Movement Lecture 5: Limb embryology

Question 1

During which weeks of development does limb development occur?

Answer 1

Weeks 4-8

Question 2

Which section of the mesoderm is the core tissue of the limb bud initially derived from?

Answer 2

Lateral plate mesoderm

Question 3

What does the mesoderm differentiate into in the limb bud, and what will this eventually form?

Answer 3

Mesenchyme

Bones and connective tissue

Question 4

Which section of the mesoderm is skeletal muscle derived from?

Answer 4

Paraxial mesoderm

Question 5

Which section of the mesoderm forms somites?

Answer 5

Paraxial mesoderm

Question 6

During which week do the somites divide to form a sclerotome and a dermomyotome?

Answer 6

Week 4

Question 7

Which of the sclerotome and dermomyotome is formed by the ventral somite and which is formed by the dorsal somite?

Answer 7

Ventral somite -> sclerotome

Dorsal somite -> dermomyotome

Question 8

What is formed from the sclerotomes?

Answer 8

Vertebral column

Question 9

What is formed from the dermomyotomes?

Answer 9

Dermis of the skin and skeletal muscles

Question 10

During which week do the myotomes divide?

Answer 10

Week 5

Question 11

Which sections are formed by the division of the myotomes?

Answer 11

Epimere

Hypomere

Question 12

Which of the epimere and hypomere is dorsal and which is ventral, and which muscles will they form?

Answer 12

Epimere = dorsal, will form intrinsic back muscles that are innervated by the dorsal rami
Hypomere = ventral, will form all other skeletal muscle that is innervated by the ventral rami

Question 13

By which week have the hypomeres formed anterior and posterior condensations?

Answer 13

Week 7

Question 14

What is the general function of the muscles derived from the anterior condensation of the hypomere in the leg?

Answer 14

Flexors and adductors

Question 15

What is the general function of the muscles derived from the posterior condensation of the hypomere in the leg?

Answer 15

Extensors and abductors

Question 16

During which weeks do the limbs rotate?

Answer 16

Weeks 6-8

Question 17

In which direction do the lower limbs rotate during development and by how many degrees?

Answer 17

90 degrees medially

Question 18

Which tissue secretes Fgf10?

Answer 18

Mesenchyme

Question 19

What is induced by Fgf10?

Answer 19

Formation of the ectoderm to form the apical ectodermal ridge at the tip of the limb bud

Question 20

Which fibroblast growth factors are produced by the apical ectodermal ridge?

Answer 20

Fgf 4 and 8

Question 21

What is induced by the fibroblast growth factors produced by the AER?

Answer 21

Mesenchyme proliferation to form the progress zone

Question 22

Which direction does the growth induced by Fgf10 occur in?

Answer 22

Proximodistal

Question 23

What condition is induced by introducing Fgf-soaked beads into an embryo?

Answer 23

Supernumeracy of the limbs

Question 24

In dorsoventral patterning, what is expressed by the dorsal ectoderm?

Answer 24

Wnt7

Question 25

In dorsoventral patterning, what is expressed by the ventral ectoderm?

Answer 25

Engrailed-1

Question 26

What is the effect of engrailed-1 on Wnt7?

Answer 26

Inhibitor

Question 27

Which of engrailed-1 and Wnt7 will cause the formation of the sole of the foot or the palm of the hand?

Answer 27

Engrailed-1

Question 28

What would happen to the foot if Wnt7 was improperly expressed?

Answer 28

Soles would form on both sides

Question 29

What is the area of the mesenchyme that controls craniocaudal patterning called?

Answer 29

Zone of polarising activity

Question 30

Is the zone of polarising activity located cranially or caudally in the limb bud?

Answer 30

Caudally

Question 31

What is expressed by the zone of polarising activity?

Answer 31

Sonic hedgehog (Shh)

Question 32

What does low concentrations of Shh induce?

Answer 32

Formation of cranial structures in the limb bud eg. thumbs and big toes

Question 33

What does high concentrations of Shh induce?

Answer 33

Formation of caudal structures in the limb bud eg. little fingers and toes

Question 34

What condition can be seen if the zone of polarising activity is transplanted so it is present both cranially and caudally in the limb bud?

Answer 34

Mirror image polydactyly

Question 35

During which week do the terminal limb buds flatten to form hand and foot plates?

Answer 35

Week 6

Question 36

What process in the AER causes digit formation?

Answer 36

Apoptosis

Question 37

What is the name for the complete absence of limbs?

Answer 37

Amelia

Question 38

What is amelia caused by?

Answer 38

Early loss of Fgf signalling

Question 39

What would cause meromelia?

Answer 39

Partial or late loss of Fgf signalling

Question 40

What is the name for the partial absence of limbs eg. only present up to the elbow?

Answer 40

Meromelia

Question 41

What is phocomelia?

Answer 41

Digits developing prematurely, with a lack of proximal limb structures "Flipper limb"

Question 42

What malformation can be caused by thalidomide?

Answer 42

Phocomelia

Question 43

What does thalidomide inhibit?

Answer 43

Fgf 8+10

Question 44

What happens if apoptosis in the AER fails?

Answer 44

Syndactly - fused digits

Question 45

What is the name for the presence of extra digits and what causes it?

Answer 45

Polydactyly | Inappropriate Shh expression

Question 46

What is the medial name for a "lobster claw" deformity?

Answer 46

Ectrodactyly

Question 47

What malformation can develop when the middle of the AER fails to form properly

Answer 47

Ectrodactyly