Lecture 1 - Limb development Flashcards Preview

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Flashcards in Lecture 1 - Limb development Deck (82):
1

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

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

2

What gene is responsible for the timing of limb development?

Hox genes

3

What direction do things develop?

Proximal to distal

4

What gene is responsible for limb identity?

T-box

5

What are the three axes limbs develop in?

Proximodistal, dorsoventral, and crainocaudal

6

What proteins are active on the proximodistal axis?

Fgf 10, fgf 8m at AER

7

What is the AER?

Apical ectodermal ridge

8

What proteins are active on the crainocaudal axis?

Shh at ZPA

9

What is the ZPA?

Zone of polarizing activity

10

What protein/region is related to the dorsoventral axis?

Dorsal ectoderm/Wnt7a

11

What direction do the forelimbs rotate?

Dorsally

12

What direction do the hindlimbs rotate?

Venterally

13

What two specific things are the HOX genes responsible for?

Where the limb buds form and development at the specific location

14

What hox genes are responsible for different bones?

Hoxa and hoxd

15

How do Hox genes regulate bone growth in general?

overlap of expression

16

What are the two primary limb structures, in order?

Limb field - limb bud

17

What signal occurs during the induction of limb development?

Fgf8 induces fgf10

18

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

Fgf10 induces Fgf8 (which induces Shh)

19

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

Maintaining cell proliferation

20

What does Shh induce during outgrowth of the limb bud?

Fgf14

21

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

Fgf8, 10, 14, and Shh

22

What are FGF10 and TBX5 responsible for together?

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

23

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

Forbud ridge appears 1-2 days before hindbud ridge

24

Where do limb buds originate from?

Ridges in ventrolateral body wall

25

What are the two cell layers in the limb bud?

Mesenchyme core and ectoderm cover

26

What are the two parts of the mesenchyme core?

Lateral plate mesoderm and paraxial mesoderm

27

What does the ectoderm cover become?

Epidermis of skin, nails, and hands

28

What does the lateral plate mesoderm become?

Cartilage, bones, and general connective tissue

29

What does the paraxial mesoderm become?

Somites and skeletal muscle

30

What region expreses Fgf10 once limb bud has formed?

Lateral plate mesoderm

31

What does fgf10 initiate?

AER

32

How does Fgf10 initiate AER?

Wnt3a and beta-catenin

33

What does AER express?

Fgf8 and Fgf4, while maintaining Fgf10

34

What interaction is the limb bud dependent on?

Limb bud mesenchyme with AER

35

What does AER induce?

Proliferation of limb bud mesenchyme

36

Where is PZ?

Area of mesenchyme proximal to AER on caudal border

37

What is PZ?

Progress zone

38

Anatomically describe AER.

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

39

What is affecting pattern formation in dorsal-vental axis?

non-AER ectoderm

40

Where does D/V signaling reside?

Dorsal ectoderm w/ Wnt7a morphogen

41

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

Ventrolateral myotome of somite

42

How is motor innervation formed in limb bud?

Ventral and dorsal branches of ventral rams follow growing muscle

43

What axis does AER direct pattern formation for?

PD

44

What happens at the terminal portion of each bud?

Becomes flattened = hands and footplates

45

What are the three limb segments?

Stylopod, Zeugopod, and Autopod

46

What does the stylopod become?

arm/thigh

47

What does the Zeugopod become?

forearm/leg

48

What does the Autopod become?

hand/feet

49

During PD axis development what occurs with the mesenchyme?

condenses into cartilage models

50

What are cartilage models?

templates for long bones

51

What is homology?

Shared ancestry between structure, gene, etc

52

What is the ZPA responsible for?

Pattern formation in Cr-Cd axis.

53

What does the ZPA express?

RA and Shh

54

What does the ZPA require for stimulation?

FGF8 and Wnt7

55

Where does FGF8 come from?

Apical ectodermal ridge

56

Where does Wnt7 come?

Dorsal ectoderm

57

What does the Shh gradient induce?

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

58

What happens when cells leave the ZPA?

stop expressing Shh

59

What do Shh decedents displace and where to?

non-ZPA cells cranially

60

What do Shh descendants give rise to?

Ulna, digits 4, 5, and contribute to 3

61

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

Digit 2 and parts of 3

62

What structures come from Shh independent cells?

Humerus, radius, and digit 1

63

What creates the pattern of development in the PD axis?

Gradient of RA and Fgf

64

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

Graded Shh signaling

65

What is hairy2?

acts as clock that controls integrated development along all axes

66

How does the AER progress?

Will break up and only cover emerging digital ray

67

How do interdigital spaces form?

Apoptosis

68

What is a pentadactyl limb?

"ancestral" five digit condition, digit reduction occurred over evolution

69

What occurs in horses in regards to digit reduction?

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

70

What are artiodactyls?

Catttle and swine

71

What occurs in artiodactyls in regards to digit reduction?

patterning changes
Digit loss and central axis shift between digits 3 and 4

72

What is the order of digit loss?

I, V, II, and IV

73

What is isometry?

Proportional relationships are preserved as size changes

74

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

Being overbuilt when small

75

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

Allometry

76

What is allometry?

Proportional changes that deviate from isometry

77

What does the equation for allometry consider?

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

78

What is positive allometry?

Character increases faster than body size (b>1)

79

What is negative allometry?

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

80

What happens if allometry is zero?

no relationship

81

What is an example of positive allometry?

Skeleton mass

82

What is an example of negative allometry?

heart rate and basal metabolic rate