cNap1 bridges centriole contact sites to maintain centrosome cohesion

Abstract

Centrioles are non-membrane bound organelles that participate in fundamental cellular processes through their ability to form physical contacts with other structures. During interphase, two mature centrioles can associate to form a single centrosome - a phenomenon known as centrosome cohesion. Centrosome cohesion is important for processes such as cell migration, and yet how it is maintained is unclear. Current models indicate that pericentriolar fibres termed rootlets, also known as the centrosome linker, entangle to maintain centriole proximity. Here, I uncover a new centriole-centriole contact site and mechanism of centrosome cohesion, based on coalescence of the proximal centriole component cNap1. Using live-cell imaging of endogenously tagged cNap1, I show that proximal centrioles form dynamic contacts in response to physical force from the cytoskeleton. Expansion microscopy reveals that cNap1 bridges between these contact sites, physically linking proximal centrioles on the nanoscale. When ectopically tethered to organelles such as lysosomes, cNap1 forms viscous and cohesive condensates that promote organelle spatial proximity. Conversely, cNap1 mutants with reduced viscosity are unable to maintain centrosome cohesion. These results define a previously unrecognised mechanism of centrosome cohesion by cNap1 assemblies at the proximal centriole and illustrate how a non-membrane bound organelle forms dynamic organelle contact sites.