Region-specific activation of oskar mRNA translation by inhibition of Bruno-mediated repression.
A complex program of translational repression, mRNA localization, and translational activation ensures that Oskar (Osk) protein accumulates only at the posterior pole of the Drosophila oocyte. Inappropriate expression of Osk disrupts embryonic axial patterning, and is lethal. A key factor in translational repression is Bruno (Bru), which binds to regulatory elements in the osk mRNA 3' UTR. After posterior localization of osk mRNA, repression by Bru must be alleviated. Here we describe an in vivo assay system to monitor the spatial pattern of Bru-dependent repression, separate from the full complexity of osk regulation. This assay reveals a form of translational activation-region-specific activation-which acts regionally in the oocyte, is not mechanistically coupled to mRNA localization, and functions by inhibiting repression by Bru. We also show that Bru dimerizes and identify mutations that disrupt this interaction to test its role in vivo. Loss of dimerization does not disrupt repression, as might have been expected from an existing model for the mechanism of repression. However, loss of dimerization does impair regional activation of translation, suggesting that dimerization may constrain, not promote, repression. Our work provides new insight into the question of how localized mRNAs become translationally active, showing that repression of osk mRNA is locally inactivated by a mechanism acting independent of mRNA localization.
Department of Molecular Biosciences, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas, United States of America.
Goheun
G
Kim
Department of Molecular Biosciences, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas, United States of America.
Chin-I
CI
Pai
Laboratory for Germline Development, RIKEN Center for Developmental Biology, Kobe, Hyogo, Japan.
Keiji
K
Sato
Proteomics Facility, Institute for Cellular and Molecular Biology and College of Pharmacy, The University of Texas at Austin, Austin, Texas, United States of America.
Maria D
MD
Person
Department of Germline Development, Division of Organogenesis, Institute of Molecular Embryology and Genetics, Kumamoto University, Kumamoto, Japan.
Akira
A
Nakamura
Department of Molecular Biosciences, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas, United States of America.
Paul M
PM
Macdonald
D020413:3' Untranslated Regions / Q000235:genetics; D000818:Animals; D019521:Body Patterning / Q000235:genetics*; D029721:Drosophila Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D009154:Mutation; D009865:Oocytes / Q000254:growth & development / Q000378:metabolism; D009866:Oogenesis / Q000235:genetics; D014176:Protein Biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid
D020413:3' Untranslated Regions; D029721:Drosophila Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; C093437:bru1 protein, Drosophila; C091675:osk protein, Drosophila