When Cells Rebel: a comparative genomics investigation into marsupial cancer susceptibility

Cancer is ubiquitous in multicellular life, yet susceptibility varies significantly between species. Previous studies have shown a genetic basis for cancer resistance in many species, but few studies have investigated the inverse: why some species are particularly susceptible to cancer. The Dasyuridae are a family of carnivorous marsupials that are frequently reported as having high rates of cancer prevalence. We hypothesised that this high susceptibility also has a genetic basis. To investigate this, we generated reference genomes for the kowari ( Dasyuroides byrnei ), a dasyurid species with one of the highest rates of reported cancer prevalence among mammals, and a non-dasyurid marsupial, the eastern barred bandicoot ( Perameles gunnii ). We used these to perform a comparative genomics analysis alongside nine previously assembled reference genomes: four dasyurid species and five non-dasyurid marsupial species. Genomes were annotated using FGENESH++ and assigned to orthogroups for input to CAFE (Computational Analysis of gene Family Evolution) analysis to identify gene families that had undergone significant expansions or contractions in each lineage. In the dasyurids, we identified large expansions in Ras genes, a family of oncogenes. Interestingly, a similar expansion of Ras genes was also identified in the bandicoot and bilby. These genes were primarily expressed in tissues such as testes, ovaries and yolk sac, so we hypothesise they serve a reproductive role. Future work is required to identify the potential roles of oncogene expansions in cancer susceptibility in these marsupial species.