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Developmental Biology. > Limb Development. > Flashcards

Limb Development. Flashcards

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1
Q

What is pattern formation?

A

The way that embryonic cells form ordered spatial arrangements of differentiated tissues.

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2
Q

The development of the limb corresponds to what axes?

A

The anterior/posterior and proximal distal axes of the body.

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3
Q

Limbs are divided up into what?

A

Limbs are divided up into different sections that will develop differently.

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4
Q

What is the he stylopod?

A

The uppermost part of a limb such as the humerus of an arm.

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5
Q

The stylopod will be connected to what part of the body?

A

The shoulder or pelvis.

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6
Q

What is the zeugopod?

A

The forearm or tibia and fibia of the leg.

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7
Q

What is the autopod?

A

The wrist, hand and fingers.

The ankle, foot and toes.

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8
Q

What is the proximal distal axis of the arm?

A

The entire length of the limb.

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9
Q

The cells that build the proximal distal axis of the arm have what problem?

A

They have a problem determining where one section of the limb ends and the other begins.

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10
Q

What is the anterior/posterior axis of the arm?

A

The thumb and little finger.

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11
Q

What is the dorsal/ventral axis of the arm?

A

The top of the hand and the palm of the hand.

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12
Q

What are the regions of the body where limb outgrowth occurs?

A

Limb fields.

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13
Q

How is the limb field specified?

A

Via a regulative process that is established by certain proteins.

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14
Q

Can the process that establishes the limb field be disrupted?

A

Yes.

Either naturally, or via experimental means.

As a result extra limbs can grow out of the body.

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15
Q

How is the limb bud formed?

A

By an outgrowth and proliferation of cells.

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16
Q

The cells responsible for the outgrowth and proliferation of the limb bud are formed by what?

A

Somatic mesoderm.

Lateral plate mesoderm and myotome.

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17
Q

The limb bud is made out of what tissue?

A

Mesoderm.

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18
Q

What family do the HOX genes belong to?

A

The homeobox family.

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19
Q

HOX genes are expressed in what pattern throughout the body?

A

In stripes.

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20
Q

The expression of different HOX genes will define what?

A

Every region along the anterior/posterior axis.

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21
Q

HOX genes code for what?

A

Regions of embryonic development along the anterior posterior axis.

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22
Q

What part of the limb is on the anterior boundary of where HOXC6 is expressed

A

The forelimb.

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23
Q

The different parts of the arm are determined by what?

A

Different HOX genes.

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24
Q

What chemical is responsible for the correct location of the limb bud?

A

Retinoic acid.

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25
Q

How does retinoic acid work?

A

By re-programming the HOX genes.

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26
Q

What happens if you remove the tail from a tadpole and place the tadpole in retinoic acid?

A

Multiple limbs will develop from the tail stump.

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27
Q

What is responsible for turning on the FGF genes?

A

Retinoic acid.

28
Q

What is responsible for establishing the location of the limb field?

A

Retinoic acid.

29
Q

What will cause the limb bud to grow and develop?

A

FGF.

30
Q

Which type of FGF is expressed in the limb field?

A

FGF 10.

31
Q

What stimulates the proliferation and outgrowth of the limb?

A

FGF.

32
Q

What gene will determine what type of limbs is grown?

A

The TBX gene.

33
Q

Which kind of TBX gene will determine the forelimbs?

A

TBX 5 will cause the development of forelimbs such as arms or wings.

34
Q

Which kind of TBX gene will determine the hindlimbs?

A

TBX 4 will cause the development of hindlimbs such as legs or feet.

35
Q

What needs to be combined with TBX for a limb to develop?

A

Retinoic acid.

36
Q

If FGF is placed at a region between TBX 5 and TBX 4, what limb will develop?

A

A hybrid or chimeric limb will be formed.

37
Q

What is the AER?

A

AER (apical ectodermal ridge).

This is a ridge on the outside of the limb bud.

38
Q

What does the AER do?

A

The AER sends signals to the progress zone.

39
Q

What do the signals that the AER sends to the progress zone do?

