In a chick embryo, the apical ectodermal ridge is excised from a wing bud, but an agarose bead soaked in recombinant FGF8 is immediately implanted at the ridge site. Distal outgrowth proceeds normally. This experiment demonstrates that the AER's essential function is to:
- A Maintain proximodistal outgrowth of the limb mesenchyme ✓
- B Establish anteroposterior digit identity
- C Induce dorsoventral polarity of the limb
- D Initiate migration of myogenic precursors from the somites
Correct answer: A. Maintain proximodistal outgrowth of the limb mesenchyme
Explanation
The AER secretes FGF8 and FGF4, which keep the underlying progress zone mesenchyme proliferating and drive proximodistal elongation. An FGF-soaked bead fully substitutes for the ridge, proving that FGF supply is the ridge's essential role. Anteroposterior identity comes from the ZPA via SHH, dorsoventral polarity from Wnt7a in the dorsal ectoderm, and myogenic precursors migrate from somites independently of the AER.
Reference: Langman's Medical Embryology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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