The centrosome is a membrane-less organelle which primarily functions as a microtubule organising centre in eukaryotic cells, to allow normal progress through the cell cycle. While centrosome amplification in the absence of p53 is a well-established feature of cancers, more recently centrosome loss was also detected in tumour tissues. The development of a small molecule (called centrinone) that blocks centrosome duplication revealed that cells with centrosome loss undergo a p53-dependent cell cycle arrest that appears to show some senescence-like features with long-term treatment. However, the nature of cell cycle arrest and its relationship with senescence are still not well understood.

The aim of this project is to investigate the temporal dynamics of p53 in centrinone-treated cells and to determine whether long-term centrinone treatment induces bona fide senescence. I have used a novel fluorescent reporter of p53 transcriptional activity in RPE1 cells and combined it with live cell lineage analysis to reveal that p53 activation upon centrinone treatment is insufficient to commit cells to cease proliferation immediately. Instead, long-term centrinone treatment is required to induce cell cycle arrest. This state is reminiscent of senescence, but the phenotype is modest compared to classical DNA damage-induced senescence.

To examine whether this phenotype is due to cellular heterogeneity or a globally slow-cycling state, I have taken a single-cell transcriptomics approach and found that long-term centrinone treatment results in two distinct sub-populations, one exhibits typical senescence features, the other appears to maintain proliferative capacity. These findings extend our understanding of the line between senescence and centrosome biology, highlighting a unique heterogeneous senescence response.