  Comparative studies of cancer-related genes allow us to gain novel
information about the evolution and function of these genes, but also to
understand cancer as a driving force in biological systems and species life
histories. So far, comparative studies of cancer genes have focused on mammals.
Here, we provide the first comparative study of cancer-related gene copy number
variation in fish. As fish are evolutionarily older and genetically more
diverse than mammals, their tumour suppression mechanisms should not only
include most of the mammalian mechanisms, but also reveal novel (but
potentially phylogenetically older) previously undetected mechanisms. We have
matched the sequenced genomes of 65 fish species from the Ensemble database
with the cancer gene information from the COSMIC database. By calculating the
number of gene copies across species using the Ensembl CAFE data (providing
species trees for gene copy number counts), we were able to develop a novel,
less resource demanding method for ortholog identification. Our analysis
demonstrates a masked relationship with cancer-related gene copy number
variation (CNV) and maximum lifespan in fish species, suggesting that higher
tumour suppressor gene CNV lengthens and oncogene CNV shortens lifespan, when
both traits are added to the model. Based on the correlation between tumour
suppressor and oncogene CNV, we were able to show which species have more
tumour suppressors in relation to oncogenes. It could therefore be suggested
that these species have stronger genetic defences against oncogenic processes.
Fish studies could yet be a largely unexplored treasure trove for understanding
the evolution and ecology of cancer, by providing novel insights into the study
of cancer and tumour suppression, in addition to the study of fish evolution,
life-history trade-offs, and ecology.
