Review Session for Quiz

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Review Session for Quiz

• Porter B121 4-5ish pm
• Monday April 24

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Dudley, Ross and Tabin (2002) A re-examination
of proximodistal patterning during vertebrate
limb development. Nature 418539-544.
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Two models for outgrowth of the limb
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What initial observation prompted the authors to
suggest an alternate hypothesis to the progress
zone model? (.5)a. FGF mouse knockouts showed
high lethality and no limb growthb. The progress
zone model doesnt explain truncation of the limb
after AER removalc. Removal of the AER produces
a truncated limb with proximal structuresd. When
the AER is removed, there is a region of the
mesenchyme that undergoes cell death.
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• Of the following, which experiment best tests the
  hypothesis that cells in the limb bud have a
  pre-specified fate? (.5)
• Remove AER, see what cells types are made
• Mark distal cells in an early limb bud and see if
  they become distal cells in the limb
• Remove factors required for proliferation see
  what cell types are made
• Transplant just the AER from an older limb bud to
  tip of younger limb bud

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Figure 1
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Figure 2
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Figure 2
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Figure 3
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Figure 4
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Figure 4
Why did the authors take only the anterior part
of the limb bud?
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Two models for outgrowth of the limb
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Related paper in same issue of NatureSun,
Mariani and Martin (2002). Functions of FGF
signalling from the apical ectodermal ridge in
limb development. Nature 418 501-508
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Double knockouts for FGF4 and FGF8
Transient early expression of FGFs allows
normal stylopod, but abnormal zeugopod and
autopod notice that there ARE distal structures,
despite absence of FGFs
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These authors found normal proliferation in the
absence of FGFs, but increased cell death
proximallyalso show that the limbs are smaller
because fewer cells condense (sox-9 expression is
decreased)suggest that distal cells can be
respecified to form more proximal cells