Summary
A bioRxiv preprint introduces Tau, a mathematical method for reconstructing and timing copy-number gains in cancer genomes. Its authors report that abrupt amplification bursts, including at oncogenes, cluster around whole-genome duplication.
A bioRxiv preprint describes Tau, a mathematical framework for reconstructing the histories of DNA copy-number gains in cancer genomes. Its authors report that many gains occurred in abrupt, multichromosomal events and that some of the largest oncogene amplifications clustered around whole-genome duplication (WGD). The work is presented as a preprint.
How Tau dates copy-number gains
Cancer cells can acquire extra copies of parts of their genomes. When a gained segment includes an oncogene, the additional copies can increase the amount of genetic material available to produce that cancer-promoting gene’s product.
The timing of these gains can be inferred from mutations carried along with them. A mutation that arose before a segment was copied may appear in multiple copies in the cancer genome; its multiplicity can therefore help place the gain relative to other events. The preprint says existing approaches have been limited by the number of possible gain histories as copy number rises, often restricting analysis to lower-copy states or specified scenarios.
Tau is designed to enumerate allele-specific routes to a copy-number state and calculate a timing for each gain. “Allele-specific” here means distinguishing gains on the two inherited versions of a chromosome. This allows the method to consider alternative sequences of events rather than assuming a predetermined history.
Gains often clustered around genome doubling
Across the pan-cancer genomes analysed, the authors report that punctuated, multichromosomal events accounted for roughly three-quarters of clonal gains. Most of these events were WGD, which increases the copy number of much of the genome. The authors describe WGD as occurring early and recurring in a subset of tumours prone to repeated doubling.
They also identify a distinct class of events, predominantly involving one chromosome copy, that recurred on chromosomes associated with particular tumour types. The highest copy-number states, meanwhile, were often reached in abrupt bursts rather than through a gradual series of gains. These bursts clustered around WGD, involved more gains than genome doubling alone would produce, and recurred at oncogenes.
The authors interpret this pattern as evidence that WGD can coincide with a period of additional, localised amplification, rather than acting only as a uniform doubling of the genome. By assigning timing to successive gains, Tau offers a way to investigate how large-scale genome changes and local oncogene amplification are ordered during cancer evolution.