Exploring the regulation of centriole size by CP110/Cep97 and their interaction network

Centrioles are cylindrical organelles that serve as templates for the assembly of centrosomes and cilia. They exhibit 9-fold symmetry and comprise a central cartwheel structure surrounded by nine microtubule (MT) blades. Within the same cell type, centriole length is consistent, suggesting that the growth of these organelles is regulated. While recent advances have been made in understanding how the growth of the cartwheel is controlled, less is known about the mechanisms mediating centriole MT length. The proteins CP110 and Cep97 localise at the distal-ends of centrioles, and are thought to ‘cap’ centriole MTs to inhibit their over-elongation. However, it is not clear whether this regulation takes place during the growth of the centriole, or afterwards to maintain proper centriole size. In this thesis, I aimed to explore the regulation of centriole size by CP110/Cep97 and their interaction network. Development of an assay to track the dynamic growth of centriole MTs in early Drosophila embryos revealed that CP110/Cep97 overexpression slowed centriole MT growth. However, this may not be due to the direct effect of these proteins on MTs; rather, CP110/Cep97 play an unexpected role in affecting the growth rate and period of the underlying cartwheel structure, which is likely separate from their role in capping centriole MTs. Cep104 and Klp10A also localise to the distal-ends of centrioles and have been shown to interact with CP110/Cep97, yet I found that they do not affect daughter centriole growth dynamics. Indeed, Cep104 appears to act downstream of CP110/Cep97. These findings lead me to propose a model whereby centriole growth dynamics in Drosophila are primarily driven by the assembly of the cartwheel structure, with centriole MTs tracking the cartwheel’s growth. Once centrioles reach their final size, proper centriole length must be maintained, and this likely involves CP110/Cep97 (in their capping role) alongside Klp10A.