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a_anatomy > Lecture 1 - Limb development > Flashcards

Lecture 1 - Limb development Flashcards

1
Q

What embryonic tissues give rise to the fore/hind limbs?

A

Ectoderm, dermatome, hypaxial portion of myotome, and somatic of lateral plate mesoderm

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2
Q

What gene is responsible for the timing of limb development?

A

Hox genes

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3
Q

What direction do things develop?

A

Proximal to distal

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4
Q

What gene is responsible for limb identity?

A

T-box

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5
Q

What are the three axes limbs develop in?

A

Proximodistal, dorsoventral, and crainocaudal

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6
Q

What proteins are active on the proximodistal axis?

A

Fgf 10, fgf 8m at AER

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7
Q

What is the AER?

A

Apical ectodermal ridge

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8
Q

What proteins are active on the crainocaudal axis?

A

Shh at ZPA

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9
Q

What is the ZPA?

A

Zone of polarizing activity

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10
Q

What protein/region is related to the dorsoventral axis?

A

Dorsal ectoderm/Wnt7a

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11
Q

What direction do the forelimbs rotate?

A

Dorsally

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12
Q

What direction do the hindlimbs rotate?

A

Venterally

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13
Q

What two specific things are the HOX genes responsible for?

A

Where the limb buds form and development at the specific location

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14
Q

What hox genes are responsible for different bones?

A

Hoxa and hoxd

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15
Q

How do Hox genes regulate bone growth in general?

A

overlap of expression

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16
Q

What are the two primary limb structures, in order?

A

Limb field - limb bud

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17
Q

What signal occurs during the induction of limb development?

A

Fgf8 induces fgf10

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18
Q

What is involved in the establishment of AER and ZPA centers?

A

Fgf10 induces Fgf8 (which induces Shh)

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19
Q

What are Fgf’s responsible for during AER and ZPA development?

A

Maintaining cell proliferation

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20
Q

What does Shh induce during outgrowth of the limb bud?

A

Fgf14

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21
Q

What are the main Fgf’s in early limb development?

A

Fgf8, 10, 14, and Shh

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22
Q

What are FGF10 and TBX5 responsible for together?

A

Induce epithelium to mesenchyme transition inducing the formation of the limb bud

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23
Q

What is the order of ridge development (fore vs hind)?

A

Forbud ridge appears 1-2 days before hindbud ridge

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24
Q

Where do limb buds originate from?

A

Ridges in ventrolateral body wall

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25
Q

What are the two cell layers in the limb bud?

A

Mesenchyme core and ectoderm cover

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26
Q

What are the two parts of the mesenchyme core?

A

Lateral plate mesoderm and paraxial mesoderm

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27
Q

What does the ectoderm cover become?

A

Epidermis of skin, nails, and hands

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28
Q

What does the lateral plate mesoderm become?

A

Cartilage, bones, and general connective tissue

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29
Q

What does the paraxial mesoderm become?

A

Somites and skeletal muscle

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30
Q

What region expreses Fgf10 once limb bud has formed?

A

Lateral plate mesoderm

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31
Q

What does fgf10 initiate?

A

AER

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32
Q

How does Fgf10 initiate AER?

A

Wnt3a and beta-catenin

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33
Q

What does AER express?

A

Fgf8 and Fgf4, while maintaining Fgf10

34
Q

What interaction is the limb bud dependent on?

A

Limb bud mesenchyme with AER

35
Q

What does AER induce?

A

Proliferation of limb bud mesenchyme

36
Q

Where is PZ?

A

Area of mesenchyme proximal to AER on caudal border

37
Q

What is PZ?

A

Progress zone

38
Q

Anatomically describe AER.

A

thickened, specialized epithelium at tip of the limb bud on dorsoventral border

39
Q

What is affecting pattern formation in dorsal-vental axis?

A

non-AER ectoderm

40
Q

Where does D/V signaling reside?

A

Dorsal ectoderm w/ Wnt7a morphogen

41
Q

Where do precursor muscle cells, that migrate to limb bud, come from?

A

Ventrolateral myotome of somite

42
Q

How is motor innervation formed in limb bud?

A

Ventral and dorsal branches of ventral rams follow growing muscle

43
Q

What axis does AER direct pattern formation for?

A

PD

44
Q

What happens at the terminal portion of each bud?

A

Becomes flattened = hands and footplates

45
Q

What are the three limb segments?

A

Stylopod, Zeugopod, and Autopod

46
Q

What does the stylopod become?

A

arm/thigh

47
Q

What does the Zeugopod become?

A

forearm/leg

48
Q

What does the Autopod become?

A

hand/feet

49
Q

During PD axis development what occurs with the mesenchyme?

A

condenses into cartilage models

50
Q

What are cartilage models?

A

templates for long bones

51
Q

What is homology?

A

Shared ancestry between structure, gene, etc

52
Q

What is the ZPA responsible for?

A

Pattern formation in Cr-Cd axis.

53
Q

What does the ZPA express?

A

RA and Shh

54
Q

What does the ZPA require for stimulation?

A

FGF8 and Wnt7

55
Q

Where does FGF8 come from?

A

Apical ectodermal ridge

56
Q

Where does Wnt7 come?

A

Dorsal ectoderm

57
Q

What does the Shh gradient induce?

A

Nested (more or less) expression of mesenchymal Hox genes.

58
Q

What happens when cells leave the ZPA?

A

stop expressing Shh

59
Q

What do Shh decedents displace and where to?

A

non-ZPA cells cranially

60
Q

What do Shh descendants give rise to?

A

Ulna, digits 4, 5, and contribute to 3

61
Q

What do cells give rise to via long-range Shh signaling?

A

Digit 2 and parts of 3

62
Q

What structures come from Shh independent cells?

A

Humerus, radius, and digit 1

63
Q

What creates the pattern of development in the PD axis?

A

Gradient of RA and Fgf

64
Q

What creates the pattern of development in Cr-Cd axis?

A

Graded Shh signaling

65
Q

What is hairy2?

A

acts as clock that controls integrated development along all axes

66
Q

How does the AER progress?

A

Will break up and only cover emerging digital ray

67
Q

How do interdigital spaces form?

A

Apoptosis

68
Q

What is a pentadactyl limb?

A

“ancestral” five digit condition, digit reduction occurred over evolution

69
Q

What occurs in horses in regards to digit reduction?

A

post-patterning changes
Digits 1 and 5 are eliminated
Digits 2 and 4 fuse (via apoptosis)

70
Q

What are artiodactyls?

A

Catttle and swine

71
Q

What occurs in artiodactyls in regards to digit reduction?

A

patterning changes

Digit loss and central axis shift between digits 3 and 4

72
Q

What is the order of digit loss?

A

I, V, II, and IV

73
Q

What is isometry?

A

Proportional relationships are preserved as size changes

74
Q

What is the solution to SA being small to amount of biologically active tissue?

A

Being overbuilt when small

75
Q

What is the solution for something growing and muscles and bones being able to keep up with growth?

A

Allometry

76
Q

What is allometry?

A

Proportional changes that deviate from isometry

77
Q

What does the equation for allometry consider?

A

A trait of interest, body size, and relationship strength of the two

78
Q

What is positive allometry?

A

Character increases faster than body size (b>1)

79
Q

What is negative allometry?

A

Increases slower then size or decreases with size (0>b<1)

80
Q

What happens if allometry is zero?

A

no relationship

81
Q

What is an example of positive allometry?

A

Skeleton mass

82
Q

What is an example of negative allometry?

A

heart rate and basal metabolic rate

a_anatomy (43 decks)

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