FGF10 secreted by the mesenchyme cells entering the limb field induce the overlying ectoderm to form the apical ectodermal ridge (AER) AER runs along distal margin of limb bud (at the dorso-ventral boundary) and functions as a major signaling center. Proliferating distal bud mesenchyme (just under AER) is called progress zone (PZ) AER, being signaling center, has three major roles: 1) Maintaining the underlying mesenchyme in a proliferating state so that there is linear proximal-distal growth of the limb 2) Maintaining expression of molecules that generate anterior-posterior axis 3) Interacting with proteins specifying dorsal- ventral axes ⇒ each cell is given precise instruction on how to differentiate AER D V Int. J. Dev. Biol. 52: 857-871 (2008) doi: 10.1387/ijdb.072416mf AER
The apical ectodermal ridge ( AER ) interacts with the limb bud mesenchyme , progress zone ( PZ ), which is directly below it. It keeps it in a state of mitotic proliferation (so that the limb bud can grow) and prevents those cells from forming cartilage before right time Four experiments described the effects of the AER on the PZ : • If the AER is removed at any time, development ceases (only structures proximal to AER are made) • If an extra AER is grafted onto an existing limb bud, additional structures (limbs or limb parts) are formed • If leg mesenchyme is placed below a wing AER, distal hindlimb structures (toes) form at the end of wing part. • If limb mesenchyme is replaced by non-limb mesenchyme beneath the AER the AER regresses and limb development stops. The effect of the AER on the underlying mesenchyme
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- Summer '14
- Developmental Biology, Limb, Mesoderm, Limb Bud