Foundations > Limb Development > Flashcards

Limb Development Flashcards

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1
Q

What are the two types of limb buds that emerge during canine development?

A

Forelimb bud and hind limb bud

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2
Q

In tetrapods, which limb bud emerges first?

A

Forelimb bud

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3
Q

What is proximo distal outgrowth fundamentally related to?

A

Epithelial mesenchymal signaling interactions

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4
Q

What axes are the limbs patterned along during development?

A

Cranial to caudal axis

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5
Q

What is the term for the organizing process that results in the formation of three germ layers?

A

Gastrulation

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6
Q

What are the three germ layers formed during gastrulation?

A
  • Ectoderm
  • Endoderm
  • Mesoderm
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7
Q

What does the ectoderm form?

A

Epidermis of the skin and central nervous system

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8
Q

What does the endoderm form?

A

Epithelial lining of the GI and respiratory tracts

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9
Q

What is the paraxial mesoderm responsible for forming?

A

Somites, which differentiate into dermis, skeletal muscle, and axial skeleton

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10
Q

From which part of the mesoderm do limb buds develop?

A

Lateral plate mesoderm

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11
Q

What is somatoplor?

A

The combination of lateral plate mesoderm covered by ectoderm

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12
Q

What is the critical period in development?

A

Times when specific molecular and cellular mechanisms involved in tissue or organ development are operational

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13
Q

What are the three critical structures involved in limb development?

A
  • Apical ectodermal ridge (AER)
  • Progress zone (PZ)
  • Zone of polarizing activity (ZPA)
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14
Q

What is the role of the apical ectodermal ridge (AER) in limb development?

A

Maintains the progress zone in a proliferative state for proximal to distal outgrowth

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15
Q

What signaling family is involved in the maintenance of the progress zone?

A

Fibroblast growth factor (FGF) family

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16
Q

What happens when the apical ectodermal ridge is removed from a limb bud?

A

Limb development stops

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17
Q

What is the result of adding an extra apical ectodermal ridge to a limb bud?

A

Formation of an extra wing tip (mirror imaging)

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18
Q

What happens when hindlimb mesoderm replaces forelimb mesoderm?

A

Proximal to distal outgrowth proceeds, resulting in the development of a hind limb

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19
Q

What condition can result from disruption of limb development?

A

Amelia

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20
Q

What evolutionary significance do some snakes have regarding limb development?

A

Primitive snakes have rudimentary hind limbs, while advanced snakes lack limb buds altogether

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21
Q

What is chondrogenesis?

A

The process of cartilage formation

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22
Q

What is ossification?

A

The process of bone formation

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23
Q

What is the zone of polarizing activity (ZPA) responsible for?

A

Driving the patterning of the digits

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24
Q

What is the role of Sonic hedgehog in limb development?

