A Phylogeny-Based Approach to Discover Mutational Processes in Primates

The accumulation of germline mutations underpins population diversity and drives genetic evolution. Despite the availability of extensive phylogenetic data, the lack of suitable methodologies has hindered the comprehensive characterization of germline mutational processes across evolutionary trees. To address this, we develop a robust three-step methodology that extracts germline mutational processes from alignments of closely related species. First, we estimate regional, branch-specific trinucleotide mutational spectra from a multispecies alignment. Second, we extract mutational processes jointly across an evolutionary clade by analyzing mutation rate variation along the genome using Reciprocal Principal Components Analysis (RPCA). Finally we filter artifactual mutational signatures using DNA symmetry. Applying this method to five primate clades and a rodent outgroup clade revealed nine distinct mutational processes. Notably, five of these processes were consistently observed across all six groups. We identified underling biological mechanism for at least seven of the processes, highlighting phenomena such as biased gene conversion, bulky lesion resolution, and maternal mutagenesis. We validated identified processes using human and non-human polymorphism data. This study offers new insights into the biology and evolution of mutagenesis in primates and introduces a methodological toolkit to investigate mutational processes across phylogenies.