Practice question

Instructive induction changes fate of responding tissue by delivering novel positional cues that redirect gene regulatory network. In recombination, epithelium that would form non-specific bud differentiates into salivary gland with branched lumens when combined with salivary mesenchyme, into mammary gland with milk production when combined with mammary mesenchyme. Mesenchymal FGF10, BMP2, Wnt signals activate specific enhancers altering epithelium transcription program via Pea3, Sox9 and GATA3. Differentiation after migration or release of morphogens describes phenomena but not fate instruction. Therefore mesenchyme instructing epithelium to acquire organ-specific architecture is canonical example of instructive induction directing pattern and cytodifferentiation during organogenesis.