Small RNA repertoire of Nematostella vectensis

Three classes of small silencing RNAs have been described in eukaryotes: short interfering RNAs, microRNAs, and Piwi-interacting RNAs. The first class has been observed in all three eukaryotic kingdoms, and is believed to be of very ancient origin; the second one has been reported in plants and in animals, hence its appearance probably pre-dated the divergence of these two kingdoms. In contrast, piRNAs seem to be restricted to animals, as they were only detected in vertebrates, insects, and nematodes. In an attempt to better determine the evolutionary age of the piRNA pathway, we sequenced the small RNA content of a cnidarian, the sea anemone Nematostel la vectensis.