Limb development

Question 1

what gives rise to the humerus?

Answer 1

stylopod

Question 2

what gives rise to the radius and ulna?

Answer 2

zeugopod

Question 3

what gives rise to the wrist bones, palm bones and digit bones?

Answer 3

distal autopod

Question 4

is the back of the hand dorsal or ventral?

Answer 4

dorsal

Question 5

is the palm of the hand dorsal or ventral?

Answer 5

ventral

Question 6

what is grieg syndrome?

Answer 6

polydactyly and syndactyly

Question 7

what causes grieg syndrome?

Answer 7

mutation in GL13

Question 8

what is apert syndrome?

Answer 8

syndactyly

Question 9

what causes apert syndrome?

Answer 9

mutations in FGFR2

Question 10

what is holt-oram syndrome?

Answer 10

phocomelia

Question 11

what causes holt-oram syndrome?

Answer 11

mutations in TBX5

Question 12

what did thalidomide cause?

Answer 12

phocomelia

Question 13

when was thalidomide given to women?

Answer 13

1956-1961

Question 14

how many babies did thalidomide affect?

Answer 14

around 2000 (only 500 survived)

Question 15

when do forelimb bids form?

Answer 15

24th day

Question 16

when do hindlimbs form?

Answer 16

28th day

Question 17

what are the limb buds formed of?

Answer 17

epidermal jacket enclosing lateral plate mesoderm

Question 18

what does the mesoderm form in the limbs?

Answer 18

most of tissues (bone, tendons, ligaments, dermis, muscle sheaths and blood vessels)

Question 19

what is the position of the limb buds determined by?

Answer 19

hox genes

Question 20

what does AER stand for?

Answer 20

acpical ectodermal ridge

Question 21

where does the AER form?

Answer 21

at the distal end of the limb bud

Question 22

what type of cells is the AER made of?

Answer 22

columnar cells

Question 23

what are TBX5 and TBX4?

Answer 23

transcription factors

Question 24

where is TBX5 transcribed?

Answer 24

forelimbs

Question 25

where is TBX4 transcribed?

Answer 25

hindlimbs

Question 26

what do mutations in TBX5 cause?

Answer 26

Holt-Oram syndrome (only affects forelimbs)

Question 27

what do mutations in TBX4 cause?

Answer 27

patella syndrome (affects bones of hips and legs)

Question 28

what forms limb muscle?

Answer 28

hypaxial myotome

Question 29

when do mytome cells migrate into limb buds?

Answer 29

5th week of development

Question 30

what does the myotome initially form?

Answer 30

large dorsal and ventral condensations

Question 31

what does the dorsal muscle mass form?

Answer 31

extensors and supinators of forelimb and extensors and abductors of hindlimbs

Question 32

what does the ventral muscle mass form?

Answer 32

flexors and pronators of forelimb and flexors and adductors of hindlimb

Question 33

which spinal nerves innervate the muscles of the forelimbs?

Answer 33

C5-T2

Question 34

which spinal nerves innervate the muscle of the hindlimbs?

Answer 34

L4-S3

Question 35

how many motor neurons innervate a single myotome during development?

Answer 35

at least 2

Question 36

how many motor neurons innervate a single mytome in an adult?

Answer 36

1 (all but one retracted soon after birth)

Question 37

which bones differentiate first?

Answer 37

humerus and femur

Question 38

what is the order of differentiation?

Answer 38

humerus/femur, radius + ulna/tibia + fibula, carpals/tarsels, metacarpals/metatarsels and finally, phalanges

Question 39

which digit differentiates first?

Answer 39

4

Question 40

what is the order of digit differentiation?

Answer 40

4, 3, 2 then 1 and 5 at same time

Question 41

what is required for limb outgrowth?

Answer 41

AER

Question 42

what will the removal of AER create?

Answer 42

a distally truncated limb as it will stop limb bud outgrowth

Question 43

what is AER the source of?

Answer 43

mitogen

Question 44

what is the mitogen responsible for promoting?

Answer 44

cell division in limb bud mesenchyme

Question 45

what is a mitogen?

Answer 45

an extracellular system that instructs cells to undergo mitosis

Question 46

if AER is removed early, what is formed?

Answer 46

the humerus

Question 47

if AER is removed late, what is formed?

Answer 47

the humerus, radius and ulna

Question 48

what is the mitogen involved in limb bud outgrowth?

Answer 48

FGF

Question 49

what does FGF do in the limb?

Answer 49

it diffuses into the limb bud mesenchyme and stimulates call proliferation, thereby promoting limb outgrowth

Question 50

FGF is essential for limb outgrowth. true or false?

Answer 50

true

Question 51

does FGF act as a morphogen?

Answer 51

there is some evidence to suggest this - phalanges receive highest concentration, radius and ulna receive the lowest and the humerus grows irrespective of FGF

Question 52

John Saunders grafted a posterior mesenchyme into an anterior mesenchyme. what was formed?

Answer 52

a duplicate set of digits, with mirror image symmetry

Question 53

what is the organising centre for patterning the anterior-posterior axis of the limb bud?

Answer 53

the posterior margin, also known as the ZPA

Question 54

what does ZPA stand for?

Answer 54

zone of polarising activity

Question 55

what digit forms in the absence of a morphogen?

Answer 55

the thumb

Question 56

what is the morphogen in the limb buds?

Answer 56

SHH

Question 57

where is shh expressed?

Answer 57

in the ZPA

Question 58

shh mimics ZPA grafts when expressed in anterior mesenchyme. true or false?

Answer 58

true

Question 59

how does shh specify digits?

Answer 59

in a concentration dependant manner

Question 60

shh is required for limb development. true or false?

Answer 60

true

Question 61

what defect can shh cause?

Answer 61

preaxial polydactyly

Question 62

what is preaxial polydactyly?

Answer 62

an extra digit on the side of the thumb

Question 63

what type of mutation causes preaxial polydactyly?

Answer 63

gain-of-function mutation which affects the enhancer controlling shh production in the zpa

Question 64

what is acheiropodia?

Answer 64

absense of distal elements of the limbs

Question 65

what causes acheiropodia?

Answer 65

deletion of DNA that controls expression of shh in zpa

Question 66

what removes the flaps of skin that connect the digits of an embryo?

Answer 66

apoptosis

Question 67

what is apoptosis?

Answer 67

programmed cell death

Question 68

what is syndactyly?

Answer 68

when two or more digits are fused together

Question 69

what causes syndactyly?

Answer 69

lack of apoptosis in interdigital region during embryogenesis

Question 70

between which digits is syndactyly most common?

Answer 70

3rd and 4th

Question 71

what are limb buds formed by?

Answer 71

the proliferating cells of the outer somatopleuric layer of the lateral plate mesoderm

Question 72

what attracts hypaxial myoblasts to the limb bud?

Answer 72

hepatocyte growth factor (HGF)

Question 73

what secrets HGF?

Answer 73

limb bud mesenchyme