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Abstract

Chromosomal instability (CIN) is a hallmark of cancer, implicated in both tumor initiation and progression. Yet, its origins in normal, untransformed tissues remain poorly understood. Polyploidy is a feature of many adult tissues – particularly in exocrine glands such as the pancreas and the mammary gland. Although polyploidy has been linked to CIN in malignancies, the role of polyploidy in mutation acquisition within naïve tissues remains largely unexplored. In this thesis, I investigate the link between polyploidy and CIN during tissue remodeling, utilizing organoid and in vivo models of pancreatic injury. I demonstrate that polyploid acinar cells contribute to regeneration by undergoing acinar-to-ductal metaplasia. This transition involves extensive cellular remodeling, including cell shrinkage, which disrupts proper spindle orientation, especially in binucleated, polyploid acinar cells. These spindle defects result in mitotic errors such as lagging chromosomes, chromatin bridges, and the formation of micronuclei. Crucially, I observe extensive DNA damage within these micronuclei, consistent with chromothripsis, revealing a pathway to CIN in untransformed cells. To explore the broader relevance of this mechanism, I employed a lactating mammary gland organoid model, that was developed under my supervision. In this model, polyploidy was induced through pregnancy hormone treatment mimicking transitions that occur to prepare the tissue for milk production during lactation. Strikingly, this model recapitulated the mitotic abnormalities and CIN observed in the pancreas, suggesting that polyploidy-associated chromosomal instability is a conserved feature of glandular tissues. Notably, all findings were obtained in primary, untransformed cells without genetic manipulation or genotoxic stress, supporting a physiological origin of CIN linked to polyploid cell division. To acquire these findings, I developed an imaging and image analysis workflow to quantitatively assess ploidy states, nuclear number, micronuclei frequency, and expression levels of key markers. This workflow is also detailed in the thesis. Together, my results uncover a novel mechanism by which normal polyploid cells contribute to CIN during tissue regeneration. This work provides new insights into the origins of chromosomal instability in regenerative contexts, highlighting the dual role of polyploidy in promoting both tissue repair and chromosomal mis segregation.