Unit 3: Limb development

Question 1

What are the 3 axis of the limb ?

Answer 1

1) Proximal-Distal
2) Anterior- Posterior
3) Dorsal- Ventral

Question 2

What 3 components is the Proximal- Distal subdivided into ?

Answer 2

1) Stylopod
2) Zeugopod
3) Autopod

Question 3

What is the stylopod ?

Answer 3

The humerus

Question 4

What is the zeugopod ?

Answer 4

The ulna and radius

Question 5

What is the autopod ?

Answer 5

The metacarpals and digits

Question 6

What germ layer gives rise to the limbs ?

Answer 6

• Lateral plate mesoderm
• Ectoderm

Question 7

What does inner limb tissue develop from ?

Answer 7

It develops from lateral plate mesoderm

Question 8

What does the limb bud consist of ?

Answer 8

Loose mesenchyme from the lateral plate mesoderm covered by epithelial tissue from ectoderm

Question 9

What is muscle formed from ?

Answer 9

Paraxial mesoderm (somites)

Question 10

What are nerves formed from ?

Answer 10

Neuroectoderm

Question 11

How is the apical ectodermal ridge formed (AER) ?

Answer 11

By a localised thickening (cuboidal to columnar shape cells)

Question 12

What is the apical ectodermal ridge (AER) ?

Answer 12

A region of thickened ectoderm at the distal (tip) end of the limb bud that plays a crucial role in regulating the growth and patterning of the developing limb

Question 13

What does removal of the AER lead to ?

Answer 13

Truncations

Question 14

What is a truncation ?

Answer 14

The absence or incomplete development of a part of a limb

Question 15

Removal of AER leads to truncations, what does this mean (2) ?

Answer 15

1) The AER regulates P-D outgrowth
2) Proximal tissues are laid down first

Question 16

What can be substituted for AER ?

Answer 16

Fibroblast growth factors (FGFs)

Question 17

What would you think the result of removing Fgf10 early during limb development would be ?

Answer 17

No signs of limb development

Question 18

Does the apical ectodermal ridge control P-D patterning ?

Answer 18

No

Question 19

What is the progress zone (PZ) ?

Answer 19

• A crucial region for the growth and patterning of limbs
• It consists of proliferating, undifferentiated mesodermal cells that move from the distal part of the limb bud towards the proximal region.

Question 20

The first cells to leave the PZ, differentiate into what identity ?

Answer 20

Proximal identity

Question 21

The last cells to leave the PZ, differentiate into what identity ?

Answer 21

Distal identity

Question 22

What set of genes that are expressed along the P-D axis, specify the fate of cells ?

Answer 22

HOX A genes

Question 23

What is the relationship between time a cell spends in PZ and HOXA gene expression ?

Answer 23

The longer a cell is in the PZ, the more HOXA genes it expresses

Question 24

What do HOXA genes determine ?

Answer 24

Wether that cell is part of the stylopod, zeugopod or autopod

Question 25

What is the zone of polarising activity (ZPA) ?

Answer 25

A specialized group of mesodermal cells located in the posterior region of the limb bud

Question 26

What does the ZPA produce ?

Answer 26

A difffusable signalling molecule whose effect is concentration dependant (Morphogen)

Question 27

What can ZPA activity be mimicked by ?

Answer 27

Sonic hedgehog (SHH)

Question 28

What genes are often expressed in cells to determine their position along an axis ?

Answer 28

HOXD genes (Determine antero-posterior identity)

Question 29

What does HOXA gene expression determine ?

Answer 29

Proximal- Distal identity

Question 30

What is D-V patterning controlled by ?

Answer 30

Ectoderm (Wnt7a is the dorsal factor)

Question 31

How is the development of the 3 axis coordinated (3) ?

Answer 31

1) AER removal leads to loss of ZPA 2) Loss of ZPA leads to loss of AER 3) Loss of dorsal ectoderm signal leads to loss of AER and therefore ZPA

Question 32

Which is the correct statement about the progress zone ? 1) It is in the ectoderm 2) It resides under the apical ectodermal bridge 3) The whole of it expresses shh 4) It is derived from paraxial mesoderm

Answer 32

2) It resides under the apical ectodermal ridge