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#AER function

2 public questions tagged with this topic.

Limb Development -ll

Which experiment demonstrated that AER function can be replaced?

Chemical nature of AER was proven by replacement experiments restoring outgrowth without ridge tissue. After surgical removal of AER from chick wing bud causing predictable proximal-distal truncation, implantation of heparin acrylic beads soaked in recombinant FGF8 or FGF4 into distal mesenchyme restored progress zone proliferation, maintained FGF10 and Gremlin expression, and allowed otherwise normal limb development including complete digits and pattern. This demonstrated AER acts primarily via secreting diffusible FGFs and that purified FGF can substitute fully for its structure and function, unlike mesoderm removal, SHH overexpression or TBX5 inhibition which do not directly address AER roles.

Ref: Niswander et al., Cell 1993, Gilbert Chapter 20: FGF bead replaces AER function.

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Limb Development -lll

Which experiment demonstrated that FGF8 can substitute for AER function in limb bud outgrowth?

Classic AER substitution proved diffusible FGFs mediate ridge function. Saunders removed chick AER causing distal arrest, then Niswander implanted heparin beads soaked in FGF8, FGF4 or FGF2 into distal mesenchyme beneath wound ectoderm. Progress zone proliferation resumed, FGF10 and Gremlin expression recovered, and a largely normal skeleton with stylopod zeugopod autopod formed. This demonstrated chemical sufficiency of FGF signaling for outgrowth and maintenance of FGF10-FGF8 feedback loop. ZPA grafts instead duplicate digits anterior-posteriorly, TBX5 deletion blocks forelimb initiation, neither addressing AER replacement.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 20: FGF bead replacement of AER experiment.

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