Practice question

Mesenchyme synthesizes inductive cues that instruct overlying epithelium during organogenesis of lung, kidney, tooth and gland. Classical tissue recombination shows mammary mesenchyme converts salivary epithelium to mammary-like branching with milk protein expression, while dermal mesenchyme directs epidermal appendage fate such as hair versus feather. Secreted FGFs, TGF-beta, Wnt antagonists and matrix metalloproteinases remodeling basement membrane instruct proliferation, invagination and cytodifferentiation programs. Mechanical support and barrier functions are secondary; apoptotic removal is not its instructive role. Thus mesenchyme provides regional positional cues that determine shape, pattern and functional differentiation of epithelial organs.