Ana1/CEP295 regulates centriolar doublet-to-triplet conversion during spermatogenesis

The centriole is well recognized for its ninefold symmetry, with nine microtubule blades arranged in a barrel-like structure. However, these blades adopt diverse architectures across evolution, ranging from microtubule singlets to triplets, and the mechanisms governing this variation and its biological significance remain largely elusive. Here we found that in Drosophila male germline cells, routine conversion of microtubule doublets to triplets is impaired in the absence of Ana1. The Ana1 N-terminal region localizes adjacent to microtubule doublets and promotes modest elongation, whereas the C-terminal region extends outward and is sufficient to support C-tubule assembly. Ana1 recruits centrobin to centrioles via its C-terminal region, and targeted recruitment of centrobin to centrioles restores C-tubule formation in an Ana1-deficient background. Restoring Ana1 expression at different developmental stages reveals that the integrity of triplet microtubules is critical for male fertility. Together, these findings identify a regulator of centriolar doublet-to-triplet conversion and provide insights into the biological significance of this process.