Supplementary Material for: Chromosomal Instability in Mouse Induced Pluripotent Stem Cells: Insights into X and Y Aneuploidies

Introduction: Induced pluripotent stem (iPS) cells share key features with embryonic stem (ES) cells, including similar limitations such as the accumulation of (epi)genetic and genomic alterations. However, sex chromosome instability in mouse iPS cells remains poorly understood. This retrospective study aims to investigate this phenomenon by analyzing mouse iPS cell clones. Specifically, we examine whether factors such as passage number, cell sex, founder cell type, or reprogramming method influence the presence or absence of sex chromosome abnormalities. Methods: Sex chromosome stability was evaluated in 26 independent male and female mouse iPS cell clones using standard karyotyping techniques. Additionally, we analyzed an artificially generated XXY iPS cell model, in which an extra X chromosome was introduced into a normal XY cell line. Statistical analyses were conducted on the karyotyping results and correlated with both continuous variables (e.g., passage number) and categorical variables (e.g., cell sex, founder cell type, and reprogramming method). Results: Female iPS cell clones displayed significantly higher levels of sex chromosome instability compared to their male counterparts, regardless of the founder cell type or reprogramming strategy. A similar pattern of X chromosome instability was also observed in the XXY iPS cell model. Conclusion: Our findings demonstrate that sex chromosome instability occurs in mouse iPS cells, as previously reported in mouse ES cells, suggesting a conserved phenomenon across pluripotent stem cell types. Importantly, the presence of multiple X chromosomes in the pluripotent state appears to contribute to this instability. Further studies are required to elucidate the underlying molecular mechanisms.