Abstract
The centriole/basal body is a eukaryotic organelle that plays essential roles in cell division and signaling. Among five known core centriole proteins, SPD-2/Cep192 is the first recruited to the site of daughter centriole formation and regulates the centriolar localization of the other components in C. elegans and in humans. However, the molecular basis for SPD-2 centriolar localization remains unknown. Here, we describe a new centriole component, the coiled-coil protein SAS-7, as a regulator of centriole duplication, assembly and elongation. Intriguingly, our genetic data suggest that SAS-7 is required for daughter centrioles to become competent for duplication, and for mother centrioles to maintain this competence. We also show that SAS-7 binds SPD-2 and regulates SPD-2 centriolar recruitment, while SAS-7 centriolar localization is SPD-2-independent. Furthermore, pericentriolar material (PCM) formation is abnormal in sas-7 mutants, and the PCM-dependent induction of cell polarity that defines the anterior-posterior body axis frequently fails. We conclude that SAS-7 functions at the earliest step in centriole duplication yet identified and plays important roles in the orchestration of centriole and PCM assembly.
Highlights
The centrosome is an evolutionarily conserved non-membranous organelle that is important for microtubule organization in most animal cells
We identified C. elegans SAS-7 as a new centriole component that is required for the daughter centriole to acquire centriole duplication competence and become a mother centriole, and for the maintenance of mother centriole duplication competence
Like SPD-2, SAS-7 is required for proper pericentriolar material (PCM) formation and for the PCM-dependent establishment of the A-P axis of cell polarity in one-cell stage embryos
Summary
The centrosome is an evolutionarily conserved non-membranous organelle that is important for microtubule organization in most animal cells. At its core is a pair of centrioles, each comprised of centriolar proteins and microtubules arranged in 9-fold radial symmetry around a structure called the cartwheel in most systems and what is thought to be its functional equivalent, the central tube, in C. elegans (Boveri, 1900; Gonczy, 2012). The two centrosomes serve as microtubule organizing centers (MTOCs) that contribute to the assembly of the bipolar mitotic spindle during cell division (Conduit et al, 2015; Woodruff et al, 2014). In non-mitotic cells, centrosomes contribute to cell motility, organelle positioning and intracellular transport (Sugioka and Sawa, 2012). The centriole is called the basal body when it serves to nucleate and anchor the microtubule-based cilia that are present on most quiescent animal cells
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