Stable centrosomal roots disentangle to allow interphase centriole independence

Abstract

The centrosome is a non-membrane bound cellular compartment consisting of two centrioles surrounded by a protein coat termed the pericentriolar material (PCM). Centrioles must remain physically associated together (a phenomenon called centrosome cohesion) for cell migration, ciliary function and mitosis, yet how this occurs in the absence of a bounding lipid membrane is unclear. One model posits that pericentriolar fibres formed from rootletin protein directly link centrioles, yet little is known about the structure, biophysical properties or assembly kinetics of such fibres. Here, I combine live cell imaging of endogenously tagged rootletin with cell fusion, and find previously unrecognised plasticity in centrosome cohesion. Rootletin forms large, diffusionally stable, bifurcating fibres, which amass slowly on mature centrioles over many hours from anaphase. Nascent centrioles (procentrioles) in contrast do not form roots, and must be licensed to do so through polo-like kinase 1 (PLK1) activity. Transient separation of roots accompanies centriolar repositioning during the interphase, suggesting that centrioles organize as independent units, each containing a discrete root. Indeed, forced induction of duplicate centriole pairs allows independent re-shuffling of individual centrioles between the pairs. Thus, collectively, these findings suggest that progressively nucleated polymers mediate the dynamic association of centrioles as either one or two interphase centrosomes, with implications for our understanding of how non-membrane bound organelles self-organise.