Béatrice Horard, Kevin Terretaz, Anne-Sophie Gosselin-Grenet, Hélène Sobry, Mathieu Sicard, Frédéric Landmann, Benjamin Loppin, Laboratoire de biologie et modélisation de la cellule (LBMC UMR 5239), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS), Centre de recherche en Biologie cellulaire de Montpellier (CRBM), Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM), Diversité, Génomes & Interactions Microorganismes - Insectes [Montpellier] (DGIMI), Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université de Montpellier (UM), Institut des Sciences de l'Evolution de Montpellier (UMR ISEM), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut de recherche pour le développement [IRD] : UR226-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM), MUSE program of the University of MontpellierAAP17REC-FRS04-GENEWOL, SchlumbergerFSER202002011118, ANR-16-CE02-0006,CIAWOL,Bases moléculaire et cellulaire de la diversité phénotypique de l'incompatibilté cytoplasmique chez les insectes(2016), ANR-10-INBS-0004,France-BioImaging,Développment d'une infrastructure française distribuée coordonnée(2010), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-École pratique des hautes études (EPHE), KARLI, Mélanie, Bases moléculaire et cellulaire de la diversité phénotypique de l'incompatibilté cytoplasmique chez les insectes - - CIAWOL2016 - ANR-16-CE02-0006 - AAPG2016 - VALID, and Développment d'une infrastructure française distribuée coordonnée - - France-BioImaging2010 - ANR-10-INBS-0004 - INBS - VALID
International audience; Wolbachia are widespread endosymbiotic bacteria that manipulate the reproduction of arthropods through a diversity of cellular mechanisms. In cytoplasmic incompatibility (CI), a sterility syndrome originally discovered in the mosquito Culex pipiens, uninfected eggs fertilized by sperm from infected males are selectively killed during embryo development following the abortive segregation of paternal chromosomes in the zygote. Despite the recent discovery of Wolbachia CI factor (cif) genes, the mechanism by which they control the fate of paternal chromosomes at fertilization remains unknown. Here, we have analyzed the cytological distribution and cellular impact of CidA and CidB, a pair of Cif proteins from the Culex-infecting Wolbachia strain wPip. We show that expression of CidB in Drosophila S2R+ cells induces apoptosis unless CidA is co-expressed and associated with its partner. In transgenic Drosophila testes, both effectors colocalize in germ cells until the histone-to-protamine transition in which only CidB is retained in maturing spermatid nuclei. We further show that CidB is similarly targeted to maturing sperm of naturally infected Culex mosquitoes. At fertilization, CidB associates with paternal DNA regions exhibiting DNA replication stress, as a likely cause of incomplete replication of paternal chromosomes at the onset of the first mitosis. Importantly, we demonstrate that inactivation of the deubiquitylase activity of CidB does not abolish its cell toxicity or its ability to induce CI in Drosophila. Our study thus demonstrates that CI functions as a transgenerational toxin-antidote system and suggests that CidB acts by poisoning paternal DNA replication in incompatible crosses.