Limb development Flashcards
(20 cards)
What initiates limb bud growth?
FGF10 from lateral plate mesoderm
What genes determine limb identity?
Tbx5 (forelimb), Tbx4 + Pitx1 (hindlimb)
What is the AER?
Apical ectodermal ridge - maintains limb outgrowth
What signal does the AER secrete?
FGF8
What is the ZPA?
The zone of polarising activity - patterns anterior-posterior axis
What does the ZPA secrete?
Sonic Hedgehog (SHH)
What gradient patterns the digits?
SHH concentration (high = posterior)
What gene specifies dorsal limb identity?
Wnt7a
What gene specifies ventral limb identity?
Engrailed-1
What does Lmx1b do?
Specifies dorsal mesenchyme in limbs
What are the three limb segments?
Stylopod (proximal), Zeugopod (middle), Autopod (distal)
Which morphogen regulates digit separation?
BMP (induces apoptosis in interdigital mesenchyme)
What is syndactyly?
Failure of interdigital apoptosis - webbed digits
What is polydactyly?
Extra digits (usually due to SHH misregulation)
What process guides limb elongation?
Proliferation and convergent extension
Where do limb muscles come from?
Somite (myotome) cells that migrate into the limb
What regulates proximo-distal patterning?
AER-FGF gradient
What regulates anterior-posterior patterning?
ZPA-SHH gradient
What regulates dorsal-ventral patterning?
Wnt7a and Engrailed-1 in ectoderm
When do limbs first appear in humans?
Week 4
