Centrioles are highly stable barrel-shaped microtubule-based structures that exist as mother-daughter pairs. In mitotic cells, centrioles recruit pericentriolar material to form centrosomes, which serve as microtubule-organizing (MTOCs) that help to establish the poles of the spindle. In interphase centrioles serve as basal bodies that direct the formation of cilia and flagella. Centrioles are assembled from a set of conserved core proteins. The coiled-coil protein SPD-2 recruits the kinase ZYG-1, which then recruits the SAS-5/SAS-6 complex to form a central scaffold. SAS-4 is the last to be recruited and is required for the addition of microtubules to the outer wall. SAS-6 is a stable component of the C. elegans centriole and plays a key structural role that helps define the nine-fold symmetry of this structure. We have identified a new mutation in the SAS-6 N-terminal globular domain that results in a novel phenotype. The
sas-6(
or1167) mutation causes a single amino acid substitution (D9V) that appears to affect centriole stability and duplication. Unlike RNAi-mediated depletion of SAS-6, which simply blocks centriole duplication, the mutant protein can only block duplication when it is both present in the mother centriole and present in the embryonic cytoplasm. This suggests some type of molecular communication between SAS-6 molecules in the mother and those being recruited to form the daughter centriole. Interestingly, centrioles assembled in this mutant also appear unstable and over time lose SAS-6 and other components such as SAS-4. Further, by electron microscopy, the
sas-6 mutant centrioles appear structurally abnormal. Together, our data suggest that SAS-6 is not just required for the assembly of centrioles, but also functions in maintaining their long-term stability. Our data also indicate that SAS-6 in the mother centriole directs the assembly of daughter centriole SAS-6.