Apical Ectodermal Ridge - Relevant Experiments

Relevant Experiments

  • AER Maintains Limb Outgrowth through FGF secretion, Mesenchyme Cells Determine Identity:

These experiments reveal that the limb mesenchyme contains the necessary information concerning limb identity, but the AER is needed to stimulate the mesenchyme to live up to its destiny (of becoming an arm, leg, etc.)

  1. When the AER is removed, limb development halts. If an FGF bead is added in the AER’s place, normal limb development proceeds.
  2. When an extra AER is added, two limbs form.
  3. When forelimb mesenchyme is replaced with hindlimb mesenchyme, a hindlimb grows.
  4. When forelimb mesenchyme is replaced with non-limb mesenchyme, the AER regresses, and limb development halts.
  5. When the AER from a late limb bud is transplanted to an earlier limb bud, the limb forms normally. The converse – transplantation of an early limb bud to a late limb bud – also results in normal limb development. However, the underlying mesoderm in the progress zone ‘’is’’ fate specified. If progress zone mesoderm is transplanted along with the AER, then additional finger/toes are formed (for an early-->late transplantation) or the finger/toes are formed too early (for a late-->early transplantation).
  • AER Formation Relies on Dorsal-Ventral Boundary:

The Precise Microenvironmental Cues present at the D-V boundary are crucial for AER formation

  1. When the limb bud is dorsalized - in limbless mutants, for example - and no dorsal-ventral boundary exists, the AER is unable to form and limb development halts.

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