The kinase ZYG-1 phosphorylates the cartwheel protein SAS-5 to drive centriole assembly in C. elegans.

Centrioles organize centrosomes, the cell's primary microtubule-organizing centers (MTOCs). Centrioles double in number each cell cycle, and mis-regulation of this process is linked to diseases such as cancer and microcephaly. In C. elegans, centriole assembly is controlled by the Plk4 related-kinase ZYG-1, which recruits the SAS-5–SAS-6 complex. While the kinase activity of ZYG-1 is required for centriole assembly, how it functions has not been established. Here we report that ZYG-1 physically interacts with and phosphorylates SAS-5 on 17 conserved serine and threonine residues in vitro. Mutational scanning reveals that serine 10 and serines 331/338/340 are indispensable for proper centriole assembly. Embryos expressing SAS-5^S10A exhibit centriole assembly failure, while those expressing SAS-5^{S331/338/340A} possess extra centrioles. We show that in the absence of serine 10 phosphorylation, the SAS-5–SAS-6 complex is recruited to centrioles, but is not stably incorporated, possibly due to a failure to coordinately recruit the microtubule-binding protein SAS-4. Our work defines the critical role of phosphorylation during centriole assembly and reveals that ZYG-1 might play a role in preventing the formation of excess centrioles. Synopsis: In C. elegans, a critical step in centriole assembly involves phosphorylation of the centriole scaffold protein SAS-5 by ZYG-1, which is required for recruitment of SAS-4 and the stable incorporation of the SAS-5-SAS-6 complex into the nascent centriole. In C. elegans, the kinase ZYG-1 phosphorylates the central scaffold protein SAS-5 to drive centriole assembly. Phosphorylation of SAS-5 on serine 10 is specifically required for stable incorporation of the SAS-5-SAS-6 complex into nascent centrioles. SAS-4, a stabilizer of nascent centrioles, is not recruited to the assembling centriole when phosphorylation of serine 10 is blocked. Serine-to-alanine mutations within the C-terminus of SAS-5 results in elevated levels of the protein and centriole amplification, suggesting that SAS-5 might be regulated by phosphorylation. In C. elegans, a critical step in centriole assembly involves phosphorylation of the centriole scaffold protein SAS-5 by ZYG-1, which is required for recruitment of SAS-4 and the stable incorporation of the SAS-5-SAS-6 complex into the nascent centriole. [ABSTRACT FROM AUTHOR]