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Flashcards in Limb development Deck (73):
1

what gives rise to the humerus?

stylopod

2

what gives rise to the radius and ulna?

zeugopod

3

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

distal autopod

4

is the back of the hand dorsal or ventral?

dorsal

5

is the palm of the hand dorsal or ventral?

ventral

6

what is grieg syndrome?

polydactyly and syndactyly

7

what causes grieg syndrome?

mutation in GL13

8

what is apert syndrome?

syndactyly

9

what causes apert syndrome?

mutations in FGFR2

10

what is holt-oram syndrome?

phocomelia

11

what causes holt-oram syndrome?

mutations in TBX5

12

what did thalidomide cause?

phocomelia

13

when was thalidomide given to women?

1956-1961

14

how many babies did thalidomide affect?

around 2000 (only 500 survived)

15

when do forelimb bids form?

24th day

16

when do hindlimbs form?

28th day

17

what are the limb buds formed of?

epidermal jacket enclosing lateral plate mesoderm

18

what does the mesoderm form in the limbs?

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

19

what is the position of the limb buds determined by?

hox genes

20

what does AER stand for?

acpical ectodermal ridge

21

where does the AER form?

at the distal end of the limb bud

22

what type of cells is the AER made of?

columnar cells

23

what are TBX5 and TBX4?

transcription factors

24

where is TBX5 transcribed?

forelimbs

25

where is TBX4 transcribed?

hindlimbs

26

what do mutations in TBX5 cause?

Holt-Oram syndrome (only affects forelimbs)

27

what do mutations in TBX4 cause?

patella syndrome (affects bones of hips and legs)

28

what forms limb muscle?

hypaxial myotome

29

when do mytome cells migrate into limb buds?

5th week of development

30

what does the myotome initially form?

large dorsal and ventral condensations

31

what does the dorsal muscle mass form?

extensors and supinators of forelimb and extensors and abductors of hindlimbs

32

what does the ventral muscle mass form?

flexors and pronators of forelimb and flexors and adductors of hindlimb

33

which spinal nerves innervate the muscles of the forelimbs?

C5-T2

34

which spinal nerves innervate the muscle of the hindlimbs?

L4-S3

35

how many motor neurons innervate a single myotome during development?

at least 2

36

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

1 (all but one retracted soon after birth)

37

which bones differentiate first?

humerus and femur

38

what is the order of differentiation?

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

39

which digit differentiates first?

4

40

what is the order of digit differentiation?

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

41

what is required for limb outgrowth?

AER

42

what will the removal of AER create?

a distally truncated limb as it will stop limb bud outgrowth

43

what is AER the source of?

mitogen

44

what is the mitogen responsible for promoting?

cell division in limb bud mesenchyme

45

what is a mitogen?

an extracellular system that instructs cells to undergo mitosis

46

if AER is removed early, what is formed?

the humerus

47

if AER is removed late, what is formed?

the humerus, radius and ulna

48

what is the mitogen involved in limb bud outgrowth?

FGF

49

what does FGF do in the limb?

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

50

FGF is essential for limb outgrowth. true or false?

true

51

does FGF act as a morphogen?

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

52

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

a duplicate set of digits, with mirror image symmetry

53

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

the posterior margin, also known as the ZPA

54

what does ZPA stand for?

zone of polarising activity

55

what digit forms in the absence of a morphogen?

the thumb

56

what is the morphogen in the limb buds?

SHH

57

where is shh expressed?

in the ZPA

58

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

true

59

how does shh specify digits?

in a concentration dependant manner

60

shh is required for limb development. true or false?

true

61

what defect can shh cause?

preaxial polydactyly

62

what is preaxial polydactyly?

an extra digit on the side of the thumb

63

what type of mutation causes preaxial polydactyly?

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

64

what is acheiropodia?

absense of distal elements of the limbs

65

what causes acheiropodia?

deletion of DNA that controls expression of shh in zpa

66

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

apoptosis

67

what is apoptosis?

programmed cell death

68

what is syndactyly?

when two or more digits are fused together

69

what causes syndactyly?

lack of apoptosis in interdigital region during embryogenesis

70

between which digits is syndactyly most common?

3rd and 4th

71

what are limb buds formed by?

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

72

what attracts hypaxial myoblasts to the limb bud?

hepatocyte growth factor (HGF)

73

what secrets HGF?

limb bud mesenchyme