title: Rac1 signalling in the Drosophila larval cellular immune response.
abstract: The Drosophila larval cellular immune response involves cells (hemocytes) that can be recruited from a hematopoietic organ located behind the brain, as well as a sessile population of cells found just underneath the larval cuticle arranged in a segmental pattern. By using two Rac1 GTPase effector-loop mutants together with epistasis studies, we show that Rac1 requires the Drosophila melanogaster Jun N-terminal kinase Basket (Bsk), as well as stable actin formation to recruit the sessile hemocyte population. We show that actin stabilization is necessary for Rac1-induced hemocyte activation by lowering cofilin (encoded by the twinstar gene tsr) expression in blood cells. Removing Bsk by RNAi suppressed Rac1-induced release of sessile hemocytes. RNAi against Bsk also suppressed Rac1 induction of lamellocytes, a specialized population of hemocytes necessary for the encapsulation of invading pathogens. Furthermore, Rac1 and Bsk are involved in regulating the formation of actin- and focal adhesion kinase (FAK)-rich placodes in hemocytes. Lastly, Rac1 and Bsk are both required for the proper encapsulation of eggs from the parasitoid wasp Leptipolina boulardi. From these data we conclude that Rac1 induces Bsk activity and stable actin formation for cellular immune activation, leading to sessile hemocyte release and an increase in the number of circulating hemocytes.
authors.affiliation: Umeå Centre for Molecular Pathogenesis (UCMP), Umeå University, S-901 87, Umeå, Sweden. micheal.williams@ucmp.umu.se
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Williams
authors.forename: Magda-Lena
authors.initials: ML
authors.lastname: Wiklund
authors.forename: Shandy
authors.initials: S
authors.lastname: Wikman
authors.forename: Dan
authors.initials: D
authors.lastname: Hultmark
mesh_terms: D051339:Actin Depolymerizing Factors / Q000378:metabolism; D000199:Actins / Q000096:biosynthesis / Q000276:immunology; D000818:Animals; D002448:Cell Adhesion / Q000276:immunology; D029721:Drosophila Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D004331:Drosophila melanogaster / Q000201:enzymology / Q000276:immunology* / Q000469:parasitology; D004790:Enzyme Induction; D005455:Fluorescent Antibody Technique / Q000379:methods*; D006434:Hemocytes / Q000166:cytology / Q000201:enzymology / Q000276:immunology*; D007111:Immunity, Cellular / Q000276:immunology; D048031:JNK Mitogen-Activated Protein Kinases / Q000276:immunology / Q000378:metabolism; D007814:Larva; D011554:Pseudopodia / Q000502:physiology; D014863:Wasps / Q000502:physiology; D020744:rac GTP-Binding Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism
chemical_list: D051339:Actin Depolymerizing Factors; D000199:Actins; D029721:Drosophila Proteins; C090146:Rac1 protein, Drosophila; D048031:JNK Mitogen-Activated Protein Kinases; D020744:rac GTP-Binding Proteins