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The chromosome segregation that occurs during most mitotic divisions is accomplished largely by forces generated by microtubules. In most cases these microtubules emanate from the centrosome-based microtubule organising centre. The centrosome is a complex structure that comprises a centriole pair surrounded by a proteinaceous nuage referred to as the pericentriolar material. At each mitotic cell division the centriole pair must split, duplicate and separate to opposing poles of the spindle in what is referred to as the centrosome cycle. However when cells cease their divisions to execute their terminal differentiation program the centrioles too must recognize this condition and accordingly arrest the centrosome cycle. Following the final division in mammalian epithelial cells the unduplicated centrioles present in the daughter cells undergo specific changes and migrate to the cell membrane where they will generate the primary cilium. These organelles are extensions of the cell membrane and can contribute to cell motility, mechanotransduction, while also playing a central role in cell signalling.
In C. elegans, cilia are restricted to the sensory neurons; differentiated epithelial cells do not possess primary cilia nor do they show evidence of a centriole/centrosome. We have shown that in specific developmental contexts the centrioles uncouple from the cell cycle, while in the epithelial cells of the gut, the vulva, and the hypodermis, the centrioles are actively eliminated following the final cell division. The epithelial cells of C. elegans therefore do not possess primary cilia potentially because their centrioles are actively eliminated upon terminal differentiation.
To investigate the process involved in centriole elimination following the final division we genetic analysis to identify mutants that do not eliminate their centrioles upon differentiation. Using a centriole-specific marker we sought to isolate mutants that disrupted the timely elimination of the centrioles in differentiated epithelia, namely in the intestine. From this pilot screen we identified one mutant that allows the centrioles to persist in the gut epithelial cells in C. elegans. These centrioles however do not become cilia suggesting that the presence of a post-mitotic centriole is not sufficient for the formation of a cilium. We will use by classic genetic analysis and novel transgenic approaches to identify genes that may block this conversion or are required to convert a mitotic centriole into a cilium.