Differential and spatial regulation of the prophenoloxidase (proPO) and proPO-activating enzyme in cuticular melanization and innate immunity in Bombyx mori pupae

• BmPPAE during development is responsible for cuticular melanization.
• Ecdysone-induced BmPO in development is responsible for cuticular melanization.
• Regulation of BmPPAE and BmPOs primes cuticular melanization and innate immunity.

Insect cuticular melanization is regulated by the prophenoloxidase (proPO)-activating system, which is also involved in the innate immune reaction. Here, we demonstrate how the differentiation of the proPO-activating system is regulated toward a cuticular melanization or innate immunity function in silkworm (Bombyx mori) pupae. Our results indicate that the differential and spatial regulation of key components, such as the proPO-activating enzyme and proPOs, primes the proPO-activating system for either cuticular melanization or innate immunity. This dual strategy for cuticular melanization in development and innate immunity upon infection demonstrates a two-pronged defense mechanism that is mediated by the priming of the proPO system.

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