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PLoS Genet. 2015 Feb 27;11(2):e1004992. doi: 10.1371/journal.pgen.1004992. eCollection 2015.

Region-specific activation of oskar mRNA translation by inhibition of Bruno-mediated repression.

Author information

1
Department of Molecular Biosciences, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas, United States of America.
2
Laboratory for Germline Development, RIKEN Center for Developmental Biology, Kobe, Hyogo, Japan.
3
Proteomics Facility, Institute for Cellular and Molecular Biology and College of Pharmacy, The University of Texas at Austin, Austin, Texas, United States of America.
4
Department of Germline Development, Division of Organogenesis, Institute of Molecular Embryology and Genetics, Kumamoto University, Kumamoto, Japan.

Abstract

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.

PMID:
25723530
PMCID:
PMC4344327
DOI:
10.1371/journal.pgen.1004992
[Indexed for MEDLINE]
Free PMC Article

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