Why do cartilaginous fish not get cancer?

Anti-cancer genes found in sharks and rays

Denis Strigun, Naked Science

American scientists have identified genes that are associated with high resistance to cancer in cartilaginous fish (Chondrichthyes). The results of the work are published in the journal BMC Genomics (Marra et al., Comparative transcriptomics of elasmobranchs and teleosts highlight important processes in adaptive immunity and regional endothermy).

The cartilaginous class includes about 1207 species of fish, including sharks (Selachii) and rays (Batoidea). Unlike higher vertebrates, the skeleton of the latter consists of cartilage that does not have bone marrow (it produces B-cells of immunity). At the same time, the immune resistance of cartilaginous fish is higher than that of bony fish (Teleostei): for example, it is believed that stingrays and sharks cannot get cancer.

It is assumed that high resistance to diseases is associated with genetic mutations that cartilaginous have accumulated over evolution. However, so far, no studies have been conducted to confirm this. To fill in the gap, scientists from Cornell University and other universities compared heart tissue samples of seven animal species: four cartilaginous and three bony fish.

For the work, the authors used samples from a white shark (Carcharodon carcharias), a giant hammerhead shark (Sphyrna mokarran), a mako shark (Isurus oxyrinchus), a yellow stingray (Urobatis jamaicensis), as well as a mechenos (Xiphias gladius), an orange-finned surgeon (Acanthurus bahianus) and a long-finned sponge (Lachnolaimus maximus). The genome was compared using RNA sequencing.

The results showed that the genome of cartilaginous fish contains a number of mutant genes. So, in sharks, scientists have found orthologs (genes that usually perform identical or similar functions – VM) of human LGMN encoding legumin and Bag1, which is involved in apoptosis. Suppression of these genes in humans is associated with tumors, whereas in sharks LGMN and Bag1 are overexpressed. Also, cartilaginous have more humoral immunity genes.

According to the authors, these data indicate the evolutionary variability of the genome of cartilaginous fish, which may be associated with their high resistance to cancer and accelerated tissue regeneration. Scientists, however, noted that the consumption of meat, for example, sharks in food hardly prevents the development of tumors: in the body of these predators, there is often a high concentration of mercury.

Portal "Eternal youth" http://vechnayamolodost.ru  30.01.2017