Collaborative Resources for
Learning Developmental Biology
Collaborative Resources for Learning Developmental Biology
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Chick Apical Ectodermal Ridge
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Kathryn Tosney

Published on SDB CoRe: Aug 21 2012

Embryonic Patterning: Axis Formation
Signaling: Secreted Signals
Mesoderm-derived: Limb Formation
Organism: Chick
Stage of Development: Embryo

Object Description

This is a scanning electron microscopic image of a chick forelimb bud with the apical ectodermal ridge (AER) protruding from its distal tip. The limb bud is the precursor tissue from which vertebrate limbs are formed.  Chick forelimb buds will grow into wings, whereas its hindlimb buds will form legs.  The limb bud consists of mesoderm enclosed in an ectodermal covering.  All of the cartilage, bone, and musculature of the limb is derived from the mesoderm.  

The AER is essential for limb outgrowth along the proximodistal axis (shoulder to fingers).  If it is removed, the limb will be truncated, forming only proximal structures.  Fibroblast growth factor (FGF) signaling between the AER and the underlying mesenchyme is integral to this process.


Benazet, J.D., Zeller, R. Vertebrate limb development: moving from classical morphogen gradients to an integrated 4-dimensional patterning system. Cold Spring Harb Perspect Biol. 1:a001339.

Wolpert,  L. Pattern formation in epithelial development: the vertebrate limb and feather bud spacing. Philos Trans R Soc Lond B Biol Sci., 1998, 353:871-875.

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