
3. Directs - digit patterning/ limb bud organization
4. Misexpression of ZPA products (Retinoic acid and SHH) leads to duplication of limb structures.
5. ZPA determines anterior (preaxial/thumb) & posterior (postaxial) axes.

Question 3

What three LATERAL PLATE MESODERM cell types contribute to limb development?

Answer 3

1. Hypaxial mesoderm
   
   1. Muscle
2. Neural Crest cells
   
   1. Schwann cells
3. Neural tube
   
   1. Motor axons (dermatome map)