title: Drosophila innate immunity: regional and functional specialization of prophenoloxidases.
abstract: BACKGROUND
  The diversification of immune systems during evolution involves the expansion of particular gene families in given phyla. A better understanding of the metazoan immune system requires an analysis of the logic underlying such immune gene amplification. This analysis is now within reach due to the ease with which we can generate multiple mutations in an organism. In this paper, we analyze the contribution of the three Drosophila prophenoloxidases (PPOs) to host defense by generating single, double and triple mutants. PPOs are enzymes that catalyze the production of melanin at the site of infection and around parasites. They are the rate-limiting enzymes that contribute to the melanization reaction, a major immune mechanism of arthropods. The number of PPO-encoding genes is variable among insects, ranging from one in the bee to ten in the mosquito.
  
  
  RESULTS
  By analyzing mutations alone and in combination, we ascribe a specific function to each of the three PPOs of Drosophila. Our study confirms that two PPOs produced by crystal cells, PPO1 and PPO2, contribute to the bulk of melanization in the hemolymph, upon septic or clean injury. In contrast, PPO3, a PPO restricted to the D. melanogaster group, is expressed in lamellocytes and contributes to melanization during the encapsulation process. Interestingly, another overlapping set of PPOs, PPO2 and PPO3, achieve melanization of the capsule upon parasitoid wasp infection.
  
  
  CONCLUSIONS
  The use of single or combined mutations allowed us to show that each PPO mutant has a specific phenotype, and that knocking out two of three genes is required to abolish fully a particular function. Thus, Drosophila PPOs have partially overlapping functions to optimize melanization in at least two conditions: following injury or during encapsulation. Since PPO3 is restricted to the D. melanogaster group, this suggests that production of PPO by lamellocytes emerged as a recent defense mechanism against parasitoid wasps. We conclude that differences in spatial localization, immediate or late availability, and mode of activation underlie the functional diversification of the three Drosophila PPOs, with each of them having non-redundant but overlapping functions.
authors.affiliation: Global Health Institute, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 19, 1015, Lausanne, Switzerland. jan.dudzic@epfl.ch.
authors.forename: Jan P
authors.initials: JP
authors.lastname: Dudzic
authors.affiliation: Invertebrate Genetics Laboratory, Genetic Strains Research Center, National Institute of Genetics, Mishima, 411-8540, Japan. skondo@nig.ac.jp.
authors.forename: Shu
authors.initials: S
authors.lastname: Kondo
authors.affiliation: Invertebrate Genetics Laboratory, Genetic Strains Research Center, National Institute of Genetics, Mishima, 411-8540, Japan. rueda@nig.ac.jp.
authors.forename: Ryu
authors.initials: R
authors.lastname: Ueda
authors.affiliation: Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester, M13 9PT, UK. casey.bergman@manchester.ac.uk.
authors.forename: Casey M
authors.initials: CM
authors.lastname: Bergman
authors.affiliation: Global Health Institute, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 19, 1015, Lausanne, Switzerland. bruno.lemaitre@epfl.ch.
authors.forename: Bruno
authors.initials: B
authors.lastname: Lemaitre
mesh_terms: D000818:Animals; D004156:Catechol Oxidase / Q000235:genetics* / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics* / Q000378:metabolism; D004331:Drosophila melanogaster / Q000201:enzymology* / Q000235:genetics / Q000276:immunology* / Q000469:parasitology; D004792:Enzyme Precursors / Q000235:genetics* / Q000378:metabolism; D005260:Female; D007113:Immunity, Innate / Q000235:genetics; D014863:Wasps / Q000502:physiology
chemical_list: D029721:Drosophila Proteins; D004792:Enzyme Precursors; C038451:pro-phenoloxidase; D004156:Catechol Oxidase