multilayered ectodermal region at the distal tip of a limb or fin bud necessary for the proper development of the underlying mesenchyme[MP,modified]. Along with the zone of polarizing activity, it is a crucial organizing region during limb development[WP]. [ MP:0001676 ]

Synonyms: apical epidermal ridge

This is just here as a test because I lose it

Term information

database cross reference


axiom lost from external ontology

relationship loss: subclass proliferative region (TAO:0000098)[TAO]

curator notes

note that media, dorsal fins etc have AERs.

depicted by

external definition

Distal ectodermal thickening which forms along the anterior-posterior limb axis. Signaling from this region influences proximal-distal patterning of the limb. Structure is missing in some lineages (salamanders, Eleutherodactylus coqui) however morphologically their indistinct distal ectoderm may still be involved in signaling.[AAO]

Proliferative region that is part of the developing fin fold or fin.[TAO]

function notes

maintaining mesenchyme in plastic proliferating state; maintaining expression of A-P axis genes; interacting with D-V proteins. Genes: AER induced by Fgf10 in mesenchyme. AER secretes Fgf8, which stimulates mitosis in the mesenchyme causing Fgf10 production - positive feedback loop

has related synonym


crista ectodermalis apicalis



taxon notes

The AER of tetrapods regresses after specification of skeletal progenitors, the AER of teleosts form an elongating fin fold