Embryology meets molecular biology: Deciphering the apical ectodermal ridge

Dev Biol. 2017 Sep 15;429(2):387-390. doi: 10.1016/j.ydbio.2017.01.017. Epub 2017 Jan 25.


More than sixty years ago, while studying feather tracks on the shoulder of the chick embryo, Dr. John Saunders used Nile Blue dye to stain the tissue. There, he noticed a darkly stained line of cells that neatly rims the tip of the growing limb bud. Rather than ignoring this observation, he followed it up by removing this tissue and found that it led to a striking truncation of the limb skeletons. This landmark experiment marks the serendipitous discovery of the apical ectodermal ridge (AER), the quintessential embryonic structure that drives the outgrowth of the limb. Dr. Saunders continued to lead the limb field for the next fifty years, not just through his own work, but also by inspiring the next generation of researchers through his infectious love of science. Together, he and those who followed ushered in the discovery of fibroblast growth factor (FGF) as the AER molecule. The seamless marriage of embryology and molecular biology that led to the decoding of the AER serves as a shining example of how discoveries are made for the rest of the developmental biology field.

Keywords: Apical ectodermal ridge; Chick; Fibroblast growth factor; Limb development; Mouse; Proximal-distal axis.

Publication types

  • Review
  • Research Support, Non-U.S. Gov't
  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Body Patterning
  • Ectoderm / embryology*
  • Embryology*
  • Fibroblast Growth Factors / metabolism
  • Gene Knockout Techniques
  • Molecular Biology*


  • Fibroblast Growth Factors