A

They cause the cell division that leads to the outgrowth of the limb.

They keep the cells in an undifferentiated state.

40
Q

Why does the AER need to keep cells in an undifferentiated state?

A

Because these cells need to form different structures such as forearm or hand.

41
Q

What part of the limb tells the cells on the limb outgrowth to form different tissues?

A

The AER.

42
Q

What happens if the AER is removed from a developing limb?

A

Limb bud outgrowth will stop.

43
Q

The signals that the AER is sending are in what form?

A

FGF.

44
Q

The FGF that is sent by the AER to the limb outgrowth will

A

It maintains the outgrowth of the limb and keeps the cells in an undifferentiated state.

45
Q

What is the progress zone theory of limb development?

A

That cells differentiate into different features due to the length of time that they spend in the progress zone.

46
Q

What is the progress early allocation model theory of limb development?

A

It suggests that regions in the limb are specified early on.

Then they proliferate into a larger block of tissue before developing.

47
Q

What genes will define the development of cells in the various regions of the limb

A

The HOX genes.

48
Q

What zone is found in the posterior region of the limb bud?

A

The ZPA.

Zone of polarising activity.

49
Q

What does the ZPA do?

A

It determines the fate of cells along the anterior posterior axis of the hand.

50
Q

How does the ZPA develop the little finger and the thumb?

A

The cells that are closest to the ZPA will make the little finger.

The cells that are furthest away will make the thumb.

51
Q

If the ZPA is transplanted into the anterior limb bud, what occurs?

A

A mirror image of the hand is formed.

The same effects occur, i.e. cells closest cells to the transplanted ZPA form the little finger and the furthest form the thumb.

52
Q

What is the theory for the method that ZPA will determine the anterior/posterior axis of the hand?

A

ZPA creates a morphogen gradient.

Where high concentration forms the little finger and the cells in the lowest amount of the gradient form a thumb.

53
Q

What are morphogens?

A

They direct the fates of cells.

54
Q

What is the morphogen that is expressed by the ZPA?

A

SHH.

55
Q

What gene determines the anterior posterior axis of the hand?

A

SHH.

56
Q

The expression of SHH from the ZPA will have what effect on the AER?

A

The ZPA will secrete SHH to maintain the AER.

If SHH is not expressed, then the limb will not fully develop.

57
Q

If SHH is removed from a developing limb, what occurs?

A

The limb will develop without a hand.

58
Q

Mutations in SHH can cause what?

A

Polydactyl hands.

Where fingers develop in the wrong places and extra digits can develop.

59
Q

How do the AER and the ZPA have a reciprocal relationship?

A

The expression of 1 will maintain the expression of the other.

60
Q

What is step 1 of limb development?

A

HOX genes induce the formation of the limb field.

This causes the expression of FGF 10 in the limb fields.

This starts the proliferation of cells in the somatic mesoderm which is the start of limb bud outgrowth.

61
Q

What is step 2 of limb development?

A

The AER is formed as a result of the expression of FGF 10.

The developing AER then expresses FGF 8 which will maintain the proliferation and undifferentiated state of the cells.

FGF 8 will also induce the ZPA.

62
Q

What is step 3 of limb development?

A

The ZPA will form as a result of the expression of FGF 8 by the AER.

The ZPA will express SHH.

This tells the AER to express FGF 4 which helps to maintain the progress zone.

63
Q

What is step 4 of limb development?

A

The TBX genes will determine whether a forelimb or hindlimb is expressed.

If TBX 5 is expressed then a forelimb will develop.

If TBX 4 is expressed then a hindlimb will develop.

64
Q

What is step 5 of limb development?

A

While limb outgrowth is occurring, HOX genes will direct the fate of the different cells along the proximal distal axis.

65
Q

What is step 6 of limb development?

A

SHH turns on different HOX genes to develop the thumb and little finger of the hand.

The concentration of SHH determines which HOX genes are turned on and will tell the HOX genes to develop a little finger or a thumb.

Developmental Biology. (21 decks)

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