Nek1 defines a branch of centriolar microtubule length control parallel to CP110-Cep97.

Centrioles maintain a characteristic length throughout the cell cycle, which is essential for the accurate functioning of centrosomes and ciliogenesis. The CP110-Cep97 complex acts as a cap on the distal end of the centriole, restricting microtubule extension. However, whether CP110-Cep97 alone or in conjunction with additional players regulates this process remains unclear. In this study, we identify the kinase Nek1 (NIMA-related kinase 1) as a key factor that works with the CP110-Cep97 complex to control centriole length. Nek1 localizes alongside CP110 and Cep97 at the distal end of the centriole and interacts with Cep97 and Cep78. Loss of Nek1 induces pronounced centriolar microtubule hyperelongation without displacement of the CP110-Cep97 complex, indicating that Nek1 restricts centriole extension through a distinct mechanism. Co-depletion of Nek1 and CP110, but not Cep78, further enhances the hyperelongation phenotype, demonstrating that Nek1 and CP110 pathways act in parallel to maintain centriole length in cycling cells. Notably, Nek1 is removed from the basal body during ciliogenesis in a Cep78-dependent manner, thereby linking Cep78 to the spatial regulation of Nek1 activity. Together, these findings establish Nek1 as an important safeguard that works with the CP110-Cep97 complex to ensure the structural integrity of centrioles.