Feedback loops in the Plk4-STIL-HsSAS6 network coordinate site selection for procentriole formation

Abstract

Centrioles are duplicated once in every cell cycle, ensuring the bipolarity of the mitotic spindle. Although the core components have been identified, how they cooperate to achieve high fidelity in centriole duplication remains poorly understood. Here, we show that in centriole duplication the accumulation of STIL and HsSAS6, components of the cartwheel structure, provides negative feedback in the centriolar dynamics of Plk4. By live-cell imaging of endogenously tagged proteins in human cells throughout the entire cell cycle, we quantitatively tracked the dynamics of the critical duplication factors: Plk4, STIL, and HsSAS6. Centriolar Plk4 peaks and then starts decreasing during the late G1 phase, which coincides with the accumulation of STIL at centrioles. Shortly thereafter, the HsSAS6 level increases steeply at the procentriole assembly site. We also show that both STIL and HsSAS6 are necessary for attenuating Plk4 levels. Furthermore, our mathematical modeling and simulation convincingly reproduce the dynamics of these three proteins at centrioles, and suggest that the STIL-HsSAS6 complex in the cartwheel has a negative feedback effect on centriolar Plk4. Combined, these findings illustrate how the dynamic behavior of and interactions between the critical duplication factors coordinate the centriole-duplication process.