海洋生物は植物ステロールを合成できる(Marine worms can synthesize phytosterols)

For most animals, cholesterol is an essential membrane lipid and signaling molecule. Plants and fungi use chemically similar molecules with one or two additional carbon atoms. Michellod et al. studied two species of gutless marine annelids and found that they produced sitosterol, a common plant lipid, as the main sterol in their lipid membranes (see the Perspective by Brocks and Bobrovskiy). A noncanonical methyltransferase that is known in plants but not previously known in bilaterian animals appears to be key in generating this sterol. Additional analyses of genomic and transcriptomic data from annelids and several other animal phyla demonstrated that this biosynthesis gene is widespread and has a complex evolutionary history. —Michael A. Funk

Sterols are vital for nearly all eukaryotes. Their distribution differs in plants and animals, with phytosterols commonly found in plants whereas most animals are dominated by cholesterol. We show that sitosterol, a common sterol of plants, is the most abundant sterol in gutless marine annelids. Using multiomics, metabolite imaging, heterologous gene expression, and enzyme assays, we show that these animals synthesize sitosterol de novo using a noncanonical C-24 sterol methyltransferase (C₂₄-SMT). This enzyme is essential for sitosterol synthesis in plants, but not known from most bilaterian animals. Our phylogenetic analyses revealed that C₂₄-SMTs are present in representatives of at least five animal phyla, indicating that the synthesis of sterols common to plants is more widespread in animals than currently known.