Centrioles are evolutionarily conserved microtubule-based cylinders that are essential components of the centrosome. Understanding centriole biogenesis is therefore of key importance, but we do not yet understand the molecular mechanism involved. In this issue, two groups address this problem. On page , Tang Tang and colleagues investigate the role of human CEP295 (Drosophila Ana1). By using super-resolution and immunogold electron microscopy, the authors show that CEP295 interacts directly with microtubules – being recruited to the proximal end of procentrioles in early S phase – when it is also localised at the centriole wall that surrounds the hSAS6 cartwheel protein. The authors further demonstrate that CEP295 is required for both CPAP- and CEP120-mediated centriole elongation, and that excess CEP295 can induce the assembly of overly long centrioles. Importantly, they show that CEP295 is essential for building the distal half of centrioles and required for post-translational modification of centriolar microtubules during centriole assembly. On page , Jordan Raff and colleagues investigate the function of Drosophila Ana1 in vivo. The authors show that ana1 mutant flies have dramatically reduced numbers of centrosomes and that Ana1 is irreversibly incorporated into daughter centrioles as they assemble in S phase. Interestingly, the authors also demonstrate a role for Ana1 in promoting centriole elongation in a dose-dependent manner and show that this activity appears to require the N-terminal 639 amino acids of Ana1. Moreover, this function of Ana1 is independent of its function in centriole stabilization, suggesting that Ana1 has at least two distinct functions at centrioles. These two complementary studies describe a new role in centriole elongation for CEP295 in human cells and Ana1 in fly cells, suggesting that this function is conserved.
