High-throughput optical mapping of replicating DNA

DNA replication is a crucial process for the universal ability of living organisms to reproduce. Existing methods to map replication genome-wide use large cell populations and therefore smooth out variability between chromosomal copies. Single-molecule methods may in principle reveal this variability. However, current methods remain refractory to automated molecule detection and measurements. Their low throughput has therefore precluded genome-wide analyses. Here, we have repurposed a commercial optical DNA mapping device, the Bionano Genomics Irys system, to map the replication signal of single DNA molecules onto genomic position at high throughput. Our methodology (HOMARD) combines fluorescent labelling of replication tracks and nicking endonuclease (NE) sites with DNA linearization in nanochannel arrays and dedicated image processing. We demonstrate the robustness of our approach by providing an ultra-high coverage (23,311 x) replication map of bacteriophage λ DNA in Xenopus egg extracts. HOMARD opens the way to genome-wide analysis of DNA replication at the single-molecule level.