AER is an acronym for Apical Ectodermal Ridge:
Limb outgrowth is dependent upon interactions between the AER and the underlying mesoderm.
If the AER is removed, the mesoderm stops dividing.
If a supernumerary AER is grafted adjacent to a developing limb, a supernumerary limb results.
Prospective limb mesoderm grafted under flank ectoderm will promote formation of an AER and a supernumerary limb.
If limb bud mesoderm is removed from an early limb bud, the AER regresses and the mesoderm ceases proliferation.
Therefore, limb outgrowth involves reciprocal interactions between the AER and underlying mesoderm.
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The patient had a greater AER presence, leading to an overgrowth of the proximal and distal phalanx of the foot (her toes). Something genetic went wrong where there was an excessive inductionary effect.
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