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E: Human Morphogenesis and Embryologically > Digit Patterning > Flashcards

Digit Patterning Flashcards

1
Q

Characteristics of all limbs?

A

Share anatomical features.

Mechanisms of formation, patterning and development are similar

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2
Q

The limb axis

A

AS62

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3
Q

The limb digits in a wing?

A

AS63

Digits 2->4

1, 5 are lost

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4
Q

The limb digits in an arm?

A

Digit 1->5

AS63

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5
Q

Limb musculature derived?

A

From dorsolateral cells of the somites

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6
Q

Dorsolateral cells of the somites?

A

Migrate into the limb to form muscle

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7
Q

How are the dorsolateral cells of the somite segmented?

A

Segmented according to the somite from which they were dervied from

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8
Q

What happens to the muscle tissue when the limb buds elongate?

A

The muscle tissue first splits into flexor and extensor components

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9
Q

What happens at 8 weeks?

A

Hindlimb development.

Laps behind forefimb development by 1 or 2 days

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10
Q

Initial outgrowth?

Induced by?

Signal?

Targets genes?

A

Induced by flank mesoderm.

FGF signal

Target geenes: Tbx4, Tbx5 and brachyary

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11
Q

Holt-Cram syndrome?

A

Tbx5 mutation

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12
Q

At the end of the 4th week of development?

A

Limb buds become visible outpocketings from the ventrolateral body wall.

The forelimb appears

Followed by the hindlimb (1-2 days after)

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13
Q

What are the limb buds initially consists of?

A

A mesenchymal core derived from the somtic layer of the lateral plate mesoderm.

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14
Q

This mesenchymal core will form?

A

The bones and connective tissues of the limb.

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15
Q

This mesenchymal core is covered by?

A

Cuboidal ectoderm

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16
Q

What happens to the ectoderm at the distal border of the limb?

A

Thickens and forms the apical ectodermal ridge.

AER.

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17
Q

What does the AER do?

A

Causes adjacent mesenchyme to rapidly proliferate.

18
Q

What do the cells far away from the AER begin to do?

A

Differentiate into cartilage and muscle.

19
Q

FGF signals

A

Supplies by the AER.

Maintains outgrowth

20
Q

What axes does the AER provide to the cells?

A

A proximal- distal identity.

21
Q

What happens to the cells that loss FGF signalling?

A

It no longer proliferates

Now differentiates.

22
Q

Progress zone model?

A

P-D identified is specified by the duration of time spent in the progress zone (ie in the proliferation phase).

FGF promotes cell division

23
Q

Two-signal mode?

A

Opposing gradients of FGF-RA patterns the axis.

High Retinion acid (from somites)- proximal

High FGF- distal

AS64

24
Q

Polarising region?

A

Known as ZPA.

Source of Shh signal by producing retinoic acid.

Acts as a morphogen to pattern the anteroposterior axis of the limb.

25
Q

Posterior region controls?

A

The closure an area of cells are to the polarising region the more posterior it will develop into

AS65

26
Q

sonic hedgehog (Shh)

A

Regulates the anteriorposterior axis

27
Q

Shh pathway when Shh is not presetn

A

Patched 1 stimulates the SMO receptor.

SMO receptor cleaves Gli.

Cleaved Gli can no longer bind to the DNA

No transcription

AS66

28
Q

Shh pathway when Shh is present?

A

Shh binds to the Patched1 receptor to repress its action.

Inhibits the SMO receptor

Gli is no longer cleaved and can bind to the DNA

Transcription occurs

AS66

29
Q

Preaxial polydactylyl?

A

Mutation in Shh pathway.

Loss of Shh-Loss of ZPA.

No patterning ie no hands or feet.

30
Q

Acheiropodia?

A

No hands or feet

31
Q

Dorso-Ventral axis patterning?

A

Ectoderm patterns the mesenchym.

Wnt7a maintains Shh expression.

Wnt7a induces lmxlb (confers dorsal fate)

32
Q

What confers a dorsal fate?

A

Lmxlb

33
Q

Cells identity?

Ie can you graft a leg cell and make it an arm one?

A

No

They do respond to local patterning cues however they retain memory of their origin

34
Q

What is important for the final form of digits?

A

Digits form when apoptosis occurs in the AER.

Seperates the AER into 5 seperate ridges.

35
Q

What is important for the final seperation of digits?

A

Achieved by additional apoptosis of the interdigital space (mesenchyme)

36
Q

Hox genes?

A

Regulates the positioning of the limbs along the craniocaudal axis in the flank regions

37
Q

FGF?

A

Regulates limb outgrowth at the AER

38
Q

Wnt?

A

Maintains Shh expression

39
Q

Shh?

A

FGF activates Shh in the ZPA.

Regulates the anteroposterior axis

40
Q

ZPA?

A

Zone of polarising activity

Produce retinoic acid.

Initiates Shh expression.

E: Human Morphogenesis and Embryologically (15 decks)

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