Cell-Cycle Withdrawal is Graded Rather Than Binary

Ashraf, Humza M.

Graduate Thesis Or Dissertation

Cell-Cycle Withdrawal is Graded Rather Than Binary Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/8336h3501

Abstract

Chemotherapy treatment elicits a variety of cellular responses such as reversible cell-cycle exit (quiescence) and irreversible arrest (senescence). However, distinguishing between the two is a challenge due to their overlapping molecular markers. To address this issue, we utilized live-cell time-lapse microscopy in this thesis to differentiate reversible from irreversible arrest in cells that are recovering from acute chemotherapeutic stress. We found that heterogeneity in cellular responses can be attributed to p53-p21 signaling, which varies based on the extent of DNA damage. In addition, we developed a new methodology to quantify senescence-associated-beta-galactosidase (SA-β-Gal), a commonly used marker for cellular senescence, and combined it with fluorescent biomarkers of irreversible cell-cycle arrest. By linking numerous senescence biomarkers to previous cell-cycle status, we discovered that the intensities of senescence biomarkers reflect the duration of cell-cycle withdrawal, rather than cellular senescence per se. This suggests that cell-cycle withdrawal is a graded process rather than a binary one, and the intensities of senescence biomarkers can indicate the likelihood of cell-cycle re-entry. Overall, our study suggests that there is no definitive point of no return for cell-cycle re-entry and that the likelihood of re-entry decreases gradually as cells progress through the continuum of cell-cycle exit. Our findings have significant implications for extracting dynamic information from snapshot data, where molecular marker combinations at different intensities encode past temporal histories of single cells and may potentially be used to predict future cell-fate outcomes.

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