The apical ectodermal ridge (AER) of the developing limb bud is maintained by a reciprocal signalling loop. Which factor from the underlying mesenchyme maintains AER integrity?

• A BMP4 from the dorsal ectoderm
• B FGF10 from the limb mesenchyme ✓
• C SHH from the ZPA
• D Wnt7a from the ventral ectoderm

Explanation

FGF10 secreted by limb bud mesenchyme acts on the overlying ectoderm to induce and maintain the AER, which in turn secretes FGF4 and FGF8 back onto the mesenchyme to sustain proliferation and proximo-distal outgrowth — the epithelial-mesenchymal FGF10–FGF8 feedback loop. SHH from the ZPA patterns the anterior-posterior axis of the limb (digit identity). Wnt7a from the dorsal ectoderm (not ventral) specifies dorsal limb identity. BMP4 promotes AER regression at the appropriate time and is also involved in interdigital apoptosis.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.