Practice question

Epithelial-mesenchymal transition enabling lateral plate accumulation into limb bud is regulated by TBX5 and Islet1 cofactor complexes forming transcriptional hubs. These T-box factors repress epithelial E-cadherin and tight junction programs, induce Snail Slug to permit delamination, increased motility and aggregation of limb field progenitors into protruding bud with elevated FGF10. Wnt3a signals via beta-catenin to induce AER but not direct EMT execution, Islet1 cooperates via Ldb1 rather than sole driver, SHH acts later in patterning. TBX5 therefore functions not only in specification but also controlling EMT and progenitor recruitment for bud morphogenesis.