title: An oskar-dependent positive feedback loop maintains the polarity of the Drosophila oocyte.
abstract: The localization of oskar mRNA to the posterior of the Drosophila oocyte defines the site of assembly of the pole plasm, which contains the abdominal and germline determinants. oskar mRNA localization requires the polarization of the microtubule cytoskeleton, which depends on the recruitment of PAR-1 to the posterior cortex in response to a signal from the follicle cells, where it induces an enrichment of microtubule plus ends. Here, we show that overexpressed oskar mRNA localizes to the middle of the oocyte, as well as the posterior. This ectopic localization depends on the premature translation of Oskar protein, which recruits PAR-1 and microtubule-plus-end markers to the oocyte center instead of the posterior pole, indicating that Oskar regulates the polarity of the cytoskeleton. Oskar also plays a role in the normal polarization of the oocyte; mutants that disrupt oskar mRNA localization or translation strongly reduce the posterior recruitment of microtubule plus ends. Thus, oskar mRNA localization is required to stabilize and amplify microtubule polarity, generating a positive feedback loop in which Oskar recruits PAR-1 to the posterior to increase the microtubule cytoskeleton's polarization, which in turn directs the localization of more oskar mRNA.
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, 108 Pfotenhauerstrasse, 01307 Dresden, Germany. zimyanin@mpi-cbg.de
authors.forename: Vitaly
authors.initials: V
authors.lastname: Zimyanin
authors.forename: Nick
authors.initials: N
authors.lastname: Lowe
authors.forename: Daniel
authors.initials: D
authors.lastname: St Johnston
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D016764:Cell Polarity / Q000502:physiology*; D003599:Cytoskeleton / Q000378:metabolism*; D004330:Drosophila / Q000378:metabolism / Q000502:physiology*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D025461:Feedback, Physiological / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D038362:Glycogen Synthase Kinase 3; D008954:Models, Biological; D009865:Oocytes / Q000502:physiology*; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger / Q000378:metabolism*
chemical_list: D029721:Drosophila Proteins; D012333:RNA, Messenger; C091675:osk protein, Drosophila; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D038362:Glycogen Synthase Kinase 3; C472496:Par-1 protein, Drosophila