Which region of the developing limb specifies the cranial-caudal axis of the developing limb bud?

Question

Quizplus · Accepted Answer

The Zone of Polarizing Activity (ZPA) is a mesenchymal tissue located at the posterior margin of the developing limb bud. It directs the cranial-caudal axis and is responsible for the formation of the posterior structures of the limb. It does this by secreting morphogens like Sonic hedgehog (Shh) that diffuse anteriorly across the developing limb bud, creating a concentration gradient that determines the pattern of digit formation along the anterior-posterior axis. The apical ectodermal ridge (AER) is responsible for directing the proximal-distal axis of the limb, while the dorsal ectoderm specifies the dorsal-ventral axis.

Which Region of the Developing Limb Specifies the Cranial-Caudal Axis