A breakthrough method uncovers how human cells kick off DNA replication
When cells divide, their genomic DNA is copied with remarkable precision once in each cycle. Flaws in this replication process can alter the genome, fueling cellular aging, cancer, and genetic disorders. Understanding how cells start duplicating their DNA is therefore essential for unraveling core biology, disease mechanisms, and even evolution.
Historically, DNA replication has been studied in microbes like E. coli and yeast. In those organisms, the replication origin—the starting point of replication—depends on a specific DNA sequence. Yet in most eukaryotic cells, including humans, the sequence itself does not dictate where replication begins. For decades, researchers wondered where and how replication starts within the human genome.
To tackle this, Masato Kanemaki and colleagues at the National Institute of Genetics introduced a new, high-precision technique called LD-OK-seq (Ligase Depletion-Okazaki sequencing) to map replication initiation sites in the human genome. By examining the proteins bound at these sites, they revealed a fundamental rule governing where human cells initiate replication.
The study showed that, apart from highly active gene regions, human cells can start DNA replication nearly anywhere in the genome. This flexibility stems from the widespread recruitment of the MCM helicase, a core driver of replication. Additionally, during early S phase, initiation frequently occurs in intergenic regions (stretches of DNA between genes), guided by the binding of the TRESLIN-MTBP complex, which activates the MCM helicase. The researchers also uncovered a counterbalancing regulatory system that modulates how TRESLIN-MTBP associates with MCM.
These insights address the core question of how human cells begin genome replication and offer new perspectives on diseases tied to replication errors—such as genomic instability disorders, cancer, aging-related conditions, and genetic ailments—as well as implications for genome evolution. In the long run, this work could pave the way for technologies that enable artificial control of DNA replication.
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