Elsevier

Developmental Biology

Volume 429, Issue 2, 15 September 2017, Pages 401-408
Developmental Biology

Review article
Saunders's framework for understanding limb development as a platform for investigating limb evolution

https://doi.org/10.1016/j.ydbio.2016.11.005Get rights and content
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Highlights

  • John W. Saunders, Jr. made seminal discoveries unveiling how chick embryos develop their limbs.

  • His discoveries unveiled how vertebrate limbs are induced, patterned, and differentiated.

  • These findings informed efforts to understand limb evolution, including flight and digit loss.

Abstract

John W. Saunders, Jr. made seminal discoveries unveiling how chick embryos develop their limbs. He discovered the apical ectodermal ridge (AER), the zone of polarizing activity (ZPA), and the domains of interdigital cell death within the developing limb and determined their function through experimental analysis. These discoveries provided the basis for subsequent molecular understanding of how vertebrate limbs are induced, patterned, and differentiated. These mechanisms are strongly conserved among the vast diversity of tetrapod limbs suggesting that relatively minor changes and tweaks to the molecular cascades are responsible for the diversity observed in nature. Analysis of the pathway systems first identified by Saunders in the context of animals displaying limb reduction show how alterations in these pathways have resulted in multiple mechanisms of limb and digit loss. Other classes of modification to these same patterning systems are seen at the root of other, novel limb morphological alterations and elaborations.

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