Gadusol is a maternally provided sunscreen that protects fish embryos from DNA damage.

Exposure to ultraviolet radiation (UVR) is harmful to living cells, leading organisms to evolve protective mechanisms against UVR-induced cellular damage and stress.1,2 UVR, particularly UVB (280-320 nm), can damage proteins and DNA, leading to errors during DNA repair and replication. Excessive UVR can induce cellular death. Aquatic organisms face risk of UV exposure as biologically harmful levels of UVB can penetrate >10 m in clear water.3 While melanin is the only known sunscreen in vertebrates, it often emerges late in embryonic development, rendering embryos of many species vulnerable during the earlier stages. Algae and microbes produce a class of sunscreening compounds known as mycosporine-like amino acids (MAAs).4 Fish eggs contain a similar compound called gadusol, whose role as a sunscreen has yet to be tested despite its discovery over 40 years ago.5 The recent finding that many vertebrate genomes contain a biosynthetic pathway for gadusol suggests that many fish may produce and use this molecule as a sunscreen.6 We generated a gadusol-deficient mutant zebrafish to investigate the role of gadusol in protecting fish embryos and larvae from UVR. Our results demonstrate that maternally provided gadusol is the primary sunscreen in embryonic and larval development, while melanin provides modest secondary protection. The gadusol biosynthetic pathway is retained in the vast majority of teleost genomes but is repeatedly lost in species whose young are no longer exposed to UVR. Our data demonstrate that gadusol is a maternally provided sunscreen that is critical for early-life survival in the most species-rich branch of the vertebrate phylogeny.

Gadusol is a maternally provided sunscreen that protects fish embryos from DNA damage.

Ultraviolet radiation (UVR) and its deleterious effects on living cells selects for UVR-protective mechanisms. Organisms across the tree of life evolved a variety of natural sunscreens to prevent UVR-induced cellular damage and stress. However, in vertebrates, only melanin is known to act as a sunscreen. Here we demonstrate that gadusol, a transparent compound discovered over 40 years ago in fish eggs, is a maternally provided sunscreen required for survival of embryonic and larval zebrafish exposed to UVR. Mutating an enzyme involved in gadusol biosynthesis increases the formation of cyclobutane pyrimidine dimers, a hallmark of UVB-induced DNA damage. Compared to the contributions of melanin and the chorion, gadusol is the primary sunscreening mechanism in embryonic and larval fish. The gadusol biosynthetic pathway is retained in the vast majority of teleost genomes but is repeatedly lost in species whose young are no longer exposed to UVR. Our data demonstrate that gadusol is a maternally provided sunscreen that is critical for early-life survival in the most species-rich branch of the vertebrate phylogeny.