Fig. 9. Model for functioning of BR-C in Tribolium metamorphosis. In young larvae, naturally occurring JH blocks pupal differentiation by repressing BR-C. JH is absent in early pupae, and its addition blocks adult morphogenesis by causing ectopic BR-C activation and death after a supernumerary pupal cuticle deposition. As both effects of JH on BR-C expression require Met, unknown stage-specific factors must modulate Met function.