Disease relevance of osk

• The posterior and anterior localization of Wolbachia resembles that of oskar and bicoid mRNAs, respectively, which define the anterior-posterior axis in the Drosophila oocyte [1].
• Oskar gains weight [2].

High impact information on osk

• Prior to reaching the posterior pole of the Drosophila oocyte, oskar mRNA is translationally silenced by Bruno binding to BREs in the 3' untranslated region [3].
• Validating current models, we directly demonstrate the mechanism proposed for Cup-mediated repression: inhibition of small ribosomal subunit recruitment to oskar mRNA [3].
• Armitage forms an asymmetric network associated with the polarized microtubule cytoskeleton and is concentrated with translationally silent oskar mRNA in the oocyte [4].
• We conclude that RNA silencing is essential for establishment of the cytoskeletal polarity that initiates embryonic axis specification and for translational control of oskar mRNA [4].
• The Drosophila homolog of C. elegans PAR-1 organizes the oocyte cytoskeleton and directs oskar mRNA localization to the posterior pole [5].

Biological context of osk

• To avoid inappropriate activation of nos, osk activity must appear only at the posterior pole of the oocyte, where the osk mRNA becomes localized during oogenesis [6].
• Here, we show that translation of osk mRNA is, and must be, repressed prior to its localization; absence of repression allows osk protein to accumulate throughout the oocyte, specifying posterior body patterning throughout the embryo [6].
• Translational repression is mediated by an ovarian protein, bruno, that binds specifically to bruno response elements (BREs), present in multiple copies in the osk mRNA 3'UTR [6].
• To date, only a single actin binding protein (TropomyosinII) has been identified with a putative role in osk mRNA and protein anchoring [7].
• Hrp48 colocalizes with osk mRNA throughout oogenesis, and interacts with its 5' and 3' regulatory regions, suggesting that it binds directly to oskar mRNA to mediate its posterior transport [8].

Anatomical context of osk

• Such analyses also reveal a requirement for Rab11 in the organization of microtubule plus ends and osk mRNA localization and translation [9].
• MOESIN crosslinks actin and cell membrane in Drosophila oocytes and is required for OSKAR anchoring [7].
• Cortical binding of oskar mRNA seems to be dependent on the actin cytoskeleton [10].
• The localization of Oskar at the posterior pole of the Drosophila oocyte induces the assembly of the pole plasm and therefore defines where the abdomen and germ cells form in the embryo [11].
• Control of oskar mRNA translation by Bruno in a novel cell-free system from Drosophila ovaries [12].

Associations of osk with chemical compounds

• We find that the nascent polypeptide-associated complex (NAC) is required for correct localization of oskar mRNA [13].
• We have identified mutations in the receptor-like transmembrane tyrosine phosphatase Lar that disorganize follicle formation, block egg chamber elongation and disrupt Oskar localization, which is an indicator of oocyte anterior-posterior polarity [14].

Physical interactions of osk

• We have explored interactions between these gene products at the molecular level and find that Oskar interacts directly with Vasa and Staufen, in a yeast two-hybrid assay [15].
• Translational repression of oskar mRNA is mediated by the RNA-binding protein Bruno, which binds to specific motifs in the oskar 3'UTR [16].
• Smaug interacts gentically and biochemically with Oskar, a key component of the pole plasm for activation of nanos mRNA and specification of the germline precursors [17].
• Premature translation of oskar in oocytes lacking the RNA-binding protein bicaudal-C [18].
• A function for kinesin I in the posterior transport of oskar mRNA and Staufen protein [19].
• The reduced number of primordial germ cells in embryos derived from lasp mutant females can be rescued only with a form of Lasp that is capable of interacting with Oskar, revealing the physiological importance of the Lasp-Oskar interaction [20].

Co-localisations of osk

• Barentsz protein colocalizes to the posterior with oskar mRNA, and this localization is oskar mRNA dependent [11].

Regulatory relationships of osk

• Furthermore, anterior patterning defects observed in embryos from sqd females expressing only the SqdS protein isoform suggest that Sqd may also play a role in the translational regulation of the mislocalized osk mRNA [21].
• A mutant Cup protein lacking this sequence fails to repress osk translation in vivo [22].
• Khc mutations that reduce the velocity of kinesin-1 transport in vitro blocked streaming yet still supported posterior localization of oskar mRNA, suggesting that streaming is not essential for the oskar localization mechanism [23].
• Here we show that Homer and Bifocal act redundantly to promote posterior anchoring of the osk gene products [24].
• aubergine enhances oskar translation in the Drosophila ovary [25].

Other interactions of osk

• In addition, we discuss the possible biological role of the Oskar-Staufen interaction [15].
• These results suggest that the Oskar-Vasa interaction constitutes an initial step in polar granule assembly [15].
• Finally, we show that in the pole plasm, Oskar protein, like Vasa and Tudor, is a component of polar granules, the germ-line-specific RNP structures [15].
• We show that Oskar prevents the rapid deadenylation of nanos mRNA by precluding its binding to Smaug, thus leading to its stabilization and translation [26].
• Pcs is expressed in the ovary and oocyte during oogenesis and again in the embryo, specifically in the developing mesoderm, throughout muscle development. pcs is first required in the ovary during oogenesis for patterning and segmentation of the early Drosophila embryo due primarily to its role in the regulation of Oskar (Osk) levels [27].
• 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 [28].

Analytical, diagnostic and therapeutic context of osk

• Immunohistochemistry reveals that Y14 is predominantly nuclear and colocalizes with oskar mRNA at the posterior pole [29].
• We colocalized ribozymes with their mRNA targets in an animal model by using the discrete RNA localization signals present in the 3' untranslated regions (UTRs) of Drosophila bicoid and oskar mRNAs [30].
• Transplantation of cytoplasm from normal embryos into mutant embryos reveals that osk-dependent activity is strictly localized at the posterior pole and has three distinct functions [31].
• The tissue- and sex-specific expression profiles and hybridizations in situ show that oskar orthologous transcripts in Anopheles gambiae and Aedes aegypti accumulate in developing oocytes of adult females and localize to the posterior poles of early embryos [32].
• As an example, molecular beacons were designed against regions of oskar mRNA, microinjected into living Drosophila melanogaster oocytes and imaged via confocal microscopy [33].

References