Lecture 21: Limb Development 1

Question 1

What is considered the actual primordium of the limb?

Answer 1

Limb disc

Question 2

If the limb disc is removed, can a limb still form?

Answer 2

Yes, via the morphogenetic field around the disc

Question 3

T/F: If the limb field is removed, no limb will form.

Answer 3

True

Question 4

Removing half the disc, dividing the disc into two halves, & fusing two discs together results in…?

Answer 4

Normal limb development

Question 5

What initiates future forelimb development?

Answer 5

Tbx5

Question 6

What initiates future hindlimb development?

Answer 6

Tbx4 & Pitx-1

Question 7

What are the initial initiators of limb development?

Answer 7

Tbx5 & Tbx4

Question 8

Expression of which molecules forms AP axis?

Answer 8

Gli-3 (anterior)

Hand-2 (posterior)

Question 9

The AP axis is fixed _____ in development & the DV axis is fixed _____ in development.

Answer 9

Early

Later

Question 10

What happens if you transplant a limb disc to the opposite side?

Answer 10

Normal limb forms with the AP axis reversed

Question 11

What happens if you rotate a limb disc 180 degrees?

Answer 11

Normal limb forms with AP axis reversed

Question 12

What did Slack establish via his “flank tissue” experiment?

Answer 12

Flank tissue posterior to limb disc organizes posterior edge of the disc (posterior organizing region)

Question 13

What substance provides the gradient for the posterior organizing region?

Answer 13

Shh, activated by retinoic acid

Question 14

T/F: The ZPA is the posterior organizing region in birds.

Answer 14

True

Question 15

What signaling molecule determines the position of the ZPA?

Answer 15

Hoxb8

Question 16

What does Shh induce the expression of in the ZPA?

Answer 16

Gremlin

Question 17

How does Gremlin affect the posterior part of the limb bud?

Answer 17

Inhibits BMP-2 which inhibits FGF-4 in AER

Inhibits Gli-3

Question 18

What is expressed in the anterior part of the limb bud to make the anterior part different from the posterior part?

Answer 18

Gli-3

Question 19

What do the dorsal and ventral parts of the ectoderm of the AER express?

Answer 19

Dorsal: Radical fringe
Ventral: En-1

Question 20

T/F: Removal of the AER results in continued outgrowth of the limb bud.

Answer 20

False, results in cessation of outgrowth of limb bud

Question 21

_____ determines morphology of the limb & _____ determines whether the limb grows.

Answer 21

Mesoderm

AER

Question 22

What do cells in the distal limb bud express?

Answer 22

Msx-1

Question 23

What creates the pattern formation in the limb?

Answer 23

Hoxd gene expression

Question 24

Which Hox gene is expressed throughout the entire limb?

Answer 24

Hoxd-9

Question 25

What does the stylopod form?

Answer 25

Humerus or femur

Question 26

What does the proximal zeugopod form?

Answer 26

Radius/Ulna or Tibia/Fibula

Question 27

What does the distal zeugopod form?

Answer 27

Carpals or tarsals

Question 28

What does the proximal autopod form?

Answer 28

Metacarpals or metatarsals

Question 29

What does the distal autopod form?

Answer 29

Phalanges

Question 30

When is mesenchyme of the limb bud determined?

Answer 30

Before closure of the neural tube

Question 31

What is the structure of the developing limb determined by?

Answer 31

Mesodermal components

Question 32

T/F: Ectoderm tells the mesoderm what to form/make.

Answer 32

False, mesoderm tells the ectoderm what to form/make

Question 33

What maintains the AER in a healthy state and where is it produced?

Answer 33

Apical Ectodermal Maintenance Factor (AEMF)

Mesoderm

Question 34

AER maintains the mesodermal cells in a _____ and _____ state.

Answer 34

Labile

Mitotic

Question 35

T/F: Apoptosis is not a mechanism for morphogenesis.

Answer 35

False, it is a method for morphogenesis