Mesenchymal stem cells within mesenchyme or the medullary cavity of a bone fracture initiate the process of intramembranous ossification.
Before limb development begins, FGF10 expression becomes restricted to the proliferating mesenchymal cells of the lateral plate mesoderm, which form the limb bud and become limb mesenchyme.
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Later, FGF10 expression is restricted to the developing limb mesenchyme, where it is stabilized by WNT8C or WNT2B.
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WNT3A = Acts as a middle man in the positive feedback loop between the AER and limb mesenchyme.