Mutation of the Bruno-responsive elements in the oskar 3′ UTR results in the unregulated translation of the oskar mRNA. This unregulated translation requires the presence of functional Staufen protein. Stamen is an RNA-binding protein that may be associated with the cy-toskeleton and is involved in mRNA localization within the oocyte. If Staufen is missing, the oskar mRNA is not translated, even in the absence of functional Bruno-responsive elements, implying that the Staufen protein is involved in the translational activation of the oskar mRNA. We have recently shown that there are separable translational repression and activation elements for the Prml mRNA. ampicillin antibiotic
Transgenic studies with reporter mRNAs fused to various portions of the Prml 3′ UTR have identified individual sequence elements that are required for translational repression, as well as others that are necessary for the alleviation of this repression. As is the case for the Drosophila oskar message, we have identified RNA-binding proteins that may be involved in the translational repression of Prml . Likewise, SPNR shares many similarities with Staufen, including the presence of double-stranded RNA-binding domains and an association with the cytoskeleton. In the future it will be important to determine whether SPNR, like Staufen, is also involved in the translational activation of localized and stored mRNAs during spermatid differentiation. Clearly, defining SPNR’s functional role in spermatogenesis will require a mutation at the SPNR locus itself, as well as further experiments aimed at directly assessing the role of manchette microtubules in RNA transport and translational activation.