A new study shows that elephants possess extra copies of a wide variety of genes associated with tumour suppression. And this could be the reason why these mammals have evolved to become huge in size and cancer-resistant. But this phenomenon is not unique to elephants. Duplication of tumour suppressor genes is quite common among elephants’ living and extinct relatives, including in small ones like Cape golden moles and elephant shrews. Tumour suppression capabilities preceded or coincided with the evolution of exceptionally big bodies, facilitating this development.
A long-standing paradox in evolutionary medicine and cancer biology is that as you get a really big body, your burden of cancer should increase because creatures with big bodies like elephants have more cells, which proves not to be true, indicating that evolution found a way to reduce cancer risk.
A well-known tumour suppressor gene, TP53 was mainly focused on for the study. It was found that they had way more extra copies of tumour suppressors than what you’d expect. The trend was found to be general in all genes, and not just TP53. They all contribute probably a little bit to cancer resistance. Elephant genomes also possess some unique duplications that may contribute to tumour suppression through genes involved in DNA repair; resistance to oxidative stress; and cellular growth, ageing and death.
The study searched for extra copies of cancer supressing genes in the DNA of Asian, African savanna and African forest elephants, as well as in a number of fellow Afrotherians, like Cape golden moles, elephant shrews, rock hyraxes, manatees, extinct woolly mammoths and extinct mastodons. Certain species belonging to a group of mammals called Xenarthra that is closely related to Afrotherians was also studied, and some extra copies of tumour suppressors were found in those animals’ genomes as well.
Reference: http://www.buffalo.edu/news/releases/2021/02/007.html
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