Limb Development Flashcards
(29 cards)
When do the limb buds first appear?
Around the end of the 4th week of development
Where does all limb tissue arise from?
Lateral plate mesoderm
What determines where on the body the limb develops?
HOX genes
Limb bud outgrowth is initiated and maintained by what? For the forelimb? Hindlimb?
Positive feedback loop of FGF10. Transcription factors control the expression of FGF10. Tbx5 in the forelimb and Tbx4 in the hindlimb
What is the pathway that initiates the FGF10 positive feedback loop?
Wnt3 –> β-catenin –> Tbx5 –> FGF10 –>FGF8 (positive feedback between FGF10 and FGF8)
What is the AER?
The apical ectodermal ridge is a condensation of ectoderm
At the AER, what is expressed in the ventral and dorsal ectoderm?
Dorsal: Wnt-7a
Ventral: Engrailed-1
Wnt3 initiates the outgrowth of the limb. What is responsible for continuing that growth?
AER
What is the progress zone?
Where cells proliferate
What is the ZPA?
The zone of polarizing activity. Secretes sonic hedgehog (SHH)
What is amelia and what does it result from?
Lack of limbs. Mutation in Wnt3
What is diplopodia and what does it result from?
Multiple feet. Duplication of the AER
What is archeiropodia and what does it result from?
Bilateral congenital amputations of the upper and lower extremities and aplasia of the hands. Lack of SHH production from the ZPA
What is polydactyly and what does it result from?
Supernumerary fingers or toes. Duplication of the ZPA
What are the two models for limb patterning?
Progress zone model: the stylopod, zeugopod, and autopod develop over time
Early specification model: the stylopod, zeugopod, and autopod are all present at initiation of limb growth
What are the cartilaginous anlage made of?
Type II collagen, type I collagen, fibronectin
How are the digits defined?
Interdigital apoptosis
What is syndactyly and how does it arise?
Fusion of adjacent fingers. Failure of interdigital apoptosis
What initiates joint formation?
Wnt14
What are the stages of bone and cartilage development in the limb?
1) bone collar stage
2) periosteal invasion
3) primary ossification center
4) creation of epiphyseal growth plate
5) secondary ossification center
How are apophyses formed?
The attachment of muscle and the force enacted on that portion of bone
Which bones take the longest to fuse their epiphyseal growth plates?
Sacrum, clavicle
What is brachydactyly and how does it arise?
Abnormal shortening of the fingers and toes. Premature closure of the epiphyseal growth plate
What kind of myoblasts migrate from the dermomyotome into the limb?
PAX3 positive cells
