Dynein Associates with <i>oskar</i> mRNPs and Is Required For Their Efficient Net Plus-End Localization in <i>Drosophila</i> Oocytes

<div><p>In order for eukaryotic cells to function properly, they must establish polarity. The <i>Drosophila</i> oocyte uses mRNA localization to establish polarity and hence provides a genetically tractable model in which to study this process. The spatial restriction of <i>oskar</i> mRNA and its subsequent protein product is necessary for embryonic patterning. The localization of <i>oskar</i> mRNA requires microtubules and microtubule-based motor proteins. Null mutants in Kinesin heavy chain (Khc), the motor subunit of the plus end-directed Kinesin-1, result in <i>oskar</i> mRNA delocalization. Although the majority of <i>oskar</i> particles are non-motile in khc nulls, a small fraction of particles display active motility. Thus, a motor other than Kinesin-1 could conceivably also participate in <i>oskar</i> mRNA localization. Here we show that Dynein heavy chain (Dhc), the motor subunit of the minus end-directed Dynein complex, extensively co-localizes with Khc and <i>oskar</i> mRNA. In addition, immunoprecipitation of the Dynein complex specifically co-precipitated <i>oskar</i> mRNA and Khc. Lastly, germline-specific depletion of Dhc resulted in <i>oskar</i> mRNA and Khc delocalization. Our results therefore suggest that efficient posterior localization of <i>oskar</i> mRNA requires the concerted activities of both Dynein and Kinesin-1.</p>