A

It is produced in the ZPA and drives digit patterning

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25
Fill in the blank: The limbs develop from an outgrowth of _______ covered in ectoderm.
Lateral plate mesoderm
26
True or False: The identity of the limb is dependent on the apical ectodermal ridge.
False
27
What happens to the cells that leave the progress zone during limb development?
They become fixed in position and differentiate into limb skeletal structures
28
What forms during hind limb development in snakes?
Rudimentary hind limb buds ## Footnote Snakes do not develop fully elaborated hind limbs despite the formation of rudimentary structures.
29
Who led the research investigation on snake limb development?
Marty Cohn and his postdoc advisor ## Footnote This research was conducted a few decades ago.
30
What colors are used to stain bone and cartilage in the study?
Bone in red and cartilage in blue ## Footnote This staining allows visualization of skeletal structures.
31
What structures were identified in the rudimentary hind limb of snakes?
Primitive femur and three elements of the pelvic girdle ## Footnote These structures are present but do not develop into full limbs.
32
What was used as a positive control in the limb bud development research?
Chicken embryo ## Footnote The chicken limb bud shows a clearly delineated apical ectodermal ridge.
33
What is observed in the chicken limb bud that is absent in the python limb bud?
Apical ectodermal ridge ## Footnote The python limb bud appears smooth without this ridge.
34
What technique was used to visualize protein expression in the limb development study?
Immunohistochemistry ## Footnote This method allows for the visualization of specific proteins involved in limb development.
35
What conclusion did the investigators reach regarding limb bud development in pythons?
Failure of signaling leads to regression of the apical ectodermal ridge ## Footnote This stalls limb development in pythons.
36
What is the condition called when there is more than the typical number of limbs?
Polymelia ## Footnote This condition can arise from duplication of the limb field or splitting of the early limb bud.
37
What is the role of the myotome in limb development?
Forms all skeletal muscle ## Footnote The myotome branches into dorsal and ventral regions for muscle formation.
38
What does the lateral plate mesoderm form in limb development?
Bone and tendons ## Footnote Myogenic cells migrate from myotomes to differentiate into skeletal muscle.
39
What signaling molecule is fundamental for digit patterning in limb development?
Sonic hedgehog ## Footnote This molecule's concentration and duration of exposure determine digit formation.
40
What happens when a chunk of the zone of polarizing activity is implanted into the cranial end of a limb bud?
Establishes an altered gradient of Sonic hedgehog ## Footnote This can lead to the formation of additional digits.
41
What does the expression of Sonic hedgehog mRNA in the limb bud indicate?
Localized to the zone of polarizing activity ## Footnote This expression forms a gradient crucial for digit identity.
42
What congenital condition is characterized by an abnormal reduction in the number of digits?
Oligodactyly ## Footnote This condition can result from absence of the ZPA or disruptions in Sonic hedgehog signaling.
43
What happens in Sonic Hedgehog knockout mice?
They exhibit no discernible digits ## Footnote Sonic Hedgehog is essential for digit formation.
44
How is the polydactyly phenotype hypothesized to be driven?
By point mutations in conserved non-coding elements ## Footnote These mutations affect enhancer regions regulating gene expression.
45
What type of experiment did researchers conduct to study polydactyly in cats?
Expressing cat genes in mice ## Footnote This approach allows observation of genetic function and expression patterns.
46
What is the outcome of inserting non-coding DNA associated with polydactyly into the mouse genome?
Ectopic expression in the cranial aspect of the developing limb ## Footnote This expression indicates a disruption in normal digit patterning.
47
What is Sonic Hedgehog required for in limb development?
Digit formation
48
What happens to digits when exposed to a Sonic Hedgehog signaling inhibitor during limb patterning?
Reduction in the number of digits
49
What colors are used to stain bone and cartilage in the typical mouse development example?
Bone is shown in red, cartilage is shown in blue
50
Where are the missing digits located in mice exposed to Sonic Hedgehog signaling inhibitors?
Caudal most digits
51
What two concurrent mechanisms sculpt the digits during limb development?
* Cell death between the digits * Proliferation at the tip of the digits
52
What is programmed cell death also known as?
Apoptosis
53
What can insufficient apoptosis lead to in limb development?
Syndactyly or abnormal webbing of the digits
54
Is syndactyly always considered abnormal?
No, it can be a typical aspect of development
55
What is the significance of apoptosis in evolution and development?
It gives rise to species-specific differences with important functions
56
What process begins with condensation of the lateral plate mesoderm during joint development?
Proximal to distal outgrowth
57
What type of ossification do bones develop through during limb development?
Endochondral ossification
58
What condition can result from disruption in fetal movement during joint development?
Arthrogryposis or crooked calf disease
59
What unique ability does the axolotl have regarding limb loss?
Limb regeneration
60
What is formed after amputation in the axolotl that aids in limb regeneration?
Blastoma
61
What is the apical ectodermal cap in limb regeneration analogous to?
Apical ectodermal ridge
62
What was the drug thalidomide originally marketed for?
To cure ailments of pregnancy
63
What type of malformations did thalidomide cause?
Major limb malformations
64
Why was thalidomide on the market for so long despite early warnings?
Active debate over its teratogenic effects
65
What concept explains why some women who took thalidomide did not have children with malformations?
Critical periods in development
66
Fill in the blank: Sonic Hedgehog is essential for _______ formation.
[digit]
67
True or False: Apoptosis is always detrimental to development.
False
68
Fill in the blank: The number of digits can be affected by exposure to a Sonic Hedgehog signaling _______.
[inhibitor]
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