Nuclear enlargement induced by overexpression of nuclear export signal is associated with abnormal nuclear division in <i>Schizosaccharomyces pombe</i>

The size of the nucleus is tightly coordinated with cell size across eukaryotes, yet the physiological significance of maintaining proper nuclear dimensions remains poorly understood. Here, we investigate how nuclear size dysregulation resulting from perturbed nucleocytoplasmic transport affects mitotic fidelity in Schizosaccharomyces pombe. Overexpression of a GFP-tagged nuclear export signal (NES-GFP) induced nuclear expansion, leading to severe growth defects and frequent errors in chromosome segregation during mitosis. Live-cell imaging revealed that enlarged nuclei underwent delayed mitotic progression and abnormal nuclear division. Strikingly, genetic suppression of nuclear expansion alleviated these defects, whereas enhancement of nuclear size exacerbated them. Together, these findings suggest that maintaining proper nuclear dimensions contributes to accurate chromosome segregation, although additional effects of NES-GFP overproduction and other factors influencing nuclear size should be further examined.