Fish and their sun-protective “superpowers”

With the summer holidays in full swing and the sun making (intermittent) appearances, it’s time to start lathering on the suntan cream! Despite the hassle and general “greasiness” of these products, suntan cream is essential to protect our skin from damaging ultraviolet (UV) A and UVB rays which can lead to sunburn, premature skin aging and cancer. But while we’re busy trying not to stick to our beach towels, it may be interesting to note that not all organisms share our sticky plight: many bacteria, algae and marine invertebrates are known to produce their own sun protection. Now, research suggests that even fish may share this useful ability.

The sun is vital for maintaining life on Earth. It provides us with essential light and heat, without which our planet would be a lifeless rock covered in ice. But sunlight comprises different forms of light, including UV radiation which is invisible to the naked eye. It is this UV radiation (specifically the UVA and UVB forms) that can be harmful to our health, causing damage to the skin’s DNA. In humans, this can result in detrimental DNA mutations occurring, leading to various skin cancers such as basal cell carcinoma and squamous cell carcinoma.

But UV radiation is also harmful to other organisms, and many bacteria, algae and invertebrates that inhabit marine environments are exposed to high levels of sunlight (e.g. reefs, rock pools, etc.), meaning they need to protect themselves against this damaging UV radiation. While we humans need to lather on the suntan cream, these clever organisms produce their own sunscreens in the form of mycosporine-like amino acids and gadusols, which are able to absorb UV radiation and provide photoprotection. Such compounds are made by an enzyme called DDGS for short, a member of the sugar phosphate cyclase “superfamily” of proteins which are involved in synthesising natural therapeutic products (e.g. the antidiabetic drug acarbase).

While mycosporine-like amino acids and gadusols have been found in more complex marine animals, such as fish, it was originally thought that these compounds had been acquired through the animal’s diet. Recently, however, a group of scientists from Oregon State University in the United States have discovered that fish can produce gadusol themselves. Interestingly, this seems to be achieved through a different pathway to that used by bacteria.

Rather than DDGS, the group found that fish (in this case, zebrafish) possess a gene responsible for making an enzyme similar to another member of the sugar phosphate cyclase superfamily, EEVS. This EEVS-like gene is found grouped with a functionally unknown gene termed MT-Ox. In fact, the researchers were able to produce their own gadusol by adding both genes to a modified strain of E Coli and growing the cells in an environment rich in the necessary components for gadusol production. This suggests the EEVS-like and MT-Ox genes are involved in the production of this UV-protective compound in fish. Importantly, both the EEVS-like and MT-Ox genes are expressed during embryonic development, providing further evidence that fish are able to synthesise gadusol, rather than simply acquiring the compound through their diet.

Unfortunately for us, the EEVS-like and MT-Ox genes are not present in the mammalian or human genome, but they do appear in other animals including amphibians, reptiles and birds, inferring that the production of UV-protective compounds may be even more widespread than once thought. And while this does not save us from the dreaded, yet essential exercise of putting on suntan cream, it certainly acts as a friendly reminder that we may not be as evolutionarily superior to these animals as we might think…which I suppose is a good thing.

Post by: Megan Barrett