van Ravesteyn, T. | Search bioRxiv

bioRxiv2026

Mitotic errors drive rapid clearance of polyploidy during intestinal regeneration despite robust centrosome clustering

Polyploid cells are increasingly recognized not only as hallmarks of cancer but also as features of regenerating tissues. During intestinal regeneration, polyploid cells are transient, yet the mechanisms underlying their clearance remain unknown. Using mouse intestinal organoids as a regeneration model, we show that, unlike in many cancer cell-line models, this clearance occurs without immediate cell-cycle arrest and is not driven by failure to establish spindle bipolarity. Instead, polyploid intestinal cells efficiently cluster supernumerary centrosomes to form bipolar spindles in an HSET-dependent manner, facilitated by delayed centrosome separation at mitotic onset. Despite this, polyploid divisions frequently produce chromosome segregation errors, including catastrophic chronocrisis. Lineage tracing reveals that progeny of such divisions is rapidly lost over subsequent generations. Increasing polyploidy during early regeneration disrupts organoid maturation, indicating that timely polyploidy clearance is required for successful regeneration. Polyploid cells are also detected in regenerating human colonic organoids, suggesting that transient polyploidy is a conserved feature of intestinal regeneration.

cell biology↗

bioRxiv2025

A Universal Scaling Law for Mitotic Spindles Driven by Chromosome Crowding

Cells regulate the size of their internal structures to maintain function in diverse biological settings1. The mitotic spindle, a molecular micro-machine responsible for chromosome segregation2, must scale to accommodate genomes varying in size by over 10,000-fold across eukaryotes3. Yet, how spindle biomechanics adapts to vastly different genome sizes remains unknown. Here, we uncover a universal spindle scaling law, where metaphase plate width scales with genome size following a power law with an exponent of [~]1/3. We hypothesize that chromosome crowding within the metaphase plate generates compressive forces as chromosomes push against each other, thereby determining spindle size and shape. Our experiments with altered chromosome number and mechanical properties in healthy and cancerous human and mouse cells, together with a theoretical model based on inter-chromosome pushing forces and mechanical manipulations of cells, confirm this hypothesis. Extending these insights across eukaryotes, we demonstrate that chromosome crowding predicts the observed power-law scaling. The biophysical constraint of chromosome crowding offers a mechanistic explanation for the evolution of open mitosis and mitotic cell rounding, enabling the division of larger genomes. Spindle adaptability to larger genomes may promote the proliferation of polyploid cells, driving not only tumor progression but also speciation during evolution.

biophysics↗