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Updated: Apr 30, 2026
Assessing the Cellular Immune Response of the Fruit Fly, Drosophila melanogaster, Using an In Vivo Phagocytosis Assay
Published on: April 10, 2019
Prophenoloxidase activation is required for survival to microbial infections in Drosophila
Olivier Binggeli1, Claudine Neyen1, Mickael Poidevin2
1Global Health Institute, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
Abstract:
The melanization reaction is a major immune response in Arthropods and involves the rapid synthesis of melanin at the site of infection and injury. A key enzyme in the melanization process is phenoloxidase (PO), which catalyzes the oxidation of phenols to quinones, which subsequently polymerize into melanin. The Drosophila genome encodes three POs, which are primarily produced as zymogens or prophenoloxidases (PPO). Two of them, PPO1 and PPO2, are produced by crystal cells. Here we have generated flies carrying deletions in PPO1 and PPO2. By analyzing these mutations alone and in combination, we clarify the functions of both PPOs in humoral melanization. Our study shows that PPO1 and PPO2 are responsible for all the PO activity in the hemolymph. While PPO1 is involved in the rapid early delivery of PO activity, PPO2 is accumulated in the crystals of crystal cells and provides a storage form that can be deployed in a later phase. Our study also reveals an important role for PPO1 and PPO2 in the survival to infection with Gram-positive bacteria and fungi, underlining the importance of melanization in insect host defense.
Insights
This study clarifies the roles of prophenoloxidases (PPOs) in Drosophila immunity. PPO1 and PPO2 are essential for melanization, insect defense against pathogens, with distinct roles in early and late immune responses.
Area of Science:
- * Insect immunology
- * Biochemistry
- * Genetics
Background:
- * Melanization is a critical immune defense in arthropods, involving melanin synthesis at sites of infection or injury.
- * Phenoloxidase (PO) is key to melanization, catalyzing reactions that form melanin.
- * Drosophila melanogaster has three PO genes encoding prophenoloxidases (PPOs), with PPO1 and PPO2 produced by crystal cells.
Purpose of the Study:
- * To elucidate the specific functions of PPO1 and PPO2 in Drosophila humoral melanization.
- * To analyze the combined and individual effects of PPO1 and PPO2 gene deletions.
- * To understand the contribution of PPO1 and PPO2 to host defense against microbial infections.
Main Methods:
- * Generation of Drosophila melanogaster lines with targeted deletions in PPO1 and PPO2 genes.
- * Analysis of phenoloxidase (PO) activity in the hemolymph of mutant flies.
- * Assessment of fly survival rates following infection with Gram-positive bacteria and fungi.
Main Results:
- * PPO1 and PPO2 are responsible for all detectable phenoloxidase (PO) activity in the hemolymph.
- * PPO1 facilitates rapid, early PO activity, while PPO2 serves as a stored, deployable reserve in crystal cells.
- * Loss of PPO1 and PPO2 significantly impairs survival against Gram-positive bacterial and fungal infections.
Conclusions:
- * PPO1 and PPO2 play distinct, complementary roles in Drosophila melanization and humoral immunity.
- * Melanization mediated by PPO1 and PPO2 is crucial for effective host defense against specific microbial pathogens.
- * This research highlights the importance of prophenoloxidases in arthropod immune responses.
