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BMS242 Developmental Biology > L15 - Drosophila Limb Formation > Flashcards

L15 - Drosophila Limb Formation Flashcards

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1
Q

What is the fundamental principle RE patterning

A

To give a cell unique identity about 3 body axes

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2
Q

What are the axes of the limb

A

A-P
D-V
P-D

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3
Q

What are the 3 skeletal elements of the vertebrate limb

A

Stylopod
Zeugopod
Autopod

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4
Q

What bone makes up the stylopod

A

Humeris

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5
Q

What bones make up the zeugopod

A

Ulna and Radius

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6
Q

What bones make up the autopods

A

Carpals and digits

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7
Q

Describe the appearance of the limb buds

A

Appear as protrusions from the flank at precise locations along the AP axis

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8
Q

The region where the limb will form is known as

A

The limb field

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9
Q

Describe the effect of transplanting cells normally making up the limb fields at the flank

A

Growth of ectopic limbs

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10
Q

Describe the effect of transplanting cells that normally make up the flank at the region where the limb normally develops

A

No limb development in that region

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11
Q

Tbx5 can be seen expressed in the

A

Forelimb buds

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12
Q

Tbx4 can be seen expressed in the

A

Hindlimb buds

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13
Q

What is the effect of forces expression of TBx5 in the hindlib bud

A

Tbx4 is turned off

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14
Q

What is the effect of a Tbx4 KO

A

Still get hind limbs developing

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15
Q

What is driving the identity of the hind limb

A

Pitx1

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16
Q

Describe the effects of knocking out Pitx1

A

No hindlimb development and expression of Tbx4 is lost

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17
Q

What does Tbx mean

A

T-box

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18
Q

What specifiies the AP axis

A

Hox genes

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19
Q

Describe the evidence that Hox genes are able to act directly without the need for RA intermediate

A

HOXC6 boundary
Marks the boundary between the thoracici and cervical vert
Also markss the position where the forelimb will form

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20
Q

What is able to mimic the action of the limb field to induce ectopic development

A

FGF soaked bead

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21
Q

Describe the process of the intitiation of the limb

A

FGF8 produced from the intermediate mesoderm
FGF10 produced from the lateral plate mesoderm
Wnt2b restricts the domain of FGF10 expression
Wnt3a induced in the limb field
FGF8 then produced at the AER acts on the progress zone

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22
Q

What are the three regions of the early limb bud

A

Progress zone
Apical ectodermal ridge
Zone of polarising activity

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23
Q

What type of cells make up the progress zone

A

Primarily mesenchymal cells

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24
Q

What does the ZPA express

A

Shh

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25
Q

Removal of the AER shwos the the AER is nescersary for

A

The progress zone and limb growth

26
Q

Describe the specificaiton of more distal skeletal elements

A

Specified as the limb grows

27
Q

How many models are the for the P-D patterning of the limb

Name them

A

2

Progress zone model
Two signal model

28
Q

Describe the progress zone model

A

Suggests that the AER is driving outgrowth of the limb
AER then acts on the progress zone
The longer a cell spends in the progress zone then the more distal a structure is formed

29
Q

Describe the two signal model of limb PD patterning

A

Initial progenitors are present for all of the skeletal derivatives
Recieve antagonistic signals according to the positions they are along the gradient

30
Q

In the two signal model what are the two gradients

A

Retinoic acid proximally

FGF distally

31
Q

What structures form under hi RA lo FGF , what genes are first expressed

A

Meis genes

Stylopods

32
Q

What gene is expressed at intermeidate levels of FGF and RA - what structures form here

A

Hox11

Zeugopod

33
Q

What gene is expressed under the influence of lo RA and hi FGF what strcutures then form

A

Autopods

Hox13 first expressed

34
Q

FGF is hi

A

Dorsally

35
Q

RA is hi

A

Proximally

36
Q

Describe what happens to limb patterning when you KO the enzyme required for the synthesis of RA

A

Lose expression of the meis gene and you lose the prominal structures

37
Q

Describe the effect of grafting the ZPA into an anterior position

A

Mirror image duplication of the autopods

38
Q

Describe what happens if the ZPA is grafteed at a very early stage

A

duplication of the ulna also

39
Q

Describe how the action of the ZPA may be mimiced

A

Using a bead soaked in Shh

OR forcing Shh expression in cells which don’t usually express

40
Q

Shh acts as a ____________

A

Classic morphogen

41
Q

Describe how Shh acts as a classic morphogen

A

Digits form depending on the concentration of Shh that they see

42
Q

Describe how mirror image duplication is also evidence for Shh acting as a morphogen

A

Now get X^2 curve - high either sides - low in the middle

43
Q

Describe the Shh mutant limb

A

Complete loss of distal most skeletal elements

Causes the loss of identity of the zeugopods - R and U forms as a single bone

44
Q

Describe what Shh from the ZPA acts on

A

Diffuses P–>A

Acts on the ZPA

45
Q

Describe what FGF from the AER acts on

A

FGF4 diffuees back to the proximal

FGF8 acts on the ZPA

46
Q

What are the three genes which have an essential role in dorso-ventral patterning

A

Wnt7a
En1
Lmx1b

47
Q

Describe where Wnt7a is expressed

A

In the dorsal edge

48
Q

Describe when En1 is expressed

A

In the ventral edge

49
Q

Describe where Lmx1b is expressed

A

In the dorsal HALF

50
Q

What is the drosophila homologue of Lmx1b

What does this control

A

Apterous

Controls the dorsal cell fate

51
Q

Describe the effect of a conditional KO of Lmx1b

A

Ventralisation of the limb
Fur forms on both sides
All cells adopt a ventral identity

52
Q

Describe the process for the formation of dorsal patterns

A 
No BMPR so no En-1
No supression of Wnt7a 
Expression of Wnt7a 
Wnt7a induces the expression of Lmx1b 
Lmx1b diffuses into the dorsal segment 
Cell take a dorsal pattern
53
Q

Describe the process for the formation of ventral patterns

A

BMPR induces expression of En-1
En-1 confers a ventral pattern to cells

En-1 supresses Wnt7a

54
Q

What is the effect of En-1

A

Supression of Wnt7a

55
Q

What is the default cell fate

A

Dorsal (must supress this fate with En-1)

56
Q

Aer secretes …. and the drives …

A

FGF4/8 driving the outgrowth of the limb

57
Q

How many modes for the outgrowth

A

Progress zone and two signals

58
Q

ZPA secretes … which forms a gradient along which axis

A

Shh - AP axis

59
Q

How are PD and AP axes coordinanted?

A

Through the reciprocal control between the AER and the ZPA

60
Q

Sum up the DV axis patternign

A

Wnt7a and BMP from dorsal and ventral cotnrol Lmx1b

61
Q

What will form in presence of lmx1b

A

Dorsal

BMS242 Developmental Biology (17 decks)

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