Practice question

Distinction between instructive and permissive induction lies in provision of novel fate information versus supportive environment. Instructive induction actively redirects competent cells toward new fate via specific instructive ligand altering gene regulatory network, e.g., mesenchyme instructing epithelium to form salivary branching via FGF10. Without instructive signal alternative fate does not occur. Permissive induction permits execution of already determined program by providing extracellular matrix, survival factors or hormones permitting differentiation but not changing fate choice. Therefore instructive requires specific signal to induce differentiation, permissive allows differentiation without specific instructive cue, relying on tissue autonomy plus environment permitting expression.