# Single-molecule tracking reveals the dynamic turnover of Ipl1 at the kinetochores in Saccharomyces cerevisiae

## TL;DR

This study uses single-molecule tracking to reveal how Ipl1, a key cell division regulator, dynamically interacts with yeast kinetochores and spindles.

## Contribution

The study introduces single-molecule imaging to uncover the dynamic recruitment and assembly of Ipl1 and other CPC components at yeast kinetochores.

## Key findings

- Ipl1 recruitment dynamics at kinetochores and spindles differ and are influenced by tension and absence of key recruiters.
- The hierarchical assembly of chromosome passenger complex members at kinetochores was observed through single-molecule tracking.
- SMIT provides a detailed dynamic view of Ipl1 trafficking in live yeast cells.

## Abstract

Unlike ensemble averaging methods, this study visualizes the single molecules of Ipl1 in live yeast cells to quantify its recruitment dynamics and assembly as a part of the CPC at the kinetochores.

Aurora kinase B, Ipl1 in Saccharomyces cerevisiae, is a master regulator of cell division, required for checkpoint regulation, spindle assembly and disassembly, chromosome segregation, and cytokinesis. Decades of research employed ensemble averaging methods to understand its dynamics and function; however, the dynamic information was lost because of population-based averaging. Here, we use single-molecule imaging and tracking (SMIT) to quantify the recruitment dynamics of Ipl1 at the kinetochores and spindles in live cells. Our data suggest that Ipl1 is recruited to these locations with different dynamics. We have demonstrated how the recruitment dynamics of Ipl1 at the kinetochores during metaphase changes in the presence and absence of tension across the kinetochores, in the absence of protein phosphatase 1 (Glc7), and in the absence of its known recruiters (Ctf19 and Bub1). The SMIT of other chromosome passenger complex members (Bir1, Nbl1, Sli15) suggests their hierarchical assembly at the kinetochore. Hence, SMIT provides a dynamic view of the Ipl1 trafficking at the kinetochores and spindles.