Practice question

Limb bud emergence requires localized epithelial-mesenchymal transition of lateral plate mesoderm orchestrated by T-box transcription factors and FGF signaling. Under influence of TBX4 in hindlimb field and TBX5 in forelimb field, coordinated with Pitx1 and Islet1 and FGF10 signaling, lateral plate epithelial cells downregulate apicobasal polarity components like ZO1, induce Snail-mediated EMT, increase proliferation and accumulate to form protruding bud mesenchyme. This transition is not SHH controlled nor solely mesoderm-to-ectoderm signaling but autonomous mesodermal change, and occurs at initiation rather than digit finalization, creating permissive condensation interacting with ectoderm to form AER.