Practice question

Instructive induction provides new positional information that changes responder fate, requiring specific ligand-receptor interaction leading to altered transcription program and commitment. For example, ureteric bud-derived GDNF induces mesenchymal-to-epithelial transition and nephron gene expression via Ret receptor and Wnt4 cascade. Permissive induction does not direct fate; competent tissue already specified only needs permissive environment like extracellular matrix or trophic factor to realize intrinsic program. Blocking instructive signal abrogates fate change, while permissive signals can be replaced by unrelated substitutes supporting survival. Therefore specificity and fate-changing instruction defines instructive versus permissive mechanisms in development.