20: Limb Development

Question 1

AER

Answer 1

Apical ectodermal ridge; a thick, multilayered band of ectoderm along the ridge of each limb bud

Question 2

What causes limb buds to bulge outward?

Answer 2

Outgrowth of mesenchyme from lateral plate mesoderm

Question 3

When do lower and upper limb buds form?

Answer 3

Upper: day 24
Lower: day 25-26

Question 4

The three regions of the limb bud and what they produce in the arm

Answer 4

1. Stylopod -> humerus
2. Zeugopod -> radius and ulna
3. Autopod -> carpals, metacarpals, phalanges

Question 5

What induces the AER?

Answer 5

FGF10

Question 6

Positive feedback loop with FGF

Answer 6

FGF8 secreted by AER -> stimulates FGF10 production-> stimulates AER

Question 7

What axis of the limb does FGF signaling regulate?

Answer 7

Proximal-distal axis

Question 8

Complete removal of AER

Answer 8

Arrests limb development

Question 9

Removal of AER at a late stage

Answer 9

Loss of more distal elements of the limb

Question 10

Transplanting an AER causes?

Answer 10

Supernumerary limbs

Question 11

When does restriction of limb cell fates occur?

Answer 11

Before limb bud outgrowth

Question 12

What happens if ZPA is grafted to cranial limb bud mesoderm?

Answer 12

Duplicated digits (polydactyl)

Question 13

What type of signaling does apoptosis to form digits require?

Answer 13

BMP signaling

Question 14

BMP in digit formation

Answer 14

BMP increases cell death; less BMP can cause webbed digits

Question 15

What innervates the dorsal and ventral muscle masses of an extremity?

Answer 15

Dorsal muscle mass: dorsal branches of ventral rami

Ventral muscle mass: ventral branches of ventral rami

Question 16

Where do limb tendons arise from vs where tendons arise from in vertebral column

Answer 16

Limb tendons: somatic layer of lateral plate mesoderm

Vertebral column tendons: syndetome of somite

Question 17

What supplies blood to limbs in development?

Answer 17

Intersegmental arteries

Question 18

Primordial vascular pattern

Answer 18

Primary axial arteries and branches

Question 19

What does primary axial A become in upper limb? (2 things)

Answer 19

Brachial artery, common interosseous artery

Question 20

What does the primary axial A become in LE? (2 things)

Answer 20

Deep artery of the thigh, anterior and posterior tibial arteries

Question 21

Primitive venous supply

Answer 21

Primary axial V drains into marginal sinus -> peripheral vein

Question 22

Rotation of limbs

Answer 22

UE: rotates laterally
LE: rotates medially