Ploidy-dependent modulation of DNA replication kinetics in Xenopus.

An important question in cell biology is how DNA replication programs scale with genome size following polyploidization, an evolutionary process that increases DNA content without proportionally extending the cell cycle duration. In particular, comparative analyses across closely related polyploid species are lacking. Here, we developed an interspecies in vitro replication system using Xenopus laevis egg extracts and sperm nuclei from three closely related Xenopus species with distinct ploidy levels: diploid (Xenopus tropicalis), tetraploid (Xenopus laevis), and dodecaploid (Xenopus eysoole). Replication in diploid nuclei was faster than in tetraploid nuclei, consistent with higher fork density and speed, as expected. Counterintuitively, replication in dodecaploid nuclei was also accelerated relative to tetraploid nuclei, indicating that increased ploidy does not necessarily prolong S phase. Given the high conservation of replication genes, our results suggest that replication programs are dynamically tuned across polyploid species, revealing an unexpected flexibility in how eukaryotic cells adapt DNA replication to large-scale genome expansion.