The γ TuRC components Grip75 and Grip128 have an essential microtubule-anchoring function in the Drosophila germline

The gamma-tubulin ring complex (gamma TuRC) forms an essential template for microtubule nucleation in animal cells. The molecular composition of the gamma TuRC has been described; however, the functions of the subunits proposed to form the cap structure remain to be characterized in vivo. In Drosophila, the core components of the gamma TuRC are essential for mitosis, whereas the cap component Grip75 is not required for viability but functions in bicoid RNA localization during oogenesis. The other cap components have not been analyzed in vivo. We report the functional characterization of the cap components Grip128 and Grip75. Animals with mutations in Dgrip128 or Dgrip75 are viable, but both males and females are sterile. Both proteins are required for the formation of distinct sets of microtubules, which facilitate bicoid RNA localization during oogenesis, the formation of the central microtubule aster connecting the meiosis II spindles in oocytes and cytokinesis in male meiosis. Grip75 and Grip128 anchor the axoneme at the nucleus during sperm elongation. We propose that Grip75 and Grip128 are required to tether microtubules at specific microtubule organizing centers, instead of being required for general microtubule nucleation. The gamma TuRC cap structure may be essential only for non-centrosome-based microtubule functions.