10/10 Limb Development - Dennis

Question 1

What is musculature derived from?

Answer 1

paraxial mesoderm which produces myotomes

Question 2

What are bones derived from?

Answer 2

lateral plate mesoderm from the somatic region

Question 3

What are tendons derived from?

Answer 3

lateral plate mesoderm from the somatic region

Question 4

At what point point are both limb buds present?

Answer 4

4th week

Question 5

At what point do hand/feet plates appear>

Answer 5

5th week

Question 6

At what point does chondrification begin?

Answer 6

5th week

Question 7

At what point do the digital rays of hands appear?

Answer 7

6th week

Question 8

At what point do we see a cartilaginous limb skeleton?

Answer 8

6th week

Question 9

At what point do the digital rays of the feet appear?

Answer 9

7th week

Question 10

At what point does osteogenesis begin?

Answer 10

7th week

Question 11

At what point does limb rotation begin?

Answer 11

7th week

Question 12

At what point do separate digits form?

Answer 12

8th week

Question 13

At what point does primary ossification begin?

Answer 13

12th week

Question 14

At what point does the upper limb bud form?

Answer 14

24 days

Question 15

At what point does the lower limb bud form>

Answer 15

28 days

Question 16

What developmental name is given to the humerus?

Answer 16

stylopod

Question 17

What developmental name is given to the forearm?

Answer 17

zeugopod

Question 18

What developmental name is given to the hand?

Answer 18

auto pod

Question 19

What induces a limb bud to form? What kind of signalling is happening?

Answer 19

Fgf10 from lateral plate mesoderm activates Wnt

These Wnt’s then induce Fgf8 in the ectoderm (the growing part of the limb bud)

Fgf8 causes production of more Fgf10

This creates a positive feedback loop

Question 20

What is proximal distal outgrowth of the limb bud controlled by?

Answer 20

Apical Ectodermal Ridge (AER)

Question 21

What does the Apical Ectodermal Ridge secrete? (AER)? What is the function of the secretion?

Answer 21

Fibroblast growth factor 8 (FGF8)

FGF8 can mimic the AER by inducing supernumerary limbs

Question 22

What Hox paralogs give rise to the stylopod?

Answer 22

Hox 9 - 10 Paralogs

Question 23

What Hox paralogs give rise to the Zeugopod?

Answer 23

Hox 11 Paralogs

Question 24

What Hox paralogs give rise to the Autopod?

Answer 24

Hox 12 - 13 paralogs

Question 25

Define Paralog?

Answer 25

genes that are related to each other because they come from a common ancestral DNA sequence

Question 26

Prior to limb bud outgrowth what is the one of the first directional restrictions seen?

Answer 26

Anterior posterior specification

Question 27

What decides the overall shape and direction of the limb bud?

Answer 27

Zone of Polarizing Activity (ZPA)

Question 28

What does the Zone of Polarizing Activity produce?

Answer 28

Sonic hedgehog (Shh)

Question 29

If you were to remove a Zone of Polarizing Activity (ZPA) and implant it into an anterior limb bud what would you expect to happen?

Answer 29

duplicate digits to the limb buds own ZPA would appear because of the additional ZPA

Question 30

What is the function of Bone Morphogenetic Protein (BMP)?

Answer 30

shapes our digits High [BMP] leads to increased cell death (apoptosis)

Question 31

Prior to limb rotation what is the orientation of the ventral and dorsal surfaces of a limb bud?

Answer 31

ventral surface faces medially dorsal surface faces laterally

Question 32

What does the dorsal muscle mass of a limb bud form?

Answer 32

upper limb --> extensors and suppinators Lower limb --> extensors and abductors muscles

Question 33

What does the ventral muscle mass of a limb bud form?

Answer 33

upper limb --> flexors and pronators muscles Lower limb --> flexors and adductor muscles

Question 34

How long does it take for a primary axial a. To establish itself in the limbs?

Answer 34

Upper limb - Day 30 Lower limb - Day 36

Question 35

What is Meromelia? What causes it?

Answer 35

absence of part of a limb Caused by late FGF signalling or partial loss of FGF signaling

Question 36

What is Amelia? What causes it?

Answer 36

Absence of the entire limb Caused by early loss of FGF signaling

Question 37

What is Polydactyly? What causes it?

Answer 37

presence of supernumerary digits Caused by overexpression of Shh (creation of a 2nd ZPA)

Question 38

Adactyly vs. Syndactyly

Answer 38

Adactyly - absence of digits Syndactyly - fusion of digits

Question 39

What is Phacomelia? What causes it?

Answer 39

Thalidomide Baby partial loss of FGF signaling or Hox disruption

Question 40

What is Ectrodactyly?

Answer 40

"lobster claw" split hand/foot deformity

Question 41

What does Shh dictate?

Answer 41

The ventral portion of the neuraltube

Question 42

What controls the dorsal-ventral axis?

Answer 42

Wnt7a - responsible for dorsal portion Lack of wnt7A dictates ventral axis (and Shh)

Question 43

What controls Wnt7a release (turns on)?

Answer 43

Lmx1b

Question 44

Where do limb tendons arise from?

Answer 44

Lateral plate mesoderm

Question 45

What artery branches of the aorta to join the primary axial a. Of the upper limb?

Answer 45

7th cervical intersegmental a.

Question 46

What artery branches of the aorta to join the primary axial a. Of the lower limb?

Answer 46

5th lumbar intersegmental a.