Tudor protein is essential for the localization of mitochondrial RNAs in polar granules of Drosophila embryos

In Drosophila, polar plasm contains polar granules, which deposit the factors required for the formation of pole cells, germ line progenitors. Polar granules are tightly associated with mitochondria in early embryos, suggesting that mitochondria could contribute to pole cell formation. We have previously reported that mitochondrial large and small rRNAs (mtrRNAs) are transported from mitochondria to polar granules prior to pole cell formation and the large rRNA is essential for pole cell formation. Here we show that the localization of mtrRNAs is diminished in embryos laid by tudor mutant females, although the polar granules are maintained. We also found that Tud protein was colocalized with mtrRNAs at the boundaries between mitochondria and polar granules when the transport of mtrRNAs takes place. These observations suggest that Tud mediates the transport of mtrRNAs from mitochondria to polar granules.