Desaturases and elongases involved in long-chain polyunsaturated fatty acid biosynthesis in aquatic animals: From genes to functions

Marine ecosystems are rich in omega-3 long-chain (C20-24) polyunsaturated fatty acids (LC-PUFA). Their production has been historically accepted to derive mostly from marine microbes. This long-standing dogma has been challenged recently by the discovery that numerous invertebrates, mostly with an aquatic life-style, have the enzyme machinery necessary for the de novo biosynthesis of polyunsaturated fatty acids (PUFA) and, from them, LC-PUFA. The key breakthrough was the detection in these animals of enzymes called methyl-end desaturases enabling PUFA de novo biosynthesis. Moreover, other enzymes with pivotal roles in LC-PUFA biosynthesis, including front-end desaturases and elongation of very long-chain fatty acids proteins, have been characterised in several non-vertebrate animal phyla. This review provides a comprehensive overview of the complement and functions of these gene/protein families in aquatic animals, particularly invertebrates and fish. Therefore, we expand and re-define our previous revision of the LC-PUFA biosynthetic enzymes present in chordates to animals as a whole, discussing how key genomic events have determined the diversity and distribution of desaturase and elongase genes in different taxa. We conclude that both invertebrates and fish display active, but markedly different, LC-PUFA biosynthetic gene networks that result from a complex evolutionary path combined with functional diversification and plasticity.

Automated summary

Traditional belief holds that marine microbes are the primary producers of omega-3 long-chain polyunsaturated fatty acids (LC-PUFA) in marine ecosystems. However, recent studies have challenged this belief by discovering that many aquatic animals also have the enzyme machinery necessary for de novo biosynthesis of PUFA and LC-PUFA. This review provides a comprehensive overview of the genes and proteins involved in LC-PUFA biosynthesis in aquatic animals, particularly invertebrates and fish. It concludes that invertebrates and fish have different, yet active, LC-PUFA biosynthetic gene networks that result from complex evolutionary processes and functional diversification.